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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 299 of 326

This practice set contains high-yield board review questions covering key concepts in 3. Adult Reconstruction (Hip & Knee). Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 5961

Topic: 3. Adult Reconstruction (Hip & Knee)

Three years following a primary total knee arthroplasty, a 68-year-old woman sustains a sudden 'pop' and inability to actively extend her knee after stumbling on a stair. Examination and imaging confirm a complete rupture of the mid-substance of the patellar tendon. The primary implants are well-fixed. What is the most appropriate and reliable surgical intervention?

. Primary end-to-end repair with heavy non-absorbable sutures.
. Primary repair augmented with a hamstring autograft.
. Extensor mechanism reconstruction using an allograft or synthetic mesh.
. Revision total knee arthroplasty using a hinged prosthesis.
. Non-operative management with cast immobilization in extension for 8 weeks.

Correct Answer & Explanation

. Extensor mechanism reconstruction using an allograft or synthetic mesh.

Explanation

Chronic or post-TKA extensor mechanism ruptures (especially patellar tendon ruptures) have a notoriously high failure rate with direct primary repair, even when augmented. The tissue quality is poor and the blood supply is compromised. The gold standard reliable treatment is a full extensor mechanism reconstruction, which is typically performed using either a complete extensor mechanism allograft (tibial tubercle, patellar tendon, patella, quad tendon) or, increasingly, synthetic mesh (e.g., Marlex mesh) which has shown excellent outcomes with immediate mobilization.

Question 5962

Topic: 3. Adult Reconstruction (Hip & Knee)

A 64-year-old male who underwent a primary metal-on-polyethylene total hip arthroplasty 5 years ago with a modular femoral head presents with new-onset persistent anterior groin pain and swelling. Radiographs show well-fixed implants. Aspiration yields sterile, straw-colored fluid. Blood tests reveal significantly elevated serum cobalt and chromium levels. MRI with MARS technique reveals a large cystic mass surrounding the hip joint. What is the most likely etiology of this pathology?

. Accelerated polyethylene wear due to third-body galling.
. Mechanically assisted crevice corrosion at the head-neck junction.
. Galvanic corrosion at the stem-cement interface.
. Indolent Propionibacterium acnes periprosthetic infection.
. Aseptic loosening secondary to high impact sporting activities.

Correct Answer & Explanation

. Mechanically assisted crevice corrosion at the head-neck junction.

Explanation

The clinical scenario describes an adverse local tissue reaction (ALTR) / aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) in a patient with a metal-on-polyethylene THA. This is classic for 'trunnionosis', which is mechanically assisted crevice corrosion and fretting wear that occurs at the modular head-neck junction (the trunnion). It leads to the release of metal ions (Cobalt and Chromium), resulting in pseudotumor formation and tissue necrosis despite the absence of a metal-on-metal bearing surface.

Question 5963

Topic: 3. Adult Reconstruction (Hip & Knee)

Two years after an uncomplicated primary posterior-stabilized total knee arthroplasty, a patient complains of recurrent knee effusions and a sensation of the knee 'giving way' specifically when descending stairs or getting out of a low chair. On examination, the knee has 0-125 degrees of motion, is stable to varus/valgus stress at 0 degrees, but has notable anteroposterior translation and laxity at 90 degrees of flexion. Which intraoperative technical error most likely caused this complication?

. Excessive resection of the distal femur.
. Excessive resection of the posterior femoral condyles.
. Undersizing the tibial polyethylene insert.
. Placing the femoral component in excessive external rotation.
. Inadequate release of the posterior cruciate ligament.

Correct Answer & Explanation

. Excessive resection of the posterior femoral condyles.

Explanation

This patient has isolated flexion instability. Flexion instability is characterized by symptoms of giving way during deep flexion activities (stairs, rising from a chair) and laxity tested at 90 degrees of flexion, while extension stability is maintained. It is caused by a flexion gap that is larger/looser than the extension gap. Common technical errors leading to this include excessive resection of the posterior femoral condyles, downsizing the femoral component without shifting it anteriorly, or creating an excessive posterior slope on the tibial cut.

Question 5964

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old patient presents with thigh pain 15 years after a primary cementless total hip arthroplasty. Radiographs show eccentric wear of the polyethylene liner and large osteolytic lesions in the proximal femur.

Which of the following macrophage pathways is most directly responsible for the massive osteolysis seen in this condition?

