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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 218 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 4341

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old patient undergoes a total knee arthroplasty (TKA). Three months post-operatively, he develops increasing knee pain, swelling, warmth, and purulent drainage from the surgical site. Synovial fluid analysis reveals a white blood cell count of 55,000 cells/ยตL with 92% neutrophils, and culture grows Methicillin-Sensitive Staphylococcus Aureus (MSSA). Which of the following is the most appropriate management strategy?

. Debridement, antibiotics, and implant retention (DAIR).
. Suppressive oral antibiotic therapy.
. One-stage revision arthroplasty with cement containing antibiotics.
. Two-stage revision arthroplasty with an antibiotic spacer.
. Arthrodesis of the knee joint.

Correct Answer & Explanation

. Two-stage revision arthroplasty with an antibiotic spacer.

Explanation

The patient presents with an acute periprosthetic joint infection (PJI) within 3 months of TKA, with purulent drainage and high WBC count, and a positive culture for MSSA. DAIR (Debridement, Antibiotics, and Implant Retention) is an option for acute infections (<3-6 weeks symptoms, stable implant, sensitive organism, healthy soft tissues), but the presence of purulent drainage and a 3-month duration makes DAIR less likely to be successful alone, as the biofilm is likely established. One-stage revision arthroplasty can be considered for acute PJI with specific criteria (good soft tissue envelope, known organism, susceptible to antibiotics, non-virulent organism). However, for established acute PJI with purulence and a virulent organism like S. aureus, a two-stage revision arthroplasty remains the gold standard. This involves removal of all components, thorough debridement, placement of an antibiotic-laden cement spacer, and 6-8 weeks of systemic antibiotics, followed by reimplantation if infection markers normalize. Suppressive antibiotics are for patients who are not surgical candidates. Arthrodesis is a salvage procedure.

Question 4342

Topic: 3. Adult Reconstruction (Hip & Knee)

A 70-year-old patient undergoes revision total hip arthroplasty (THA) for aseptic loosening of a cemented femoral stem. Intraoperatively, significant femoral bone loss is noted, corresponding to Paprosky Type 3B, with minimal intact host bone proximally and a wide diaphyseal canal. Which of the following femoral components is generally considered the most appropriate for reconstruction in this scenario?

. A standard cemented femoral stem.
. A short-stem uncemented femoral component.
. A modular extensively coated uncemented stem with distal fixation.
. An impaction grafting technique with a cemented stem.
. A calcar-replacing cemented stem.

Correct Answer & Explanation

. A modular extensively coated uncemented stem with distal fixation.

Explanation

Paprosky Type 3B femoral bone loss signifies extensive proximal femoral bone loss, often extending below the lesser trochanter, with an enlarged diaphyseal canal and no significant metaphyseal bone for press-fit. In such cases, a modular extensively coated uncemented femoral stem with primary distal fixation (engaging cortical bone distally) is the most appropriate reconstructive option. These stems bypass the deficient proximal bone and achieve stable fixation in the healthier diaphyseal bone. Standard cemented or short-stem uncemented components rely on intact proximal bone which is absent. Impaction grafting is an option but for Type 3B it often requires specific expertise and can be challenging for significant defects. Calcar-replacing stems are for specific metaphyseal defects and typically require intact proximal bone.

Question 4343

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old female with a history of primary total hip arthroplasty (metal-on-polyethylene) 8 years ago presents with new-onset groin pain. Radiographs show a well-fixed stem and cup with no osteolysis. A joint aspiration yields fluid with a normal cell count but elevated cobalt and chromium ions. MRI demonstrates a solid periprosthetic soft-tissue mass. What is the most likely pathophysiologic mechanism for this presentation?

