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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 272 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 5421

Topic: 3. Adult Reconstruction (Hip & Knee)

During a posterior cruciate ligament (PCL)-retaining total knee arthroplasty, a critical principle to remember

is to

. accurately tension the PCL.
. use bony resection to adjust the joint line.
. maintain a small amount of residual deformity.
. use intraoperative fluoroscopy to ensure femoral roll back.

Correct Answer & Explanation

. accurately tension the PCL.

Explanation

Maintenance of the joint line and accurately tensioning the PCL are critical in the proper execution of a PCL-retaining total knee arthroplasty. Appropriate tension helps ensure femoral rollback and avoid stiffness or instability. Raising the joint line to help ensure full extension should be avoided in cruciate- retaining knees, because doing so creates an unfavorable kinematic environment. The three important principles of surgical technique needed to maintain appropriate tensioning of the PCL include 1) choosing the proper femur size to reproduce the native femoral anterior/posterior dimension, 2) reproducing the joint line by resecting as much tibia from the healthy side as will be replaced by the smallest thickness of the tibial component and, 3) ensuring that full extension is achieved by soft-tissue releases and not by taking additional distal femur, as may be done in a posterior stabilized approach. Another important principle is to re-create the natural degree of the patient’s posterior tibial slope to avoid tightness inflexion.

Question 5422

Topic: 3. Adult Reconstruction (Hip & Knee)

Figures below depict the AP and lateral radiographs obtained from a 64-year-old man with long-standing

right knee osteoarthritis and pain that is unresponsive to nonsurgical treatment. The patient undergoes navigated cruciate-retaining right total knee arthroplasty. After surgery, this patient continues to experience pain and swelling of the knee with recurrent effusions. He returns to the office reporting continued pain 2 years after surgery. He describes instability, particularly when descending stairs. On examination, range of motion of 0° to 120° is observed, with no extensor lag. Slope of the tibial component is 7°. The knee is stable to varus and valgus stress in extension, but flexion instability is present in both the anterior-posterior direction and the varus-valgus direction. Bracing leads to a slight decrease in symptoms but is not well tolerated. Isokinetic testing demonstrates decreased knee extension velocity at

mid push. Radiographs demonstrate well-aligned and fixed knee implants. An infection work-up is negative. What is the most appropriate surgical intervention at this time?

. Tibial polyethylene exchange
. Revision of the femoral and tibial components and conversion to a posterior stabilized insert
. Revision of the femoral and tibial components to a constrained rotating hinge prosthesis
. Isolated femoral component revision and upsizing of the femoral implant with a new posterior cruciate ligament (PCL)-retaining polyethylene insert

Correct Answer & Explanation

. Tibial polyethylene exchange

Explanation

The patient’s symptoms at follow-up—pain, swelling, and difficulty descending stairs—suggest knee flexion instability. Considering his history, an incompetent PCL must be considered. Revision of the knee to a posterior stabilized or nonlinked constrained condylar implant (depending on the condition of the ligaments) likely is needed to address his symptoms. The difference in extension stability and flexion stability makes polyethylene exchange a poor option. A constrained rotating hinge design is not necessary. Repeat use of a PCL-retaining insert is not recommended. Tibial and femoral revision both are required. Correction of excessive slope will be attained with tibial revision, femoral component revision is required to convert to a PCL-substituting design. There is also an opportunity to increase posterior condylar offset if needed.

Question 5423

Topic: Total Knee Arthroplasty (TKA)

Figure below shows the standing AP radiograph obtained from a 55-year-old man who has a 5-year history

of daily left knee medial joint line pain with weight-bearing activities. He denies night pain or symptoms of instability. On examination, his range of motion is 0° to 140°. He has a mild, fully correctable varus deformity and a negative Lachman test result. Nonsurgical treatment has failed. Unicompartmental knee arthroplasty (UKA) is discussed with the patient. The most appropriate next radiographic evaluation should be

. MRI of the left knee to evaluate the lateral compartment.
. a CT arthrogram to evaluate the status of the medial and lateral meniscus.
. a stress radiograph to evaluate correction of the varus deformity.
. a sunrise view to determine the status of the patellofemoral joint.

