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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 123 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 2441

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old male undergoes a single-stage revision total knee arthroplasty (TKA) for a chronic prosthetic joint infection (PJI) caused by methicillin-resistant Staphylococcus aureus (MRSA). During the revision surgery, thorough debridement, implant removal, and placement of new implants with antibiotic-loaded cement are performed. What is the MOST crucial aspect of his postoperative antibiotic regimen?

. Intravenous vancomycin for 6 weeks, followed by oral rifampin for 3 months.
. Oral cephalexin for 6 months.
. Intravenous daptomycin for 2 weeks, then discontinue antibiotics.
. Directed intravenous antibiotics for 6-12 weeks, followed by oral suppression if indicated, based on sensitivities.
. No antibiotics are needed post-operatively, as the infection was removed surgically.

Correct Answer & Explanation

. Directed intravenous antibiotics for 6-12 weeks, followed by oral suppression if indicated, based on sensitivities.

Explanation

For PJI, particularly with organisms like MRSA, a single-stage revision often requires prolonged, targeted antibiotic therapy. The MOST crucial aspect is directed intravenous antibiotics for a prolonged period (typically 6-12 weeks), followed by oral suppressive therapy if indicated, based on the specific sensitivities of the isolated organism. Vancomycin and rifampin combination is a common regimen for MRSA PJI, but the exact duration and specific agents (intravenous vs. oral, combination therapy) must be based on intraoperative cultures and sensitivity results. Discontinuing antibiotics after 2 weeks is insufficient for chronic PJI. Oral cephalexin would not cover MRSA and would be inadequate. Saying no antibiotics are needed is incorrect, as surgical debridement alone is rarely sufficient for chronic PJI.

Question 2442

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old patient presents with a painful total knee arthroplasty (TKA) 2 years post-surgery. Inflammatory markers show ESR of 55 mm/hr and CRP of 45 mg/L. Joint aspiration yields purulent fluid. What is the MOST definitive diagnostic criterion for periprosthetic joint infection (PJI) according to the Musculoskeletal Infection Society (MSIS) 2018 criteria?

. Elevated CRP (>10 mg/L) and ESR (>30 mm/hr).
. Synovial fluid leukocyte count >3,000 cells/ยตL with >80% neutrophils.
. Purulence found in the joint or fistula communicating with the joint.
. Single positive culture for a low-virulence organism.
. Alpha-defensin test positive in synovial fluid.

Correct Answer & Explanation

. Purulence found in the joint or fistula communicating with the joint.

Explanation

According to the Musculoskeletal Infection Society (MSIS) 2018 criteria for periprosthetic joint infection (PJI), the presence of a sinus tract communicating with the joint OR purulence in the joint identified during aspiration or surgery is a major criterion that, by itself, is sufficient for a definitive diagnosis of PJI. While other findings such as elevated ESR/CRP, high synovial fluid leukocyte count/neutrophil percentage, or positive alpha-defensin are strong indicators, they usually require combinations to meet the diagnostic criteria. A single positive culture, especially for a low-virulence organism, is often not sufficient alone without corroborating evidence.

Question 2443

Topic: 3. Adult Reconstruction (Hip & Knee)
A 72-year-old female presents to the emergency department after a low-energy fall, complaining of severe right hip pain. She has a history of total hip arthroplasty (THA) performed 15 years prior. Radiographs reveal a periprosthetic femoral fracture involving the proximal femur around a well-fixed femoral stem, with a stable cement mantle. The fracture extends distal to the lesser trochanter but above the distal tip of the femoral component. There is no evidence of implant loosening. According to the Vancouver Classification, which type of fracture does this most likely represent, and what is the generally recommended treatment?
. Type A: Greater Trochanter; ORIF with tension band wiring.
. Type B1; Open reduction and internal fixation (ORIF) with cerclage wires and plating.
. Type B2; Revision to a longer, often calcar-replacing, femoral stem.
. Type B3; Extensive femoral reconstruction with allograft or modular revision stem.
. Type C; ORIF with plating, extending well beyond the tip of the prosthesis.

Correct Answer & Explanation

. Type B1; Open reduction and internal fixation (ORIF) with cerclage wires and plating.

