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

Question 1

A 65-year-old man is undergoing a primary total hip arthroplasty (THA). The surgeon selects a high-offset femoral stem that increases femoral offset without altering leg length. Compared to a standard offset stem, what is the primary biomechanical consequence of this modification?

Explanation

Increasing femoral offset shifts the femur laterally, which increases the abductor moment arm. A longer abductor moment arm means the abductor muscles require less force to balance the pelvis. Because joint reaction force is heavily dependent on the vector sum of body weight and abductor muscle force, decreasing the required abductor force significantly decreases the overall joint reaction force, leading to improved mechanics and theoretically less wear.

Question 2

During a primary total knee arthroplasty (TKA), trial components are inserted. The surgeon observes that the knee is perfectly balanced and stable in full extension, but it is excessively tight in 90 degrees of flexion. Which of the following is the most appropriate surgical step to balance the knee?

Explanation

A knee that is balanced in extension but tight in flexion requires an increase in the flexion gap without altering the extension gap. Downsizing the femoral component (which effectively decreases the anteroposterior dimension of the femur) increases the flexion gap. Resecting more proximal tibia would increase both gaps symmetrically. Resecting more distal femur would only affect the extension gap.

Question 3

A 55-year-old woman with a metal-on-metal THA presents with progressive groin pain 4 years postoperatively. Advanced imaging reveals a large solid and cystic pelvic mass. A subsequent biopsy of the pseudotumor demonstrates a dense perivascular lymphocytic infiltrate. This pathology is a result of which immunological mechanism?

Explanation

The classic histological finding of aseptic lymphocyte-dominated vasculitis-associated lesions (ALVAL) in metal-on-metal implants is a dense perivascular lymphocytic infiltrate. This represents a delayed, cell-mediated Type IV hypersensitivity reaction to metal ions (primarily cobalt and chromium).

Question 4

A resident is performing a single-bundle anterior cruciate ligament (ACL) reconstruction. If the femoral tunnel is erroneously placed too far anteriorly (shallow) within the intercondylar notch, what abnormal graft tensioning pattern will result?

Explanation

Proper femoral tunnel placement is critical for isometric graft tension. A femoral tunnel placed too far anteriorly (anterior to the anatomic footprint) will result in an ACL graft that is excessively tight in flexion (often restricting flexion or stretching the graft) and loose in extension.

Question 5

During a direct anterior (Smith-Petersen) approach for a total hip arthroplasty, the surgeon dissects through the superficial internervous plane. This plane separates muscles innervated by which two nerves?

Explanation

The direct anterior approach utilizes a true internervous and intermuscular plane. The superficial interval is between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve). The deep interval is between the rectus femoris (femoral nerve) and the gluteus medius (superior gluteal nerve).

Question 6

Based on classical criteria, which of the following is considered an absolute contraindication for a medial unicompartmental knee arthroplasty (UKA) in a patient with medial compartment osteoarthritis?

Explanation

Classic criteria for UKA (Kozinn and Scott) list ACL deficiency, inflammatory arthritis, flexion contracture > 15 degrees, fixed varus > 10 degrees, and fixed valgus > 5 degrees as absolute contraindications. While age > 55 and weight > 82 kg were previously relative contraindications, modern literature has largely debunked them. Mild PF joint disease is also typically well-tolerated. For board examination purposes, ACL deficiency remains the classical absolute contraindication among these choices.

Question 7

A 45-year-old male sustains a complete avulsion of the posterior root of the medial meniscus. Biomechanical studies indicate that the resulting contact pressures in the medial compartment of the knee are most functionally equivalent to which of the following conditions?

Explanation

The meniscal roots are essential for anchoring the meniscus and converting axial loads into circumferential hoop stresses. Complete avulsion of the posterior medial meniscal root eliminates these hoop stresses and leads to meniscal extrusion, rendering the joint biomechanically equivalent to having undergone a total meniscectomy.

Question 8

A 68-year-old woman presents with persistent lateral anterior knee pain and clinical evidence of lateral patellar subluxation 1 year after a primary TKA. During revision surgery, malrotation of the components is suspected. Which of the following technical errors is the most common cause of lateral patellar maltracking in TKA?

Explanation

Internal rotation of either the femoral or tibial component relative to their anatomical axes increases the Q-angle, leading to lateral patellar maltracking. To optimize patellar tracking, the femoral component is typically externally rotated (relative to the posterior condylar axis) and the patellar button is placed medially.

Question 9

According to the 2018 International Consensus Meeting (ICM) criteria for Periprosthetic Joint Infection (PJI), a synovial fluid analysis from a painful 2-year-old THA reveals a white blood cell (WBC) count of 4,500 cells/µL and 85% polymorphonuclear neutrophils (PMNs). How are these specific laboratory results interpreted in the diagnostic scoring algorithm?

Explanation

Under the 2018 ICM criteria for PJI, elevated synovial WBC count (> 3,000 cells/µL) and elevated synovial PMN percentage (> 80%) are both minor criteria. The WBC count gives 3 points and the PMN% gives 2 points toward the diagnosis of PJI (a score of 6 or higher is diagnostic).

Question 10

A 32-year-old man with a history of systemic lupus erythematosus and high-dose corticosteroid use presents with severe left groin pain. Radiographs show a distinct subchondral lucency (crescent sign) in the femoral head without joint space narrowing. What is the most reliable and definitive surgical treatment for this patient?