Correct Answer & Explanation

. MRI of the left knee to evaluate the lateral compartment.

Explanation

A patient with medial compartment arthritis and a correctable varus deformity with no clinical or examination findings of knee instability most likely has an intact anterior cruciate ligament (ACL). The pattern of medial compartment osteoarthritis most commonly associated with an intact ACL is that of anteromedial osteoarthritis. An incompetent ACL is commonly associated with a fixed varus deformity and radiographic signs of posteromedial wear. An incompetent ACL is a relative contraindication to a mobile-bearing UKA. When evaluating patients for a mobile-bearing UKA, a stress radiograph aids the orthopaedic surgeon in determining the correction of the varus deformity and assessing the lateral compartment. An inability to fully correct the deformity or narrowing of the lateral compartment with valgus stress should influence the surgeon against UKA. Joint registries across the world have shown decreased survivorship associated with TKA and UKA in men compared with other age groups, but survivorship is lower for UKA than for TKA. No studies to date have shown any differences in survivorship between fixed-bearing and mobile-bearing UKAs. The complication that is unique to mobile-bearing UKA is bearing spinout, which occurs in less than 1% of mobile-bearing UKA procedures. In vivo and in vitro polyethylene wear in mobile-bearing UKA are low. Arthritis may progressfaster in patients with mobile-bearing UKAs than in those with fixed-bearing UKAs.

Question 5424

Topic: 3. Adult Reconstruction (Hip & Knee)

Compared with retention of the native patella in primary total knee arthroplasty, routine patellar

resurfacing is associated with

. no patellar complications.
. an increased occurrence of anterior knee pain.
. a reduced patellar fracture rate.
. a reduced risk for revision surgery.

Correct Answer & Explanation

. no patellar complications.

Explanation

Despite concerns regarding fracture, osteonecrosis, and patellar clunk, the routine retention of the native patella during primary total knee replacement is associated with a 20% to 30% increased revision risk inlarge joint registries. In addition, the retention of the native patella results in a 5.7% revision surgery ratein patients with anterior knee pain.

Question 5425

Topic: 3. Adult Reconstruction (Hip & Knee)

Figures below represent the radiographs obtained from a 37-year-old man with severe right knee pain. He has

a history of prior tibial osteotomy for adolescent tibia vara but notes residual bowing of his legs. On examination, he is 5'8" tall and weighs 322 pounds. He has a waddling gait with a bilateral varus thrust and

20° varus deformity of both legs. His right knee range of motion is 0° to 120° with a fixed varus deformity. What is the best next step?

. Total knee arthroplasty with standard components
. Correction of tibial deformity with osteotomy and nonsurgical management of the osteoarthritis
. Arthrodesis with a long antegrade nail
. Total knee arthroplasty with a constrained device

Correct Answer & Explanation

. Total knee arthroplasty with standard components

Explanation

This patient has severe, uncorrectable varus deformity and pain from end-stage osteoarthritis secondary to prior adolescent tibia vara. Although he is young to consider arthroplasty, this option is likely to give him the most functional limb, compared with arthrodesis with a long antegrade nail. During arthroplasty surgery, his knee will likely require extensive medial release to achieve anatomic limb alignment. Standard components in total knee arthroplasty likely would result in lateral instability, so this option isnot the best answer. The best choice is total knee arthroplasty with a constrained device, which addsconstraint to the knee to provide balance.

Question 5426

Topic: 3. Adult Reconstruction (Hip & Knee)

An 85-year-old obese woman has left knee pain. She had surgery 5 years ago for a patellar nonunion after

total knee arthroplasty that was complicated by infection, which was treated with implant removal and patellectomy. She has not been ambulatory since then. She states she is no longer on antibiotics. She has moderate pain, but her primary problem is instability of the knee. She has a 40° extensor lag. Darkening of the skin is present distal to the incision consistent with venous stasis changes. The erythrocyte sedimentation rate is 12 mm/h (reference range 0 to 20 mm/h) and her C-reactive protein level is 1.0 mg/L

(reference range 0.08 to 3.1 mg/L). Left knee aspiration shows a white blood cell count of 800 and 20%

neutrophils. What is the best next step?