Explanation

The image shows a periprosthetic femoral fracture associated with a total hip arthroplasty. The fracture is located around a well-fixed femoral stem, extending distal to the lesser trochanter but above the distal tip of the component. This description aligns with a Vancouver B1 fracture. The Vancouver Classification categorizes periprosthetic femoral fractures based on location, stem stability, and bone stock: Type A: Fractures involving the trochanteric region. Type B: Fractures around or just distal to the femoral stem. B1: Stable femoral component. B2: Loose femoral component. B3: Loose femoral component with poor femoral bone stock. Type C: Fractures well distal to the femoral stem. Given the description of a 'well-fixed femoral stem' and a fracture around it, Vancouver B1 is the correct classification. The recommended treatment for Vancouver B1 fractures is open reduction and internal fixation (ORIF) with cerclage wires and plating to achieve stable fixation while preserving the well-fixed stem.

Question 2444

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old obese male with poorly controlled diabetes and a history of previous methicillin-resistant Staphylococcus aureus (MRSA) bacteremia undergoes a total knee arthroplasty (TKA). Two weeks post-operatively, he develops increasing knee pain, swelling, warmth, and erythema. Aspiration of the knee joint yields purulent fluid. Synovial fluid analysis shows a WBC count of 90,000 cells/ยตL with 95% neutrophils, and a positive Gram stain for Gram-positive cocci. What is the MOST appropriate definitive surgical management approach for this acute periprosthetic joint infection (PJI) if the implant is deemed stable?

. Immediate total knee arthroplasty revision with a two-stage exchange.
. Irrigation and debridement (I&D) with polyethylene exchange and prolonged antibiotic therapy.
. Long-term suppressive oral antibiotic therapy without surgery.
. Arthrodesis of the knee joint.
. Amputation above the knee.

Correct Answer & Explanation

. Immediate total knee arthroplasty revision with a two-stage exchange.

Explanation

This patient presents with an acute periprosthetic joint infection (PJI) within 2 weeks of TKA, characterized by classic signs of infection (pain, swelling, warmth, erythema), purulent aspirate, very high synovial WBC count, and positive Gram stain. The organism is MRSA, a virulent pathogen.For acute PJI (symptoms < 3-4 weeks from index surgery or hematogenous onset), if the implant is stable and there is no extensive osteomyelitis or sepsis, a debridement, antibiotics, and implant retention (DAIR) procedure is often considered. This involves irrigation and debridement, exchange of modular components (polyethylene liner), and prolonged culture-specific antibiotic therapy. However, the presence of MRSA, a highly virulent organism, makes DAIR less successful. While the question states 'if the implant is deemed stable', the aggressive nature of MRSA and the early onset of infection often lead to failure of DAIR, pushing towards a more aggressive approach.A two-stage exchange arthroplasty is the gold standard for chronic PJI or acute PJI with virulent organisms or when DAIR has failed. It involves removal of all components, extensive debridement, placement of an antibiotic-loaded cement spacer, and 6-8 weeks of systemic antibiotics, followed by reimplantation of a new TKA once infection markers normalize. Given the context of a highly virulent organism (MRSA) and the severity of presentation, even with a 'stable' implant, a two-stage exchange carries a higher success rate than DAIR.Rationale for options:A. Immediate TKA revision with a two-stage exchange is often considered the most reliable approach for acute PJI caused by virulent organisms like MRSA, or if there's extensive soft tissue involvement, even if the implant is stable. The high virulence of MRSA makes DAIR success rates lower. This is the correct answer.B. Irrigation and debridement (I&D) with polyethylene exchange and prolonged antibiotic therapy (DAIR) is an option for acute PJI, especially with less virulent organisms and a truly stable implant. However, its success rate is lower with MRSA. So, while an option, it's not themost appropriate definitiveapproach for MRSA in many centers.C. Long-term suppressive oral antibiotic therapy without surgery is reserved for patients who are not surgical candidates, or for chronic low-grade infections, and is associated with persistent infection and limited success.D. Arthrodesis is a salvage procedure for failed PJI treatment or severe irreparable destruction, sacrificing motion for infection eradication and pain relief.E. Amputation is a last resort for uncontrolled, limb-threatening infection or sepsis that fails all other surgical and antibiotic treatments.

