ABOS MCQs (Set 3): Hip & Knee Arthroplasty Questions

Question 1

Figure 30 shows the MRI scan of a 68-year-old woman who has left hip pain. What is the most appropriate treatment?

Explanation

The patient has a large zone of osteonecrosis of the left femoral head. The wedge-shaped zone of decreased signal intensity on the T1 image in the subchondral region of the femoral head is typical. Based on these findings, total hip arthroplasty is the most appropriate treatment. Open reduction and internal fixation will not help this condition. Incisional biopsy is indicated only if the MRI scan shows a probable neoplasm. Resection of the proximal femur is indicated only for aggressive malignancy. Arthrodesis may be considered in a younger patient but not in a 68-year-old individual. Other treatments, not listed, such as core decompression, vascularized fibular transplant, and osteotomy may be options in selected patients. Urbaniak JR, Jones JP Jr (eds): Osteonecrosis: Etiology, Diagnosis, and Treatment. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1997, pp 213-223.

Question 2

There is increasing concern about the ethical relationship of orthopaedists to the orthopaedic equipment industry. Which of the following describes the most appropriate relationship?

Explanation

It is appropriate for orthopaedic surgeons to have relationships with industry as long as the relationship is for the good of the patient and no "quid pro quo" intent exists. A grant to cover registration at a CME event is appropriate but travel and hotel for a spouse is not. For orthopaedists who are faculty at a meeting sponsored by industry, it is appropriate for travel and expenses to be covered for that faculty member. Care must be exercised that the faculty member contributes in an amount appropriate for the expenses paid. The faculty member must ensure that information presented is unbiased and based on reasonable data and opinion. Consulting agreements should spell out specifically the duties of the agreement and payment should be appropriate for the time spent. There should be a defined work product for the consulting. Agreements that are thinly veiled payments for use of a company's products must be avoided. In all cases, the agreements must stand up to public scrutiny. Restricted grants for specific industry-sponsored programs aimed at residents are not appropriate. Unrestricted grants intended for attendance at approved CME courses are appropriate. Dinners at which information is presented about topics that can aid in patient care are appropriate as long as the expense is reasonable ($100 or less/person) and the guest list includes individuals who can use the information in a patient case. Clearly a "premium" dinner for office staff to review new surgical instrumentation would not pass this test.

Question 3

A 30-year-old patient has had severe left hip pain and difficulty ambulating, necessitating the use of a cane, for the past 6 months. A photomicrograph of the femoral head sectioned at the time of surgery is shown in Figure 31. What is the most likely diagnosis?

Explanation

The photomicrograph demonstrates a wedge-shaped infarct with femoral head collapse; therefore, the diagnosis is osteonecrosis of the femoral head. Perthes disease and osteoarthritis do not involve a wedge-shaped defect. Tuberculosis of the hip joint results in greater destruction of the articular cartilage. Basset LW, Mirra JM, Cracchiolo A III: Ischemic necrosis of the femoral head: Correlation between magnetic resonance imaging and histologic sections. Clin Orthop 1987;223:181-187.

Question 4

When comparing mobile-bearing total knee arthroplasty (TKA) to fixed-bearing total condylar arthroplasty, the mobile-bearing procedure provides

Explanation

Survivorship is similar in the two groups. In a recent study, mobile-bearing TKAs showed a slightly higher maximum flexion than the total condylar fixed-bearing-type designs (112 degrees versus 108 degrees with no difference in recovery rate). Using a fixed-bearing or a mobile-bearing design did not seem to influence the recovery rate in early results after knee arthroplasty. Mobile-bearing arthroplasties are suggested, in theory, to offer a reduction in polyethylene wear; however, clinical studies have not yet proven this. Recovery rates have yet to be statistically seen as improved with either method. Differences in strength have not been shown. Aglietti P, Baldini A, Buzzi R, et al: Comparison of mobile-bearing and fixed-bearing total knee arthroplasty: A prospective randomized study. J Arthroplasty 2005;20:145-153. Sorrells RB: The rotating platform mobile bearing TKA. Orthopedics 1996;19:793-796.