. Revision total knee arthroplasty with primary quadriceps tendon repair
. Hinged knee arthroplasty with full extensor mechanism allograft
. Arthrotomy with debridement and antegrade knee arthrodesis nailing
. Two-stage revision knee arthroplasty and quadriceps repair with Achilles allograft

Correct Answer & Explanation

. Revision total knee arthroplasty with primary quadriceps tendon repair

Explanation

This patient is elderly, obese, and nonambulatory and has a chronic quadriceps tendon rupture after infected total knee arthroplasty. Her potential for ambulation after revision total knee arthroplasty is very low. Primary repair of the tendon is unlikely to be successful, even with augmentation, so revision total knee arthroplasty with primary quadriceps tendon repair and two-stage revision knee arthroplasty and quadricep repair with Achilles allograft are not the best management techniques. Extensor mechanism allograft could be done but would have a high failure rate in a patient of this size. No sign of infection is seen, based on laboratory studies, so a two-stage procedure is not necessary. The best management although not optimal, would be treatment in a drop-lock brace. Arthrodesis is also an option, but would have a high complication rate, and in a patient that is nonambulatory, a fused knee would be increasinglydifficult with activities of daily living and mobility.

Question 5427

Topic: 3. Adult Reconstruction (Hip & Knee)

Figures below depict the radiographs obtained from a 53-year-old man who has had swelling in his right

knee for 2 years, with minimal pain. He did not note an injury to the knee but has been unable to ambulate without crutches during this period. His past history is unremarkable, and he denies a history

of diabetes or back problems. The social history reveals that he emigrated from China, and he works at a desk job. Physical examination shows a healthy man in no acute distress. Range of motion of the right knee is 5° to 120° actively and 0° to 120° passively, without pain. Sensation is decreased on the bottom of both feet, but otherwise the neurologic examination is unremarkable. Laboratory testing reveals a positive rapid plasma reagin (RPR) test. What is the best next step?

. Open reduction and internal fixation
. Hinged total knee arthroplasty
. Arthrodesis using an intramedullary nail
. Irrigation and debridement with spacer placement

Correct Answer & Explanation

. Open reduction and internal fixation

Explanation

This patient has a neuropathic knee caused by neurosyphilis, as shown by the joint destruction on the radiographs, with a lack of pain and a positive RPR test. He has a low-demand job and would be best treated with a hinged knee arthroplasty to provide stability for his knee.

Question 5428

Topic: 3. Adult Reconstruction (Hip & Knee)

At the time of revision knee arthroplasty, a surgeon performs a rectus snip to gain exposure to the knee.

When compared with a standard parapatellar approach, what is the expected outcome?

. Improvement in range of motion
. Reduction in range of motion
. Increase in extensor mechanism lag
. No differences in motion and strength

Correct Answer & Explanation

. Improvement in range of motion

Explanation

Rectus snip during total knee arthroplasty has no effect on motion or strength at long-term follow-up. It has not been associated with extensor mechanism lag.

Question 5429

Topic: 3. Adult Reconstruction (Hip & Knee)
Hip pain of 1-month duration has developed in a 72-year-old man with a previous total hip arthroplasty. He underwent dental work 6 weeks ago. Aspiration shows a white blood cell count of more than 6,000 cells/μL (reference range 4,500 to 11,000 cells/μL) and the presence of gram-positive cocci in clusters on Gram stain. The orthopaedic surgeon recommends urgent debridement and irrigation. Fixation of the components is judged to be stable, and the surgeon elects to retain the implants. What is this patient's prognosis for infection resolution?
. Good because it is a gram-positive organism
. Good because it is an acute infection
. Poor because it is a gram-positive organism
. Poor because it is a late infection