Explanation

The presence of a crescent sign on plain radiographs signifies subchondral collapse (Ficat III / Steinberg III) of the femoral head due to osteonecrosis. Once mechanical collapse has occurred, joint-preserving procedures such as core decompression or vascularized fibular grafting have a high failure rate. Total hip arthroplasty provides the most reliable pain relief and functional improvement.

Question 11

A 78-year-old woman sustains a periprosthetic femur fracture around a cemented, polished taper-slip THA stem. Radiographs demonstrate the fracture is located just distal to the tip of the stem. The stem is radiographically loose, but there is excellent proximal femoral bone stock. Which classification and corresponding treatment are most appropriate?

Explanation

This is a Vancouver B2 fracture. The fracture occurs around or just distal to the tip of the stem (Type B), the stem is loose (Type 2), but the bone stock is adequate (distinguishing it from B3, which has poor bone stock). The gold standard treatment for a Vancouver B2 fracture is revision of the femoral component to a long-stem bypass prosthesis, achieving fixation distal to the fracture.

Question 12

During kinematic analysis of a posterior cruciate-retaining (CR) total knee arthroplasty, the patient is noted to have paradoxical anterior sliding of the femur on the tibia during deep flexion. What is the primary cause of this kinematic abnormality?

Explanation

In a normal knee or properly balanced CR TKA, the intact posterior cruciate ligament (PCL) engages during flexion to pull the femur posteriorly, a motion known as femoral rollback. If the PCL is insufficient, overly lax, or accidentally completely sectioned in a CR design, it fails to induce rollback, and the femur paradoxically slides anteriorly during flexion, potentially leading to limited motion and increased wear.

Question 13

You are performing a medial patellofemoral ligament (MPFL) reconstruction for recurrent patellar instability. To place the femoral tunnel anatomically, you use Schöttle's point on a strictly lateral fluoroscopic view. Where is this point located relative to key radiographic landmarks?

Explanation

Schöttle's point represents the anatomic femoral origin of the MPFL. On a strict lateral radiograph, it is located approximately 1 mm anterior to a line extending from the posterior femoral cortex, 2.5 mm distal to the posterior origin of the medial femoral condyle, and proximal to Blumensaat's line.

Question 14

A 24-year-old professional hockey player presents with deep anterior groin pain exacerbated by hip flexion and internal rotation. An AP pelvis radiograph demonstrates a 'crossover sign', where the anterior wall of the acetabulum crosses lateral to the posterior wall before reaching the lateral edge of the sourcil. This radiographic finding is pathognomonic for which condition?

Explanation

The crossover sign is the classic radiographic indicator of cranial or global acetabular retroversion, a common cause of pincer-type femoroacetabular impingement (FAI). Normally, the anterior wall line remains medial to the posterior wall line throughout its course.

Question 15

A 45-year-old man underwent an uncomplicated THA utilizing a ceramic-on-ceramic bearing surface. At his 2-year follow-up, he complains of a loud, audible 'squeaking' sound from his hip when transitioning from sitting to standing. Which of the following factors is most strongly associated with the development of this complication?

Explanation

Squeaking is a specific complication associated with ceramic-on-ceramic total hip arthroplasty. It is highly correlated with edge loading of the ceramic bearings, which occurs due to micro-separation and stripe wear. This is most frequently caused by component malposition, such as excessive acetabular cup inclination or incorrect anteversion.

Question 16

A 28-year-old male sustains a multi-ligamentous knee injury. Physical examination includes a dial test, which reveals 15 degrees of asymmetric increased external rotation of the tibia at 30 degrees of knee flexion compared to the uninjured side. However, external rotation is symmetric at 90 degrees of flexion. This pattern isolates injury to which structure(s)?

Explanation

The dial test assesses for posterolateral instability. Asymmetric external rotation of >10 degrees at 30 degrees of flexion only indicates an isolated posterolateral corner (PLC) injury. If the asymmetry is present at both 30 degrees and 90 degrees of flexion, it signifies a combined PLC and PCL injury.

Question 17

During a standard posterior approach (Moore/Southern) to the hip, which critical blood vessel is typically encountered near the superior border of the quadratus femoris and must be identified and coagulated to prevent significant postoperative hematoma?

Explanation

The ascending branch of the medial circumflex femoral artery (MCFA), also known as the posterior retinacular artery, crosses the operative field at the superior border of the quadratus femoris and the inferior border of the obturator externus. It is routinely encountered during the posterior approach and must be carefully cauterized or ligated to prevent bleeding.

Question 18

A 35-year-old male presents with a Schatzker IV (medial) tibial plateau fracture following a high-energy motor vehicle accident. Given the fracture pattern, what is the most critical immediate clinical assessment required in the emergency department?

Explanation

A Schatzker IV fracture involves the medial tibial plateau and is typically the result of a high-energy varus force. It is clinically considered part of the knee dislocation spectrum. Because of the close proximity of the popliteal artery and the high-energy trauma, there is a significant risk of popliteal artery injury, making vascular assessment (e.g., ABI) the most critical immediate step.

Question 19

During a primary TKA using a measured resection technique, trial components are placed. The knee exhibits a 15-degree flexion contracture (tight in extension) but demonstrates excessive varus-valgus play at 90 degrees of flexion (loose in flexion). Which of the following adjustments will best resolve this specific mismatch?

Explanation

The knee is tight in extension, which requires increasing the extension gap by resecting more distal femur. The knee is loose in flexion, which requires decreasing the flexion gap by adding posterior femoral offset (upsizing the femoral component in the A-P dimension). Resecting more distal femur and upsizing the femoral component addresses both issues simultaneously without altering the tibial resection.