. Activation of the RANK-RANKL pathway
. Type IV hypersensitivity reaction to metal ions
. Phagocytosis of PMMA debris leading to apoptosis
. Direct bacterial colonization of the polyethylene
. Complement-mediated osteoblast inhibition

Correct Answer & Explanation

. Activation of the RANK-RANKL pathway

Explanation

Aseptic loosening secondary to polyethylene wear debris is primarily mediated by macrophages. Phagocytosis of submicron (0.1-1.0 micrometer) particulate debris by macrophages leads to the release of pro-inflammatory cytokines (such as TNF-alpha, IL-1, and IL-6). These cytokines subsequently upregulate the RANK-RANKL pathway, heavily stimulating osteoclast differentiation and osteoclast-mediated bone resorption.

Question 5965

Topic: 3. Adult Reconstruction (Hip & Knee)

In Total Hip Arthroplasty (THA), ceramic-on-ceramic (CoC) bearing surfaces offer the lowest wear rates among conventional options. Which of the following is a recognized complication uniquely and specifically associated with CoC bearings compared to metal-on-polyethylene (MoP) bearings?

. Metallosis and ALVAL (Aseptic Lymphocytic Vasculitis Associated Lesions)
. Squeaking during gait
. Trunnionosis due to galvanic corrosion
. Massive volumetric wear with rapid osteolysis
. Higher rates of early dislocation due to jump distance

Correct Answer & Explanation

. Squeaking during gait

Explanation

Squeaking is an auditory complication specific to Ceramic-on-Ceramic (CoC) bearing surfaces in THA, occurring in up to 1-10% of cases. It is often linked to micro-separation during swing phase, edge loading, or component malposition. ALVAL and trunnionosis are related to metal implants, while massive volumetric wear is a historical hallmark of MoP bearings.

Question 5966

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty, the use of highly cross-linked polyethylene (HXLPE) has significantly reduced the incidence of wear and subsequent osteolysis compared to conventional polyethylene. However, the radiation process used to improve cross-linking most directly results in which of the following mechanical trade-offs?

. Increased ultimate tensile strength
. Increased fatigue resistance
. Decreased oxidation resistance if unannealed
. Decreased fracture toughness
. Increased elastic modulus

Correct Answer & Explanation

. Decreased fracture toughness

Explanation

Increasing cross-linking via gamma or electron beam irradiation significantly decreases wear but concurrently decreases mechanical properties such as fracture toughness, yield strength, and ultimate tensile strength. It also generates free radicals that must be extinguished (e.g., via remelting or annealing) to prevent long-term oxidation.

Question 5967

Topic: 3. Adult Reconstruction (Hip & Knee)

A 60-year-old man presents with severe groin pain and a large soft-tissue mass 5 years after an uncomplicated primary metal-on-polyethylene total hip arthroplasty. Laboratory studies show markedly elevated serum cobalt levels and normal chromium levels. Which of the following is the most likely source of the metal debris generating this adverse local tissue reaction?

. Acetabular shell-liner interface
. Femoral head-neck modular junction
. Bearing surface wear
. Femoral stem-cement interface
. Acetabular screw fretting

Correct Answer & Explanation

. Femoral head-neck modular junction

Explanation

Elevated cobalt levels out of proportion to chromium in a metal-on-polyethylene THA is highly suggestive of mechanically assisted crevice corrosion (MACC), or trunnionosis, occurring at the modular femoral head-neck junction.

Question 5968

Topic: 3. Adult Reconstruction (Hip & Knee)

In a posterior-stabilized (PS) total knee arthroplasty, the post-cam mechanism engages to substitute for the function of the excised posterior cruciate ligament (PCL). In a standard PS design, during which phase of knee range of motion does the femoral cam typically engage the tibial post?

. Early flexion (0 to 30 degrees)
. Mid-flexion (70 to 80 degrees)
. Late flexion (120 to 140 degrees)
. Full extension
. Hyperextension

Correct Answer & Explanation

. Mid-flexion (70 to 80 degrees)

Explanation

In standard posterior-stabilized TKA designs, the femoral cam typically engages the tibial post at mid-flexion (around 70 to 80 degrees). This interaction provides posterior femoral rollback, mimicking the function of the PCL, which optimizes knee flexion and prevents paradoxical anterior translation of the femur.

Question 5969

Topic: 3. Adult Reconstruction (Hip & Knee)

The introduction of highly cross-linked polyethylene (HXLPE) in total hip arthroplasty has drastically reduced volumetric wear rates. However, increasing the radiation dose to achieve higher levels of cross-linking predominantly compromises which mechanical property?

. Elastic modulus
. Ultimate tensile strength
. Fatigue crack propagation resistance (fracture toughness)
. Compressive yield strength
. Surface hardness

Correct Answer & Explanation

. Fatigue crack propagation resistance (fracture toughness)

Explanation

While high radiation cross-linking improves wear resistance, it significantly reduces the fracture toughness and fatigue crack propagation resistance of the polyethylene, increasing the risk of mechanical failure.