Correct Answer & Explanation

. Poor because it is a late infection

Explanation

The patient has a late infection of at least 4 weeks symptomatic duration that most likely is hematogenous in etiology. This infection is not an acute hematogenous infection that can successfully be treated with irrigation and debridement. Retention of the implants with debridement and irrigation alone has been associated with a poor prognosis. In a recent study, the success rate was only 44% in a series of 104 patients at a mean 5.7-year follow-up. In one study of 50 infections attributable to MRSA or methicillin-resistant Staphylococcus epidermidis organisms treated with a two-stage protocol, the failure rate was 21%. Patients who experienced successful infection treatment had lower functional outcome measures using the Western Ontario and McMaster Universities Osteoarthritis Index, the University of California Los Angeles Activity Score, and the 12-item Oxford Knee Score, however.

Question 5430

Topic: 3. Adult Reconstruction (Hip & Knee)

A 40-year-old man with a history of Legg-Calve-Perthes disease underwent a right hip resurfacing 3 years

ago with no perioperative complications. Hip pain has developed gradually during the last 4 months. Radiographs show no evidence of fixation loosening or any adverse changes at the femoral neck. No periarticular osteolysis is evident. What is the most appropriate management of this condition?

. Continue to observe with repeat radiographs in 6 months
. Fluoroscopic-guided iliopsoas tendon cortisone injection
. Hip aspiration
. Serum cobalt and chromium levels and metal-reduction MRI scan

Correct Answer & Explanation

. Continue to observe with repeat radiographs in 6 months

Explanation

Controversy persists over what exactly is the best approach to managing patients with metal-on-metal (MOM) hip arthroplasties. All patients with painful MOM hip arthroplasties should be examined for fixation loosening, wear/osteolysis, and infection—no differently than patients without MOM hip arthroplasties. It is recommended to obtain serum trace element levels. If the levels are high, cross- sectional imaging should be obtained to determine whether any pseudotumor or tissue necrosis is present around the hip arthroplasty. Hip aspiration should be considered if concern for infection exists. Adverse tissue reaction has been identified to occur around MOM hip arthroplasties. The predominant histologic feature is tissue necrosis with infiltration of lymphocytes and plasma cells.

Question 5431

Topic: 3. Adult Reconstruction (Hip & Knee)

In patients undergoing elective hip or knee arthroplasty who are not at elevated risk (beyond the risk associated

with the surgery) for venous thromboembolism or bleeding, using pharmacologic agents and/or mechanical compressive devices for the prevention of venous thromboembolism was assigned what grade of recommendation by the 2011 AAOS Clinical Practice Guideline, Preventing Venous Thromboembolic Disease in Patients Undergoing Elective Hip and Knee Arthroplasty?

. Strong
. Moderate
. Limited
. Inconclusive

Correct Answer & Explanation

. Strong

Explanation

Using pharmacologic agents and/or mechanical compressive devices for the prevention of venous thromboembolism in patients undergoing elective hip or knee arthroplasty who are not at elevated risk beyond that of the surgery itself for venous thromboembolism or bleeding was given a moderate grade ofrecommendation in the 2011 AAOS Clinical Practice Guideline referenced above.

Question 5432

Topic: 3. Adult Reconstruction (Hip & Knee)

A 40-year-old man with a history of Legg-Calve-Perthes disease underwent a right hip resurfacing 3 years

ago with no perioperative complications. Hip pain has developed gradually during the last 4 months. Radiographs show no evidence of fixation loosening or any adverse changes at the femoral neck. No periarticular osteolysis is evident. A large intra-articular and intrapelvic pseudotumor has developed. What predominant histological feature(s) is/are present in such a lesion?

