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Orthopedic Ob Reconstru Review | Dr Hutaif Hip & Knee R -...

Orthopedic Hip And Knee Review | Dr Hutaif Hip & Knee R -...

23 Apr 2026 150 min read 111 Views
Illustration of pm tria aj - Dr. Mohammed Hutaif

Key Takeaway

Your ultimate guide to ORTHOPEDIC MCQS ONLINE HIP AND KNEE RECON 07 starts here. For total knee arthroplasty (TKA) following a patellectomy, a posterior cruciate ligament-substituting implant offers the most predictable outcome. This implant type addresses altered knee biomechanics, reducing stress on the posterior cruciate ligament compared to PCL-sparing designs. Research confirms its superiority for stability. This guidance is crucial for procedures like pm tria aj in orthopedic practice.

Orthopedic Hip And Knee Review | Dr Hutaif Hip & Knee R -...

Comprehensive 100-Question Exam


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Question 1

A 45-year-old active male undergoes a total hip arthroplasty (THA) with a ceramic-on-ceramic bearing. At 2 years postoperatively, he complains of a reproducible squeaking noise when bending down. What is the most common biomechanical cause associated with this phenomenon?





Explanation

Squeaking in ceramic-on-ceramic THA is uniquely associated with component impingement, edge loading, and resulting stripe wear on the ceramic head, which permanently alters the fluid-film lubrication dynamics.

Question 2

During a posterior-stabilized TKA, trial components are inserted. The knee is perfectly balanced and stable in full extension, but it is significantly tight in 90 degrees of flexion. What is the most appropriate intraoperative step to achieve a balanced gap?





Explanation

If the knee is balanced in extension but tight in flexion, the flexion gap must be increased selectively. Downsizing the femoral component using an anterior referencing system keeps the anterior flange flush but resects more posterior condylar bone, selectively opening the flexion gap without affecting the balanced extension gap.

Question 3

An 80-year-old female presents with a periprosthetic femur fracture around her cemented THA stem following a mechanical fall. Radiographs demonstrate a fracture at the tip of the stem. The stem appears radiographically loose, but there is adequate remaining proximal femoral bone stock. What is the correct Vancouver classification and most appropriate treatment?





Explanation

Vancouver B2 fractures occur around or just distal to the stem tip with a loose prosthesis but adequate bone stock. The standard of care is revision arthroplasty using a long, diaphyseal-engaging uncemented stem to bypass the fracture by at least two cortical diameters.

Question 4

Following a total knee arthroplasty, the surgeon notices lateral patellar maltracking during trial reduction. Which of the following component adjustments would most effectively improve patellar tracking?





Explanation

Medializing the patellar component decreases the Q-angle, effectively improving patellar tracking. Internal rotation of the femur or tibia, or medializing the femoral component, would increase the Q-angle and exacerbate lateral tracking.

Question 5

A surgeon is performing a primary THA using a direct lateral (Hardinge) approach. Which of the following structures is at greatest risk of denervation if the proximal split in the gluteus medius exceeds 5 cm from the greater trochanter?





Explanation

The superior gluteal nerve supplies the gluteus medius, minimus, and tensor fasciae latae. It courses approximately 3 to 5 cm proximal to the tip of the greater trochanter. Extending the abductor split beyond 5 cm puts the nerve at high risk, leading to abductor weakness and a postoperative Trendelenburg gait.

Question 6

During a posterior cruciate-retaining TKA, the surgeon enthusiastically resects the posterior aspect of the tibial plateau, accidentally injuring the popliteal artery. Anatomically, at what level relative to the joint line is the popliteal artery positioned closest to the posterior capsule?





Explanation

The popliteal artery lies closest to the posterior capsule directly at the level of the knee joint line. It is tethered proximally by the adductor hiatus and distally by the soleus arch, making it highly susceptible to injury during the tibial cut or overly aggressive posterior capsular releases.

Question 7

A 55-year-old male presents with deep groin pain and a palpable anterior thigh mass 6 years after a metal-on-metal THA. Serum cobalt and chromium levels are highly elevated. MRI reveals a complex cystic mass communicating with the joint space. What histological finding is most characteristic of this condition?





Explanation

Adverse Local Tissue Reaction (ALTR) or Aseptic Lymphocytic Vasculitis-Associated Lesion (ALVAL) secondary to metal-on-metal implants is a Type IV delayed hypersensitivity reaction. Histologically, it is defined by an extensive diffuse perivascular lymphocytic infiltrate, tissue necrosis, and macrophages containing metallic wear debris.

Question 8

When evaluating knee kinematics, which of the following properties is a primary design characteristic of a posterior-stabilized (PS) total knee arthroplasty compared to a cruciate-retaining (CR) design?





Explanation

In a posterior-stabilized (PS) knee, the cam-post mechanism engages (typically at 60-70 degrees of flexion) to enforce posterior femoral rollback. This is a mechanical substitution for the excised PCL, unlike CR knees which rely on native PCL tension.

Question 9

A patient complains of a severely elongated leg immediately after a primary THA. Radiographs demonstrate an increased vertical distance from the teardrop to the lesser trochanter compared to the native contralateral side, with symmetric femoral offset. Which specific intraoperative error most likely occurred?





Explanation

An increased teardrop-to-lesser trochanter distance indicates the femoral stem sits too high relative to the pelvis. If the femoral neck is cut too high (proximally), more calcar is left intact, causing the standard stem to sit proud and directly increasing leg length. A high hip center would generally decrease leg length.

Question 10

According to the classic Kozinn and Scott criteria, which of the following is considered an absolute contraindication to a medial unicompartmental knee arthroplasty (UKA)?





Explanation

Inflammatory arthritis (e.g., rheumatoid arthritis) is an absolute contraindication to UKA due to global joint involvement. Other classic contraindications include fixed varus >15 degrees, fixed valgus >20 degrees, flexion contracture >15 degrees, and ACL deficiency (though debated in modern mobile-bearing UKA). Age >60 is actually a supportive indication.

Question 11

During a revision THA, an Extended Trochanteric Osteotomy (ETO) is performed to remove a well-fixed cementless stem. Which of the following vessels provides the primary critical blood supply to the osteotomized greater trochanteric fragment to ensure union?





Explanation

The ETO fragment maintains its vascularity through its preserved soft tissue attachments, specifically the vastus lateralis muscle. The vastus lateralis is supplied predominantly by the descending branch of the lateral femoral circumflex artery.

Question 12

A 65-year-old female presents with a painful catch and an audible pop in her knee when extending from 45 degrees of flexion to full extension. She underwent a posterior-stabilized TKA 1 year ago. What is the most likely etiology of her symptoms?





Explanation

Patellar clunk syndrome is uniquely associated with posterior-stabilized (PS) TKA designs. A fibrous nodule develops at the superior pole of the patella (deep surface of the quadriceps tendon). During deep flexion, the nodule falls into the intercondylar box and 'clunks' out upon extension (usually between 30 and 45 degrees). Treatment is arthroscopic debridement.

Question 13

A 35-year-old male on chronic corticosteroids develops severe left groin pain. Radiographs reveal a subchondral radiolucent line (crescent sign) in the femoral head without flattening or joint space narrowing. MRI confirms osteonecrosis. What is the most definitive and appropriate treatment?





Explanation

A crescent sign defines Ficat Stage III (subchondral fracture/collapse). Once structural collapse has occurred, joint-preserving operations such as core decompression are highly ineffective. Total hip arthroplasty (THA) is the definitive standard of care for symptomatic Stage III/IV AVN, even in young patients.

Question 14

A 72-year-old male sustains an acute, complete rupture of the patellar tendon 3 weeks following a primary TKA. Radiographs show the implants are perfectly positioned and well-fixed. What is the most reliable surgical management for this devastating complication?





Explanation

Complete extensor mechanism disruption after a TKA has notoriously poor outcomes when managed with direct repair, even with wire augmentation. The most reliable and accepted salvage procedure, assuming well-fixed implants, is reconstruction with a complete extensor mechanism allograft (or occasionally synthetic mesh).