. Polyethylene wear debris inducing macrophage activation
. Mechanically assisted crevice corrosion at the head-neck junction
. Third-body wear from retained PMMA cement
. Galvanic corrosion between the titanium stem and cobalt-chromium shell
. Delayed low-virulence infection by Cutibacterium acnes

Correct Answer & Explanation

. Mechanically assisted crevice corrosion at the head-neck junction

Explanation

The scenario describes trunnionosis, which is mechanically assisted crevice corrosion at the modular head-neck junction (the trunnion). Even in metal-on-polyethylene bearings, fretting and crevice corrosion at this modular interface can generate metal ions (elevated cobalt and chromium) and debris, leading to an adverse local tissue reaction (ALTR) or pseudotumor.

Question 4344

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total knee arthroplasty, the surgeon inadvertently internally rotates the femoral component by 5 degrees relative to the surgical transepicondylar axis. Which of the following is the most likely clinical consequence of this technical error?

. Medial patellar subluxation
. Increased tension on the medial collateral ligament in flexion
. Lateral patellar tracking and potential subluxation
. Excessive femoral rollback in deep flexion
. Gap imbalance causing a tight extension gap and loose flexion gap

Correct Answer & Explanation

. Lateral patellar tracking and potential subluxation

Explanation

Internal rotation of the femoral component in a TKA shifts the trochlear groove medially, which effectively increases the Q-angle. This relative change leads to lateral patellar maltracking, thereby increasing the risk of lateral patellar subluxation or dislocation. It also typically creates an asymmetric flexion gap that is tight medially.

Question 4345

Topic: 3. Adult Reconstruction (Hip & Knee)

A 70-year-old male presents 2 years after a primary total hip arthroplasty with a draining sinus tract communicating with the hip joint. According to the 2018 Musculoskeletal Infection Society (MSIS) / International Consensus Meeting (ICM) criteria for periprosthetic joint infection (PJI), which of the following is true regarding this patient's diagnosis?

. A synovial fluid leukocyte count >3,000 cells/uL is strictly required to confirm PJI
. A sinus tract communicating with the joint is a major criterion and definitively diagnoses PJI
. Two positive periprosthetic tissue cultures with different organisms are required for definitive diagnosis
. Elevated serum CRP and ESR are mandatory for diagnosis
. An elevated synovial alpha-defensin test is required as a major criterion

Correct Answer & Explanation

. A sinus tract communicating with the joint is a major criterion and definitively diagnoses PJI

Explanation

According to the 2018 MSIS/ICM criteria, the presence of a sinus tract communicating with the prosthesis OR two positive tissue/fluid cultures isolating the exact same organism are considered 'major criteria.' The presence of either of these major criteria is definitively diagnostic for a periprosthetic joint infection (PJI) without the need for minor criteria scoring (such as ESR, CRP, synovial WBC count, or alpha-defensin).

Question 4346

Topic: Total Hip Arthroplasty (THA)

A patient with severe coxa vara and a functional leg length discrepancy of 4 cm is scheduled for a subtrochanteric osteotomy. To maximally correct both the mechanical axis and the leg length discrepancy simultaneously, which procedure is most appropriate?

. Varus-producing osteotomy with acute shortening
. Valgus-producing osteotomy combined with gradual distraction osteogenesis
. Medial displacement osteotomy of the femoral shaft
. Greater trochanteric advancement only
. Distal femoral lengthening with no proximal correction

Correct Answer & Explanation

. Valgus-producing osteotomy combined with gradual distraction osteogenesis

Explanation

Coxa vara is treated with a valgus-producing osteotomy to restore the neck-shaft angle and abductor mechanics. Combining this with gradual distraction osteogenesis using an external fixator or lengthening nail simultaneously corrects the profound leg length discrepancy.

Question 4347

Topic: Total Hip Arthroplasty (THA)

A patient requires correction of a distal tibial procurvatum deformity. The CORA is at the ankle joint line. According to Paley's Rule 3, if a supramalleolar osteotomy is performed proximal to the CORA and the hinge is placed at the osteotomy site, what is the resultant geometric deformity?

