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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 262 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 5221

Topic: 3. Adult Reconstruction (Hip & Knee)

A 66-year-old male presents with a painful TKA 2 years postoperatively. Synovial fluid aspiration reveals a WBC count of 4,500 cells/uL with 85% PMNs. The synovial alpha-defensin immunoassay is positive. No sinus tract or purulence is present. Based on the 2018 Evidence-Based International Consensus Meeting (ICM) criteria, what is the correct diagnosis?

. Aseptic loosening
. Possible periprosthetic joint infection
. Confirmed periprosthetic joint infection
. Crystal arthropathy
. Adverse local tissue reaction

Correct Answer & Explanation

. Aseptic loosening

Explanation

Under the 2018 ICM criteria, a score of 6 or greater is diagnostic for PJI. A positive alpha-defensin (3 points), elevated WBC (3 points), and elevated PMN% (2 points) totals 8 points, firmly confirming an infected periprosthetic joint.

Question 5222

Topic: 3. Adult Reconstruction (Hip & Knee)

A 72-year-old female is undergoing revision total hip arthroplasty for aseptic loosening. Intraoperative assessment of the acetabulum reveals superior migration of the cup of 3.5 cm, medial migration past the Kohler line, and an ischiolytic lesion. There is severe superior bone loss with less than 40% host bone contact available for the new component, but the anterior and posterior columns remain intact. What is the most appropriate acetabular reconstruction strategy?

. Impaction bone grafting with a cemented polyethylene cup
. Standard hemispherical fully porous-coated cup with multiple screws
. Highly porous trabecular metal cup with a superior metal augment
. Cup-cage construct
. Anti-protrusio cage alone

Correct Answer & Explanation

. Impaction bone grafting with a cemented polyethylene cup

Explanation

The scenario describes a Paprosky 3B acetabular defect (superior migration >3cm, medial migration, ischiolytic lesion, and <40% host bone contact), without pelvic discontinuity (columns intact). The gold standard for this level of severe uncontained bone loss is a highly porous (e.g., trabecular metal) cup with metal augments to substitute for the massive structural bone loss. A cup-cage is typically reserved for pelvic discontinuity, while standard hemispherical cups will fail due to lack of adequate biological fixation (<50% host bone contact).

Question 5223

Topic: 3. Adult Reconstruction (Hip & Knee)
A 65-year-old male is evaluated for a painful total knee arthroplasty (TKA) 2 years postoperatively. Serum CRP is 18 mg/L and ESR is 45 mm/hr. Synovial fluid aspiration demonstrates a WBC count of 4,800 cells/ยตL with 75% PMNs. An alpha-defensin test is positive. According to the 2018 International Consensus Meeting (ICM) criteria, what is the most appropriate next step in management?
. Repeat aspiration in 2 weeks to confirm
. Prescribe a 6-week course of oral antibiotics
. Proceed with isolated polyethylene liner exchange
. Proceed with revision arthroplasty (single or two-stage exchange)
. Observation and physical therapy

Correct Answer & Explanation

. Proceed with revision arthroplasty (single or two-stage exchange)

Explanation

According to the 2018 ICM criteria, the diagnosis of periprosthetic joint infection (PJI) is definitively confirmed based on the scoring system. A positive alpha-defensin (3 points), elevated synovial WBC/PMN (3 points), and elevated serum inflammatory markers (2 points) yield a score well above the threshold for definitive PJI (score โ‰ฅ6). The standard of care for a chronic PJI (>4 weeks post-op) is revision arthroplasty, most commonly a two-stage exchange in North America, or single-stage in highly selected cases. Liner exchange with retention of components (DAIR) is contraindicated for chronic infections.

Question 5224

Topic: Total Knee Arthroplasty (TKA)

During a primary TKA, the surgeon uses spacer blocks to assess gap kinematics. The extension gap is symmetric and well-balanced. However, the flexion gap is symmetric but significantly tight, preventing adequate knee flexion with the trial components. Which of the following technical adjustments is the most appropriate next step to balance the knee?