Question 5

Based on the type of articulation shown in Figure 32, wear is not affected by which of the following factors?

Explanation

Wear in total hip arthroplasty is a very complex phenomenon. The radial mismatch of the femoral head to the acetabular component has been shown in multiple studies to be a significant factor in wear. The mismatch can neither be too small nor too large. When the mismatch is too small, seizing of the implants can occur. When the mismatch is too large, contact stresses increase and produce exceptionally high wear. The ideal radial mismatch should be approximately 50 microns. Surface roughness and ball sphericity are two items that are extremely important with respect to wear. High carbon content has been shown to decrease wear. This device has a very large head-to-neck ratio, so impingement-related wear is unlikely. Amstutz HC, Grigoris P: Metal on metal bearings in hip arthroplasty. Clin Orthop 1996;329:S11-S34. Amstutz HC, Campbell P, McKellop H, et al: Metal on metal total hip replacement workshop consensus document. Clin Orthop 1996;329:S297-S303.

Question 6

Figure 33 shows the venogram of a patient who has a long history of alcohol abuse. Warfarin should be used cautiously because of the interaction with which of the following factors?

Explanation

Warfarin acts by inhibiting clotting factors II, VII, IX, X. The actual mechanism of action is by inhibition of hepatic enzymes, vitamin K epoxide, and perhaps vitamin K reductase. This inhibition results in lack of carboxylation of vitamin K-dependent proteins (II, VII, IX, X). The anticoagulant effect of warfarin can be reversed with vitamin K or fresh-frozen plasma. The use of alcohol may lead to liver dysfunction and an even more limited margin of available factors. Lieberman JR, Wollaeger J, Dorey F, et al: The efficacy of prophylaxis with low-dose warfarin for prevention of pulmonary embolism following total hip arthroplasty. J Bone Joint Surg Am 1997;79:319-325.

Question 7

A 78-year-old patient undergoing revision total knee arthroplasty has bone loss throughout the knee at the time of revision. A distal femoral augment is used to restore the joint line. One month after surgery, the patient reports pain and is unable to ambulate. A lateral radiograph is shown in Figure 34. What is the most likely etiology of this problem?

Explanation

Instability is a leading cause of failure following total knee arthroplasty. Instability can present as global instability, extension gap (varus/valgus) instability, or flexion gap (anterior/posterior) instability. Treatment options are numerous based on the exact pathology. The radiograph reveals anterior/posterior instability with dislocation consistent with flexion gap instability. A loose flexion gap can allow the femoral component to ride above the tibial cam post mechanism, resulting in dislocation. Distal femoral augments treat extension gap instability, whereas tibial augments can treat both flexion and extension gap instability. Posterior condyle augments at the distal femur can also be used to treat flexion gap instability. Flexion gap instability is further aggravated by extension mechanism incompetence. Note the excessively thin patella on the lateral radiograph. Pagnano MW, Hanssen AD, Lewallen DG, et al: Flexion instability after primary cruciate retaining total knee arthroplasty. Clin Orthop 1998;356:39-46. McAuley J, Engh GA, Ammeen DJ: Treatment of the unstable total knee arthroplasty. Inst Course Lect 2004;53:237-241.

Question 8

Figure 35 shows the AP radiograph of a patient who underwent a previous upper tibial osteotomy (UTO). The patient may be at risk for which of the following during total knee arthroplasty (TKA)?

Explanation

The results of TKA for patients with a prior UTO are reported to be slightly suboptimal. The major problems are patella baja, difficulty in exposure, and instability. Most of the patients exhibit some degree of instability prior to TKA, and ligamentous balancing may be difficult. Ligamentous structures are at risk of rupture during the difficult exposure. The problem of ligamentous balancing is exacerbated by the change in the joint slope that can occur after UTO. Parvizi J, Hanssen AD, Spangehl MJ: Total knee arthroplasty following proximal tibial osteotomy: Risk factors for failure. J Bone Joint Surg Am 2004;86:474-479.

