A 20-year-old male military recruit reports a 5-day history of progressive deep groin pain that is made worse with weight-bearing activities and running. His initial coronal T2-weighted MRI scan is shown in Figure 75. His initial treatment should con

Crutches with protected weight bearing

A 59-year-old woman with a history of osteoporosis is involved in a high-speed motor vehicle accident,resulting in left hip pain and deformity. The initial radiograph from the trauma bay is shown in Figure 1. Postreduction CT is shown in Figures

Open reduction and internal fixation (ORIF) of the acetabular fracture with concomitant acute total hip arthroplasty

A 28-year-old man has a painful nodule on the plantar aspect of his foot in the midarch. Use of a soft orthosis has failed to provide relief. Examination reveals that the mass is approximately 2 1/2 cm in diameter, firm, and tender to palpation. An M

resection of the entire plantar fascia.

A young gymnast fell awkwardly onto an outstretched hand during a competition. At the time of impact, his forearm was positioned in supination. Axial and posterolateral forces were loaded along the forearm into the elbow and the elbow underwent a sig

Coronoid fracture, olecranon fracture and elbow dislocation

Orthopedic Reconstruction MCQ Review by Dr. Hutaif

Question 1

During pre-operative templating for a primary total hip arthroplasty (THA), the surgeon decides to use a high-offset femoral stem instead of a standard-offset stem of the same neck length. What is the primary biomechanical effect of this decision?

Explanation

Increasing the femoral offset lateralizes the proximal femur, which increases the abductor moment arm. By increasing the abductor moment arm, less force is required by the abductor muscles to maintain the pelvis level during single-leg stance. This subsequently decreases the overall joint reaction force across the hip joint, reducing wear rates. It does not independently increase leg length.

Question 2

A 45-year-old active male undergoes a total hip arthroplasty with a ceramic-on-ceramic bearing surface. Two years later, he complains of a new, audible sound coming from his hip during ambulation. What is the most likely specific cause of this phenomenon?

Explanation

Squeaking is a well-documented complication specific to ceramic-on-ceramic (CoC) bearings. It is strongly associated with component malpositioning (particularly excessive cup anteversion or inclination), which leads to edge loading. Edge loading results in stripe wear on the ceramic head and micro-separation during the swing phase of gait, producing the audible squeak.

Question 3

When performing a direct anterior approach to the hip for a total hip arthroplasty, the surgeon exploits an internervous plane. Which of the following accurately describes the muscles and their respective innervations that define this plane superficially?

Explanation

The superficial internervous plane for the direct anterior approach (Smith-Petersen) to the hip is between the tensor fasciae latae (supplied by the superior gluteal nerve) and the sartorius (supplied by the femoral nerve). The deep internervous plane is between the rectus femoris (femoral nerve) and the gluteus medius (superior gluteal nerve).

Question 4

During a revision total knee arthroplasty (TKA), the surgeon uses a smaller femoral component and makes up the flexion space by using a thicker polyethylene insert. What is the most likely geometric consequence of this technical decision?

Explanation

Using a smaller femoral component increases the flexion gap. To balance this, a thicker polyethylene insert is often used. However, this elevates the joint line relative to the tibial tubercle. An elevated joint line leads to relative patella baja (infera), which can alter patellar kinematics, cause anterior knee pain, restrict range of motion, and increase the risk of patellar impingement against the tibial tray.

Question 5

According to the Musculoskeletal Infection Society (MSIS) criteria for periprosthetic joint infection (PJI), which of the following is considered a definitive major criterion for diagnosing PJI?

Explanation

According to the consensus MSIS criteria, the definitive major criteria for PJI are: 1) A sinus tract communicating directly with the joint space, or 2) Two positive periprosthetic cultures with phenotypically identical organisms. The other options are considered minor criteria (elevated ESR/CRP, elevated synovial WBC/PMN %, positive alpha-defensin, or a single positive culture).

Question 6

A 68-year-old male presents with deep thigh pain 12 years after a cementless total hip arthroplasty. Radiographs demonstrate eccentric positioning of the femoral head within the acetabular cup and extensive periprosthetic radiolucencies.

What is the primary cellular mediator of the osteolysis demonstrated in this condition?

Explanation

The clinical scenario and radiograph describe aseptic loosening due to osteolysis, classically driven by polyethylene wear debris (particle disease). The primary mechanism is the phagocytosis of submicron (0.1 to 10 micrometers) particulate debris by macrophages. These activated macrophages release pro-inflammatory cytokines (TNF-alpha, IL-1, IL-6), which stimulate osteoclastogenesis via the RANK/RANKL pathway, leading to localized bone resorption.

Question 7

A patient complains of a painful catching sensation in their knee one year after undergoing a posterior-stabilized (PS) total knee arthroplasty. The physical examination reveals an audible pop as the knee is actively extended. At what arc of motion does 'patellar clunk syndrome' most classically occur?