Question 5970

Topic: 3. Adult Reconstruction (Hip & Knee)

During a total hip arthroplasty, the surgeon opts for a ceramic-on-ceramic bearing surface. Which of the following is a recognized unique disadvantage of this specific bearing combination compared to metal-on-polyethylene?

. Increased volumetric wear rates
. Higher rate of osteolysis
. Audible squeaking during gait
. Trunnionosis
. Galvanic corrosion

Correct Answer & Explanation

. Audible squeaking during gait

Explanation

Ceramic-on-ceramic bearings offer extremely low volumetric wear rates and negligible osteolysis but are uniquely associated with audible 'squeaking' (reported in up to 10% of patients), which can be a significant source of patient dissatisfaction. Trunnionosis is a concern primarily with metal heads on titanium stems.

Question 5971

Topic: Total Hip Arthroplasty (THA)

Which of the following surgical steps has been shown in the literature to be the most critical in reducing the risk of dislocation following primary total hip arthroplasty (THA) using a posterior approach?

. Use of a femoral head larger than 36 mm
. Routine use of a constrained acetabular liner
. Meticulous repair of the short external rotators and capsule
. Increasing femoral offset by 10 mm
. Placement of the acetabular component in exactly 30 degrees of anteversion

Correct Answer & Explanation

. Meticulous repair of the short external rotators and capsule

Explanation

Meticulous repair of the posterior soft-tissue envelope (capsule and short external rotators) has been consistently shown to significantly reduce dislocation rates following a posterior approach THA, bringing them comparable to anterolateral approaches. While larger heads increase the jump distance, posterior repair remains the critical technical defense against early posterior dislocation.

Question 5972

Topic: 3. Adult Reconstruction (Hip & Knee)

In the pathogenesis of aseptic loosening secondary to particulate wear debris in total joint arthroplasty, which cell type is primarily responsible for phagocytosing the debris and initiating the inflammatory cascade?

. T-lymphocytes
. B-lymphocytes
. Macrophages
. Polymorphonuclear leukocytes
. Osteocytes

Correct Answer & Explanation

. Macrophages

Explanation

Macrophages phagocytose polyethylene and other wear particles, becoming activated and releasing inflammatory cytokines like IL-1, IL-6, and TNF-alpha. These cytokines stimulate osteoclasts, ultimately leading to periprosthetic osteolysis.

Question 5973

Topic: 3. Adult Reconstruction (Hip & Knee)
Low molecular weight heparin (LMWH) is commonly used for VTE prophylaxis following total joint arthroplasty. What is its primary biochemical mechanism of action?
. Directly inhibits Factor Xa
. Inhibits Vitamin K epoxide reductase
. Binds to antithrombin III, enhancing its inhibition of Factor Xa
. Directly inhibits thrombin (Factor IIa)
. Inhibits ADP-induced platelet aggregation

Correct Answer & Explanation

. Binds to antithrombin III, enhancing its inhibition of Factor Xa

Explanation

LMWH binds to and potentiates antithrombin III, primarily accelerating its inhibition of Factor Xa. Unlike unfractionated heparin, it has a much smaller effect on thrombin (Factor IIa).

Question 5974

Topic: 3. Adult Reconstruction (Hip & Knee)

An orthopedic researcher is studying an extremely rare complication of total hip arthroplasty. To maximize statistical efficiency and feasibility, which study design is most appropriate?

. Randomized controlled trial
. Prospective cohort study
. Case-control study
. Cross-sectional survey
. Systematic review

Correct Answer & Explanation

. Case-control study

Explanation

Case-control studies are highly efficient for investigating rare diseases or outcomes. They identify patients who already have the condition (cases) and match them with those who do not (controls) to retrospectively analyze risk factors using odds ratios.

Question 5975

Topic: 3. Adult Reconstruction (Hip & Knee)

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

. WBC > 50,000 cells/\u00b5L, PMN > 90%
. WBC > 10,000 cells/\u00b5L, PMN > 50%
. WBC > 5,000 cells/\u00b5L, PMN > 60%
. WBC > 3,000 cells/\u00b5L, PMN > 80%
. WBC > 1,500 cells/\u00b5L, PMN > 65%

Correct Answer & Explanation

. WBC > 3,000 cells/\u00b5L, PMN > 80%

Explanation

According to the MSIS criteria, a synovial fluid leukocyte count greater than 3,000 cells/\u00b5L and a polymorphonuclear (PMN) percentage > 80% strongly supports the diagnosis of chronic periprosthetic joint infection. Acute infections (e.g., within 4 weeks post-op) typically use higher cutoffs, such as WBC > 10,000.