. Pure angulation without translation.
. Angulation with collinear realignment of the mechanical axes.
. Angulation with a new translation deformity (parallel axis shift).
. Pure translation without angulation.
. Spontaneous correction of both angulation and leg length discrepancy.

Correct Answer & Explanation

. Angulation with a new translation deformity (parallel axis shift).

Explanation

Paley's Rule 3 states that if the osteotomy and the hinge are both placed at a location different from the CORA, the result is angulation complicated by a new translation deformity. The axes will end up parallel but not collinear.

Question 4348

Topic: 3. Adult Reconstruction (Hip & Knee)

A 14-year-old presents with symptomatic coxa valga and a 3 cm leg length discrepancy. A varus-producing proximal femoral osteotomy is planned. According to Paley's Rule 2, if the osteotomy is made at the intertrochanteric line but the CORA is in the femoral neck, placing the hinge at the CORA will result in:

. Pure angulation without any translation.
. Angulation with expected translation allowing complete axis alignment.
. Angulation with a permanent residual translation deformity.
. A high risk of femoral head avascular necrosis.
. Inevitable impingement of the greater trochanter.

Correct Answer & Explanation

. Angulation with expected translation allowing complete axis alignment.

Explanation

Paley's Rule 2 states that if the osteotomy is at a different level than the CORA, but the hinge is placed precisely at the CORA, the mechanical axes will fully realign. The correction will inherently include translation at the osteotomy site, which is desired to align the axes.

Question 4349

Topic: 3. Adult Reconstruction (Hip & Knee)

A 25-year-old male sustains a transverse femoral shaft fracture. Examination reveals short stature, a beaked nose, and a history of delayed cranial suture closure. Hand radiographs show acro-osteolysis of the distal phalanges, and all bones appear densely sclerotic. Which gene is most likely mutated?

. TCIRG1
. Cathepsin K
. LRP5
. SOST
. FGFR2

Correct Answer & Explanation

. Cathepsin K

Explanation

Pycnodysostosis is an autosomal recessive osteosclerosing dysplasia caused by a deficiency of Cathepsin K, an enzyme essential for osteoclast-mediated degradation of type I collagen. Clinical hallmarks include dense, fragile bones, acro-osteolysis, and characteristic facial features.

Question 4350

Topic: 3. Adult Reconstruction (Hip & Knee)

A 28-year-old male presents with a transverse, non-comminuted femur fracture after a minor fall. He has short stature, an obtuse mandibular angle, delayed closure of cranial sutures, and stubby fingers. Radiographs show generalized osteosclerosis and acro-osteolysis of the distal phalanges. Which of the following is the underlying molecular defect?

. Carbonic anhydrase II deficiency
. Defective chloride channel 7 (CLCN7)
. Transforming growth factor beta 1 (TGFB1) overactivity
. Cartilage-derived morphogenetic protein-1 deficiency
. Cathepsin K deficiency

Correct Answer & Explanation

. Cathepsin K deficiency

Explanation

The clinical features (osteosclerosis, acro-osteolysis, obtuse mandible, delayed sutures) are pathognomonic for Pycnodysostosis. It is an autosomal recessive disorder caused by a deficiency in Cathepsin K, impairing osteoclast degradation of bone matrix proteins.

Question 4351

Topic: 3. Adult Reconstruction (Hip & Knee)

A 25-year-old male presents with a nonunion of a midshaft femur fracture. He exhibits short stature, prominent eyes, a beaked nose, and hypoplastic distal phalanges (acro-osteolysis). Radiographs reveal generalized osteosclerosis and open cranial sutures. What is the specific enzyme deficiency responsible for this underlying bone dysplasia?

. Carbonic anhydrase II
. Cathepsin K
. Tartrate-resistant acid phosphatase
. Tissue-nonspecific alkaline phosphatase
. Lysyl hydroxylase

Correct Answer & Explanation

. Cathepsin K

Explanation

Pycnodysostosis is an autosomal recessive osteosclerosing dysplasia caused by a deficiency in Cathepsin K, an enzyme secreted by osteoclasts to degrade type I collagen in the bone matrix. Clinical hallmarks include delayed closure of cranial sutures, acro-osteolysis of the distal phalanges, and brittle, dense bones.