Explanation

Patellar clunk syndrome is a complication classically associated with posterior-stabilized (PS) TKA designs. It is caused by the formation of a fibrosynovial nodule at the superior pole of the patella. As the knee extends from a flexed position (typically catching around 30 to 45 degrees of flexion), the nodule pops out of the intercondylar box of the femoral component, causing a painful clunk.

Question 8

Trunnionosis, or wear at the head-neck junction of a modular femoral stem, has become increasingly recognized in total hip arthroplasty. Which of the following implant combinations represents the highest risk factor for developing symptomatic trunnionosis?

Explanation

Trunnionosis is caused by mechanically assisted crevice corrosion (fretting and galvanic corrosion). Risk factors include dissimilar metals (galvanic corrosion), larger femoral heads (which increase the toggle and frictional torque at the trunnion), and high-offset necks. A large (e.g., 36-mm) cobalt-chrome head on a titanium stem presents both mixed metals and increased torque, maximizing the risk for trunnionosis.

Question 9

During preoperative planning for a revision total hip arthroplasty, the surgeon identifies a Paprosky Type IIIB acetabular defect. Which of the following radiographic findings definitively characterizes a Type IIIB defect rather than a Type IIIA defect?

Explanation

The Paprosky classification for acetabular defects guides reconstruction. Type IIIA is characterized by 10-to-noon bone loss with superior migration > 3 cm, but an intact Kohler's line (the component migrates "up and out"). Type IIIB indicates severe superior and medial bone loss, resulting in > 3 cm superior migration and disruption of Kohler's line / the teardrop (the component migrates "up and in").

Question 10

A 72-year-old female sustains a fall and presents with a periprosthetic femur fracture around a cemented total hip arthroplasty placed 10 years ago. Radiographs show a fracture at the tip of the stem. The stem appears to have subsided 1 cm, and there is an intact medial calcar with good diaphyseal bone stock. Based on the Vancouver classification, what is the most appropriate definitive management?

Explanation

This is a Vancouver B2 periprosthetic fracture. The fracture is around or just below the tip of the stem (Type B), the stem is loose as evidenced by subsidence (differentiating it from B1), but there is adequate remaining bone stock (differentiating it from B3). The standard of care for a Vancouver B2 fracture is revision to a long stem (fluted, tapered, or fully porous-coated) that bypasses the fracture by at least two cortical diameters.

Question 11

During a primary total knee arthroplasty, the surgeon inadvertently places the femoral component in 5 degrees of internal rotation relative to the surgical transepicondylar axis. What is the expected clinical and biomechanical consequence of this malrotation?

Explanation

Internal rotation of the femoral component in TKA effectively moves the lateral condyle anteriorly and the medial condyle posteriorly. This has two primary effects: 1) It medially translates the trochlear groove, increasing the Q-angle and driving the patella to track laterally (lateral subluxation). 2) By taking less bone off the posterior medial condyle, it results in a tight medial flexion gap (asymmetric flexion space).

Question 12

Highly cross-linked polyethylene (XLPE) has dramatically reduced the incidence of wear and osteolysis in modern total hip arthroplasty. Which step in the manufacturing process of XLPE is essential for eliminating the free radicals created during the cross-linking phase, thereby improving oxidative stability?

Explanation

XLPE is typically created by exposing conventional ultra-high-molecular-weight polyethylene to high doses of gamma irradiation (e.g., 5-10 Mrad). This breaks carbon-hydrogen bonds, forming free radicals that recombine to create cross-links. However, residual free radicals can cause severe oxidative degradation over time. Thermal treatment (remelting above the melting point, or annealing below the melting point) is essential to extinguish these residual free radicals and confer long-term oxidative stability. Adding Vitamin E is an alternative modern method to quench free radicals without melting.

Question 13

A 65-year-old male with a history of a multilevel lumbar spinal fusion (L2-S1) presents for a primary total hip arthroplasty. Because his spine is functionally stiff and fixed in a 'flatback' (decreased lumbar lordosis) posture, his pelvis cannot properly retrovert when transitioning from standing to sitting. How should the surgeon adjust the acetabular component positioning to minimize the risk of posterior dislocation?

Explanation

Normal spinopelvic mechanics involve pelvic retroversion during sitting, which functionally increases acetabular anteversion and clears the anterior femur to prevent anterior impingement and posterior dislocation. A patient with a stiff spine and flatback deformity cannot retrovert their pelvis when sitting. Therefore, to prevent anterior impingement and posterior dislocation in flexion, the surgeon must manually compensate by placing the acetabular component in increased anteversion during the index surgery.

Question 14

A 78-year-old female presents for revision total knee arthroplasty due to aseptic loosening. Intraoperatively, following removal of the components and minimal debridement, the surgeon notes complete incompetence of both the Medial Collateral Ligament (MCL) and the Lateral Collateral Ligament (LCL), accompanied by a massive flexion gap. What is the most appropriate level of constraint for the new implant?