Question 9

Figure 36 shows the radiograph of a patient who has hip pain and is unable to ambulate. What is the most appropriate management for this patient?

Explanation

The patient has a periprosthetic fracture of the greater trochanter - Vancouver A. The reason for the fracture of the greater trochanter is the extensive periarticular osteolysis that has occurred as a result of polyethylene wear. The latter is demonstrated by eccentric seating of the large femoral head in the acetabulum. The most appropriate management is to reverse the osteolysis process, which involves exchange of the acetabular liner with or without revision of the other components depending on their fixation and position. The greater trochanter can also be fixed during revision surgery. Duncan CP, Masri BA: Fractures of the femur after hip replacement. Instr Course Lect 1995;44:293-304.

Question 10

When polyethylene is exposed to radiation and subsequently heated, certain chemical changes occur in the material. Which of the following statements best describes these changes?

Explanation

Exposure of polyethylene to radiation and then heating it to quench the free radicals leads to a cross-linked material. It converts a high molecular weight polyethylene macromolecule to an interpenetrating network structure of polymer chains. The ductility of the material is decreased, hence the greater risk of fracture. While the wear rate (measured as fewer and smaller particles) against a smooth counterface is markedly reduced, cross-linked polyethylene has shown a larger increase in wear rate when a rougher counterface is used compared to noncross-linked material. Due to reduced mechanical strength, highly cross-linked polyethylene is less resistant to abrasive wear.

Question 11

Familial (Leiden) thrombophilia is of importance in joint arthroplasty because of an abnormality in the clotting cascade. Which of the following statements best describes the condition?

Explanation

Factor V Leiden is a disease caused by an abnormality of factor V in which a single amino acid substitution of glutamine for arginine in the protein C cleavage region leads to decreased inactivation of factor V and thus a greater tendency to form clots. More than half of all individuals with Factor V Leiden will develop deep venous thrombosis in the presence of a single additional risk factor such as long bone fracture or total joint arthroplasty.

Question 12

Figure 37 reveals a periprosthetic fracture around a cemented femoral stem in an 81-year-old patient with Paget's disease and mild coagulopathy. What is the most appropriate reconstructive management on the femoral side?

Explanation

This is an example of a Vancouver B3 periprosthetic fracture that consists of a fracture around a loose femoral stem with poor proximal bone support. Therefore, open reduction and internal fixation is not an option. PFR is an excellent choice for elderly inactive patients with poor femoral bone stock. The surgery can be performed in an expeditious manner, which is very important in a patient with mild coagulopathy. Impaction allografting and APC are both options for younger patients who have bone stock that needs to be restored. The results of revision arthroplasty using proximally coated stems, especially under these circumstances, are poor. Duncan CP, Masri BA: Fractures of the femur after hip replacement. Instr Course Lect 1995;44:293-304. Parvizi J, Sim FH: Proximal femoral replacements with megaprostheses. Clin Orthop 2004;420:169-175.

Question 13

A patient with a documented allergy to nickel requires a total knee arthroplasty. Which of the following prostheses is most likely to provide long-term success in this individual?

Explanation

Nickel allergy is not an infrequent preoperative finding. The ramifications of such allergies in arthroplasty patients are poorly understood at this time. Stainless steel and cobalt-chromium alloys contain relatively high concentrations of nickel. Titanium, oxidized zirconium, and polyethylene do not contain significant amounts of nickel. Titanium is not a good surface for the articulating portion of the femoral component because of its propensity for metallosis. Oxidized zirconium is the only suitable femoral component for patients allergic to nickel. A modular titanium tibial component or an all-polyethylene tibial component would be satisfactory for these patients. Laskin RS: An oxidized Zr ceramic surfaced femoral component for total knee arthroplasty. Clin Orthop 2003;416:191-196.

Question 14

Which of the following is accurate regarding low-molecular-weight heparin used for deep venous thrombosis (DVT) prophylaxis in total joint arthroplasty?