Question 4352

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 International Consensus Meeting on Periprosthetic Joint Infection, which of the following findings is considered a definitive major criterion for diagnosing a periprosthetic joint infection (PJI)?

. Elevated serum C-reactive protein (>10 mg/L) and D-dimer (>860 ng/mL)
. A single positive intraoperative tissue culture growing Staphylococcus epidermidis
. Purulence in the affected joint without an isolated organism
. A sinus tract communicating with the prosthesis
. Synovial fluid white blood cell count >3,000 cells/uL with >80% polymorphonuclear neutrophils

Correct Answer & Explanation

. A sinus tract communicating with the prosthesis

Explanation

The 2018 ICM criteria define a major criterion as either a sinus tract communicating with the joint or two positive periprosthetic cultures with phenotypically identical organisms. The presence of either major criterion is diagnostic for PJI.

Question 4353

Topic: 3. Adult Reconstruction (Hip & Knee)

A 45-year-old female presents with severe hand stiffness, progressive dysphagia, and fingertip ulcerations. Radiographs of her hands demonstrate acro-osteolysis and subcutaneous soft tissue calcifications.

Which of the following autoantibodies is most specific for the diffuse cutaneous form of this systemic disease?

. Anti-centromere antibody
. Anti-Scl-70 (anti-topoisomerase I) antibody
. Anti-cyclic citrullinated peptide (anti-CCP) antibody
. Anti-double stranded DNA (anti-dsDNA) antibody
. Anti-Jo-1 antibody

Correct Answer & Explanation

. Anti-Scl-70 (anti-topoisomerase I) antibody

Explanation

The clinical and radiographic presentation is consistent with systemic sclerosis (scleroderma). Anti-Scl-70 antibodies are highly specific for the diffuse cutaneous form of systemic sclerosis, which carries a higher risk of interstitial lung disease.

Question 4354

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old man develops acute onset of right knee pain, swelling, and erythema 18 days after a primary total knee arthroplasty. Aspiration yields a synovial WBC count of 55,000 cells/uL. He is scheduled for debridement, antibiotics, and implant retention (DAIR). To maximize the success rate of this procedure, what intraoperative step MUST be performed?

. Exchange of the femoral component only
. Exchange of the tibial tray only
. Exchange of the polyethylene insert
. Retention of all components and continuous postoperative irrigation
. Drilling of the femoral and tibial metaphyses

Correct Answer & Explanation

. Exchange of the polyethylene insert

Explanation

During a DAIR procedure for an acute periprosthetic joint infection, exchanging the modular polyethylene insert is critical. This allows access to the posterior joint space for thorough debridement and removes the biofilm adherent to the polymer.

Question 4355

Topic: 3. Adult Reconstruction (Hip & Knee)

Synovial fluid alpha-defensin testing is an important adjunct in diagnosing periprosthetic joint infection. What is the precise biological origin and function of alpha-defensin?

. A cytokine produced by macrophages to stimulate fibroblast proliferation
. An acute-phase reactant synthesized in the liver in response to IL-6
. An antimicrobial peptide released by activated neutrophils to destroy pathogens
. An enzyme released by bacteria that degrades the extracellular matrix
. A breakdown product of bacterial cell walls during antibiotic therapy

Correct Answer & Explanation

. An antimicrobial peptide released by activated neutrophils to destroy pathogens

Explanation

Alpha-defensin is an antimicrobial peptide released by host neutrophils in response to the presence of pathogens. It is a highly sensitive and specific biomarker for PJI and is not significantly affected by prior antibiotic administration.