Explanation

The choice of constraint in TKA depends on collateral ligament integrity and gap balancing. A Varus-Valgus Constrained (VVC) implant relies on a tall tibial post and deep femoral box to provide coronal stability but requires at least one intact collateral ligament (preferably the MCL) and relatively balanced gaps. When there is global ligamentous incompetence (both MCL and LCL deficient) or severe uncorrectable gap mismatches (e.g., massive flexion gap), a linked rotating hinge prosthesis is indicated to prevent subluxation or dislocation.

Question 15

During a primary posterior-stabilized total knee arthroplasty, trial reduction reveals that the knee is perfectly balanced and symmetric in full extension, but the joint is significantly tight symmetrically in 90 degrees of flexion. Which of the following surgical steps is the most appropriate initial maneuver to balance this knee?

Explanation

A knee that is tight in flexion but symmetric and balanced in extension requires an increase in the flexion gap without altering the extension gap. The posterior femoral condylar resection affects only the flexion gap. Downsizing the femoral component (shifting the anterior cut referencing to take more posterior bone) will open the flexion gap while leaving the distal femoral cut (and thus the extension gap) unchanged.

Question 16

Optimizing modifiable risk factors prior to total joint arthroplasty significantly reduces the risk of periprosthetic joint infection (PJI) and wound complications. According to current American Association of Hip and Knee Surgeons (AAHKS) guidelines, what are the recommended preoperative thresholds for HbA1c and serum albumin in an elective total joint replacement?

Explanation

Preoperative medical optimization is critical. Poor glycemic control (HbA1c > 7.0% or 7.5% depending on specific institutional protocols, but strictly > 7.0% is widely cited for highest risk reduction) and malnutrition (serum albumin < 3.5 g/dL, transferrin < 200 mg/dL, or total lymphocyte count < 1500 cells/mm3) are strong independent risk factors for surgical site infection and delayed wound healing. The standard accepted minimum thresholds are HbA1c < 7.0% and Albumin > 3.5 g/dL.

Question 17

Corrosion at modular junctions in total joint arthroplasty can lead to early implant failure. Which type of corrosion is defined as the mechanical destruction of the passivating oxide layer on the metal surface due to micromotion, followed by rapid electrochemical dissolution of the underlying exposed metal?

Explanation

Fretting corrosion occurs at the contact sites of two materials under load subjected to minute relative motion (micromotion), such as a modular head-neck junction. This micromotion mechanically strips the protective passive oxide film from the metal surface, exposing the highly reactive bare metal to the corrosive fluid environment, leading to accelerated wear and metal ion release. Galvanic corrosion, in contrast, requires two dissimilar metals electrically coupled in an electrolyte.

Question 18

A 70-year-old female presents with an inability to actively extend her knee 6 months following a primary total knee arthroplasty. Clinical examination and imaging confirm a chronic disruption of the extensor mechanism at the mid-substance of the patellar tendon. The components are well-fixed without evidence of infection. What is the most reliable reconstructive option for this chronic failure?

Explanation

Extensor mechanism disruption after TKA is a catastrophic complication. Primary repair of chronic disruptions yields unacceptably high failure rates due to poor tissue quality and tension. The standard of care for chronic patellar tendon ruptures in the setting of TKA is reconstruction using an extensor mechanism allograft (tibial tubercle, patellar tendon, patella, quad tendon) or synthetic mesh (e.g., Marlex mesh), which acts as a scaffold for fibrous tissue ingrowth.

Question 19

A patient with a documented severe metal allergy is scheduled for a primary total knee arthroplasty. If the patient has a true hypersensitivity reaction to standard orthopedic implants, which of the following best describes the pathophysiologic mechanism and the most common offending metal?

Explanation

Metal hypersensitivity in total joint arthroplasty is a Type IV cell-mediated (delayed) hypersensitivity reaction. It is mediated by T-lymphocytes rather than antibodies. The most common metal sensitizers in the general population, and historically the culprits in symptomatic orthopedic implants (specifically stainless steel or cobalt-chrome alloys), are Nickel, Cobalt, and Chromium. Nickel is the most prevalent contact allergen overall.

Question 20

A 75-year-old male sustains a posterior dislocation of his total hip arthroplasty. He reports that his primary surgery was 15 years ago, and he has never had a dislocation prior to this event. Assuming no recent trauma or neurological decline, what is the most common pathophysiologic mechanism for a 'late' (>5 years post-op) THA dislocation?

Explanation

Dislocations occurring many years (>5 years) after the index THA are typically caused by gradual wear of the polyethylene liner. Volumetric wear of the liner leads to eccentric positioning of the femoral head within the cup, which decreases the "jump distance" (the effective head size) required for dislocation and concurrently generates capsular and soft tissue laxity (the "dead space" effect). This combination makes the hip progressively unstable.