Question 20

A patient presents with persistent anterior knee pain and a subjective feeling of instability 6 months following a primary TKA. Standing radiographs demonstrate a significantly elevated joint line and secondary patella baja. Which of the following complications is most specifically associated with an elevated joint line in TKA?

Explanation

Elevation of the joint line during TKA often results from excessive distal femoral resection combined with a thicker tibial polyethylene insert to balance the extension gap. This alters the isometry of the collateral ligaments as the knee moves through the arc of motion, leading to laxity in mid-flexion (mid-flexion instability). It also leads to relative patella baja, causing anterior knee pain.

Question 21

A 58-year-old woman undergoes a primary total hip arthroplasty (THA). To optimize hip biomechanics, the surgeon places the acetabular component medially and inferiorly to restore the anatomical center of rotation (COR). What is the effect of this component positioning on the overall joint reaction force (JRF) and the required abductor muscle force?

Explanation

Medializing the COR increases the abductor moment arm and decreases the body weight moment arm. This mechanical advantage reduces the force required by the abductors to maintain a level pelvis, which subsequently decreases the overall joint reaction force.

Question 22

During a primary total knee arthroplasty (TKA) using a gap-balancing technique, the surgeon notes that with the trial components in place, the knee is symmetrically loose in full extension but perfectly balanced at 90 degrees of flexion. Which of the following is the most appropriate corrective action?

Explanation

A knee that is loose in extension but balanced in flexion has an isolated enlarged extension gap. Decreasing the distal femoral resection (or using distal femoral augments) tightens the extension gap without affecting the flexion gap.

Question 23

A 68-year-old man presents with a Vancouver B2 periprosthetic femur fracture 8 years after a primary THA. Radiographs reveal a grossly loose femoral stem, but the proximal femoral bone stock remains adequate. What is the most appropriate surgical management?

Explanation

A Vancouver B2 fracture is characterized by a loose prosthesis with adequate surrounding bone stock. The standard of care is revision to a cementless long stem that bypasses the most distal fracture line by at least two cortical diameters, supplemented with cerclage cables.

Question 24

A 72-year-old woman presents with anterior knee pain and a "catching" sensation 18 months after a posterior-stabilized (PS) TKA. Clinical examination reveals a palpable and audible clunk as the knee moves actively from flexion into extension. What is the most likely etiology of this complication?

Explanation

Patellar clunk syndrome is a complication primarily associated with PS TKA designs. It occurs when a fibrous nodule forms on the undersurface of the distal quadriceps tendon or superior patellar pole, catching in the intercondylar box of the femur during extension.

Question 25

A 45-year-old active male is evaluated for a ceramic-on-ceramic THA. Which of the following acetabular component positioning errors is most strongly associated with the development of postoperative "squeaking" in this specific bearing surface?

Explanation

High cup inclination (steep cup angle > 50 degrees) and malversion can lead to edge loading in ceramic bearings. Edge loading causes loss of fluid film lubrication, resulting in stripe wear and the characteristic squeaking phenomenon.

Question 26

In the direct anterior approach for THA (Smith-Petersen interval), the superficial internervous plane is developed between which of the following pairs of muscles?

Explanation

The direct anterior approach utilizes the true internervous plane between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve).

Question 27

A 60-year-old man presents with severe groin pain 5 years after receiving a metal-on-polyethylene THA utilizing a large-diameter cobalt-chromium head on a titanium alloy stem. Laboratory tests show elevated serum cobalt levels with normal serum chromium. What is the most likely diagnosis?

Explanation

Mechanically assisted crevice corrosion (trunnionosis) occurs at the modular head-neck junction. It classically presents with an isolated elevation of serum cobalt relative to chromium and can lead to adverse local tissue reactions.

Question 28

When placing acetabular screws during a primary THA, the surgeon must be aware of the pelvic safe zones to avoid catastrophic neurovascular injury. Placement of a screw in the anterior-inferior quadrant places which of the following structures at highest risk?

Explanation

The anterior-inferior quadrant is considered a "danger zone" during acetabular screw placement because it places the obturator nerve and vessels at high risk. The anterior-superior quadrant risks the external iliac vessels.

Question 29

A surgeon is performing a cruciate-retaining TKA. With trial components in place, the knee is well-balanced in extension but exhibits excessive tightness and limited range of motion in flexion, along with paradoxical anterior tibial translation. What is the primary anatomical structure responsible for this finding?

Explanation

In a cruciate-retaining TKA, an excessively tight posterior cruciate ligament prevents normal posterior femoral rollback. This causes the flexion gap to be excessively tight and leads to paradoxical anterior sliding of the femur on the tibia during flexion.

Question 30

A patient with a failed TKA requires revision surgery. The surgeon identifies an AORI Type 3 defect, characterized by severe metaphyseal bone loss that compromises the origins of the collateral ligaments. Which of the following constraint levels is definitively required?

Explanation

AORI Type 3 defects involve massive bone loss that compromises the medial and lateral collateral ligament attachments. A rotating-hinge implant provides linked stability and is required to substitute for profound collateral ligament deficiency.

Question 31

A 55-year-old female presents with recurrent posterior dislocations following a primary THA. Radiographs demonstrate the acetabular component is placed in 10 degrees of retroversion. What is the primary biomechanical mechanism of dislocation in this specific setting?

Explanation

Acetabular retroversion causes early bony impingement of the anterior femoral neck against the prominent anterior rim of the cup during internal rotation and flexion. This impingement serves as a fulcrum, levering the femoral head out of the cup posteriorly.