Question 4356

Topic: 3. Adult Reconstruction (Hip & Knee)

When treating a chronic periprosthetic knee infection with a two-stage exchange arthroplasty, what is a primary biomechanical or surgical advantage of utilizing an articulating antibiotic spacer rather than a static spacer?

. It provides superior local antibiotic elution kinetics
. It eliminates the risk of spacer dislocation
. It facilitates exposure during the second-stage reimplantation
. It allows for earlier full weight-bearing on the affected limb
. It is indicated in cases with massive segmental bone loss and absent collateral ligaments

Correct Answer & Explanation

. It facilitates exposure during the second-stage reimplantation

Explanation

Articulating spacers maintain the length of collateral ligaments and allow interval range of motion, which prevents severe soft-tissue contractures. This significantly facilitates joint exposure and functional recovery during the second-stage reimplantation.

Question 4357

Topic: 3. Adult Reconstruction (Hip & Knee)

A 62-year-old man undergoes revision of an anatomic total shoulder arthroplasty due to aseptic loosening. Preoperative aspiration was negative. However, 12 days after the revision surgery, 4 out of 5 intraoperative tissue cultures become positive for an organism. Which of the following is the most likely pathogen?

. Staphylococcus aureus
. Pseudomonas aeruginosa
. Cutibacterium acnes
. Streptococcus agalactiae
. Escherichia coli

Correct Answer & Explanation

. Cutibacterium acnes

Explanation

Cutibacterium (formerly Propionibacterium) acnes is an indolent, anaerobic, Gram-positive bacillus commonly implicated in shoulder periprosthetic joint infections. It is slow-growing and frequently requires cultures to be held for up to 14 days to be detected.

Question 4358

Topic: 3. Adult Reconstruction (Hip & Knee)

A rapid colorimetric leukocyte esterase strip test is frequently used in the evaluation of periprosthetic joint infection. What is the major limitation of using this test on aspirated synovial fluid?

. It requires a minimum of 48 hours to yield results
. It is uninterpretable if the synovial fluid is heavily blood-stained
. It exclusively detects Gram-negative bacterial infections
. It cross-reacts with local anesthetics, causing false negatives
. It requires expensive, proprietary laboratory equipment to read

Correct Answer & Explanation

. It is uninterpretable if the synovial fluid is heavily blood-stained

Explanation

Leukocyte esterase strips are inexpensive and provide rapid results by detecting an enzyme released by neutrophils. However, their major limitation is that heavy red blood cell contamination (bloody aspirate) makes the colorimetric change uninterpretable.

Question 4359

Topic: 3. Adult Reconstruction (Hip & Knee)

According to the 2018 International Consensus Meeting (ICM) criteria, which of the following is considered a definitive major criterion for diagnosing a periprosthetic joint infection (PJI)?

. Elevated serum CRP > 10 mg/L and D-dimer > 860 ng/mL
. Synovial fluid WBC > 3000 cells/ยตL
. A single positive periprosthetic tissue culture
. A sinus tract communicating with the joint
. Frank purulence noted within the joint space

Correct Answer & Explanation

. A sinus tract communicating with the joint

Explanation

The 2018 ICM criteria define two major criteria for definitive PJI: a communicating sinus tract or two positive periprosthetic cultures with phenotypically identical organisms. Purulence, elevated serum markers, and synovial WBC are considered minor criteria.

Question 4360

Topic: 3. Adult Reconstruction (Hip & Knee)

A 62-year-old man presents with insidious shoulder stiffness 2 years after an anatomic total shoulder arthroplasty. Aspiration yields no fluid, so intraoperative tissue cultures are obtained during revision. How long must these cultures be held to reliably detect the most likely causative organism?

. 3 days
. 5 days
. 7 days
. 14 days
. 21 days

Correct Answer & Explanation

. 14 days

Explanation

Cutibacterium acnes is a slow-growing, Gram-positive anaerobic rod that is the most common cause of shoulder PJI. Cultures must be held for a minimum of 14 days to minimize false-negative results.

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