Question 21

During a primary total knee arthroplasty, trial reduction reveals a symmetric extension gap but a flexion gap that is tight both medially and laterally. Which of the following adjustments is the most appropriate next step?

Explanation

A tight flexion gap with a balanced extension gap implies the anteroposterior dimension of the femoral component is too large. Downsizing the femoral component using anterior referencing increases posterior condylar resection, enlarging the flexion gap without affecting the extension gap.

Question 22

A surgeon is performing a posterior-stabilized total knee arthroplasty. After making the initial bone cuts and inserting trial components, the knee is symmetric and stable in extension, but the flexion gap is unacceptably tight. Which of the following is the most appropriate surgical adjustment to correct this imbalance?

Explanation

A tight flexion gap with a balanced extension gap requires downsizing the femoral component while maintaining the same anterior reference. This selectively increases the flexion gap by reducing the posterior condylar offset without affecting the extension gap.

Question 23

A 68-year-old male with severe ankylosing spondylitis and a fused lumbar spine is planned for a primary total hip arthroplasty. How should the surgeon alter the standard acetabular cup positioning to minimize the risk of posterior dislocation?

Explanation

Patients with a stiff lumbar spine fail to increase pelvic tilt during sitting, putting them at high risk for posterior dislocation. To compensate for the lack of dynamic spinopelvic adaptation, the surgeon must increase the acetabular anteversion.

Question 24

A 65-year-old male presents with groin pain three years after a cementless total hip arthroplasty utilizing a metal-on-polyethylene bearing surface. Laboratory workup reveals substantially elevated serum cobalt levels with normal chromium levels. What is the most likely etiology of his symptoms?

Explanation

Elevated cobalt levels out of proportion to chromium in a metal-on-polyethylene THA is classic for trunnionosis. This represents mechanocorrosion (fretting and crevice corrosion) at the modular head-neck junction.

Question 25

During a primary total knee arthroplasty, internal rotation of the tibial component relative to the tibial tubercle will most likely result in which of the following complications?

Explanation

Internal rotation of the tibial component effectively lateralizes the tibial tubercle relative to the trochlear groove. This increases the Q-angle and leads to lateral patellar tracking, subluxation, or dislocation.

Question 26

A 75-year-old patient reports a new-onset "clunking" sensation and pain in their knee when transitioning from a seated to a standing position, one year after a posterior-stabilized total knee arthroplasty. What is the most likely pathophysiologic mechanism for this finding?

Explanation

Patellar clunk syndrome is primarily associated with posterior-stabilized TKA designs. It occurs when a fibrous nodule develops at the superior pole of the patella and catches in the intercondylar notch of the femoral component during extension from a flexed position.

Question 27

A 78-year-old female presents to the emergency department after a low-energy fall. She underwent a cementless primary total hip arthroplasty 8 years ago. Radiographs demonstrate a displaced spiral fracture around the distal aspect of a well-fixed porous-coated femoral stem with excellent surrounding bone stock.

According to the Vancouver classification, what is the most appropriate surgical management?

Explanation

This describes a Vancouver B1 periprosthetic fracture (fracture around a well-fixed stem with good bone stock). The standard of care for a Vancouver B1 fracture is open reduction and internal fixation, typically utilizing plates and cables/screws.

Question 28

When performing a medial parapatellar arthrotomy for a total knee arthroplasty, avoiding injury to the superior lateral geniculate artery is critical to prevent which of the following complications?

Explanation

The superior lateral geniculate artery is a major blood supply to the patella. Sacrificing it during a medial parapatellar approach, which already disrupts medial vessels, significantly increases the risk of patellar avascular necrosis.

Question 29

A surgeon is evaluating a 60-year-old male for a revision total hip arthroplasty due to aseptic loosening. The surgeon plans to utilize a highly porous, uncemented hemispherical acetabular component to achieve a stable center of rotation. Moving the hip center of rotation medially and inferiorly accomplishes which of the following biomechanical advantages?

Explanation

Medializing the center of rotation decreases the body weight moment arm, while inferior placement helps restore the abductor moment arm. Together, these alterations significantly decrease the overall joint reaction force on the hip.

Question 30

A 55-year-old female undergoes a direct anterior approach for a total hip arthroplasty. Post-operatively, she complains of numbness over the anterolateral aspect of her thigh. Which nerve is most likely affected, and what is its anatomic relationship to the surgical interval?

Explanation

The lateral femoral cutaneous nerve (LFCN) is at risk during the direct anterior approach. It classically courses superficial to the sartorius muscle and can be injured during superficial dissection or retraction.

Question 31

During a primary total knee arthroplasty, a surgeon notes that the joint is balanced in both flexion and extension, but there is significant opening on the medial side at 45 degrees of flexion. What is the most likely cause of this mid-flexion instability?