. Recut the distal femur to remove more bone
. Release the posterior cruciate ligament (PCL) and upsize the tibial polyethylene
. Downsize the femoral component and maintain the anterior referencing
. Decrease the posterior slope of the tibial cut
. Release the medial collateral ligament (MCL)

Correct Answer & Explanation

. Recut the distal femur to remove more bone

Explanation

The scenario describes a 'balanced extension, tight flexion' gap mismatch. Modifying the distal femoral cut or the overall polyethylene thickness will affect BOTH gaps. Releasing the PCL primarily affects the flexion gap but often necessitates switching to a posterior stabilized (PS) construct if not already planned, and upsizing poly would tighten extension. Downsizing the femoral component (which decreases the AP dimension of the femur) removes more posterior femoral condyle bone, thereby opening the flexion gap without altering the extension gap. Increasing (not decreasing) tibial slope would also open the flexion gap, but downsizing the femur is the most direct and standard adjustment.

Question 5225

Topic: 3. Adult Reconstruction (Hip & Knee)

A 60-year-old male with a metal-on-polyethylene THA presents with an 8-month history of progressive groin pain. Radiographs show a well-fixed stem and cup. MRI reveals a large, thick-walled cystic fluid collection surrounding the hip joint. Aspiration yields yellow fluid, negative cultures, and a WBC count of 500 cells/ยตL. Serum cobalt is 18 ppb and chromium is 2 ppb. What is the primary pathophysiologic mechanism driving this complication?

. Macrophage-mediated phagocytosis of submicron polyethylene debris
. Mechanically assisted crevice corrosion at the head-neck taper
. Direct bacterial biofilm seeding of the modular junction
. Third-body wear from retained cement particles
. Osteoclast hyperactivation secondary to stress shielding

Correct Answer & Explanation

. Macrophage-mediated phagocytosis of submicron polyethylene debris

Explanation

The clinical presentation (cystic pseudotumor, groin pain, negative cultures) combined with dramatically elevated cobalt levels relative to chromium (Co > Cr) in a metal-on-polyethylene THA is pathognomonic for trunnionosis. This is driven by mechanically assisted crevice corrosion (MACC) at the modular head-neck taper junction. Polyethylene wear osteolysis (Option A) would not elevate serum metal ions or typically present with an ALVAL-type pseudotumor.

Question 5226

Topic: 3. Adult Reconstruction (Hip & Knee)

In planning a revision total hip arthroplasty, the surgeon evaluates the femoral bone stock. There is complete loss of metaphyseal cancellous bone, and diaphyseal bone loss extends 2 cm distal to the lesser trochanter. However, the diaphyseal isthmus remains intact with 5 cm of scratch fit available. What is the correct Paprosky Femoral classification and the most appropriate reconstructive strategy?

. Type 2; Fully porous coated cylindrical stem
. Type 3A; Fully porous coated cylindrical stem or tapered fluted modular stem
. Type 3B; Tapered fluted modular stem
. Type 4; Impaction grafting with cemented stem
. Type 3A; Proximal femoral replacement

Correct Answer & Explanation

. Type 2; Fully porous coated cylindrical stem

Explanation

This describes a Paprosky Type 3A femoral defect. Type 3A defects have severe metaphyseal damage and diaphyseal bone loss extending past the lesser trochanter, but crucially retain >4 cm of intact diaphyseal bone at the isthmus to achieve reliable distal fixation. The recommended implant is a fully porous-coated cylindrical stem (6-8 inches) or a tapered fluted modular stem. Type 3B defects have <4 cm of intact diaphyseal scratch fit.

Question 5227

Topic: Total Knee Arthroplasty (TKA)

During a complex primary TKA for a severe fixed valgus deformity, the medial collateral ligament (MCL) is inadvertently transected mid-substance and is deemed completely incompetent and irreparable. Which of the following implant constraints is required to provide adequate stability?

. Cruciate Retaining (CR)
. Posterior Stabilized (PS)
. Constrained Condylar Knee (CCK)
. Rotating Hinge
. Fixed Bearing Unicompartmental Knee

Correct Answer & Explanation

. Cruciate Retaining (CR)

Explanation

A completely incompetent, absent, or irreparable MCL in total knee arthroplasty necessitates a rotating hinge construct. A Constrained Condylar Knee (CCK) utilizes a tall tibial post to provide varus/valgus stability, but it relies on functional collateral ligaments to act as checkreins; it will fail early or subluxate if the primary stabilizer (MCL) is completely deficient. CR and PS implants offer no coronal plane constraint.

Question 5228

Topic: Total Knee Arthroplasty (TKA)

A 66-year-old patient undergoes revision TKA. The surgeon utilizes thick tibial and femoral augments to manage bone loss. Postoperatively, the patient reports a painful catch and mid-flexion instability. Lateral radiographs show the inferior pole of the patella is abnormally close to the tibial plateau. What intraoperative technical error most likely led to this complication?