Question 2445

Topic: Total Hip Arthroplasty (THA)
A 14-year-old male with a history of slipped capital femoral epiphysis (SCFE) treated with in situ pinning 2 years ago presents with new onset, severe right hip pain and inability to bear weight. Radiographs show no change in the pin position but reveal subtle flattening and sclerosis of the femoral head epiphysis, consistent with avascular necrosis (AVN). What is the most appropriate management strategy for this complication?
. Removal of the in situ pin and observation.
. Core decompression with bone grafting.
. Total hip arthroplasty (THA).
. Intertrochanteric osteotomy to reorient the femoral head.
. Conservative management with protected weight-bearing and NSAIDs.

Correct Answer & Explanation

. Total hip arthroplasty (THA).

Explanation

The patient has developed avascular necrosis (AVN) of the femoral head, a severe complication of SCFE. Radiographic findings of flattening and sclerosis indicate Ficat Stage III or IV, where collapse has occurred. Core decompression is indicated for pre-collapse stages (I or II). Intertrochanteric osteotomy is generally for residual deformity or segmental AVN with preserved cartilage. In a 14-year-old with painful, collapsed AVN, THA is the most definitive option for pain relief and functional restoration, despite concerns regarding implant longevity in young patients.

Question 2446

Topic: Total Hip Arthroplasty (THA)

A 62-year-old female presents with recurrent episodes of left hip dislocation following a primary total hip arthroplasty performed 3 months ago via a posterior approach. She has undergone two closed reductions. Clinical examination reveals no leg length discrepancy or neurovascular deficits. Radiographs, shown below, indicate appropriate acetabular and femoral component positioning without evidence of loosening.

Given the recurrent dislocations with well-positioned components, what is the MOST appropriate next surgical management strategy?

. Revision of the acetabular component to a more constrained liner.
. Revision of the femoral component to a larger head size.
. Conversion to a dual-mobility articulation.
. Open reduction and repair of the posterior capsule.
. Abductor advancement and trochanteric osteotomy.

Correct Answer & Explanation

. Conversion to a dual-mobility articulation.

Explanation

The image shows a total hip arthroplasty. The patient has recurrent hip dislocations after THA despite well-positioned components. This scenario often suggests soft tissue laxity or impingement, or an issue with the prosthetic articulation itself. Given the well-positioned components, simply increasing head size or repairing the capsule might not be sufficient to prevent recurrence, especially with a posterior approach where capsular and external rotator repair are crucial.A dual-mobility (DM) articulation is a common and effective solution for recurrent hip instability, particularly when component position is acceptable. It uses a small femoral head that articulates within a larger polyethylene liner, which then articulates within the acetabular cup. This 'ball-within-a-ball' design significantly increases the jumping distance required for dislocation, thereby enhancing stability.Rationale for options:A. Revision to a more constrained liner might increase stability but also significantly increases stress at the liner-shell interface and can lead to early failure or loosening. It is usually reserved for highly unstable hips where other options have failed, or when neuromuscular deficiencies are present.B. Revision of the femoral component to a larger head size can increase jumping distance and stability, and is often considered a first-line solution. However, it may still not be sufficient for recurrent dislocations, especially if there are ongoing soft tissue issues or if the initial head size was already adequate for typical primary THA.C. Conversion to a dual-mobility articulation offers a significant increase in stability and has shown excellent results in reducing dislocation rates in challenging cases, including recurrent dislocations with well-positioned components. It provides a larger 'effective' head size without increasing impingement risks as much as constrained liners. This is often the most appropriate and effective choice for recurrent dislocations when components are well-positioned. This is the correct answer.D. Open reduction and repair of the posterior capsule might be indicated if the original repair was inadequate, but for recurrent dislocations after initial good repair, it may not be sufficient on its own without addressing the articulation.E. Abductor advancement and trochanteric osteotomy might be considered for abductor insufficiency but are not the primary solution for recurrent dislocation from a biomechanical perspective of impingement/jumping distance.