Explanation

Mid-flexion instability (instability between 30 and 60 degrees despite stability in extension and 90 degrees flexion) is most commonly caused by elevation of the joint line. This alters the tension of the collateral ligaments in the mid-flexion arc.

Question 32

A 70-year-old patient with a history of a metal-on-metal total hip arthroplasty presents with a large symptomatic pseudotumor. Histological examination of the periprosthetic tissue is most likely to demonstrate which of the following patterns?

Explanation

Adverse local tissue reaction (ALTR) or ALVAL in metal-on-metal hips is characterized histologically by a perivascular lymphocytic infiltrate (type IV delayed hypersensitivity) and macrophages containing metal debris.

Question 33

In the setting of a revision total knee arthroplasty, the surgeon identifies an Anderson Orthopaedic Research Institute (AORI) Type III bone defect of the proximal tibia. What is the defining characteristic of this defect and the most appropriate reconstructive option?

Explanation

AORI Type III defects involve severe bone loss that compromises a major portion of the condyle or plateau and frequently includes disruption of the collateral ligament attachments. Reconstruction often requires massive structural allografts, custom mega-prostheses, or hinged designs.

Question 34

Tranexamic acid (TXA) is routinely used in total joint arthroplasty to reduce blood loss. What is the specific mechanism of action of this pharmacological agent?

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It competitively inhibits plasminogen activation by binding to lysine receptor sites, thereby preventing the conversion of plasminogen to plasmin and inhibiting fibrinolysis.

Question 35

Which of the following scenarios is an absolute indication for using a linked (rotating hinge) prosthesis in a revision total knee arthroplasty?

Explanation

A completely deficient or incompetent medial collateral ligament cannot be managed with a constrained non-hinged (CCK) implant because the varus-valgus constraint is insufficient. It mandates a linked or rotating hinge prosthesis to provide adequate coronal plane stability.

Question 36

During the posterior approach to the hip, protecting the blood supply to the femoral head in the setting of a femoral neck fracture is not required; however, understanding the vascular anatomy is critical to limit bleeding. The medial femoral circumflex artery (MFCA) provides the primary blood supply to the head. Where is the deep branch of the MFCA anatomically located during this approach?

Explanation

The deep branch of the medial femoral circumflex artery passes consistently between the pectineus and iliopsoas, then courses posteriorly between the quadratus femoris and obturator externus muscles. Surgeons must be cautious when releasing the quadratus femoris to avoid brisk bleeding.

Question 37

A surgeon is evaluating a painful total knee arthroplasty (TKA) utilizing the 2018 Musculoskeletal Infection Society (MSIS) criteria. Which of the following isolated laboratory findings is considered a major criterion, diagnosing a periprosthetic joint infection outright?

Explanation

Under the 2018 MSIS/ICM criteria, the two major criteria that definitively diagnose a periprosthetic joint infection are a sinus tract communicating with the joint or two positive periprosthetic cultures with phenotypically identical organisms.

Question 38

A 45-year-old male undergoes a hip resurfacing arthroplasty. Six months later, he sustains a fracture of the femoral neck. Which of the following surgical factors most significantly increases the risk of this specific complication?

Explanation

Varus positioning of the femoral component in hip resurfacing shifts the load laterally, increasing tensile forces on the superior femoral neck. This significantly increases the risk of a post-operative femoral neck fracture.

Question 39

When templating for a total hip arthroplasty, the surgeon notes an anticipated leg length discrepancy. Lowering the center of rotation of the acetabular component without changing the femoral neck cut or stem size will result in which of the following?

Explanation

Lowering (inferiorizing) the acetabular center of rotation pushes the entire femur distally, thereby increasing leg length. It does not alter the horizontal distance (femoral offset) between the center of rotation and the femoral axis.

Question 40

A 60-year-old female presents with acute pain and inability to actively extend her knee 3 weeks after a primary total knee arthroplasty. Examination reveals a palpable gap at the superior pole of the patella. What is the most appropriate management strategy?

Explanation

Quadriceps tendon ruptures following TKA generally require operative intervention. Due to poor tissue quality and high failure rates of primary repair, augmentation with synthetic mesh or allograft is the standard of care to achieve a stable reconstruction.

Question 41

In kinematic alignment (KA) for total knee arthroplasty, the primary surgical goal differs significantly from mechanical alignment (MA). Which of the following best describes the core principle of kinematic alignment?

Explanation

Kinematic alignment aims to restore the patient's pre-arthritic anatomy and native joint lines by aligning the implants with the natural kinematic axes of the knee. This minimizes the need for soft tissue releases, unlike traditional mechanical alignment.

Question 42

During a primary total knee arthroplasty, the surgeon inadvertently places the femoral component in excessive internal rotation. Which of the following is the most likely consequence of this error?