. Polymorphonuclear leukocytes
. Extracellular metal-wear debris
. Cement particles within the macrophages
. Lymphocytes and plasma cells

Correct Answer & Explanation

. Polymorphonuclear leukocytes

Explanation

Controversy persists over what exactly is the best approach to managing patients with metal-on-metal (MOM) hip arthroplasties. All patients with painful MOM hip arthroplasties should be examined for fixation loosening, wear/osteolysis, and infection—no differently than patients without MOM hip arthroplasties. It is recommended to obtain serum trace element levels. If the levels are high, cross- sectional imaging should be obtained to determine whether any pseudotumor or tissue necrosis is present around the hip arthroplasty. Hip aspiration should be considered if concern for infection exists. Adverse tissue reaction has been identified to occur around MOM hip arthroplasties. The predominant histologicfeature is tissue necrosis with infiltration of lymphocytes and plasma cells.

Question 5433

Topic: 3. Adult Reconstruction (Hip & Knee)

A 57-year-old woman experiences pain 1 year after total knee arthroplasty (TKA). She reports sharp

anterior pain and a painful catching sensation that is aggravated by rising from a chair or climbing stairs. Physical examination reveals a mild effusion and a range of motion of 2° to 130°, with patellar crepitus. The symptoms are reproduced by resisted knee extension. Radiographs show a well-aligned posterior- stabilized TKA without evidence of component loosening. What is the recommended treatment for this patient?

. Physical therapy
. Arthroscopic synovectomy
. Tibial insert revision
. Femoral component revision

Correct Answer & Explanation

. Physical therapy

Explanation

Patellar clunk syndrome is caused by the development of a fibrous nodule on the posterior aspect of the quadriceps tendon at its insertion into the patella. It causes a painful catching sensation when the extensormechanism traverses over the trochlear notch as the knee extends from 45° of flexion to 30° from full extension. It characteristically occurs in posterior stabilized total knee arthroplasties and appears to be related to femoral component design. The syndrome can usually be prevented by excising the residual synovial fold just proximal to the patella. Flexion gap instability can also cause a painful total knee arthroplasty but is less common in posterior stabilized implants. Femoral component malrotation can cause pain attributable to a flexion gap imbalance or patellar tracking problems. Polyethylene wear would be unlikely after just 1 year. Patellar clunk syndrome can usually be addressed successfully with arthroscopic synovectomy. Recurrence is uncommon. Physical therapy may help to strengthen the quadriceps following synovectomy but would not resolve the clunk syndrome symptoms. Femoral or tibial insert revision is not indicated if patellar clunk syndrome is the only problem resulting in a painfultotal knee arthroplasty.

Question 5434

Topic: 3. Adult Reconstruction (Hip & Knee)

Venous thromboembolism may occur after total joint arthroplasty. The risk of this complication is

elevated in patients with

. a BMI lower than 30.
. diabetes mellitus, with a hemoglobin A1c test result less than 7.
. tranexamic acid use.
. metabolic syndrome.

Correct Answer & Explanation

. a BMI lower than 30.

Explanation

Obesity, a prior history of venous thromboembolism, and metabolic syndrome have all been associated with an increased risk of thromboembolism. A recent meta-analysis showed that diabetes had no significant relationship with venous thromboembolism following hip or knee arthroplasty. Tranexamic acid is an antifibrinolytic agent that has been shown to reduce blood loss substantially following hip and knee arthroplasty. It has also been shown to be safe in patients with severe medial comorbidities and a prior history of venous thromboembolism.

Question 5435

Topic: 3. Adult Reconstruction (Hip & Knee)

A 70-year old woman undergoes revision total knee arthroplasty for tibial component aseptic loosening.

She is concerned about recurrent loosening, and tibial stem fixation options during revision are reviewed. Figure below displays a radiograph of the revision technique used for this patient. What is the incidence of intraoperative tibial shaft fracture that is associated with this type of revision surgery?