Explanation

Low-molecular-weight heparin is highly bioavailable with a half-life of 3 to 18 hours. This is greater than the 1 hour half-life of unfractionated heparin. Low-molecular-weight heparin offers an advantage over unfractionated heparin by selectively targeting Factor Xa while having a lesser effect on circulating thrombin (Factor IIa). Circulating thrombin Factor IIa is needed for local hemostasis at the site of the surgical wound. Clinical studies have shown a reduction by one third in the incidence of thrombocytopenia with the use of low-molecular-weight heparin. Low-molecular-weight heparin has been shown to demonstrate similar clinical results compared to warfarin with respect to preventing thromboembolic disease after total hip arthroplasty and complications such as bleeding. Zimlich RH, Fulbright BM, Friedman RJ: Current status of anticoagulation therapy after total hip and total knee arthroplasty. J Am Acad Orthop Surg 1996;4:54-62. Colwell CW Jr, Spiro TE, Trowbridge AA, et al: Use of enoxaparin, a low-molecular-weight heparin, and unfractionated heparin for the prevention of deep venous thrombosis after elective hip replacement: A clinical trial comparing efficacy and safety. J Bone Joint Surg Am 1994;76:3-14.

Question 15

A 42-year-old man reports the recent onset of right hip pain. A radiograph and MRI scan are shown in Figures 38a and 38b. A WBC count, erythrocyte sedimentation rate, and hip aspiration are within normal limits. Management should now consist of

Explanation

Transient osteoporosis of the hip is an uncommon problem, usually affecting women in the last trimester of pregnancy and middle-aged men. Symptoms include pain in the involved hip with temporary osteopenia; however, there is no joint space involvement. In this patient, the imaging findings are consistent with transient osteoporosis. Short TR/TE (repetition time/echo time) images reveal diffusely decreased signal intensity in the femoral head and intracapsular region of the femoral neck. Increased signal intensity is seen with increased T2-weighting. Within a few months, the pain, as well as the imaging findings, will completely resolve without intervention. Distinguishing the diffuse features of transient osteoporosis of the hip from the segmental findings of osteonecrosis is essential. Unlike transient osteoporosis of the hip, osteonecrosis will have a double-density signal on MRI and may progress radiographically. Surgical intervention and oral corticosteriods are not indicated for treatment. Protected weight bearing until the pain resolves may decrease symptoms while the transient osteoporosis resolves. Potter H, Moran M, Scheider R, et al: Magnetic resonance imaging in diagnosis of transient osteoporosis of the hip. Clin Orthop 1992;280:223-229. Bijl M, van Leeuwen MA, van Rijswijk MH: Transient osteoporosis of the hip: Presentation of typical cases for review of the literature. Clin Exp Rheumatol 1999;17:601-604.

Question 16

During cemented total hip arthroplasty, peak pulmonary embolization of marrow contents occurs when the

Explanation

Peak embolization is observed during femoral stem insertion. Embolization is also observed during acetabular preparation and hip reduction. Lewallen DG, Parvizi J, Ereth MH: Perioperative mortality associated with hip and knee arthroplasty, in Morrey BF (ed): Joint Replacement Arthroplasty, ed 3. Philadelphia, PA, Churchill-Livingstone, 2003, pp 119-127.

Question 17

What are the optimal conditions for leaving the acetabular shell in place, replacing the acetabular liner, and grafting the osteolytic defect shown in Figure 39?

Explanation

Dense pods of ingrowth into the porous coating of cementless ingrowth sockets are seen. Channels through the non-ingrown portion allow access to the trabecular bone of the ilium. Polyethylene wear debris can enter these areas through screw holes. Expansile, lytic lesions can result, which can become large without compromising implant fixation. Loosening is late and results from catastrophic loss of bone. A well-fixed acetabular component with a modular design, a well-designed locking mechanism, and a good survivorship history is a candidate for exchange of the liner and grafting of the osteolytic lesion. Ries MD: Complications in primary total hip arthroplasty: Avoidance and management. Wear. Instr Course Lect 2003;52:257-265. Dumbleton JH, Manley MT, Edidin AA: A literature review of the association between wear rate and osteolysis in total hip arthroplasty. J Arthroplasty 2002;17:649-661.