Question 2447

Topic: 3. Adult Reconstruction (Hip & Knee)
A 17-year-old male presents with chronic, progressive right hip pain and a limping gait for the past 6 months. Physical examination reveals a restricted range of motion, particularly internal rotation and abduction, and a positive Trendelenburg sign. Radiographs show a flattened and irregular femoral head epiphysis with increased density and widening of the physeal plate, consistent with Legg-Calvรฉ-Perthes disease (LCPD). He is classified as Catterall Group IV with poor prognosis factors (e.g., age > 8 years, lateral pillar collapse). Given the advanced age (approaching skeletal maturity) and poor prognostic indicators, what is the most appropriate surgical management strategy to improve hip containment and long-term outcomes?
. Continued non-weight-bearing and use of an abduction orthosis.
. Core decompression of the femoral head.
. Femoral varus osteotomy.
. Pelvic osteotomy (e.g., Salter innominate osteotomy).
. Total hip arthroplasty (THA).

Correct Answer & Explanation

. Femoral varus osteotomy.

Explanation

In older children (typically > 8 years) with severe LCPD and poor prognostic factors, containment surgery is indicated to improve the coverage of the femoral head. A femoral varus osteotomy is a standard procedure to redirect the femoral head into the acetabulum, improving congruence and containment.

Question 2448

Topic: 3. Adult Reconstruction (Hip & Knee)

A 70-year-old male with a history of recurrent left total hip arthroplasty (THA) dislocations and significant abductor deficiency presents for evaluation. He has previously undergone two revisions, including a constrained liner, but continues to dislocate. Radiographs indicate stable, well-positioned components. He is now considering further surgical intervention due to severe functional limitation and pain. What is the MOST appropriate management strategy to address his persistent instability?

. Repeat revision to a more constrained liner with larger head.
. Revision to a dual-mobility articulation.
. Open reduction with abductor tendon repair and gluteal muscle transfer.
. Placement of a hinged external fixator for 6 weeks.
. Surgical arthrodesis of the hip joint.

Correct Answer & Explanation

. Open reduction with abductor tendon repair and gluteal muscle transfer.

Explanation

The patient has failed multiple prior surgical attempts (including a constrained liner) to address recurrent THA dislocations, despite well-positioned components, and has associated abductor deficiency. This is a very challenging scenario of persistent instability.In such complex cases, particularly when simpler solutions like larger heads or dual mobility have failed or are deemed insufficient, further surgical options are limited. A dual-mobility articulation is generally excellent for recurrent instability, but the question states he has failed previous revisions, including a constrained liner. This implies a very high risk of dislocation.For recurrent dislocations that persist after dual mobility or even constrained liners, and particularly with severe abductor deficiency (which removes a major dynamic stabilizer), further options include:1.Abductor repair/reconstruction: If abductor deficiency is the primary cause.2.Greater trochanteric advancement: To improve abductor lever arm.3.Hip arthrodesis: As a salvage option, sacrificing motion for stability and pain relief.4.Complete removal of components (Girdlestone arthroplasty): As a last resort for chronic infection or intractable pain/instability, leaving a pseudarthrosis.Given the options, and the severe, persistent instability after multiple revisions (including constrained liner), an abductor repair and potentially gluteal muscle transfer (e.g., gluteus maximus or vastus lateralis transfer) is a reconstructive attempt to restore dynamic stability. This directly addresses the abductor deficiency, which is highlighted in the scenario. While arthrodesis is a salvage option, addressing the abductor deficiency offers a chance to maintain motion.Rationale for options:A. Repeat revision to a constrained liner with larger head is unlikely to be more successful given the failure of a previous constrained liner and the underlying abductor deficiency.B. Revision to a dual-mobility articulation is a strong option for recurrent instability, but the scenario implies failure of even constrained liners, suggesting a dual-mobility might not be enough or was already tried if 'revisions' were comprehensive.C. Open reduction with abductor tendon repair and gluteal muscle transfer directly addresses the underlying abductor deficiency, which is a significant contributor to instability, especially when components are well-positioned. This reconstructive approach aims to restore dynamic stability and function. This is the correct answer.D. Placement of a hinged external fixator is not a definitive long-term solution for chronic THA instability.E. Surgical arthrodesis of the hip joint is a salvage procedure that sacrifices motion for stability and pain relief. While an option for intractable instability, a reconstructive attempt to restore some motion (like abductor transfer) is usually preferred if feasible.