Explanation

Internal rotation of the femoral component translates the trochlear groove medially, relatively lateralizing the tibial tubercle and increasing the Q-angle. This commonly results in lateral patellar maltracking, tilt, and potential subluxation.

Question 43

A 68-year-old female presents with groin pain two years after an uncomplicated total hip arthroplasty using a metal-on-polyethylene bearing with a titanium stem and a large diameter cobalt-chrome head. Inflammatory markers are normal, but metal artifact reduction sequence (MARS) MRI shows a pseudotumor. What is the most likely source of the pathology?

Explanation

Adverse local tissue reactions (ALTR) can occur in metal-on-polyethylene THAs due to mechanically assisted crevice corrosion (trunnionosis) at the modular head-neck junction. This risk is elevated with large-diameter, heavy cobalt-chrome heads on titanium stems.

Question 44

In evaluating a patient with a stiff spine (lumbar fusion from L2 to pelvis) planned for a total hip arthroplasty, understanding spinopelvic kinematics is crucial. Because the pelvis fails to retrovert when the patient transitions from standing to sitting, what dislocation risk is significantly increased?

Explanation

In a patient with a fused or stiff lumbopelvic junction, the pelvis cannot retrovert during sitting to naturally increase functional acetabular anteversion. This leads to anterior bony impingement and a high risk of posterior dislocation when seated.

Question 45

During a cruciate-retaining (CR) total knee arthroplasty, the surgeon notes that the trial components demonstrate anterior lift-off of the tibial tray during deep flexion. What is the most appropriate management step to resolve this intraoperative finding?

Explanation

Anterior lift-off of the tibial tray during deep flexion in a CR knee is a classic sign of a tight posterior cruciate ligament (PCL). Releasing or recessing the PCL will balance the flexion gap and prevent this paradoxical kinematic issue.

Question 46

A surgeon is performing a total hip arthroplasty using the direct lateral (Hardinge) approach. To prevent an iatrogenic Trendelenburg gait, the proximal split of the gluteus medius should not extend more than 3 to 5 cm proximal to the tip of the greater trochanter. Which structure is protected by this limitation?

Explanation

The superior gluteal nerve innervates the gluteus medius and minimus, passing approximately 3 to 5 cm proximal to the tip of the greater trochanter. Extending the muscular split beyond this point risks denervating the abductors, resulting in a postoperative Trendelenburg lurch.

Question 47

According to the Musculoskeletal Infection Society (MSIS) criteria, which of the following synovial fluid profiles is most consistent with a chronic periprosthetic joint infection in a knee arthroplasty?

Explanation

For chronic PJI (>6 weeks post-op), a synovial fluid WBC count greater than 3,000 cells/µL and a polymorphonuclear (PMN) percentage > 80% are highly suggestive of infection according to MSIS criteria.

Question 48

A patient with osteoarthritis presents with a fixed varus deformity of 15 degrees and a flexion contracture of 20 degrees. Why is a medial unicompartmental knee arthroplasty (UKA) contraindicated in this patient?

Explanation

Absolute contraindications for unicompartmental knee arthroplasty include a fixed varus deformity >10 degrees and a flexion contracture >15 degrees. UKA is a resurfacing procedure that cannot effectively release or balance severe, fixed soft tissue contractures without early failure.

Question 49

When placing screws in the acetabular component during a total hip arthroplasty, the posterior-superior quadrant is generally considered the 'safe zone'. Which major vascular structure is at greatest risk if a screw penetrates the anterior-superior quadrant?

Explanation

The anterior-superior quadrant is considered a danger zone due to the proximity of the external iliac vessels. Screws in the anterior-inferior quadrant risk the obturator nerve and vessels.

Question 50

A 55-year-old male with a history of severe slipped capital femoral epiphysis (SCFE) undergoes a total hip arthroplasty. During the operation, the surgeon finds it difficult to restore femoral offset without excessively lengthening the limb. Sinking the femoral stem deeper is not possible due to a narrow diaphysis. What is the most appropriate next step?

Explanation

A high-offset femoral stem increases the abductor lever arm (offset) without increasing vertical height (leg length). This is ideal when offset must be increased, but leg length is already equal or slightly long.

Question 51

A patient complains of a stiff knee six months after a primary total knee arthroplasty. Range of motion is 10 to 80 degrees. Radiographs show the femoral component is oversized and placed in excessive flexion. Which of the following kinematics best explains the limited flexion?

Explanation

An oversized femoral component, particularly one placed in excessive flexion, increases the anteroposterior diameter of the femur, tightening the flexion gap and overstuffing the patellofemoral joint. This physically blocks deep flexion.

Question 52

Which of the following modifications in total hip arthroplasty bearing surfaces utilizes a free radical scavenger to minimize in vivo oxidation while maintaining mechanical strength?