Question 18

A 53-year-old patient is seen in the emergency department after sustaining a fall onto her left hip. A current radiograph is shown in Figure 40. What is the best treatment option?

Explanation

The patient has sustained a Vancouver B2 periprosthetic femoral fracture (a femoral fracture that occurs around or just distal to a loose stem, with adequate proximal bone stock). The stem is no longer fixed to proximal bone; therefore, retention of the femoral component is not recommended. Nonsurgical management is contraindicated because of the high risk of nonunion and malunion with significant component settling in the distal fragment and leg shortening. Revision femoral arthoplasty must attain distal fixation in adequate host bone, which is usually successful with a porous-coated cylindrical stem. Parvizi J, Rapuri VR, Purtill JJ, et al: Treatment protocol for proximal femoral periprosthetic fractures. J Bone Joint Surg Am 2004;86:8-16.

Question 19

A 67-year-old patient seen in the emergency department reports the acute onset of pain and is unable to ambulate. History reveals that the patient underwent surgical treatment for a periprosthetic femoral fracture 6 months ago. A radiograph is shown in Figure 41. What is the best treatment option at this time?

Explanation

The radiograph reveals a periprosthetic fracture at the tip of the stem with a stable cemented implant. This is classified as a Vancouver type B1 periprosthetic fracture. An attempt at internal fixation has already failed; therefore, the most predictable results would be achieved with distal fixation. After removal of the well-fixed cemented implant, the proximal bone may not be suitable for proximal fixation. Adequate bone stock is available such that an allograft prosthetic composite or a tumor prosthesis is not necessary. The best option is a long stem implant with distal fixation, which serves as an intramedullary device to restore alignment and increase the likelihood of union. Cortical onlay strut grafts are used as an adjunct to definitive fixation. Younger AS, Dunwoody I, Duncan CP: Periprosthetic hip and knee fractures: The scope of the problem. Inst Course Lect 1998;47:251-256.

Question 20

With the increasing availability of total hip arthroplasty (THA) to younger patients with hip osteoarthritis, there has been increased use of alternative bearing surfaces. Compared to a ceramic-on-ceramic articulation, which of the following is a specific advantage of a metal-on-metal bearing surface?

Explanation

Alternative bearing surfaces in THA have received much attention in recent years as more and more hip arthroplasties are being performed on younger patients with hip arthritis. The two most popular nonmetal-on-polyethylene bearing surfaces are metal-on-metal and ceramic-on-ceramic. There are arguments supporting the use of either, but ceramic bearings have been shown to have a theoretic increased risk of fracture compared with cobalt-chromium. This has been shown to be clinically relevant with zirconium ceramics. Newer alumina ceramics are being produced with lower porosity and grain size and with higher density and purity, resulting in lower fracture risk but still greater than that of cobalt-chromium. Heisel C, Silva M, Schmalzried TP: Bearing surface options for total hip replacement in young patients. Instr Course Lect 2004;53:49-65.

Question 21

Which of the following prophylactic regimens for the prevention of deep venous thrombosis after knee arthroplasty has received a grade 1A recommendation in favor of its use from the American College of Chest Physicians (ACCP) in the 2004 guidelines?

Explanation

In the 2004 ACCP guidelines, there were three prophylactic regimens that received a grade 1A favorable recommendation. These included low-molecular-weight heparin, warfarin, or fondaparinux, as long as they are used for at least 10 days. If warfarin is used, the target INR should be 2.0 to 3.0, according to the guidelines. Pneumatic compression sleeves have gained popularity in the orthopaedic community but have not received a grade 1A rating from the ACCP at this time. Use of aspirin by itself is discouraged by the ACCP.