. Undersizing the femoral component
. Using a tibial insert that was too thin
. Elevating the joint line
. Lowering the joint line
. Placing the femoral component in excessive external rotation

Correct Answer & Explanation

. Undersizing the femoral component

Explanation

Elevating the joint line is a common complication in revision TKA when distal femoral bone loss is not adequately compensated with distal femoral augments, and a thicker polyethylene is used instead. This elevates the tibiofemoral joint line relative to the patella. Because the patellar tendon length remains fixed to the tibial tubercle, the patella sits lower relative to the joint line (patella baja/infra). This alters patellofemoral tracking, causes anterior knee pain, limits flexion, and can lead to mid-flexion instability.

Question 5229

Topic: 3. Adult Reconstruction (Hip & Knee)

In a revision THA setting, a patient presents with massive acetabular osteolysis. Preoperative radiographs reveal a distinct transverse fracture line through the acetabular fossa and medial translation of the inferior hemipelvis relative to the superior hemipelvis. What is the diagnosis, and what is the most appropriate intraoperative implant consideration?

. Paprosky 3A defect; Standard hemispherical cup with multi-hole screws
. Pelvic discontinuity; Cup-cage construct or custom triflange component
. Protrusio acetabuli; Impaction bone grafting and a cemented cup
. Ischial osteolysis; Highly porous cup with an inferior augment
. Anterior column defect; Jumbo cup

Correct Answer & Explanation

. Paprosky 3A defect; Standard hemispherical cup with multi-hole screws

Explanation

The clinical description of a transverse fracture line through the fossa with independent movement/translation of the superior and inferior hemipelvis is the definition of pelvic discontinuity. To bridge and stabilize this defect, constructs that secure the ilium to the ischium/pubis are required. A cup-cage construct, custom triflange component, or a highly porous cup with half-pin distraction are the standard of care.

Question 5230

Topic: Total Hip Arthroplasty (THA)

A 75-year-old male with Parkinson's disease and a history of recurrent posterior hip dislocations is scheduled for revision THA. A dual mobility construct is selected. What is the primary biomechanical advantage of a dual mobility bearing that reduces dislocation risk?

. It provides a constrained locking ring that physically prevents the head from escaping the liner
. It increases the effective head diameter to increase jump distance while allowing motion at two separate articulations
. It shifts the center of rotation medially to increase the abductor moment arm
. It severely restricts total arc of motion, thereby preventing impingement
. It utilizes a completely fixed acetabular liner to eliminate sheer forces

Correct Answer & Explanation

. It provides a constrained locking ring that physically prevents the head from escaping the liner

Explanation

A dual mobility bearing features a small inner metal or ceramic head that articulates within a larger unconstrained mobile polyethylene head, which in turn articulates within the metallic acetabular shell. The primary advantage is an increased effective head diameter (the size of the large poly head), which drastically increases the jump distance required for dislocation. The dual articulation minimizes wear compared to a traditional monolithic large head design.

Question 5231

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old patient underwent the first stage of a two-stage exchange for a chronic MRSA periprosthetic hip infection. An articulating antibiotic spacer was placed. According to established protocols, when is the optimal time to evaluate the patient for the second-stage reimplantation?

. Immediately upon normalization of serum CRP, typically at 2 weeks
. After completing a minimum 6-week course of appropriate IV antibiotics, followed by an antibiotic holiday, assuming favorable clinical and serological status
. At exactly 3 months post-operatively, regardless of inflammatory marker trends
. After 1 year of continuous oral suppressive antibiotic therapy
. Only when a repeat joint aspiration produces zero white blood cells

Correct Answer & Explanation

. Immediately upon normalization of serum CRP, typically at 2 weeks

Explanation

The standard protocol for two-stage exchange arthroplasty for PJI requires completion of culture-directed systemic antibiotic therapy (typically 4-6 weeks of IV antibiotics), followed by an 'antibiotic holiday' (often 2-4 weeks) off all antibiotics. If the joint remains clinically quiescent and inflammatory markers trend down or normalize, the patient is cleared for reimplantation. Aspiration may be performed to ensure negative cultures prior to stage 2.

Question 5232

Topic: Total Knee Arthroplasty (TKA)

A 68-year-old female presents 3 years post-TKA with the sudden inability to actively extend her knee after a fall. Examination reveals a palpable gap at the superior pole of the patella. For this chronic, full-thickness quadriceps tendon tear in the setting of a TKA, what is the most reliable surgical treatment option to restore extensor mechanism continuity?