Question 2449

Topic: 3. Adult Reconstruction (Hip & Knee)

A 72-year-old male undergoes revision total knee arthroplasty (TKA) for aseptic loosening of the tibial component. During the surgery, a significant uncontained cavitary defect is identified in the proximal tibia, consistent with a Paprosky Type 2 bone defect. The defect extends to the metaphyseal bone but does not compromise the cortical rim for rotational stability. What is the MOST appropriate reconstructive option for this defect?

. Primary cement fixation of the new tibial component.
. Use of a metal augment (wedge or block) with cement fixation.
. Placement of an extensively porous-coated uncemented stem with a metal cone.
. Structural allograft reconstruction with a custom implant.
. Methyl methacrylate cement packing alone.

Correct Answer & Explanation

. Use of a metal augment (wedge or block) with cement fixation.

Explanation

The patient has a Paprosky Type 2 tibial bone defect in revision TKA. This defect is a contained cavitary or segmental defect involving less than 50% of the condylar width, with an intact metaphyseal cortical rim. The key characteristic is that the metaphyseal cortical rim is sufficiently intact to provide rotational stability, but the defect requires augmentation.For contained cavitary or segmental defects where the cortical rim provides support, metal augments (wedges or blocks) are the preferred reconstructive option. These augments restore the bone stock, provide a stable platform for the new component, and can be cemented or screwed into place. Cement packing alone is insufficient for structural defects, and uncemented stems with metal cones are typically for more severe, uncontained defects or when significant metaphyseal bone loss prevents stable fixation with augments.Rationale for options:A. Primary cement fixation alone is insufficient for a Paprosky Type 2 defect as it does not address the bone loss and could lead to early loosening.B. Use of a metal augment (wedge or block) with cement fixation is the standard and most appropriate reconstructive technique for contained Paprosky Type 2 tibial bone defects in revision TKA. The augment restores the bone stock and provides a stable foundation. This is the correct answer.C. Placement of an extensively porous-coated uncemented stem with a metal cone is typically used for more severe Paprosky Type 3 defects, where there is significant metaphyseal bone loss and compromise of the cortical rim, requiring extensive metaphyseal fixation.D. Structural allograft reconstruction with a custom implant is reserved for very extensive, complex defects (Paprosky Type 4 or severe Type 3) with massive bone loss, often requiring custom components.E. Methyl methacrylate cement packing alone is insufficient for a structural defect and would be prone to early failure.

Question 2450

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty (THA), the use of highly cross-linked polyethylene (HXLPE) has significantly reduced wear rates compared to conventional polyethylene. However, the process of cross-linking via irradiation alters the material's mechanical properties. Which of the following best describes a mechanical trade-off associated with high-dose irradiation cross-linking?

. Increased ultimate tensile strength
. Increased resistance to fatigue crack propagation
. Decreased ductility and fracture toughness
. Decreased elastic modulus
. Increased adhesive wear

Correct Answer & Explanation

. Decreased ductility and fracture toughness

Explanation

Irradiation is used to break carbon-hydrogen bonds and create free radicals that combine to form cross-links, significantly increasing abrasive wear resistance. However, this process decreases several mechanical properties of the polyethylene, notably decreasing ductility, fracture toughness, and resistance to fatigue crack propagation. To mitigate free radical oxidation, the material is often remelted or annealed, which can further slightly reduce mechanical strength but improves oxidative stability.

Question 2451

Topic: Total Hip Arthroplasty (THA)

A 55-year-old male who underwent a ceramic-on-ceramic total hip arthroplasty 3 years ago presents to the clinic complaining of a loud 'squeaking' sound coming from his hip when he walks. He denies pain. Which of the following component malpositions is most strongly associated with this complication?