Question 32

According to the Musculoskeletal Infection Society (MSIS) and International Consensus Meeting criteria, which of the following is considered an absolute major criterion for diagnosing a periprosthetic joint infection (PJI)?

Explanation

The absolute major criteria for definitive diagnosis of a PJI are either a sinus tract communicating with the prosthesis or two positive periprosthetic cultures with phenotypically identical organisms. The other options are considered minor criteria.

Question 33

During a primary TKA for a severe varus deformity, the medial compartment remains excessively tight in both flexion and extension after standard bone resections. Which of the following soft tissue structures should ideally be released first to correct this imbalance?

Explanation

In the stepwise soft tissue release for a severe varus knee, the deep medial collateral ligament is typically released first. If further balancing is needed, subsequent releases may include the posteromedial capsule and progressive fractional lengthening of the superficial MCL.

Question 34

A 38-year-old man undergoes a hip resurfacing arthroplasty. Postoperatively, he is closely monitored for the most common early mode of catastrophic failure, femoral neck fracture. Which of the following intraoperative technical factors most significantly increases this risk?

Explanation

Varus positioning of the femoral component in hip resurfacing increases shear stresses across the femoral neck and induces superior neck notching. This significantly elevates the biomechanical risk of a postoperative femoral neck fracture.

Question 35

In evaluating a patient for a potential unicompartmental knee arthroplasty (UKA), which of the following scenarios is traditionally considered an absolute contraindication?

Explanation

Inflammatory arthropathies, such as rheumatoid arthritis, involve the entire synovial lining of the joint. They are an absolute contraindication for UKA because the underlying systemic disease will aggressively progress in the unresurfaced compartments.

Question 36

During a primary total knee arthroplasty (TKA), the surgeon evaluates the trial components and finds the knee is tight in full extension but symmetric and perfectly balanced at 90 degrees of flexion. What is the most appropriate surgical step to achieve balance?

Explanation

Resecting more distal femur increases the size of the extension gap without affecting the flexion gap. Recutting the tibia would inappropriately increase both gaps, making the knee loose in flexion.

Question 37

A 70-year-old woman is evaluated for a primary THA. Standing and sitting lateral spinopelvic radiographs reveal a change in pelvic tilt of 5 degrees. How does this stiff spinopelvic relationship influence acetabular component positioning?

Explanation

A stiff spine (change in pelvic tilt < 10 degrees) fails to dynamically retrovert the pelvis during sitting, leading to anterior impingement. The acetabular cup must be placed in slightly more anteversion to accommodate flexion and prevent posterior dislocation.

Question 38

A 45-year-old active male underwent a THA with a ceramic-on-ceramic bearing. Three years later, he complains of an audible squeaking sound during movement but denies pain. What is the most likely biomechanical etiology of this phenomenon?

Explanation

Squeaking in ceramic-on-ceramic THA is highly associated with edge loading, often secondary to acetabular cup malposition (steep inclination or severe malversion). Edge loading results in stripe wear, disruption of fluid film lubrication, and subsequent noise.

Question 39

A 78-year-old female presents with a periprosthetic femur fracture around a cemented polished taper slip stem. Radiographs demonstrate a fracture at the tip of the stem with extensive proximal bone loss and osteolysis, rendering the proximal femur unsupportive. What is the most appropriate definitive management?

Explanation

This is a Vancouver B3 fracture characterized by a loose stem and severely compromised proximal bone stock. Proximal femoral replacement is the most reliable option in elderly patients, allowing immediate weight-bearing and functional recovery.

Question 40

Following implantation of trial components in a TKA, the surgeon notes a tendency for lateral patellar subluxation. Both the flexion and extension gaps are symmetric and balanced. Which of the following technical errors is most likely responsible?

Explanation

Internal rotation of either the femoral or tibial components increases the Q-angle, leading to lateral patellar tracking. Externally rotating the components or medializing the patellar dome improves central patellar tracking.

Question 41

A patient presents with a painful TKA 2 years postoperatively. Joint aspiration yields a synovial WBC count of 4,500 cells/mcL with 75% PMNs, and serum CRP is 15 mg/L. Which additional test provides the highest specificity for confirming periprosthetic joint infection (PJI)?

Explanation

Synovial alpha-defensin is a highly specific biomarker for PJI, released by neutrophils in response to pathogens. It maintains high specificity regardless of systemic inflammatory conditions or prior antibiotic use.

Question 42

During acetabular shell fixation in a primary THA, a screw is placed in the anterosuperior quadrant of the acetabulum (based on the Wasielewski quadrant system). Which vascular structure is at greatest risk of iatrogenic injury?

Explanation

The anterosuperior quadrant places the external iliac vessels at high risk if screws penetrate the inner cortex. The posterosuperior quadrant is considered the safe zone, although excessively long screws can injure the superior gluteal vessels.

Question 43

A 65-year-old female complains of a painful catching sensation and a palpable "clunk" when extending her knee from a flexed position, one year after receiving a posterior-stabilized (PS) TKA. What is the underlying pathology?

Explanation

Patellar clunk syndrome occurs in posterior-stabilized (PS) knees when a fibrosynovial nodule forms at the superior pole of the patella. During active knee extension, this nodule catches in the femoral intercondylar box, producing a painful clunk.

Question 44

In preoperative templating for a primary THA, medializing the center of rotation of the acetabulum without altering femoral offset achieves which distinct biomechanical advantage?