Question 15

When evaluating radiographs of a cementless femoral stem at 2 years postoperatively, which of the following findings is the most reliable and specific indicator of successful bone ingrowth (osseointegration) according to Engh's criteria?





Explanation

According to Engh's criteria, the presence of endosteal spot welds (new bone bridging the gap from the endosteum to the implant's porous coating) is a primary and highly reliable indicator of biological bone ingrowth. Continuous radiolucencies indicate fibrous stable fixation or loosening.

Question 16

A surgeon routinely utilizes intravenous Tranexamic Acid (TXA) to minimize blood loss during bilateral TKA. What is the primary pharmacologic mechanism of action of TXA?





Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It acts as an antifibrinolytic by competitively inhibiting the activation of plasminogen to plasmin. By blocking plasmin formation, it prevents the degradation of fibrin clots, thereby safely reducing surgical bleeding.

Question 17

A 28-year-old male hockey player presents with anterior groin pain exacerbated by deep hip flexion and internal rotation. AP pelvis radiographs reveal a prominent 'crossover sign' and a positive 'ischial spine sign'. Which of the following underlying conditions is most consistent with these exact radiographic findings?





Explanation

The crossover sign (anterior wall projecting lateral to the posterior wall proximally) and a prominent ischial spine sign are classic radiographic hallmarks of acetabular retroversion. This retroversion leads to anterior over-coverage of the femoral head, producing Pincer-type femoroacetabular impingement (FAI).

Question 18

In the emerging paradigm of Kinematic Alignment (KA) for Total Knee Arthroplasty, what is the primary overarching goal regarding the final positioning of the components?





Explanation

Kinematic Alignment (KA) aims to co-align the axes of the components with the three native kinematic axes of the knee, effectively restoring the patient's unique pre-arthritic joint line, thereby resurfacing the joint without the need for routine ligament releases. This contrasts with Mechanical Alignment (MA) which dictates orthogonal bone cuts.

Question 19

During a primary THA, accurate acetabular component positioning is critical to prevent dislocation. According to the classic Lewinnek 'safe zone', what are the optimal target angles for acetabular cup inclination (abduction) and anteversion, respectively?





Explanation

Lewinnek established the widely taught historical 'safe zone' for acetabular cup placement as 40 degrees +/- 10 degrees of inclination (abduction) and 15 degrees +/- 10 degrees of anteversion. Cups placed outside these parameters have historically demonstrated a statistically higher rate of dislocation.

Question 20

A patient presents with a painful, swollen knee 2 years post-TKA. According to the 2018 International Consensus Meeting (ICM) criteria, which of the following objective findings serves as a 'major criterion' that is independently diagnostic of a chronic periprosthetic joint infection?





Explanation

According to the 2018 ICM (and MSIS) criteria, the two major criteria for diagnosing PJI are: 1) Two positive periprosthetic cultures yielding the same phenotypically identical organism, or 2) The presence of a sinus tract communicating directly with the joint. Either is independently diagnostic. Elevated WBC, high PMN%, Alpha-defensin, and a single positive culture act only as minor criteria.

Question 21

A 68-year-old male with a history of an L3-S1 instrumented spinal fusion is planning to undergo a total hip arthroplasty (THA). Evaluation of his spinopelvic parameters demonstrates a stiff spinopelvic junction with an inability to increase his pelvic tilt when transitioning from a standing to a seated position. To minimize the risk of dislocation, how should the acetabular component positioning be modified?





Explanation

In patients with a fused or stiff lumbar spine, the pelvis fails to posteriorly tilt when moving from standing to sitting. Normal posterior pelvic tilt functionally increases acetabular anteversion, allowing clearance for the proximal femur in hip flexion. Without this compensatory tilt, the anterior femur impinges on the anterior acetabulum during sitting, levering the head out posteriorly. To compensate, the surgeon should increase the operative anteversion of the acetabular component.

Question 22

During a cruciate-retaining total knee arthroplasty (CR-TKA), the surgeon inserts the trial components and assesses the gaps. The knee is stable and well-balanced at 90 degrees of flexion, but it is tight in full extension, lacking 10 degrees of full extension. What is the most appropriate next step in surgical management?





Explanation

An isolated tight extension gap with a well-balanced flexion gap is managed by addressing the structures that solely affect extension. Resecting more distal femur increases the extension gap without altering the flexion gap. Downsizing the femoral component or releasing the PCL would primarily affect the flexion gap. Resecting more proximal tibia would increase both the flexion and extension gaps symmetrically, making the knee loose in flexion.

Question 23

Which of the following thermal processing methods for highly cross-linked polyethylene (HXLPE) is associated with the lowest level of measurable free radicals, but also results in a reduction of the material's yield and fatigue strength?





Explanation

Remelting HXLPE (heating above its melting point, typically >135°C) eliminates nearly all free radicals, providing excellent oxidative resistance. However, it alters the crystalline structure, which decreases mechanical properties such as yield strength, ultimate tensile strength, and fatigue strength. Annealing (heating below the melting point) preserves mechanical strength but leaves residual free radicals, increasing the risk of in vivo oxidation over time.

Question 24

A 78-year-old female sustains a periprosthetic femur fracture around her cemented THA stem after a fall. Radiographs show a transverse fracture at the tip of the stem. The stem is radiographically loose. Furthermore, there is massive osteolysis of the proximal femur with an absent calcar and complete loss of the greater trochanteric bone stock. According to the Vancouver classification, what is the grade and the most appropriate management?





Explanation

This is a Vancouver B3 fracture, defined as a fracture around the stem or just below it (B) with a loose implant (2/3) and severely deficient proximal bone stock (3). While B2 fractures (loose stem, good bone stock) are typically treated with a long cementless fluted tapered stem, B3 fractures often require a proximal femoral replacement (tumor prosthesis) or an extensively porous-coated stem if some distal metaphyseal/diaphyseal bone remains reconstructable.

Question 25

When planning a medial opening-wedge high tibial osteotomy (HTO) for a 45-year-old male with medial compartment osteoarthritis and varus malalignment, the mechanical axis (weight-bearing line) is typically shifted to pass through a specific target point on the tibial plateau. What is the generally accepted target location (Fujisawa point) measured from the medial edge of the tibial plateau?





Explanation

The Fujisawa point is the optimal target for the mechanical axis following an HTO for medial compartment osteoarthritis. It is located at 62.5% of the tibial plateau width from the medial edge (slightly lateral to the lateral tibial spine), which moderately unloads the diseased medial compartment by shifting the weight-bearing axis into the healthy lateral compartment.

Question 26

During a cruciate-retaining (CR) total knee arthroplasty, the surgeon notes that the anterior aspect of the tibial tray lifts off the baseplate during deep flexion, and there is excessive posterior femoral rollback. What is the most likely cause of this kinematic abnormality?





Explanation

A tight PCL in a CR-TKA acts as a tether during knee flexion, causing excessive femoral rollback. As the femur is pulled forcefully posterior on the tibia, it creates a 'teeter-totter' effect that can cause the anterior aspect of the tibial component to lift off. This requires PCL recession or release.

Question 27

A 65-year-old female presents with an audible and painful 'clunk' when extending her knee from a flexed position. She underwent a posterior-stabilized (PS) total knee arthroplasty 18 months ago. Nonoperative management has failed. What is the primary pathoanatomic cause of her symptoms?





Explanation

Patellar clunk syndrome is historically associated with PS total knee arthroplasties. It occurs when a fibrous nodule forms on the deep, posterior surface of the quadriceps tendon, just proximal to the superior pole of the patella. As the knee extends from deep flexion, this nodule catches in the superior aspect of the femoral intercondylar box, causing a painful clunk. Treatment is arthroscopic or open excision of the nodule.

Question 28

Which of the following is classically considered an absolute contraindication for a medial unicompartmental knee arthroplasty (UKA)?