. Acetabular cup retroversion
. Femoral stem retroversion
. Steep acetabular cup inclination (vertical placement)
. Insufficient femoral offset

Correct Answer & Explanation

. Steep acetabular cup inclination (vertical placement)

Explanation

Squeaking in ceramic-on-ceramic total hip arthroplasty is a well-documented phenomenon caused by altered tribology. It is most strongly associated with edge loading of the ceramic bearings. Edge loading occurs most frequently when the acetabular cup is placed with excessive steepness (high abduction/inclination angle) or excessive anteversion.

Question 2452

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty (TKA), trial components are inserted. The knee is symmetric and stable in full extension, but the flexion space is excessively tight, preventing full flexion. Which of the following surgical modifications is the most appropriate next step to correct this mismatch?

. Resect more distal femur.
. Decrease the anterior-posterior size of the femoral component.
. Increase the size of the femoral component.
. Increase the thickness of the polyethylene insert.
. Perform an extensive posterior capsular release.

Correct Answer & Explanation

. Decrease the anterior-posterior size of the femoral component.

Explanation

A knee that is balanced in extension but tight in flexion requires an increase in the flexion gap without altering the extension gap. Decreasing the size of the femoral component (downsizing) resects more posterior condylar bone, which increases the flexion space. Resecting more distal femur would increase the extension space. Changing the polyethylene thickness affects both gaps equally.

Question 2453

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty (TKA), the surgeon evaluates the trial components and finds that the knee is perfectly balanced and symmetric in full extension, but significantly tight in 90 degrees of flexion. Which of the following adjustments is the most appropriate next step to balance the knee?

. Recut the proximal tibia to increase the posterior slope
. Increase the thickness of the polyethylene insert
. Resect more distal femur
. Decrease the anteroposterior (AP) size of the femoral component
. Release the posterior cruciate ligament (PCL)

Correct Answer & Explanation

. Decrease the anteroposterior (AP) size of the femoral component

Explanation

A knee that is tight in flexion but balanced in extension has a tighter flexion gap than extension gap. Decreasing the AP size of the femoral component reduces the posterior condylar offset, thereby increasing the flexion gap without affecting the extension gap.

Question 2454

Topic: 3. Adult Reconstruction (Hip & Knee)

In a patient undergoing revision of a metal-on-metal total hip arthroplasty, intraoperative findings include a cystic pseudotumor. Histopathology of the periprosthetic tissue reveals a pronounced perivascular lymphocytic infiltrate. This finding is most characteristic of which condition?

. Aseptic loosening secondary to polyethylene wear
. Acute periprosthetic joint infection
. Aseptic Lymphocytic Vasculitis-Associated Lesions (ALVAL)
. Metallosis due to catastrophic trunnion failure
. Foreign body granulomatous reaction to bone cement

Correct Answer & Explanation

. Aseptic Lymphocytic Vasculitis-Associated Lesions (ALVAL)

Explanation

ALVAL represents a Type IV delayed hypersensitivity reaction to metal ions. Its hallmark histologic feature is a dense, perivascular infiltrate of lymphocytes, distinguishing it from a standard foreign-body macrophage response seen in normal wear.

Question 2455

Topic: 3. Adult Reconstruction (Hip & Knee)



A 65-year-old male presents with groin pain 5 years after a primary THA using a metal-on-polyethylene bearing with a large diameter titanium femoral head and a modular cobalt-chromium neck. Inflammatory markers are normal. Aspiration yields fluid with 300 WBCs/uL and 50% PMNs. MRI with MARS reveals a solid soft tissue mass and fluid collection. What is the most likely diagnosis, and what serum markers should be checked?

. Adverse reaction to metal debris (ARMD) from bearing surface wear; check serum cobalt and chromium levels.
. Periprosthetic joint infection; check alpha-defensin.
. Metallosis from femoral stem osteolysis; check serum titanium levels.
. Mechanically assisted crevice corrosion (MACC) at the modular junction; check serum cobalt and chromium levels.
. Polyethylene wear; no serum markers needed.

Correct Answer & Explanation

. Mechanically assisted crevice corrosion (MACC) at the modular junction; check serum cobalt and chromium levels.