Explanation

Medializing the acetabular center of rotation decreases the body weight lever arm. This mechanical advantage reduces the force required by the abductors to maintain a level pelvis, substantially decreasing the hip joint reaction force.

Question 45

When choosing between a cruciate-retaining (CR) and a posterior-stabilized (PS) TKA design, the surgeon must consider implant kinematics. A PS TKA relies on the cam-post mechanism to specifically substitute for which native function?

Explanation

The intact posterior cruciate ligament (PCL) drives posterior femoral rollback during deep knee flexion to maximize flexion angle and clear the posterior anatomy. In a PS TKA, the PCL is excised, and the cam-post mechanism engages to recreate this essential rollback.

Question 46

The direct anterior (Smith-Petersen) approach to the hip utilizes an internervous plane between muscles supplied by which two specific nerves?

Explanation

The direct anterior approach utilizes a true internervous and intermuscular plane. It dissects between the tensor fasciae latae (supplied by the superior gluteal nerve) and the sartorius/rectus femoris (supplied by the femoral nerve).

Question 47

A 72-year-old man underwent a primary TKA 14 days ago. He now presents with 3 days of severe knee pain, erythema, and a draining sinus tract. Synovial aspiration grows Staphylococcus aureus. What is the most appropriate initial surgical management?

Explanation

Debridement, antibiotics, and implant retention (DAIR) with a modular polyethylene exchange is the standard of care for acute postoperative periprosthetic joint infections occurring within 4 weeks of the index surgery when the implants remain stable.

Question 48

A 60-year-old male presents with unexplained groin pain 7 years after a THA utilizing a large-diameter cobalt-chrome head on a titanium stem. Imaging shows no osteolysis. Serum cobalt levels are significantly elevated, while chromium levels are normal. What is the most likely diagnosis?

Explanation

Trunnionosis, or mechanically assisted crevice corrosion (MACC), occurs at the modular head-neck taper junction, especially with large metal heads on titanium stems. It typically presents with disproportionately elevated serum cobalt relative to chromium.

Question 49

A 35-year-old male with a history of high-dose corticosteroid use is diagnosed with osteonecrosis of the femoral head. MRI reveals subchondral edema but no subchondral collapse (Ficat Stage II). What is the primary physiological rationale for performing a core decompression?

Explanation

Core decompression aims to physically drill into the necrotic lesion to reduce the elevated intraosseous pressure characteristic of early-stage AVN. This pressure relief alleviates pain and creates a channel to facilitate the ingrowth of new vascular tissue.

Question 50

A 72-year-old woman with a history of a T10-to-pelvis posterior spinal fusion presents for a primary total hip arthroplasty (THA). Given her stiff spinopelvic articulation, which of the following adjustments to the acetabular component positioning is most appropriate to minimize the risk of dislocation?

Explanation

Patients with a stiff spine cannot increase pelvic tilt (retrovert) during sitting, risking anterior impingement and posterior dislocation. Increasing the target acetabular anteversion helps compensate for this lack of dynamic pelvic mobility.

Question 51

A 68-year-old man undergoes revision THA for aseptic loosening. Preoperative planning involves placing screws into the acetabulum for supplementary cup fixation. According to Wasielewski's quadrant system, screw placement in the anterior-superior quadrant places which of the following structures at highest risk of injury?

Explanation

The anterior-superior quadrant contains the external iliac artery and vein, making screw placement here dangerous. The posterior-superior quadrant is considered the 'safe zone' for acetabular screw placement.

Question 52

During a trial reduction of a primary total knee arthroplasty (TKA), the surgeon notes that the patella subluxates laterally during flexion. A lateral retinacular release is being considered. Which of the following component malpositions is the most likely primary cause of this abnormal patellar tracking?

Explanation

Internal rotation of the femoral or tibial components, as well as medialization of the femoral component or lateralization of the patellar button, increases the Q-angle and drives lateral patellar maltracking.

Question 53

A 79-year-old female presents to the emergency department with thigh pain and inability to bear weight after a mechanical fall. Radiographs demonstrate a displaced spiral fracture around the tip of her cementless THA stem. The stem shows subsidence and radiolucencies indicative of loosening. According to the Vancouver classification, what is the best surgical management?

Explanation

This is a Vancouver B2 periprosthetic fracture (fracture around a loose stem with adequate bone stock). The gold standard treatment is revision to a long bypass stem that extends at least two cortical diameters past the most distal fracture line.

Question 54

In total knee arthroplasty (TKA), the popliteal artery is at risk of iatrogenic injury. At which anatomical step of the procedure is the popliteal artery most vulnerable to direct laceration?

Explanation

The popliteal artery is tethered by the middle genicular artery and lies in closest proximity to the posterior capsule at the level of the tibial plateau, making it highly vulnerable during the tibial bone cut.

Question 55

A patient with a posterior-stabilized (PS) TKA develops restricted mid-flexion and a sense of 'tightness' despite adequate gap balancing. Postoperative radiographs reveal that the joint line has been significantly elevated. What is the primary kinematic consequence of joint line elevation in a PS TKA?

Explanation

Elevating the joint line in a PS knee moves the tibial post proximally relative to the femoral cam, causing early cam-post engagement. This restricts flexion and increases the risk of post wear or fracture.

Question 56

A 50-year-old man presents with progressive groin pain 10 years after receiving a cementless THA with a conventional metal-on-polyethylene bearing. Radiographs reveal focal expansile osteolysis of the proximal femur. Which of the following cell types is the primary driver of this osteolytic process?