Explanation

Inflammatory arthropathy (such as rheumatoid arthritis) is considered an absolute contraindication to UKA due to the systemic, pan-articular nature of the disease, which almost universally leads to progression in the unresurfaced compartments. Age, moderate obesity, asymptomatic patellofemoral OA, and minor flexion contractures (<15 degrees) are not absolute contraindications according to modern criteria.

Question 29

A surgeon is performing a surgical dislocation of the hip using the Ganz approach to treat femoroacetabular impingement. To protect the deep branch of the medial femoral circumflex artery (MFCA), which of the following structures must be meticulously preserved and left attached to the femur?





Explanation

During a Ganz surgical dislocation of the hip, the blood supply to the femoral head (deep branch of the MFCA) must be protected. The MFCA runs posterior to the obturator externus and anterior to the triceps coxae (obturator internus and gemelli). Preserving the obturator externus and performing the capsulotomy anterior to the lesser trochanter protects the deep branch of the MFCA.

Question 30

A patient with a non-metal-on-metal (MoM) total hip arthroplasty (titanium stem, cobalt-chromium head, highly cross-linked polyethylene liner) presents 6 years postoperatively with groin pain. Imaging reveals a large periprosthetic fluid collection. Aspiration shows cloudy fluid with a low neutrophil count but high cobalt levels. What combination of implant factors most significantly increases the risk of this complication?





Explanation

This patient has trunnionosis (mechanically assisted crevice corrosion at the head-neck taper). The use of large-diameter heavy cobalt-chromium (CoCr) heads on standard or thin titanium trunnions increases the lever arm and torque at the taper junction, exacerbating fretting and corrosion. This can lead to an adverse local tissue reaction (ALTR) or pseudotumor despite a metal-on-polyethylene bearing surface.

Question 31

During a total knee arthroplasty for a severe fixed valgus deformity, the surgeon notes that the knee is perfectly balanced in flexion, but remains excessively tight laterally in full extension. Which of the following structures is the primary restraint to lateral opening in extension and should be the first targeted for release?





Explanation

When correcting a valgus knee, the IT band is tight in extension and relatively lax in flexion. If the knee is tight laterally only in extension, releasing or pie-crusting the IT band will correct the extension gap without affecting the flexion gap. The popliteus is tight in flexion, and the LCL is a primary stabilizer in both flexion and extension.

Question 32

In the surgical treatment of a patient with Crowe Type IV developmental dysplasia of the hip (DDH), the surgeon decides to place the acetabular component in the true anatomical paleocenter. What additional surgical step is most frequently required to successfully reduce the hip and minimize the risk of sciatic nerve palsy?





Explanation

Crowe IV DDH is characterized by a high hip dislocation (>100% subluxation). Pulling the femur down to the true acetabulum stretches the surrounding neurovascular structures, particularly the sciatic nerve. To safely reduce the hip to the anatomical center without causing sciatic nerve palsy, a subtrochanteric shortening osteotomy of the femur is typically required.

Question 33

A 28-year-old male is diagnosed with pre-collapse (ARCO Stage II) avascular necrosis of the femoral head. He is scheduled for a free vascularized fibular graft (FVFG). What is the primary vascular pedicle harvested with the fibular graft for this procedure?





Explanation

The free vascularized fibular graft (FVFG) relies on the peroneal artery and its venae comitantes as its vascular pedicle. The graft is typically anastomosed to the lateral femoral circumflex artery and its corresponding veins to provide structural support and a new blood supply to the necrotic femoral head.

Question 34

A 72-year-old female presents with an inability to perform a straight leg raise 3 years after a primary total knee arthroplasty. Imaging and clinical exam confirm a chronic, retracted patellar tendon rupture. Given the high failure rate of primary repair in this setting, what is the most reliable and durable reconstructive option?





Explanation

Chronic extensor mechanism disruption after TKA is a catastrophic complication. Primary repair, even with augmentation, has unacceptably high failure rates in the chronic setting. The gold standard for reconstruction is an extensor mechanism allograft (comprising the tibial tubercle, patellar tendon, patella, and quadriceps tendon), rigidly fixed to the host tibia and tensioned tightly in full extension.

Question 35

The Bernese periacetabular osteotomy (PAO) is an essential joint-preserving procedure for symptomatic acetabular dysplasia. Which of the following bony structures of the pelvis is intentionally left INTACT during a standard PAO to maintain the stability of the pelvic ring?





Explanation

The Bernese PAO consists of a series of specific bone cuts: an incomplete ischial osteotomy, a complete pubic ramus osteotomy, and a complete supra-acetabular iliac osteotomy (anterior column). The posterior column of the ilium/ischium is intentionally left intact, which preserves the structural continuity of the pelvic ring and allows for immediate postoperative mobilization.

Question 36

Metal-on-metal (MoM) hip resurfacing arthroplasty (HRA) is occasionally considered for young, active patients. However, strict patient selection is required to prevent early failure. Which of the following patient profiles is universally considered a poor candidate (or absolute contraindication) for HRA due to high failure rates from adverse local tissue reaction and femoral neck fracture?





Explanation

Female gender, small femoral head component size (<48 mm), and underlying diagnoses of DDH or AVN (with large cystic changes) are major risk factors for failure in HRA. Small component sizes in MoM bearings lead to reduced fluid-film lubrication, higher wear rates, and increased metal ion release. Additionally, females have a higher rate of femoral neck fractures post-HRA.

Question 37

During a complex revision total knee arthroplasty for a failed aseptic TKA, the surgeon encounters severe, uncontained metaphyseal bone loss (AORI Type 2b defect). The surgeon decides to use highly porous metaphyseal metal cones. What is the correct principle of fixation regarding the interface between the cone, the host bone, and the revision tibial baseplate/stem?





Explanation

Metaphyseal cones (made of highly porous metal like tantalum or 3D-printed titanium) are distinct from metaphyseal sleeves. Cones are implanted independently of the final components and rely on press-fit into the host bone for primary stability and eventual biologic ingrowth. The revision tibial baseplate and stem are then cemented into the center of the cone. In contrast, sleeves are modularly locked to the stem via a taper.

Question 38

A 70-year-old female undergoes a revision THA for aseptic loosening. Intraoperatively, the surgeon identifies a complete transverse separation between the superior and inferior halves of the acetabulum, with the inferior hemipelvis moving independently of the ilium. Which of the following reconstructive strategies is considered the most reliable modern approach to address this specific defect?





Explanation

The clinical description is pathognomonic for a pelvic discontinuity. In the setting of a chronic pelvic discontinuity, bridging the defect and providing rigid stability between the superior and inferior halves of the pelvis is required. Modern, reliable treatments utilize highly porous metal, such as a cup-cage construct or a custom 3D-printed triflange implant, which stabilizes the discontinuity and allows for bone ingrowth.

Question 39

A 66-year-old male presents with a painful total knee arthroplasty 4 years postoperatively. Blood work shows an ESR of 35 mm/hr and CRP of 18 mg/L. Aspiration yields 2,500 WBC/μL with 65% neutrophils. To definitively support a diagnosis of periprosthetic joint infection (PJI), the synovial fluid is sent for biomarker analysis. Which of the following synovial biomarkers is highly specific for PJI and acts by disrupting bacterial cell membranes?





Explanation

Alpha-defensin is an antimicrobial peptide released by neutrophils in response to infection. It works by inserting into and disrupting bacterial cell membranes. It has been shown to be highly sensitive and specific for the diagnosis of PJI, performing well even in cases where traditional inflammatory markers or cell counts are borderline. It is recognized as a major criterion in the MSIS/ICM definition of PJI.

Question 40

Adverse local tissue reaction (ALTR) or Aseptic Lymphocytic Vasculitis Associated Lesions (ALVAL) is a known complication of metal-on-metal hip arthroplasty. Histologically, this phenomenon is characterized by an extensive perivascular lymphocytic infiltrate. What is the underlying immunological mechanism of this specific reaction?