. 0% to 1% with press-fit tibial stems
. 3% to 5% with press-fit tibial stems
. 3% to 5% with cemented tibial stems
. More than 5% with press-fit tibial stems

Correct Answer & Explanation

. 0% to 1% with press-fit tibial stems

Explanation

Using press-fit tibial stems during a hybrid revision total knee arthroplasty is associated with a 3% to 5% incidence of intraoperative tibial shaft fracture. Diaphyseal fixation of press-fit stems has the advantage of setting component alignment, dispersing forces on the proximal tibia, and offers excellent clinical results. The disadvantages include proximal and distal tibia anatomic mismatch and tibial shaft fracture. Cipriano and associates reported a tibial shaft fracture incidence of 4.9% in a series of 420 consecutiveknee revisions. All fractures healed with nonsurgical management, and none led to implant loosening. In this patient, it is important to recognize on the radiograph that this technique is a hybrid method of revision total knee arthroplasty, with cementation along the tibial tray and metaphysis and with press-fit fixation of the diaphyseal engaging stem. Then, it is important to know the risk and management of intraoperative diaphyseal tibial fractures. Cemented tibial stems are associated with a low rate of intraoperative fracture, because the implant is typically undersized to allow for an appropriate cement mantle. Option C is incorrect, because this revision is not cemented. Option A underestimates the incidence of fracture,whereas D overestimates the rate of fracture.

Question 5436

Topic: 3. Adult Reconstruction (Hip & Knee)

Figures below depict the radiographs obtained from a 60-year-old man with instability and pain 1 year after

primary right total knee arthroplasty. He states that he had surgery on two occasions for a tendon rupture that was repaired with sutures but that his knee popped again, and now the leg is unable to hold his weight. On examination, he is in no acute distress. His height is 6'3", and he weighs 240 pounds. He is ambulatory with crutches. Range of motion of the right knee is 50° to 120° actively and 0° to 120° passively. More than 10° of varus/valgus laxity and more than 5 mm of anteroposterior drawer are present. A palpable defect is observed in the tissue just proximal to the patella. The incision is well healed. The erythrocyte sedimentation rate is 46 mm/h (reference range 0 to 20 mm/h) and the C-reactive protein level is 2.04 mg/L (reference range 0.08 to

3.1 mg/L). Aspiration of the right knee reveals hazy yellow fluid with a white blood cell count of 120 and 1%

neutrophils. No growth of organisms is seen on routine culture. What is the best next step?

. Revision total knee arthroplasty with extensor mechanism allograft
. Revision total knee arthroplasty with liner change and primary quadriceps repair
. Resection knee arthroplasty and arthrodesis with antegrade nail
. Two-stage revision total knee arthroplasty with extensor mechanism allograft

Correct Answer & Explanation

. Revision total knee arthroplasty with extensor mechanism allograft

Explanation

This patient has a chronic quadriceps tendon rupture after total knee arthroplasty. Two previous primary repair attempts have failed, which is not surprising based on the poor results of primary repair reported in the literature. The patient also has an unstable knee and will require revision of some or all of the prosthesis to achieve a stable knee. Revision total knee arthroplasty with extensor mechanism allograft allows an allograft reconstruction of the ruptured quadriceps tendon. The other option is to utilize a synthetic mesh extensor mechanism reconstruction. These are likely to have the best result in this situation. Revision total knee arthroplasty with liner change and primary quadriceps repair is not the best form of management, because it involves a third attempt at primary tendon repair, which will likely fail again. Resection knee arthroplasty and arthrodesis with antegrade nail is a possible option but is not the best, because it would likely make driving and other daily activities difficult. Two-stage revision totalknee arthroplasty with extensor mechanism allograft is not the best option because the laboratory resultsshow no signs of infection, so a single-stage procedure is preferred.

Question 5437

Topic: 3. Adult Reconstruction (Hip & Knee)
A 60-year-old man who underwent left partial knee arthroplasty 6 months earlier was doing well until he experienced left knee pain and swelling for 4 weeks following a dental procedure. The left knee aspirate was bloody, with a white blood cell count of 8,000 and 70% neutrophils. Culture grew group B Streptococcus (Granulicatella adiacens), and serologies were elevated, with an erythrocyte sedimentation rate of 55 mm/h (reference range: 0 to 20 mm/h) and a C-reactive protein level of 24 mg/L (reference range: 0.08 to 3.1 mg/L). What is the best next step?
. Arthroscopic debridement
. Two-stage total knee revision arthroplasty
. Resection arthroplasty without an antibiotic impregnated cement spacer
. Knee fusion