Explanation

Wear-debris induced osteolysis is primarily mediated by macrophages, which phagocytose polyethylene particles and subsequently release cytokines (TNF-alpha, IL-1, IL-6) that stimulate osteoclastic bone resorption.

Question 57

A 66-year-old male with severe varus osteoarthritis is undergoing a primary TKA. During the procedure, the medial gap remains tight in both flexion and extension despite removal of peripheral osteophytes. What is the most appropriate sequential release to balance this varus deformity?

Explanation

For a tight medial compartment, sequential release begins with peripheral osteophytes and the deep MCL, followed by the posteromedial capsule. If still tight, pie-crusting or release of the superficial MCL is performed.

Question 58

A surgeon utilizes the direct anterior approach for a primary THA. This approach exploits an internervous and intermuscular plane. Which of the following accurately describes the superficial interval used in this approach?

Explanation

The superficial internervous plane of the direct anterior (Smith-Petersen) approach is between the sartorius (femoral nerve) and the tensor fasciae latae (superior gluteal nerve).

Question 59

A 45-year-old woman reports an audible 'squeaking' sound from her hip when walking, 3 years after a ceramic-on-ceramic THA. Which of the following biomechanical phenomena is most strongly associated with the onset of squeaking in these bearings?

Explanation

Squeaking in ceramic-on-ceramic bearings is strongly associated with edge loading, which disrupts the fluid film lubrication and causes stripe wear. This is often due to cup malposition, such as excessive abduction or anteversion.

Question 60

Restoring the anatomical hip center during THA for developmental dysplasia of the hip (DDH) is preferred over placing the cup in a high hip center. Biomechanically, what is the primary advantage of lowering the hip center to its true anatomical location?

Explanation

Restoring the anatomical (inferior and medial) hip center increases the mechanical advantage (moment arm) of the abductor muscles. This reduces the muscle force required for pelvic stability, thereby significantly decreasing the overall joint reactive force.

Question 61

During gap balancing in a primary TKA, the surgeon notes that the flexion gap is symmetrically loose by 4 mm, while the extension gap is perfectly balanced. Which of the following adjustments is most appropriate to balance the knee?

Explanation

A knee that is loose in flexion but balanced in extension requires an isolated decrease in the flexion gap. Upsizing the femoral component increases its AP dimension, filling the flexion gap without affecting the distal femoral extension gap.

Question 62

A 68-year-old man develops severe anterior groin pain when rising from a seated position or lifting his leg into a car, 1 year after a THA. Radiographs show the acetabular cup is in 45 degrees of abduction and 20 degrees of anteversion. An ultrasound-guided injection relieves the pain temporarily. What is the most likely etiology?

Explanation

Groin pain with active hip flexion (e.g., getting in/out of a car) coupled with symptom relief from an injection is classic for iliopsoas impingement. This is typically caused by a prominent anterior edge of the acetabular component.

Question 63

A patient with a failed metal-on-metal THA presents with systemic symptoms, including fatigue, visual impairment, and exertional dyspnea. Laboratory testing reveals elevated serum cobalt levels. Which of the following cardiac manifestations is a recognized complication of cobalt toxicity?

Explanation

Systemic cobalt toxicity (arthroprosthetic cobaltism) can cause devastating neuro-ocular and cardiovascular effects. The classic cardiac manifestation is a toxic dilated cardiomyopathy, which can be fatal if the implants are not revised.

Question 64

A 35-year-old man presents with chronic hip pain. Radiographs demonstrate a crescent sign in the superior femoral head with maintenance of the joint space. What is the most appropriate surgical treatment?

Explanation

The presence of a crescent sign indicates subchondral collapse (Ficat Stage III). Once collapse has occurred, joint-preserving procedures (like core decompression) have a high failure rate, making THA the most reliable treatment.

Question 65

A 68-year-old patient who underwent a posterior-stabilized TKA two years ago presents with an audible and palpable 'clunk' in the anterior knee when extending the knee from a flexed position. The clunk reliably occurs at roughly 35 degrees of flexion. What is the primary pathology driving this phenomenon?

Explanation

'Patellar clunk syndrome' occurs in posterior-stabilized knees when a fibrous nodule forms on the undersurface of the quadriceps tendon or superior patellar pole. As the knee extends, this nodule catches in the intercondylar box and pops out with a clunk at 30-45 degrees of flexion.

Question 66

A 65-year-old woman is evaluated for a suspected periprosthetic joint infection (PJI) 2 years after a TKA. A synovial fluid aspirate is sent for analysis. According to the 2018 International Consensus Meeting (ICM) criteria, which of the following synovial fluid biomarkers is considered a major diagnostic criterion for chronic PJI?

Explanation

Under the MSIS and ICM criteria, a positive synovial fluid alpha-defensin test (along with a sinus tract or two positive cultures) serves as a major criterion, possessing high sensitivity and specificity for diagnosing PJI.

Question 67

A patient sustains an acute extensor mechanism rupture (complete patellar tendon avulsion) 3 weeks after a primary TKA. Due to poor tissue quality, a primary repair is augmented. Among the following options, which reconstruction technique provides the most reliable long-term clinical outcome?

Explanation

Primary repair of extensor mechanism ruptures post-TKA has an extremely high failure rate. Synthetic mesh (e.g., Marlex) or complete extensor mechanism allograft reconstruction are the preferred techniques with the most durable outcomes.