Explanation

ALVAL (Aseptic Lymphocytic Vasculitis Associated Lesions) is widely accepted to be a Type IV delayed-type hypersensitivity reaction to metal ions (specifically cobalt and chromium). It is mediated by T-lymphocytes, leading to the characteristic perivascular lymphocytic infiltrate seen on histology. This is distinct from the macrophage-dominated foreign body reaction seen in particulate polyethylene wear (osteolysis).

Question 41

A 74-year-old female presents for revision of a failed total hip arthroplasty. Preoperative radiographs and intraoperative findings demonstrate severe acetabular bone loss with a transverse defect separating the superior and inferior hemipelvis, indicating independent movement of the lower half of the pelvis. According to the Paprosky classification, this is a Type 3B defect with pelvic discontinuity. What is the most reliable reconstructive option to achieve stable fixation in this scenario?





Explanation

Pelvic discontinuity requires stabilization of the superior and inferior halves of the pelvis while providing a stable socket for the femoral head. A cup-cage construct, custom triflange acetabular component, or distraction with a highly porous metal cup are the most reliable methods to span the discontinuity and achieve rigid fixation. Jumbo cups and high hip centers do not inherently stabilize the discontinuity, leading to high failure rates.

Question 42

A 68-year-old male with a history of an L2-to-pelvis fusion for degenerative scoliosis is undergoing a primary total hip arthroplasty. Due to his fused lumbosacral spine, his pelvis cannot tilt posteriorly when transitioning from standing to sitting. What complication is he at the highest risk for, and what compensatory adjustment should the surgeon make regarding acetabular cup positioning?





Explanation

Normally, when transitioning from standing to sitting, the lumbar spine flexes and the pelvis tilts posteriorly, which functionally increases acetabular anteversion and clears the femur to prevent impingement. In a stiff spine (e.g., L2-pelvis fusion), the pelvis cannot tilt posteriorly when sitting. Thus, the cup remains relatively retroverted, leading to anterior impingement and posterior dislocation. To compensate, the surgeon should increase the anteversion of the acetabular cup.

Question 43

During a primary posterior-stabilized total knee arthroplasty, the trial reduction reveals that the knee is symmetric and well-balanced in full extension, but the medial and lateral compartments are both excessively tight in 90 degrees of flexion. Which of the following adjustments is the most appropriate next step?





Explanation

A knee that is tight in flexion but balanced in extension has a tight flexion gap. Resecting more distal femur or releasing the posterior capsule affects the extension gap. Increasing the tibial slope increases the flexion gap but alters tibial bone stock and kinematics. Downsizing the femoral component using an anterior referencing system reduces the AP dimension of the femur (thinner posterior condyles), thereby increasing the flexion gap without altering the extension gap.

Question 44

A 76-year-old male sustained a periprosthetic fracture of the femur 8 years after a primary cementless total hip arthroplasty. Radiographs show a fracture traversing the stem near the tip. The femoral stem has subsided by 2 cm and is visibly loose. However, the proximal femoral bone stock remains of good quality. According to the Vancouver classification, what is the fracture type and the recommended treatment?





Explanation

This is a Vancouver B2 fracture (fracture around the stem, loose implant, good bone stock). The gold standard treatment is bypassing the fracture and revising the loose implant using a long, extensively porous-coated or fluted tapered cementless diaphyseal-engaging stem. B1 fractures have a well-fixed stem (treated with ORIF), while B3 fractures have poor bone stock (requiring proximal femoral replacement or allograft-prosthesis composite).

Question 45

A 65-year-old female presents with an inability to actively extend her knee 3 months after a primary total knee arthroplasty. Ultrasound confirms a complete mid-substance rupture of the patellar tendon. Primary repair is deemed unfeasible due to poor tissue quality. If an extensor mechanism allograft is utilized for reconstruction, in what position must the allograft be tensioned during fixation to ensure success?





Explanation

Extensor mechanism allograft or synthetic mesh reconstruction for chronic patellar tendon ruptures post-TKA must be tensioned tightly in full extension. Tensioning the graft in any degree of flexion will result in an extensor lag once the patient begins rehabilitation, as the graft inevitably stretches out over time.

Question 46

A 60-year-old male presents with groin pain and a palpable mass 6 years after a primary metal-on-polyethylene total hip arthroplasty. He received a titanium stem with a 36-mm cobalt-chromium head. Inflammatory markers are normal, and joint aspiration reveals no growth. MRI shows a cystic mass compressing the femoral nerve. Which of the following serum metal ion profiles is most characteristic of his underlying diagnosis?





Explanation

The scenario describes mechanically assisted crevice corrosion (MACC), or trunnionosis, at the head-neck junction of a metal-on-polyethylene (MoP) THA, typically involving a large CoCr head on a titanium stem. This produces adverse local tissue reactions (ALVAL). The hallmark serum profile for trunnionosis is elevated Cobalt levels disproportionately higher than Chromium levels (Co >> Cr), whereas metal-on-metal bearing wear typically produces equally elevated Co and Cr.

Question 47

During a primary total knee arthroplasty, an orthopedic surgeon evaluates the patellar tracking before definitive component implantation. The patella tracks laterally and tends to subluxate during deep flexion. Which of the following component malpositions is the most common iatrogenic cause of this finding?





Explanation

Internal rotation of either the femoral or tibial components increases the Q-angle and lateralizes the tibial tubercle relative to the trochlear groove, leading to lateral patellar maltracking. To optimize patellar tracking, the femoral and tibial components should be positioned in slight external rotation relative to the posterior condylar and tibial anatomic axes. Medializing (rather than lateralizing) the patellar component actually improves tracking.

Question 48

A patient with a cruciate-retaining (CR) total knee arthroplasty complains of the knee 'giving way' when descending stairs. Video fluoroscopy reveals paradoxical anterior sliding of the femur on the tibia during early-to-mid knee flexion. What is the primary biomechanical cause of this phenomenon?





Explanation

In a native knee and a well-functioning CR TKA, the femur rolls back posteriorly on the tibia during flexion, guided by the tension of the posterior cruciate ligament (PCL). If the PCL is attenuated, ruptured, or functionally incompetent (or if the flexion gap is too loose), the femur fails to roll back and instead slides anteriorly on the tibia during flexion (paradoxical anterior sliding). This leads to a sensation of instability, particularly when descending stairs.

Question 49

A 24-year-old collegiate hockey player presents with chronic groin pain exacerbated by hip flexion and internal rotation. Radiographs demonstrate an alpha angle of 65 degrees on the modified Dunn lateral view, with no joint space narrowing. This pathology is primarily caused by an osseous deformity located at which specific region of the proximal femur?





Explanation

The patient has Cam-type Femoroacetabular Impingement (FAI), indicated by an alpha angle >55 degrees. The classic Cam lesion (an aspherical extension of articular cartilage) is characteristically located at the anterosuperior aspect of the femoral head-neck junction. During hip flexion and internal rotation, this prominence impinges against the anterosuperior acetabular labrum and articular cartilage, causing pain and labral tearing.

Question 50

Which of the following conditions is considered an absolute contraindication to utilizing a mobile-bearing medial unicompartmental knee arthroplasty (e.g., Oxford UKA)?





Explanation

Anterior cruciate ligament (ACL) deficiency is an absolute contraindication for a mobile-bearing unicompartmental knee arthroplasty (UKA). Without an intact ACL, abnormal anteroposterior translation occurs, leading to posterior subluxation of the femur on the tibia in flexion and a high risk of bearing spin-out/dislocation. Age, weight, and asymptomatic patellofemoral chondromalacia are not strict contraindications based on current guidelines.

Question 51

According to the 2018 International Consensus Meeting (ICM) Criteria for Periprosthetic Joint Infection (PJI), which of the following findings is considered a definitive 'Major Criterion' establishing the diagnosis of PJI without the need for further scoring?





Explanation

Under the 2018 ICM criteria, the two major criteria (either of which definitively diagnoses a PJI independently) are: 1) A sinus tract communicating with the joint, and 2) Two positive periprosthetic cultures with phenotypically identical organisms. Elevated alpha-defensin, elevated CRP, elevated synovial WBC, and a single positive culture are minor criteria that contribute points to an aggregate score.