Question 5976

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty, trial reduction demonstrates that the knee is well-balanced in full extension but excessively tight in 90 degrees of flexion. Which of the following surgical modifications is the most appropriate step to achieve a balanced gap?

. Resect more of the distal femur
. Recut the proximal tibia to increase the posterior slope
. Upsize the femoral component
. Downsize the femoral component
. Release the posterior capsule

Correct Answer & Explanation

. Downsize the femoral component

Explanation

Downsizing the femoral component reduces the anteroposterior dimension, effectively increasing the flexion gap without altering the extension gap. Resecting more distal femur or releasing the posterior capsule would affect the extension gap.

Question 5977

Topic: 3. Adult Reconstruction (Hip & Knee)

In the biomechanical reconstruction of a total hip arthroplasty, intentionally increasing the femoral offset (moving the greater trochanter further laterally relative to the center of rotation) has which of the following direct mechanical effects?

. Increases the joint reaction force across the acetabulum
. Decreases the tension of the abductor musculature
. Increases the abductor moment arm and decreases the joint reaction force
. Decreases the abductor moment arm and increases the joint reaction force
. Predisposes the patient to early anterior dislocation

Correct Answer & Explanation

. Increases the abductor moment arm and decreases the joint reaction force

Explanation

Increasing femoral offset increases the abductor moment arm. This mechanical advantage means less abductor muscle force is required to stabilize the pelvis, which in turn decreases the overall joint reaction force across the hip.

Question 5978

Topic: 3. Adult Reconstruction (Hip & Knee)
In total hip arthroplasty, the volumetric wear rate of an ultra-high molecular weight polyethylene (UHMWPE) liner is theoretically proportional to which of the following variables?
. The square of the femoral head radius
. The third power of the femoral head radius
. The inverse of the femoral head radius
. The square of the acetabular cup thickness
. The inverse of the acetabular cup thickness

Correct Answer & Explanation

. The square of the femoral head radius

Explanation

Volumetric wear in total hip arthroplasty is a function of the sliding distance per gait cycle and the contact area. Based on the Archard wear equation and geometric relationships, volumetric wear is directly proportional to the square of the radius of the femoral head. While larger heads decrease the risk of dislocation, they traditionally increase the volumetric wear of the polyethylene liner.

Question 5979

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old man presents with aseptic loosening 12 years after a total hip arthroplasty using a highly cross-linked polyethylene liner. Which of the following best describes the primary biological cascade leading to periprosthetic osteolysis in this patient?

. Macrophage phagocytosis of submicron particles leading to TNF-alpha and IL-1 release
. Lymphocyte-mediated type IV hypersensitivity reaction to metal ions
. Neutrophil-driven enzymatic degradation of periprosthetic bone
. Fibroblast proliferation induced by transforming growth factor-beta
. Direct osteoclast activation by mechanical fluid pressure waves

Correct Answer & Explanation

. Macrophage phagocytosis of submicron particles leading to TNF-alpha and IL-1 release

Explanation

Wear debris, primarily submicron polyethylene particles, are phagocytosed by macrophages. These activated macrophages then release pro-inflammatory cytokines such as TNF-alpha, IL-1, and IL-6. This inflammatory cascade stimulates osteoclastogenesis via the RANKL pathway, ultimately leading to periprosthetic osteolysis.

Question 5980

Topic: 3. Adult Reconstruction (Hip & Knee)
A 60-year-old female presents with base of thumb pain. Radiographs demonstrate severe joint space narrowing, subchondral sclerosis, and osteophytes larger than 2 mm at the trapeziometacarpal joint. Additionally, there is complete loss of joint space at the scaphotrapezial-trapezoid (STT) joint. According to the Eaton-Littler classification, what stage is this disease, and what specific surgical option is relatively contraindicated compared to earlier stages?
. Stage II; Trapeziometacarpal arthrodesis is contraindicated
. Stage III; Ligament reconstruction tendon interposition (LRTI) is contraindicated
. Stage IV; Isolated trapeziometacarpal arthrodesis is contraindicated
. Stage III; Hematoma distraction arthroplasty is contraindicated
. Stage IV; Total joint arthroplasty with trapezial excision is contraindicated

Correct Answer & Explanation

. Stage IV; Isolated trapeziometacarpal arthrodesis is contraindicated

Explanation

The patient has pantrapezial arthritis (involving both the CMC and STT joints), which is Eaton-Littler Stage IV. An isolated trapeziometacarpal (CMC) arthrodesis or hemiarthroplasty that retains the trapezium is contraindicated in Stage IV because the patient will continue to experience pain from the arthritic STT joint. Procedures that excise the trapezium (like LRTI or hematoma distraction arthroplasty) address both areas and are indicated.

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