. Primary end-to-end repair using heavy non-absorbable sutures
. Reconstruction using a synthetic mesh or whole extensor mechanism allograft
. Patellectomy and primary tendon-to-tendon repair
. Revision to a rotating hinge knee
. Non-operative management with a cylinder cast in extension for 12 weeks

Correct Answer & Explanation

. Primary end-to-end repair using heavy non-absorbable sutures

Explanation

Extensor mechanism disruption in the setting of a TKA is a devastating complication. Primary repair of chronic tears or poor quality tissue in this setting has a notoriously high failure rate. The most reliable and durable surgical options are reconstruction with an allograft (entire extensor mechanism: tibial tubercle, patella, quadriceps tendon) or synthetic mesh (e.g., Marlex mesh), which has gained significant popularity due to high success rates and lack of disease transmission risk.

Question 5233

Topic: Total Hip Arthroplasty (THA)

Which of the following intraoperative variables most significantly increases the risk of posterior dislocation following a primary THA performed via a posterior approach?

. Placement of the acetabular component in 30 degrees of anteversion
. Use of a 36-mm femoral head instead of a 28-mm head
. Failure to repair the short external rotators and posterior capsule
. Lengthening the operative leg by 10 mm relative to the contralateral side
. Increasing the femoral offset by 5 mm

Correct Answer & Explanation

. Placement of the acetabular component in 30 degrees of anteversion

Explanation

The posterior approach disrupts the posterior soft tissue envelope (capsule and short external rotators). Failure to perform a robust posterior soft-tissue repair significantly increases the risk of early posterior dislocation. Conversely, increased acetabular anteversion, larger femoral head size (increases jump distance), increased leg length, and increased offset all serve to increase soft tissue tension and mechanical stability, thereby decreasing dislocation risk.

Question 5234

Topic: Total Knee Arthroplasty (TKA)

A 62-year-old male is evaluated 8 weeks after a primary TKA complaining of severe stiffness. His active range of motion is 15 to 75 degrees. Radiographs demonstrate well-fixed and well-positioned components. Inflammatory markers (CRP/ESR) are strictly within normal limits, and pain is minimal at rest. Supervised physical therapy has reached a plateau over the last 3 weeks. What is the most appropriate next step in management?

. Revision TKA with a downsized femoral component
. Manipulation under anesthesia (MUA)
. Arthroscopic lysis of adhesions
. Open lysis of adhesions with polyethylene liner exchange
. Discharge from physical therapy and observation for 6 months

Correct Answer & Explanation

. Revision TKA with a downsized femoral component

Explanation

The patient is presenting with arthrofibrosis after TKA. He is in the optimal window (6-12 weeks post-op) for Manipulation Under Anesthesia (MUA). Infection has been ruled out (normal markers), components are mechanically sound, and conservative measures (PT) have failed. Delaying beyond 12 weeks drastically reduces the efficacy of MUA due to mature collagen cross-linking. Arthroscopic or open lysis is reserved for refractory cases after a failed MUA.

Question 5235

Topic: Total Hip Arthroplasty (THA)

A patient presents 6 months after a right THA complaining that the operative leg feels longer. On physical examination, the distance from the anterior superior iliac spine (ASIS) to the medial malleolus is strictly equal bilaterally. However, the distance from the umbilicus to the medial malleolus is 2 cm greater on the right. Anteroposterior pelvic radiographs demonstrate that the lesser trochanters are perfectly level relative to the ischial tuberosities. What is the most likely etiology of the patient's symptoms?

. Use of an oversized femoral head length (+8mm)
. Acetabular cup placed inferior to the anatomic tear drop
. Fixed pelvic obliquity secondary to spinal deformity or soft tissue contracture
. Subsidence of the femoral stem on the contralateral side
. Excessive offset of the femoral stem

Correct Answer & Explanation

. Use of an oversized femoral head length (+8mm)

Explanation

The patient has an apparent (functional) leg length discrepancy, not a true (anatomic) leg length discrepancy. True leg length is measured from ASIS to medial malleolus, which is equal here, and confirmed radiographically by level lesser trochanters. Apparent leg length is measured from the umbilicus to the medial malleolus. A discrepancy in apparent length with equal true length is caused by pelvic obliquity, often driven by lumbar scoliosis, fixed spinal deformity, or adductor/abductor contractures.