Question 68

Trunnionosis, or mechanically assisted crevice corrosion at the head-neck taper, has emerged as a significant cause of adverse local tissue reactions in modern THA. Which combination of implant factors is most associated with an increased risk of trunnionosis?

Explanation

A large femoral head increases the frictional torque transmitted to the head-neck junction. Combined with a high offset, this maximizes bending moments and micromotion at the taper, strongly increasing the risk of trunnionosis.

Question 69

A 70-year-old man presents with an acute hematogenous periprosthetic joint infection of his THA. He has had symptoms for 5 days, and his implant has been in place for 3 years. Radiographs show well-fixed components. He undergoes Debridement, Antibiotics, and Implant Retention (DAIR). Which crucial surgical step must be included to maximize the success of DAIR?

Explanation

For a DAIR procedure to be successful, standard protocol dictates a thorough synovectomy, copious irrigation, and mandatory exchange of all modular components (liner and head) to eliminate biofilm harbored at the modular interfaces.

Question 70

A 70-year-old woman with a multi-level lumbar spinal fusion from L2 to the sacrum is scheduled for a primary total hip arthroplasty (THA). Preoperative lateral pelvic radiographs reveal a stiff spinopelvic junction with an inability to increase pelvic tilt during sitting. To minimize the risk of dislocation in this patient, how should the acetabular component positioning be modified?

Explanation

Patients with a fused or stiff lumbar spine fail to increase posterior pelvic tilt when sitting, predisposing them to anterior impingement and posterior dislocation. Increasing cup anteversion and inclination compensates for the lack of dynamic spinopelvic mobility and reduces this risk.

Question 71

During a primary total knee arthroplasty (TKA), the surgeon evaluates patellar tracking after trial placement. The patella subluxates laterally during flexion despite a normal Q-angle preoperatively. Which of the following technical errors is the most likely cause of this abnormal patellar kinematics?

Explanation

Internal rotation of the femoral component shifts the trochlear groove medially, effectively increasing the Q-angle and causing lateral patellar maltracking. External rotation of the femoral and tibial components generally improves patellar tracking.

Question 72

A 72-year-old man presents with chronic pain and stiffness in his right knee 14 months after a primary TKA. Joint aspiration yields synovial fluid with a white blood cell count of 4,500 cells/mcL and 88% polymorphonuclear leukocytes (PMNs). Cultures are pending, but clinical suspicion for periprosthetic joint infection (PJI) is high. Assuming the implant is firmly fixed, what is the most appropriate definitive management?

Explanation

The patient meets the criteria for a chronic PJI (WBC > 3,000 cells/mcL and > 80% PMNs after 4 weeks post-op). Two-stage exchange arthroplasty remains the gold standard in North America for chronic PJI to ensure eradication of the biofilm before reimplantation.

Question 73

A 45-year-old man underwent a primary THA using a ceramic-on-ceramic bearing. Three years postoperatively, he complains of an audible squeaking sound from the hip during deep flexion activities, though he is pain-free. What is the most significant risk factor for this phenomenon?

Explanation

Squeaking in ceramic-on-ceramic THA is strongly associated with edge loading, which typically occurs due to excessive steepness (high inclination) or malversion of the acetabular component. This leads to stripe wear and disruption of the fluid film lubrication.

Question 74

A 78-year-old woman sustains a fall 8 years after a cemented THA. Radiographs demonstrate a displaced periprosthetic fracture of the proximal femur that propagates around the tip of the stem. The stem is visibly subsided and grossly loose, but the proximal femoral bone stock remains adequate. According to the Vancouver classification, what is the most appropriate surgical treatment?

Explanation

This is a Vancouver B2 fracture (fracture around the stem, loose implant, adequate bone stock). The standard of care is revision arthroplasty using a long, uncemented diaphyseal-engaging stem that bypasses the fracture by at least two cortical diameters.

Question 75

While trialing components during a primary TKA, the surgeon notes that the knee is symmetric and stable at 90 degrees of flexion, but it is symmetric and excessively loose in full extension. Which of the following intraoperative adjustments is the best step to balance the knee?

Explanation

A knee that is stable in flexion but loose in extension indicates an isolated extension gap laxity. Using distal femoral augments (or reducing the distal femoral resection) tightens the extension gap without affecting the flexion gap.

Question 76

A surgeon is utilizing the direct anterior approach for a primary THA. This approach exploits a true internervous plane. Between which two muscles is the superficial surgical interval developed?

Explanation

The superficial interval of the direct anterior (Smith-Petersen) approach is between the tensor fasciae latae (innervated by the superior gluteal nerve) and the sartorius (innervated by the femoral nerve). This provides a true internervous and intermuscular plane.

Question 77

A 68-year-old man presents with thigh pain 15 years after an uncemented THA. Radiographs show significant eccentric wear of the polyethylene liner and massive expansile radiolucent lesions in the proximal femur. Which of the following cells is the primary mediator directly phagocytosing wear particles to initiate this pathologic cascade?

Explanation

Osteolysis in arthroplasty is primarily initiated by macrophages, which phagocytose submicron polyethylene wear particles. Activated macrophages then release pro-inflammatory cytokines (TNF-alpha, IL-1, IL-6) that upregulate the RANKL pathway, stimulating osteoclastic bone resorption.

Question 78

During a TKA for a severe varus deformity, the surgeon proceeds with a sequential medial release. After releasing the deep medial collateral ligament (MCL) and posteromedial capsule, the knee remains tight medially in flexion. Which structure, serving as the primary restraint to valgus stress at 90 degrees of flexion, must be addressed next?