Question 52

In the setting of revision total knee arthroplasty with Anderson Orthopaedic Research Institute (AORI) Type 2B (severe metaphyseal) bone defects, both highly porous cones and metaphyseal sleeves can be used for fixation. What is the primary biomechanical difference in how metaphyseal sleeves engage the construct compared to porous cones?





Explanation

Metaphyseal sleeves are modular components that interlock with the revision stem and femoral/tibial component via a Morse taper, forming a single, rigidly connected construct that achieves biological fixation to the host bone. Highly porous cones, on the other hand, are implanted independently into the host metaphyseal bone to fill defects, and the revision implant is then cemented into the center of the cone.

Question 53

During a total hip arthroplasty, the surgeon elects to use an extended offset femoral stem instead of a standard offset stem, without changing the vertical height or leg length. What is the primary biomechanical consequence of increasing femoral offset?





Explanation

Increasing femoral offset moves the femur laterally away from the center of rotation (without altering leg length). This increases the abductor moment arm (lever arm), which means the abductor muscles need to generate less force to maintain a level pelvis. Consequently, the overall joint reaction force across the hip is decreased. It also increases soft-tissue tension, reducing the risk of impingement and dislocation.

Question 54

A 65-year-old female presents with the sudden onset of severe medial knee pain while walking. She denies any trauma. Radiographs of the knee are unremarkable. MRI reveals bone marrow edema in the medial femoral condyle with a focal subchondral hypointense crescent. Which of the following is the most appropriate initial management for this condition?





Explanation

The clinical presentation and MRI findings are classic for spontaneous osteonecrosis of the knee (SPONK), now more accurately termed a subchondral insufficiency fracture of the knee (SIFK). It overwhelmingly affects older females in the medial femoral condyle. Initial management is non-operative, focusing on protected weight-bearing and analgesia, as a significant portion will heal without surgical intervention. Surgery is reserved for collapse and secondary osteoarthritis.

Question 55

A 45-year-old patient undergoes a ceramic-on-ceramic total hip arthroplasty. Three years later, the patient complains of an audible squeaking noise from the hip during ambulation. What surgical factor is most strongly associated with the development of this complication?





Explanation

Squeaking is a well-known complication unique to hard-on-hard bearings, particularly ceramic-on-ceramic (CoC) THA. It is strongly associated with edge loading and stripe wear, which result from component malposition. Specifically, steep acetabular cup inclination (often >50 degrees) or version mismatches lead to the femoral head loading on the edge of the ceramic liner, disrupting fluid film lubrication and causing the squeak.

Question 56

An 82-year-old female presents with a displaced supracondylar femur fracture just proximal to a posterior-stabilized total knee arthroplasty. Radiographs indicate that the femoral component has subsided and is grossly loose. According to the Rorabeck classification, what is the grade of this fracture, and what is the definitive surgical treatment?





Explanation

The Rorabeck classification is used for periprosthetic femur fractures above a TKA. Type I: undisplaced, implant stable. Type II: displaced, implant stable. Type III: implant loose, regardless of displacement. Because the femoral component in this patient is grossly loose, it is a Rorabeck Type III. The standard treatment is revision arthroplasty using a distal femoral replacement (megaprosthesis) or a revision TKA with diaphyseal engaging stems, as ORIF will fail if the implant is loose.

Question 57

A 38-year-old female with Crowe Type IV developmental dysplasia of the hip (DDH) is undergoing a total hip arthroplasty. The femoral head is completely dislocated superior to the true acetabulum. To place the acetabular cup in the anatomic true acetabulum while preventing sciatic nerve stretch injury, what specific surgical adjunct is most frequently required?





Explanation

In Crowe IV DDH, the hip is completely dislocated, and the soft tissues have contracted over many years. Bringing the femur down to an anatomic cup in the true acetabulum stretches the sciatic nerve, with a high risk of neuropraxia or permanent injury if the limb is lengthened more than 4 cm. A subtrochanteric shortening osteotomy of the femur is required to safely reduce the hip into the true acetabulum while protecting the sciatic nerve.

Question 58

Which of the following describes the fundamental goal of 'Kinematic Alignment' in total knee arthroplasty compared to traditional 'Mechanical Alignment'?





Explanation

Kinematic alignment (KA) aims to restore the pre-arthritic constitutional alignment and kinematics of the knee by co-aligning the transverse axes of the TKA components with the native kinematic axes of the joint. This often involves placing the tibial component in slight varus and the femoral component in slight valgus (matching the native joint line), minimizing the need for soft-tissue releases. Mechanical alignment aims for a neutral (0 degree) mechanical axis with cuts perpendicular to the mechanical axes of the tibia and femur.

Question 59

Tranexamic acid (TXA) is widely utilized in total hip and knee arthroplasty protocols to minimize perioperative blood loss. Which of the following accurately describes its pharmacological mechanism of action?





Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It functions as an antifibrinolytic by reversibly and competitively binding to the lysine receptor sites on plasminogen. This prevents plasminogen from converting into plasmin, thereby preventing the degradation of fibrin clots and significantly reducing surgical bleeding.

Question 60

A patient with a history of a metal-on-metal hip resurfacing arthroplasty undergoes revision surgery for a suspected pseudotumor. Intraoperative tissue samples are sent for histopathological analysis. Which of the following histologic findings is the hallmark of an adverse local tissue reaction (ALVAL) associated with metal-on-metal wear debris?





Explanation

Adverse local tissue reaction (ALVAL - aseptic lymphocyte-dominated vasculitis-associated lesion) is a type IV delayed hypersensitivity reaction to metal ions (cobalt and chromium). The classic histological hallmark is a dense perivascular infiltrate of lymphocytes (T-cells) along with tissue necrosis and fibrin exudation. Birefringent particles and foreign body giant cells are characteristic of polyethylene wear (osteolysis), not metal-on-metal ALVAL.

Question 61

A 65-year-old female presents with an audible and palpable 'clunk' at 40 degrees of flexion as she extends her knee, 1 year after a posterior-stabilized TKA. Which of the following implant design factors is most directly associated with the development of patellar clunk syndrome?





Explanation

Patellar clunk syndrome occurs primarily in posterior-stabilized TKA due to the formation of a fibrous nodule at the superior pole of the patella. This nodule catches in the intercondylar box of the femoral component during extension (typically around 30-45 degrees of flexion). Older PS designs with a sharp, square anterior-superior edge of the intercondylar box were highly associated with this complication. Modern designs have lowered and rounded this edge, decreasing the incidence.

Question 62

A 72-year-old male with a history of a multi-level lumbar spinal fusion (L2-S1) is undergoing a primary THA. Preoperative standing and sitting lateral spinopelvic radiographs show a change in sacral slope of 5 degrees. How should the acetabular cup positioning be altered to minimize the risk of posterior dislocation during sitting?





Explanation

Normal spinopelvic mechanics involve posterior pelvic tilt when moving from standing to sitting, which functionally increases acetabular anteversion and clears the anterior femur. A stiff spine (defined as <10 degree change in sacral slope from standing to sitting) fails to posteriorly tilt the pelvis during sitting. Because the pelvis does not tilt posteriorly, the cup does not functionally antevert, leading to anterior impingement and posterior dislocation during sitting. To compensate for this lack of dynamic anteversion, the surgeon should place the cup with increased anteversion and increased inclination (target anteversion ~20-25 degrees, inclination ~45-50) or use a dual mobility implant.

Question 63

A 64-year-old male presents with groin pain 6 years after a primary metal-on-polyethylene THA with a large-diameter cobalt-chromium head. Inflammatory markers are normal, but MARS MRI reveals a solid, thick-walled soft tissue mass compressing the femoral vein. Aspiration yields sterile, turbid fluid. What is the most likely primary source of this complication?