Explanation

Mechanically assisted crevice corrosion (MACC) at the head-neck or neck-stem junction (trunnionosis) is a recognized complication, especially with mixed metal combinations (e.g., Ti and CoCr) or large femoral heads. Checking serum Co and Cr levels helps in diagnosing trunnionosis in metal-on-polyethylene bearings, as the bearing itself does not produce metal ions. The local tissue reaction is an adverse local tissue reaction (ALTR) often characterized by solid or cystic masses.

Question 2456

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary posterior-stabilized total knee arthroplasty, after making the standard bone cuts, the trial components are inserted. The knee is tight in extension but balanced in flexion. Which of the following is the most appropriate next step?

. Increase the posterior slope of the tibial cut.
. Downsize the femoral component.
. Resect more distal femur.
. Resect more proximal tibia.
. Release the posterior cruciate ligament.

Correct Answer & Explanation

. Resect more distal femur.

Explanation

A knee that is tight in extension and balanced in flexion indicates an extension gap that is too small relative to the flexion gap. Resecting more distal femur increases the extension gap without affecting the flexion gap. Resecting more proximal tibia would increase both the flexion and extension gaps symmetrically.

Question 2457

Topic: 3. Adult Reconstruction (Hip & Knee)
When considering bearing surfaces in total hip arthroplasty, which of the following combinations has the lowest volumetric wear rate in laboratory testing?
. Cobalt-chromium on highly cross-linked polyethylene.
. Ceramic on highly cross-linked polyethylene.
. Ceramic on ceramic.
. Cobalt-chromium on standard ultra-high molecular weight polyethylene (UHMWPE).
. Oxidized zirconium on highly cross-linked polyethylene.

Correct Answer & Explanation

. Ceramic on ceramic.

Explanation

Ceramic-on-ceramic bearing surfaces exhibit the lowest volumetric wear rates of any THA bearing combination. They are highly scratch-resistant and hydrophilic, which provides excellent boundary lubrication. However, their use is limited by concerns over component squeaking, catastrophic ceramic fracture, and technically demanding insertion.

Question 2458

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 International Consensus Meeting (ICM) criteria, which of the following findings serves as a definitive 'major criterion' for the diagnosis of a periprosthetic joint infection (PJI)?

. A synovial fluid white blood cell count greater than 3,000 cells/uL
. Elevated serum C-reactive protein (CRP) > 10 mg/L
. Positive alpha-defensin immunoassay
. A sinus tract communicating directly with the joint
. A single positive intraoperative tissue culture

Correct Answer & Explanation

. A sinus tract communicating directly with the joint

Explanation

Under the 2018 ICM criteria, the two major criteria for definitive PJI are a sinus tract communicating with the joint and two positive cultures identifying the same organism. All other options are considered minor criteria.

Question 2459

Topic: 3. Adult Reconstruction (Hip & Knee)

A surgeon utilizing the direct lateral (Hardinge) approach for a total hip arthroplasty splits the gluteus medius muscle. To avoid iatrogenic injury causing a postoperative Trendelenburg gait, the superior splitting of the gluteus medius must not extend beyond what distance proximal to the greater trochanter?

. 1 cm
. 3 cm
. 5 cm
. 7 cm
. 9 cm

Correct Answer & Explanation

. 5 cm

Explanation

The superior gluteal nerve innervates the gluteus medius and minimus. To prevent denervation during the direct lateral approach, the split should not extend beyond 3 to 5 cm proximal to the tip of the greater trochanter.

Question 2460

Topic: 3. Adult Reconstruction (Hip & Knee)

A 72-year-old male is 1 year status post a posterior-stabilized total knee arthroplasty. He complains of a painful catching sensation at the anterior knee when extending from a flexed position. Radiographs show well-fixed components with appropriate sizing. What is the most appropriate management?

. Revision of the femoral component
. Arthroscopic or open excision of the suprapatellar fibrous nodule
. Polyethylene liner exchange
. Patellar component revision
. Quadriceps lengthening

Correct Answer & Explanation

. Arthroscopic or open excision of the suprapatellar fibrous nodule

Explanation

The patient has patellar clunk syndrome, caused by a fibrous nodule at the superior pole of the patella catching in the intercondylar box of a posterior-stabilized femur. Treatment is arthroscopic or open debridement of the fibrous nodule.

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