Explanation

The superficial MCL is the primary restraint to valgus stress at both full extension and 90 degrees of flexion. In severe varus deformities, it often requires subperiosteal elevation or partial release to balance the flexion gap.

Question 79

A 60-year-old man with a dual-mobility, metal-on-polyethylene THA presents with a large fluid collection around the hip and soft tissue necrosis, despite normal ESR and CRP levels. Aspiration shows a low cellularity fluid. This adverse local tissue reaction (ALTR) is most likely secondary to wear and corrosion at which interface?

Explanation

ALTR in non-metal-on-metal implants is typically caused by mechanically assisted crevice corrosion (trunnionosis) at the modular head-neck taper junction. This releases metal ions that trigger a destructive, non-infectious inflammatory response.

Question 80

Hip resurfacing arthroplasty preserves femoral bone stock but carries specific risks. Which of the following patients is universally considered to have a strict contraindication to metal-on-metal hip resurfacing?

Explanation

Females, particularly those of childbearing age and those requiring smaller component sizes (e.g., < 48 mm femoral head), have unacceptably high failure rates and risks of metallosis. Thus, female gender and small head size are major contraindications for hip resurfacing.

Question 81

A patient presents with anterior knee pain and a palpable, audible catch as the knee extends from 40 degrees of flexion to full extension, one year after a primary TKA. This complication (patellar clunk syndrome) is most classically associated with which type of implant design?

Explanation

Patellar clunk syndrome occurs primarily in posterior-stabilized (PS) knee designs. A fibrotic nodule forms at the superior pole of the patella and catches in the intercondylar box of the femoral component during knee extension.

Question 82

A 32-year-old man on chronic corticosteroids presents with severe groin pain. Radiographs of the hip are normal, but an MRI demonstrates an area of subchondral edema and a serpiginous line in the anterosuperior femoral head without subchondral collapse (Ficat Stage IIA). What is the most appropriate initial surgical intervention?

Explanation

In pre-collapse stages of osteonecrosis of the femoral head (Ficat I and IIA), core decompression is indicated to reduce intraosseous pressure and promote revascularization. Once subchondral collapse (crescent sign) occurs, THA is typically required.

Question 83

Following a primary THA, a patient complains that the operative leg feels significantly longer. Clinical examination and scanograms confirm a true 2 cm leg length discrepancy. Assuming the femoral neck osteotomy was performed perfectly according to preoperative templating, which intraoperative error most likely caused this outcome?

Explanation

Leaving the femoral stem proud (inadequate seating depth) directly lengthens the leg compared to the preoperative template. Offset primarily affects abductor tension and horizontal position, whereas seating depth directly alters vertical leg length.

Question 84

Tranexamic acid (TXA) is routinely utilized in total joint arthroplasty to reduce blood loss and transfusion requirements. What is the specific pharmacological mechanism of action of TXA?

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It competitively binds to the lysine receptor sites on plasminogen, preventing its activation to plasmin, thereby inhibiting fibrinolysis and stabilizing clots.

Question 85

A surgeon is performing a TKA on a patient with a severe fixed valgus deformity. A lateral parapatellar approach is utilized. During gap balancing, the lateral extension gap remains excessively tight. Which of the following lateral structures is typically released first to balance the extension gap in a valgus knee?

Explanation

In a severe valgus knee, the iliotibial (IT) band is the primary tether in extension. It is typically the first structure selectively released or pie-crusted off Gerdy's tubercle to correct a tight lateral extension gap.

Question 86

A 65-year-old patient experiences recurrent posterior dislocations of their THA. CT imaging reveals the acetabular component is in 45 degrees of inclination and 0 degrees of anteversion, while the femoral stem is in 15 degrees of anteversion. What is the most appropriate surgical treatment?

Explanation

The acetabular cup is placed in 0 degrees of anteversion, falling well outside the safe zone (~15-25 degrees of anteversion), which directly causes posterior instability. Revising the acetabular component to appropriate anteversion addresses the primary anatomic failure.

Question 87

An 82-year-old nursing home resident with multiple medical comorbidities develops a late chronic PJI of a TKA with Staphylococcus epidermidis. The implants are well-fixed, and the patient is deemed too high-risk for revision surgery. For chronic suppressive antibiotic therapy to be successful, which of the following criteria MUST be met?

Explanation

Chronic suppressive therapy is a salvage option for patients unfit for surgery. Success requires a well-fixed implant, absence of systemic sepsis, and an infecting organism that is susceptible to safe, highly bioavailable oral antibiotics.

Question 88

A patient complains of a sensation of the knee "giving way" when descending stairs 6 months after a TKA. Clinical examination reveals the knee is perfectly stable to varus and valgus stress in full extension, but demonstrates significant laxity in varus and valgus at 90 degrees of flexion. Which of the following surgical errors is the most likely cause?

Explanation

Instability isolated to flexion is known as flexion instability. It is classically caused by undersizing the AP dimension of the femoral component, which fails to adequately tension the collateral ligaments when the knee is flexed.

Question 89

During the fixation of an uncemented acetabular cup in THA, the surgeon decides to place supplementary screws. According to the quadrant system described by Wasielewski, screw placement in the anteroinferior quadrant places which of the following vascular structures at greatest risk of direct injury?

Explanation

The anteroinferior quadrant is considered the 'danger zone' for screw placement due to the high risk of penetrating the obturator nerve and vessels. The posterosuperior quadrant is the safest zone for screw placement.

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

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

Key Takeaway

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

Chapter Index