Explanation

The patient has an Adverse Local Tissue Reaction (ALTR) or pseudotumor, which in a metal-on-polyethylene THA is typically caused by trunnionosis (fretting and crevice corrosion at the modular head-neck junction). Risk factors include a large diameter head (>36mm), cobalt-chromium heads on titanium stems, increased head offset, and higher BMI. It leads to metal ion release (elevated serum Co and Cr) and a local hypersensitivity/toxicity reaction.

Question 64

An 82-year-old female sustains a periprosthetic femur fracture around a cemented THA stem 12 years postoperatively. Radiographs demonstrate a fracture around the distal tip of the stem, with severe proximal femoral osteolysis, cortical thinning, and a completely loose implant. There is poor proximal bone stock, but the distal diaphyseal bone is robust. What is the most appropriate definitive management?





Explanation

This is a Vancouver B3 periprosthetic fracture: the fracture is around or just distal to the stem (B), the stem is loose (3), and the proximal bone stock is poor/inadequate. While fluted tapered titanium stems are the gold standard for Vancouver B2 fractures (loose stem, good proximal bone stock), Vancouver B3 fractures in elderly, lower-demand patients are optimally treated with a proximal femoral replacement (tumor prosthesis). This allows for immediate weight-bearing and avoids the high complication rates of attempting to bypass massive proximal bone defects with complex allograft-prosthesis composites or standard revision stems in frail patients.

Question 65

A 68-year-old male undergoes a primary TKA. During intraoperative trialing, the knee is completely stable in extension but exhibits significant laxity to varus and valgus stress at 90 degrees of flexion. Which of the following steps is the most appropriate next maneuver to balance the knee?





Explanation

Flexion instability (laxity in flexion but stable in extension) implies a flexion gap that is larger than the extension gap. To decrease the flexion gap without altering the extension gap, the surgeon can upsize the femoral component (increasing the posterior condylar offset/AP dimension) and use an offset tibial poly or shift the component posteriorly. Alternatively, translating the same-sized femoral component posteriorly decreases the flexion gap. Recutting the distal femur would increase the extension gap (making it symmetric but overall loose, requiring a thicker poly). Increasing posterior slope increases the flexion gap, worsening the instability.

Question 66

During a revision TKA for aseptic loosening, the surgeon utilizes a large distal femoral augment to compensate for bone loss and subsequently inserts a polyethylene liner that is 4 mm thicker than the original to achieve stability. Postoperatively, the patient has limited knee flexion and anterior knee pain. What is the most likely biomechanical consequence of elevating the joint line in this manner?





Explanation

Elevating the joint line during TKA (often due to over-resecting the distal femur and compensating with a thicker poly, or failing to restore distal femoral bone loss in revision) leads to relative/pseudo patella baja. The distance between the tibial tubercle and the joint line is decreased. This causes altered patellofemoral kinematics, restricted knee flexion, anterior knee pain, and potential impingement of the patella or patellar tendon against the anterior lip of the tibial polyethylene insert.

Question 67

A surgeon is performing a THA using the direct lateral (Hardinge) approach. To protect the superior gluteal nerve, the proximal split in the gluteus medius should not extend beyond a certain distance from the tip of the greater trochanter. What is the generally accepted safe distance limit for this split?





Explanation

The superior gluteal nerve innervates the gluteus medius, minimus, and tensor fasciae latae. During a direct lateral approach, the gluteus medius is split longitudinally. The main trunk of the superior gluteal nerve lies approximately 5 cm proximal to the tip of the greater trochanter. Extending the split further than 5 cm proximally puts the nerve at high risk of iatrogenic injury, which would result in a permanent Trendelenburg gait.

Question 68

A 59-year-old female presents with unexplained chronic pain, stiffness, and recurrent knee effusions 2 years after a primary TKA. Infection workup is negative, and radiographs show well-fixed components. She reports a history of severe skin reactions to cheap jewelry. Which of the following tests is currently considered the most appropriate initial diagnostic step for suspected metal hypersensitivity in this context?





Explanation

In cases of suspected metal hypersensitivity post-TKA, after ruling out infection, instability, and aseptic loosening, cutaneous patch testing remains the most widely accepted and accessible first-line test, despite its limitations in predicting deep joint reactions. LTT is available but often considered a second-line or adjunctive test due to cost and varying standardization. However, the diagnosis remains largely clinical and of exclusion. Many boards test skin patch testing as the classic 'next step' to confirm a cutaneous allergy to nickel/cobalt, followed by considering revision if the suspicion is high enough.

Question 69

A 45-year-old male complains of a loud 'squeaking' noise coming from his hip while walking, 4 years following a ceramic-on-ceramic THA. Which of the following biomechanical factors is most strongly associated with the development of squeaking in ceramic-on-ceramic hips?





Explanation

Squeaking in ceramic-on-ceramic (CoC) THA is a well-documented phenomenon. It is most commonly associated with 'stripe wear' which results from edge loading. Edge loading occurs when the femoral head contacts the rim of the acetabular liner, resulting in localized wear and loss of fluid film lubrication. This is typically caused by component malposition, specifically high cup inclination (>50 degrees) or extremes of anteversion.

Question 70

During a cruciate-retaining (CR) TKA, the surgeon notices that the knee 'books open' anteriorly as it is flexed, and the femoral component rolls paradoxically anteriorly on the tibia during deep flexion. What is the primary cause of this kinematic abnormality?





Explanation

Paradoxical anterior rolling of the femur on the tibia during flexion in a CR TKA is a classic sign of a tight posterior cruciate ligament (PCL). A tight PCL forces the femur to rock back or hinge, causing the anterior portion of the joint to open like a book and driving the femur forward on the tibial plateau. Management involves incrementally releasing the PCL or increasing the posterior tibial slope to loosen the flexion space and PCL.

Question 71

A patient undergoes a primary THA via the direct anterior (Smith-Petersen) approach. Postoperatively, she reports a burning sensation and numbness over the anterolateral aspect of her thigh. Which nerve is most likely affected, and between which two muscles does it typically emerge in the proximal thigh?





Explanation

The lateral femoral cutaneous nerve (LFCN) is highly susceptible to injury during the direct anterior approach to the hip. The LFCN typically emerges in the proximal thigh between the tensor fasciae latae (TFL) and the sartorius muscle, coursing superficially. The internervous plane for the direct anterior approach is also between the sartorius (femoral nerve) and TFL (superior gluteal nerve) superficially.

Question 72

A 65-year-old male presents with acute onset of extreme left knee pain, swelling, and fever (38.8°C) 18 days after a primary TKA. Joint aspirate yields 65,000 WBC/µL with 92% neutrophils. The patient is taken for Debridement, Antibiotics, and Implant Retention (DAIR). Which of the following factors is most crucial for the success of this procedure?





Explanation

In the setting of acute periprosthetic joint infection (PJI) treated with DAIR, exchanging the modular components (polyethylene insert) is highly recommended and correlated with significantly higher infection eradication rates. It allows access to the posterior compartment for thorough debridement and removes bacteria adhering to the modular interface.

Question 73

A 70-year-old female experiences recurrent anterior dislocations of her THA. Operative notes and CT imaging indicate that the combined version (McKibbin index) of her acetabular and femoral components is significantly abnormal. Which of the following combinations of component version is most likely responsible for anterior dislocation?





Explanation

Anterior dislocation of a THA is classically associated with excessive combined anteversion (excessive acetabular anteversion + excessive femoral anteversion). Conversely, posterior dislocation is associated with decreased combined anteversion (retroversion of the cup and/or stem). The combined version should ideally fall within the safe zone of 25 to 45 degrees to maintain stability.

Question 74

During a primary TKA, a surgeon uses a reciprocating saw to complete the posterior condylar cuts and inadvertently injures the popliteal artery. Anatomically, at what level does the popliteal artery run closest to the posterior capsule of the knee joint, making it most vulnerable to injury during TKA?