Explanation

Vitamin E (alpha-tocopherol) acts as a powerful antioxidant and free radical scavenger. Infusing highly cross-linked polyethylene with Vitamin E prevents oxidation without the need for post-irradiation melting, thereby preserving mechanical and fatigue strength.

Question 53

During pre-operative templating for a complex revision total hip arthroplasty, the surgeon classifies the acetabular defect as Paprosky Type IIIB. Which of the following radiographic findings defines this defect?

Explanation

Paprosky Type IIIB acetabular defects are characterized by severe bone loss with superior migration > 3 cm and violation of Kohler's line (medial migration/pelvic discontinuity). Type IIIA involves superior migration > 3 cm but with an intact Kohler's line.

Question 54

A 68-year-old female presents for a primary total hip arthroplasty. Preoperative radiographs reveal a long spinal fusion from T10 to the pelvis with a significantly decreased sacral slope and a retroverted pelvis. Based on her spinopelvic mechanics, this patient is at the greatest risk for which of the following complications?

Explanation

A patient with a fused lumbar spine in flatback deformity (retroverted pelvis) cannot dynamically accommodate postural changes. The fixed retroversion increases functional anteversion when standing, placing the patient at a high risk for anterior impingement and subsequent anterior dislocation.

Question 55

During a primary total knee arthroplasty (TKA), the surgeon checks the gap kinematics with spacer blocks. The extension gap is symmetric and perfectly balanced, but the flexion gap is unacceptably tight symmetrically. What is the most appropriate surgical step to balance the knee?

Explanation

A symmetrically tight flexion gap with a balanced extension gap is best treated by downsizing the femoral component. This increases the anteroposterior dimension of the flexion space without altering the extension gap.

Question 56

A 55-year-old male with a metal-on-polyethylene total hip arthroplasty utilizing a large-diameter cobalt-chromium head on a titanium stem presents with groin pain and a large cystic mass. Aspiration yields sterile, thick, dark fluid. What is the primary pathophysiologic mechanism responsible for this presentation?

Explanation

This patient has trunnionosis (mechanically assisted crevice corrosion), exacerbated by the use of a large-diameter cobalt-chromium head on a titanium stem. Fretting at the modular head-neck junction disrupts the passivation layer, leading to localized corrosion, adverse local tissue reactions, and pseudotumor formation.

Question 57

A 78-year-old female presents to the emergency department after a mechanical fall. She has a painful, shortened right leg. Radiographs demonstrate a fracture around her cemented femoral stem.

Assuming the radiograph shows a fracture at the tip of the stem with evidence of a loose implant but adequate distal bone stock, what is the most appropriate definitive management?

Explanation

A periprosthetic fracture at the tip of the stem with a loose component and adequate distal bone stock is classified as a Vancouver B2 fracture. The gold standard treatment is revision arthroplasty utilizing a long, cementless, diaphyseal-engaging stem that bypasses the fracture site by at least two cortical diameters.

Question 58

In the diagnostic algorithm for a suspected periprosthetic joint infection (PJI), a synovial fluid alpha-defensin test is ordered. What is the specific biological origin and function of alpha-defensin in this clinical context?

Explanation

Alpha-defensin is a highly specific antimicrobial peptide released by neutrophils in response to pathogens. Its presence in synovial fluid is a major criterion for diagnosing periprosthetic joint infection due to its high sensitivity and specificity.

Question 59

A 65-year-old patient who underwent a posterior-stabilized (PS) total knee arthroplasty two years ago complains of an audible and painful 'pop' at the anterior knee when extending from a flexed position. What is the anatomical basis of this specific complication?

Explanation

Patellar clunk syndrome is uniquely associated with posterior-stabilized TKA designs. It occurs when a fibrous nodule develops at the superior pole of the patella and gets caught in the intercondylar box of the femoral component during active extension.

Question 60

During preoperative templating for a primary total hip arthroplasty, the surgeon plans to place the acetabular component medial to the anatomic center of rotation. What is the primary biomechanical effect of this medialization?

Explanation

Medializing the center of rotation of the hip decreases the lever arm of the body weight. According to static hip biomechanics, this significantly decreases the overall joint reaction force on the hip.

Question 61

A patient presents with persistent anterior knee pain and lateral patellar subluxation 6 months following a primary total knee arthroplasty. CT imaging is ordered to assess component rotation. Which of the following component malrotations is the most likely cause of this patellofemoral tracking issue?

Explanation

Internal rotation of the tibial component or the femoral component lateralizes the tibial tubercle relative to the trochlear groove. This increases the Q-angle, leading to lateral patellar maltracking and anterior knee pain.

Question 62

When performing a direct lateral (Hardinge) approach for a total hip arthroplasty, the surgeon must split the gluteus medius. To prevent denervation of the anterior portion of the gluteus medius and the tensor fasciae latae, the proximal split must not exceed what safe distance from the tip of the greater trochanter?