Correct Answer & Explanation

. Two-stage total knee revision arthroplasty

Explanation

This complication is best addressed with either a single-stage or two-stage total knee arthroplasty. A recent report suggests that a single-stage arthroplasty can be effective, although many surgeons would perform a two-stage procedure with an articulating or static spacer. Arthroscopic debridement would be ineffective, especially given 4 weeks of symptoms. Resection arthroplasty without a spacer would leave an unstable and poorly functioning extremity. Knee fusion should be used as a salvage procedure.

Question 5438

Topic: 3. Adult Reconstruction (Hip & Knee)

A 72-year-old female presents with anterior knee pain and a palpable, painful "clunk" sensation when actively extending her knee from a flexed position (typically between 30 and 45 degrees of flexion). She underwent a posterior-stabilized (PS) total knee arthroplasty (TKA) 18 months ago. What is the most likely etiology of her symptoms?

. Aseptic loosening of the tibial tray with resultant subsidence
. Catastrophic polyethylene wear of the patellar button
. Fibrous nodule entrapment within the intercondylar box
. Undersized femoral component causing mid-flexion instability
. Chronic medial collateral ligament insufficiency

Correct Answer & Explanation

. Aseptic loosening of the tibial tray with resultant subsidence

Explanation

The clinical scenario describes classic 'Patellar Clunk Syndrome.' This is an entity primarily associated with traditional posterior-stabilized (PS) TKA designs. It is caused by the formation of a fibrous, fibrosynovial nodule at the superior pole of the patella. As the knee is flexed, this nodule drops into the intercondylar box of the femoral component. As the knee actively extends (usually around 30-45 degrees), the nodule gets caught on the superior margin of the intercondylar box, suddenly popping out with an audible and palpable 'clunk' and causing anterior knee pain. Treatment involves arthroscopic or open excision of the nodule.

Question 5439

Topic: 3. Adult Reconstruction (Hip & Knee)
A 68-year-old patient undergoing an elective total hip arthroplasty has a known history of Factor V Leiden mutation. The hypercoagulable state induced by this specific genetic anomaly is primarily due to:
. Resistance of mutated Factor V to degradation by Activated Protein C
. Congenital deficiency of Antithrombin III
. Increased affinity of prothrombin for platelets
. Overproduction of von Willebrand factor
. Constitutive activation of Factor Xa independently of the intrinsic pathway

Correct Answer & Explanation

. Resistance of mutated Factor V to degradation by Activated Protein C

Explanation

Factor V Leiden is an autosomal dominant genetic condition that exhibits incomplete penetrance. The mutation alters the cleavage site of the Factor V molecule, making it resistant to degradation by Activated Protein C (APC). This loss of negative feedback in the coagulation cascade leads to unchecked generation of thrombin and a significantly increased risk of venous thromboembolism.

Question 5440

Topic: 3. Adult Reconstruction (Hip & Knee)

A newly developed synovial fluid biomarker test for periprosthetic joint infection (PJI) is evaluated in a cohort of 200 total knee revisions. 100 patients have a confirmed PJI (gold standard), and the test is positive in 90 of them. 100 patients are uninfected, but the test is positive in 20 of them. What is the Negative Predictive Value (NPV) of this new biomarker test?

. 80.0%
. 88.9%
. 90.0%
. 91.1%
. 95.0%

Correct Answer & Explanation

. 80.0%

Explanation

Negative Predictive Value (NPV) is the probability that subjects with a negative screening test truly don't have the disease. NPV = True Negatives / Total Negative Tests. The uninfected group has 100 people, with 20 false positives, meaning 80 True Negatives. The infected group has 100 people, with 90 true positives, meaning 10 False Negatives. Total negative tests = 80 (TN) + 10 (FN) = 90. NPV = 80 / 90 = 0.8888, or 88.9%.

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