Explanation

The popliteal artery is closest to the posterior capsule and bone at the level of the proximal tibial bone cut (just distal to the joint line). Studies show the distance from the posterior tibial cortex to the artery can be as little as 2-3 mm. Furthermore, it is tethered at the soleal arch, making it immobile and highly susceptible to injury from penetrating instruments (like a saw blade plunging past the posterior cortex) during the tibial resection.

Question 75

A 78-year-old female with severe rheumatoid arthritis presents for primary TKA. Intraoperatively, the medial collateral ligament (MCL) is found to be completely incompetent and cannot be primarily repaired or imbricated to achieve stability. Which of the following bearing designs is most appropriate?





Explanation

In the setting of a completely incompetent or deficient medial collateral ligament (MCL), a varus-valgus constrained (VVC) prosthesis is usually insufficient because it relies on functional collateral ligaments to prevent excessive stress on the stabilizing post (which can lead to post failure/breakage). A rotating-hinge knee prosthesis is indicated for severe collateral ligament deficiency (especially MCL), massive bone loss, or extensor mechanism deficiency with global instability, as the hinge mechanism intrinsically provides coronal plane stability without relying on the MCL.

Question 76

A 72-year-old female on long-term bisphosphonate therapy for osteoporosis presents with thigh pain. Radiographs reveal a transverse fracture of the lateral femoral cortex with localized cortical thickening (beaking), extending halfway across the diaphysis. This fracture is located 2 cm distal to the tip of a well-fixed, uncemented standard-length THA stem inserted 8 years ago. What is the most appropriate management?





Explanation

This is an incomplete atypical femur fracture (AFF) associated with bisphosphonate use, occurring as a periprosthetic lesion (Vancouver C equivalent). Because it is incomplete but symptomatic with classic AFF features (transverse, lateral beak), prophylactic fixation is indicated to prevent completion. Since there is an ipsilateral THA stem, an antegrade intramedullary nail is impossible. A retrograde nail is an option if the distance allows, but a lateral spanning locking plate overlapping the stem (often with cables proximally and locking screws distally) is the standard surgical approach for a periprosthetic AFF near a well-fixed stem. Revision THA is unnecessarily invasive since the stem is well-fixed.

Question 77

A 65-year-old male with a history of multiple revision THAs presents with severe groin pain. Radiographs demonstrate an acetabular component that has migrated 3 cm superomedially. A CT scan reveals discontinuity of the anterior and posterior columns of the hemipelvis. Which of the following reconstructive options provides the most rigid mechanical fixation for pelvic discontinuity in this setting?





Explanation

Pelvic discontinuity (a separation of the superior pelvis/ilium from the inferior pelvis/ischium and pubis) is a severe complication in revision THA. Standard hemispherical cups cannot bridge the discontinuity effectively to provide stable long-term fixation. Reconstructive options include cup-cage constructs, custom triflange acetabular components (CTAC), or distraction using a trabecular metal jumbo cup (if adequate bone stock exists). Among the choices, the custom triflange acetabular component provides the most rigid and reliable mechanical fixation by spanning the defect and anchoring to the ilium, ischium, and pubis using patient-specific matching.

Question 78

A 70-year-old male presents with inability to perform a straight leg raise 6 months after a TKA. Examination and ultrasound reveal a chronic, complete rupture of the patellar tendon with a 4 cm gap. The tibial tubercle is intact, and the components are well-fixed. What is the most reliable surgical reconstruction method for this chronic defect?





Explanation

Chronic patellar tendon ruptures post-TKA with significant gap formation cannot be treated successfully with primary repair (tissue is poor quality, high failure rate). The gold standard treatments for chronic extensor mechanism disruption post-TKA are either an extensor mechanism allograft (using a block of tibial bone, patellar tendon, patella, and quadriceps tendon) or reconstruction using synthetic mesh (e.g., Marlex mesh). Both have shown comparable, reasonable salvage rates in modern literature, vastly outperforming primary repair or autograft augmentation in the setting of TKA.

Question 79

In the context of kinematic alignment for primary TKA, the procedure aims to restore the pre-arthritic native joint lines. When compared to traditional mechanical alignment, what is the most characteristic coronal alignment profile of the final components in a patient with constitutional varus?





Explanation

Constitutional varus usually arises from a combination of distal femoral valgus (relative to the mechanical axis) and proximal tibial varus (joint line obliquity). Kinematic alignment (KA) aims to co-align the axes of the components with the three kinematic axes of the knee, effectively restoring the patient's native joint line. In a patient with constitutional varus, this typically results in the femoral component being placed in slightly more valgus (compared to the mechanical axis cut of 0 degrees) and the tibial component being placed in varus to match the native proximal tibial joint line obliquity.

Question 80

During a primary THA, the surgeon chooses a 36-mm femoral head over a 28-mm femoral head to improve hip stability. Assuming the same head-neck ratio, what is the primary biomechanical advantage that decreases the risk of dislocation with the larger femoral head?





Explanation

Larger femoral heads provide greater stability primarily by increasing the 'jump distance'—the distance the femoral head must translate laterally before it completely escapes the acetabular rim. A larger head also increases the head-neck ratio (assuming the neck diameter remains constant), which improves the impingement-free range of motion. However, the direct mechanical barrier to dislocation once subluxation begins is the increased jump distance. Note that larger heads increase (not decrease) volumetric wear, though modern highly cross-linked polyethylene handles this well.

Question 81

A 65-year-old female presents with worsening groin pain 8 years after a metal-on-metal total hip arthroplasty. A MARS MRI reveals a large, thick-walled cystic collection around the hip joint without sinus tracts. Aspiration is negative for acute infection. Which of the following is the hallmark histological finding of the capsular tissue in this condition?





Explanation

The patient has an adverse local tissue reaction (ALTR) or ALVAL (Aseptic Lymphocytic Vasculitis-Associated Lesion) secondary to metal-on-metal wear. ALVAL is characterized by a delayed-type hypersensitivity reaction (Type IV) leading to a dense perivascular lymphocytic infiltrate, tissue necrosis, and fibrin exudation.

Question 82

A 72-year-old female experiences a chronic, complete patellar tendon rupture following a primary total knee arthroplasty (TKA). She is planned for an extensor mechanism reconstruction utilizing synthetic Marlex mesh. What is the most critical technical step for a successful outcome regarding mesh tensioning?





Explanation

Extensor mechanism reconstruction post-TKA using Marlex mesh requires rigid, secure fixation to the tibial tubercle and patella/quadriceps, tensioned optimally with the knee in full, maximal extension. Any laxity or tensioning in flexion will reliably result in a clinically significant postoperative extensor lag.

Question 83

Dual mobility acetabular components are frequently used in revision THA to minimize the risk of dislocation. Which biomechanical principle provides the primary enhancement of stability in dual mobility constructs?





Explanation

Dual mobility cups feature a standard femoral head that articulates within a large polyethylene liner, which in turn articulates within the metal acetabular shell. The large outer diameter of the mobile polyethylene liner increases the effective head size and the jump distance required for the hip to dislocate.

Question 84

An 85-year-old low-demand female sustains a periprosthetic femur fracture around a cemented total hip arthroplasty. Radiographs demonstrate a fracture around the tip of the stem with a loose implant and severe proximal femoral bone loss (Vancouver B3). What is the most reliable surgical management to allow early weight-bearing?





Explanation

Vancouver B3 fractures are characterized by a loose stem and severely compromised proximal bone stock. In elderly, low-demand patients, a proximal femoral replacement bypasses the compromised bone and allows immediate full weight-bearing, offering a lower complication profile compared to complex impaction grafting in this population.

Question 85

A patient presents with persistent lateral patellar subluxation and anterior knee pain after a primary TKA. A postoperative CT scan is obtained to evaluate component rotation. Which combination of component malrotation is the most common cause of iatrogenic lateral patellar tracking?





Explanation

Internal rotation of the femoral component shifts the trochlear groove medially, while internal rotation of the tibial component effectively lateralizes the tibial tubercle relative to the trochlea. Both of these rotational errors increase the Q-angle, exacerbating lateral patellar maltracking and anterior knee pain.