Explanation

The superior gluteal nerve crosses approximately 5 cm proximal to the tip of the greater trochanter. Extending the gluteus medius split beyond this 5 cm 'safe zone' risks denervating the anterior gluteus medius, gluteus minimus, and tensor fasciae latae.

Question 63

In the process of aseptic loosening of a total joint arthroplasty, particulate wear debris initiates a biologic cascade leading to osteolysis. Which of the following cells is the primary initiator of this inflammatory cascade by phagocytosing the debris?

Explanation

Macrophages phagocytose particulate wear debris (such as polyethylene particles) and subsequently release pro-inflammatory cytokines like TNF-alpha, IL-1, and IL-6. This initiates a signaling cascade that upregulates RANKL, leading to osteoclast activation and periprosthetic osteolysis.

Question 64

A surgeon is performing a cruciate-retaining (CR) total knee arthroplasty. Upon trialing the components, the surgeon notes that the anterior aspect of the tibial tray lifts off the baseplate during deep flexion. What is the most likely cause of this phenomenon?

Explanation

In a CR total knee arthroplasty, an excessively tight posterior cruciate ligament (PCL) causes excessive posterior femoral rollback during deep flexion. This tethering effect hinges the joint, lifting the anterior aspect of the tibial component.

Question 65

A 62-year-old male is being evaluated for a unicompartmental knee arthroplasty (UKA) for isolated medial compartment osteoarthritis. According to the classic Kozinn and Scott criteria, which of the following is an absolute contraindication for a medial UKA?

Explanation

Inflammatory arthritis (such as rheumatoid arthritis) is a strict contraindication for unicompartmental knee arthroplasty due to the global, progressive nature of the disease. Ideal candidates are non-obese, have an intact ACL, unicompartmental disease, correctable varus, and minimal flexion contractures (<15 degrees).

Question 66

A 70-year-old male returns to the clinic 14 days after a primary total knee arthroplasty with an acutely swollen, red, and painful knee. He has had fevers for 24 hours. Aspiration confirms acute periprosthetic joint infection with a well-fixed implant. Which treatment has the highest likelihood of success for retaining his current implant?

Explanation

DAIR (Debridement, Antibiotics, and Implant Retention) is most successful in acute hematogenous infections or early postoperative infections (typically < 3-4 weeks) when the implants are well-fixed. Crucially, the modular polyethylene liner must be exchanged to allow thorough debridement of the posterior capsule.

Question 67

The use of a larger femoral head in total hip arthroplasty reduces the risk of dislocation primarily through which biomechanical mechanism?

Explanation

A larger femoral head increases the 'jump distance' - the distance the femoral head must translate before it dislocates from the acetabulum. It also increases the head-neck ratio, which improves the arc of motion before component-to-component impingement occurs.

Question 68

During a total knee arthroplasty for a fixed valgus deformity, the surgeon notes that the lateral gap is critically tight in flexion but balanced in extension. Which structure should be preferentially released to correct this specific gap mismatch?

Explanation

In the setting of a valgus knee, the popliteus tendon primarily affects the flexion gap. If the knee is tight laterally only in flexion, isolated release of the popliteus is indicated; conversely, the IT band primarily affects the extension gap.

Question 69

While performing an anterolateral approach to the hip, the surgeon proceeds to release the reflected head of the rectus femoris to improve acetabular exposure. Ligation of which of the following vascular structures is necessary to prevent significant hemorrhage during this step?

Explanation

The ascending branch of the lateral femoral circumflex artery transverses the operative field between the tensor fasciae latae and the sartorius/rectus interval. It must be identified and ligated during an anterolateral or direct anterior approach to prevent severe postoperative hematoma.

Question 70

A 75-year-old female presents for revision total hip arthroplasty. Pelvic radiographs demonstrate severe acetabular bone loss. The teardrop is obliterated, Kohler's line is discontinuous (broken), and the hip center has migrated 4 cm superiorly and 2 cm medially. What is the correct Paprosky classification for this defect?

Explanation

A Paprosky Type 3B defect is characterized by severe superior migration (>3 cm) and severe medial migration (>1 cm) with disruption of Kohler's line, indicating loss of the medial wall. Type 3A defects feature superior migration but have an intact Kohler's line.

Question 71

In revision total knee arthroplasty, massive uncontained metaphyseal bone defects (AORI Type IIb or III) are identified in both the distal femur and proximal tibia. Which of the following reconstructive options provides the best long-term biologic fixation and construct rigidity for these specific defects?

Explanation

Highly porous metaphyseal cones and sleeves are the gold standard for managing severe, uncontained metaphyseal bone loss (AORI IIb/III) in revision TKA. They provide excellent initial mechanical stability and promote long-term biologic osteointegration.

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

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

Key Takeaway

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

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