Question 5236

Topic: 3. Adult Reconstruction (Hip & Knee)

In total hip arthroplasty, the 'jump distance' is defined as the distance the femoral head center must travel to dislocate over the rim of the acetabular component. Which of the following modifications most significantly increases the jump distance without altering the component position?

. Using a constrained liner
. Increasing the femoral head size
. Decreasing the acetabular cup anteversion
. Increasing the acetabular cup inclination
. Decreasing the femoral neck offset

Correct Answer & Explanation

. Using a constrained liner

Explanation

The jump distance is the distance the center of the femoral head must translate to dislocate from the acetabular socket. Increasing the femoral head size increases the radius of the head, thereby proportionally increasing the jump distance and providing greater stability against dislocation.

Question 5237

Topic: 3. Adult Reconstruction (Hip & Knee)

During a total knee arthroplasty (TKA), the surgeon decides to use a posterior-stabilized (PS) design instead of a cruciate-retaining (CR) design. Which of the following biomechanical phenomena is exclusively facilitated by the cam-and-post mechanism in the PS design?

. Prevention of posterior tibial subluxation in extension
. Facilitation of paradoxical anterior femoral translation during flexion
. Obligatory femoral rollback during deep flexion
. Prevention of varus-valgus instability in mid-flexion
. Restoration of the screw-home mechanism in terminal extension

Correct Answer & Explanation

. Prevention of posterior tibial subluxation in extension

Explanation

In a normal knee, the posterior cruciate ligament (PCL) facilitates posterior femoral rollback during flexion, which improves clearance and increases the lever arm of the extensor mechanism. In a PS TKA, the PCL is sacrificed, and the cam-and-post mechanism is designed to reproduce this obligatory femoral rollback during deep flexion.

Question 5238

Topic: 3. Adult Reconstruction (Hip & Knee)
A 65-year-old female presents with a painful total knee arthroplasty 3 years postoperatively. Her serum CRP is 15 mg/L (normal < 10) and ESR is 40 mm/hr. A joint aspiration is performed. Which of the following synovial fluid profiles is most definitively diagnostic of a chronic periprosthetic joint infection according to the 2018 Evidence-Based International Consensus Meeting criteria?
. Leukocyte count of 1,500 cells/ยตL with 60% PMNs
. Leukocyte count of 2,500 cells/ยตL with 75% PMNs
. Synovial fluid alpha-defensin test positive alone
. Positive leukocyte esterase (++) and synovial fluid PMN% of 85%
. Positive culture for Staphylococcus epidermidis in a single sample

Correct Answer & Explanation

. Positive leukocyte esterase (++) and synovial fluid PMN% of 85%

Explanation

According to the 2018 ICM criteria, a score of >= 6 indicates infection. Elevated CRP (score 1) and ESR (score 1) provide 2 points. A positive leukocyte esterase (++) gives a score of 3, and a PMN% > 80% gives a score of 2. The combination (1+1+3+2 = 7) definitively diagnoses PJI. Alpha-defensin alone gives 3 points.

Question 5239

Topic: Total Hip Arthroplasty (THA)

A surgeon aims to increase femoral offset during a total hip arthroplasty without increasing leg length. Which of the following techniques will best achieve this goal?

. Using a longer femoral head neck length
. Decreasing the depth of femoral stem insertion
. Using a lateralized (high-offset) femoral stem
. Decreasing the acetabular component abduction angle
. Increasing the anteversion of the acetabular component

Correct Answer & Explanation

. Using a longer femoral head neck length

Explanation

A lateralized or high-offset femoral stem is designed specifically to increase the offset (the perpendicular distance from the center of rotation to the anatomical axis of the femur) without changing the vertical height (leg length). Increasing the femoral head length or decreasing stem insertion depth would inadvertently increase leg length.

Question 5240

Topic: 3. Adult Reconstruction (Hip & Knee)

Following trial reduction in a total knee arthroplasty, the patella is found to track laterally and tilts during flexion.

Which of the following component position errors is the most likely cause?

. Internal rotation of the femoral component
. External rotation of the femoral component
. External rotation of the tibial component
. Medialization of the femoral component
. Lateralization of the tibial component

Correct Answer & Explanation

. Internal rotation of the femoral component

Explanation

Internal rotation of the femoral component medially translates the trochlear groove, effectively increasing the Q-angle. This alters the extensor mechanism vector, leading to lateral tracking and tilting of the patella.

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