Question 86

During hip arthroscopy, establishing the anterior portal requires careful anatomic knowledge. Placing the anterior portal too medial or deep puts which of the following nerves at highest risk?





Explanation

The anterior portal for hip arthroscopy is established slightly lateral to the intersection of a vertical line from the ASIS and a horizontal line from the tip of the greater trochanter. It carries a significant risk of injury to the lateral femoral cutaneous nerve (LFCN) branches and the femoral nerve if placed too medial.

Question 87

The alpha-defensin immunoassay has become a highly accurate diagnostic test for periprosthetic joint infection (PJI). What is the biological origin of alpha-defensin in the synovial fluid of an infected joint?





Explanation

Alpha-defensin is a naturally occurring antimicrobial peptide that is released from the granules of activated host neutrophils in response to the presence of pathogens. It serves as an excellent synovial fluid biomarker for periprosthetic joint infection due to its high sensitivity and specificity.

Question 88

A 62-year-old male who underwent an isolated medial unicompartmental knee arthroplasty (UKA) 8 years ago presents with new-onset generalized knee pain. Radiographs show a well-fixed medial implant. What is the most common cause of late failure (>5 years) in a medial UKA?





Explanation

While early and midterm failures of UKA are often due to aseptic loosening or technical errors (e.g., overcorrection), late failure (occurring >5 years postoperatively) is most commonly caused by the natural progression of osteoarthritis in the unresurfaced lateral or patellofemoral compartments.

Question 89

The direct anterior approach (Smith-Petersen) for total hip arthroplasty utilizes a true internervous and intermuscular plane. This plane separates muscles innervated by which two nerves?





Explanation

The direct anterior approach uses the internervous plane between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve). The deep dissection passes between the rectus femoris (femoral nerve) and gluteus medius (superior gluteal nerve).

Question 90

A 55-year-old male complains of a high-pitched squeaking noise from his hip when walking, 3 years after a primary THA with a ceramic-on-ceramic bearing. What is the primary biomechanical risk factor associated with this phenomenon?





Explanation

Squeaking is a known complication of ceramic-on-ceramic bearings. It is strongly correlated with micro-separation, edge loading, and resultant stripe wear on the ceramic head. The most common underlying cause of edge loading is acetabular cup malposition (e.g., excessive steep inclination or inappropriate version).

Question 91

A 40-year-old active female presents with symptomatic, isolated lateral compartment knee osteoarthritis. Standing alignment radiographs demonstrate a mechanical valgus deformity of 14 degrees originating from the distal femur. Which surgical intervention is most appropriate?





Explanation

For isolated lateral compartment osteoarthritis in a young, active patient with a significant valgus deformity originating from the femur, a distal femoral osteotomy (DFO) is indicated. A medial closing wedge DFO (or lateral opening wedge DFO) effectively corrects the mechanical axis away from the lateral compartment.

Question 92

Modern total hip arthroplasty frequently utilizes highly cross-linked polyethylene (HXLPE) to reduce wear. After gamma irradiation to create cross-links, the polyethylene is often subjected to a thermal process called remelting. What is the primary purpose of remelting?





Explanation

Gamma irradiation generates cross-links that improve wear resistance, but it also cleaves polymer chains, leaving behind free radicals. If left untreated, these free radicals react with oxygen over time, causing oxidative degradation and embrittlement. Remelting the polyethylene above its melting point extinguishes these free radicals, though it slightly decreases the material's fatigue strength.

Question 93

Kinematic studies of the normal human knee demonstrate specific coupled motions during deep flexion. Which of the following best describes the normal kinematic movement of the femoral condyles on the tibia from 0 to 120 degrees of flexion?





Explanation

Normal knee kinematics follow a 'medial pivot' pattern. The medial femoral condyle acts as a ball-and-socket joint with minimal anteroposterior translation, while the lateral femoral condyle undergoes significant posterior translation (rollback) as the knee flexes. This coupled internal rotation of the tibia (or external rotation of the femur) aids in maximizing deep flexion.

Question 94

In the evaluation of femoroacetabular impingement (FAI), atypical extra-articular impingement must be considered. Subspine impingement specifically involves pathological abutment between the anterior distal femoral neck and which of the following structures?





Explanation

Subspine impingement is an extra-articular form of FAI characterized by abutment between a hypertrophic or distally extending anterior inferior iliac spine (AIIS) and the anterior femoral neck during hip flexion. It is often a sequela of previous rectus femoris avulsion injuries.

Question 95

During a cruciate-retaining (CR) total knee arthroplasty, the surgeon notices that the tibial tray repeatedly lifts off anteriorly (book-opening) when the knee is brought into deep flexion. What is the most likely technical cause of this intraoperative finding?





Explanation

In a CR TKA, if the PCL is retained but is excessively tight, it acts as an unyielding tether during flexion. This forces the femur to roll back excessively on the tibia, applying increased pressure on the posterior lip of the tibial polyethylene and causing the anterior aspect of the tibial tray to lift off ('book opening').

Question 96

During a complex revision THA for aseptic loosening in a 70-year-old female, the surgeon intraoperatively identifies severe acetabular bone loss. The superior hemipelvis moves completely independently of the inferior hemipelvis. Which of the following reconstructive options provides the necessary stability for this specific defect?





Explanation

The patient has pelvic discontinuity, defined as a complete uncoupling of the superior (ilium) and inferior (ischium/pubis) halves of the pelvis. Standard hemispherical cups cannot bridge and stabilize this defect. Rigid fixation bridging the discontinuity is required, best achieved with a cup-cage construct, a custom triflange acetabular component, or a pelvic distraction approach with a highly porous jumbo cup.

Question 97

A 38-year-old male on long-term systemic corticosteroids for lupus presents with atraumatic hip pain. MRI confirms osteonecrosis of the femoral head. What is the primary cellular pathophysiology underlying corticosteroid-induced osteonecrosis?





Explanation

Corticosteroids alter the differentiation pathway of mesenchymal stem cells, favoring adipogenesis over osteogenesis. The resulting hypertrophy of fat cells within the rigid bony confines of the femoral head increases intraosseous pressure, which compresses thin-walled venules and arterioles, ultimately leading to ischemia and osteonecrosis.

Question 98

Antibiotic-loaded acrylic bone cement (ALABC) is commonly used for prophylaxis and treatment of periprosthetic joint infection. Which of the following antibiotics is NOT appropriate for incorporation into PMMA bone cement due to its severe heat lability?





Explanation

The polymerization of polymethyl methacrylate (PMMA) bone cement is a highly exothermic reaction that can reach temperatures over 80-100 degrees Celsius in vivo. Antibiotics mixed into PMMA must be heat-stable, water-soluble, and available in powder form. Penicillins and most cephalosporins are heat-labile and degrade during polymerization, whereas aminoglycosides (tobramycin, gentamicin) and vancomycin are heat-stable.

Question 99

During a posterolateral corner (PLC) reconstruction of the knee, surgical dissection near the fibular head places the common peroneal nerve at risk. What is the normal anatomic relationship of the common peroneal nerve as it crosses the knee joint?





Explanation

The common peroneal nerve descends in the lateral aspect of the popliteal fossa, coursing posterior and medial to the tendon of the biceps femoris. It then travels distally and laterally to wrap around the neck of the fibula, deep to the peroneus longus muscle, making it highly susceptible to injury during PLC reconstruction or fibular head avulsions.

Question 100

A surgeon is templating a primary total hip arthroplasty and decides to utilize a high-offset femoral stem to restore the patient's native anatomy without increasing the leg length. Biomechanically, what is the primary consequence of successfully increasing the femoral offset?





Explanation

Increasing femoral offset moves the femur laterally relative to the center of rotation of the hip. This directly increases the length of the lever arm for the abductor muscles (abductor moment arm). Because the abductors have a greater mechanical advantage, they require less force to balance the pelvis, which consequently decreases the overall joint reaction force across the hip joint.

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