Question 22

In the radiograph shown in Figure 42, the fracture pattern around this well-fixed stem is classified as Vancouver type

Explanation

The Vancouver classifications describes periprosthetic hip fractures in the following way. Type A fractures are in the trochanteric region. Type B1 fractures occur around the stem or at the tip in the face of a well-fixed stem. These are usually treated with open reduction and internal fixation, usually including struts, cable, and/or cable plates. Type B2 fractures occur in the same region with a loose stem. Type B3 fractures occur with a loose stem where the proximal bone is of poor quality and/or severely comminuted. Type C fractures occur well below the stem. Pellicci PM, Tria AJ Jr, Garvin KL (eds): Orthopaedic Knowledge Update: Hip and Knee Reconstruction 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 149-154. Parvizi J, Rapuri VR, Purtill JJ, et al: Treatment protocol for proximal femoral periprosthetic fractures. J Bone Joint Surg Am 2004;86:8-16.

Question 23

Figures 43a and 43b show the T1- and T2-weighted MRI scans of a 78-year-old woman who reports the sudden atraumatic onset of well-localized medial knee pain. Pain is worse at night and also occurs with weight-bearing activity. What is the most likely diagnosis?

Explanation

Osteonecrosis of the tibial plateau occurs infrequently. The symptoms are similar to those of idiopathic osteonecrosis of the medial femoral condyle and include pain and tenderness of the medial aspect of the knee and a slight synovitis. The range of motion of the knee remains within normal limits, and no gross deformity is present. Osteonecrosis of the tibial plateau is easily misdiagnosed as degenerative meniscus or osteoarthritis of the compartment of the knee. Review of lateral radiographs may reveal an osteopenic area in the subchondral bone of the medial tibial plateau. The diagnosis is more easily established with a bone scan where increased uptake of radionucleides is shown over the medial tibial plateau. In osteoarthritic involvement of the medial compartment, uptake is over both the medial femoral condyle and the medial tibial plateau, whereas if osteoarthritis involves the entire knee, uptake is diffuse over the entire joint. Radiographic findings in complex regional pain syndrome are normal as opposed to the findings for osteonecrosis or osteoarthritis. Osteosarcoma has a characteristic radiographic appearance of a bone-forming tumor. Loose bodies can derive from osteochondral fractures; a history of trauma is usually elicited. Osteoarthritis usually presents with joint space narrowing accompanying the weight-bearing pain. Soucacos PN, Berris AE, Xenakis TH, et al: Knee osteonecrosis: Distinguishing features in differential diagnosis, in Urbanik JR, Jones JD (eds): Osteonecrosis. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1997, pp 413-424.

Question 24

Figure 44 shows the radiograph of a 65-year-old man who underwent a revision arthroplasty to remove a loose, cemented femoral stem. When planning the postoperative restrictions, the surgeon should be aware that

Explanation

The transfemoral approach, also known as the extended trochanteric osteotomy, is an important technique to master for revision hip surgery. When performed correctly, it allows excellent exposure of the femoral canal and aids in exposure of the acetabulum. As demonstrated in the study cited, however, it markedly reduces the torque that the composite can withstand without failure. This type of basic science study is important to guide postoperative rehabilitation.

Question 25

A 75-year-old patient returns for follow-up after undergoing bilateral total hip arthroplasty (THA). The right hip is a hybrid THA performed 12 years ago, whereas the left hip is a cementless THA performed 10 years ago. Both acetabular components are the same type, same size, and from the same manufacturer. Both femoral heads are 28-mm cobalt-chromium components. What is the most likely explanation for the advanced polyethylene wear in one hip?

Explanation

Over the past three decades, gamma irradiation and air has been the most common method of sterilizing polyethylene used in total joint arthroplasty. This method of sterilization results in breakage of the chemical bonds within the polymer. While this promotes cross-linking, it also leaves the polyethylene vulnerable to oxidation, especially if packaged in an air environment. Oxidation has been shown to decrease polyethylene's molecular weight, ultimate tensile strength, elongation, and toughness which results in a stiffer, more brittle material that is less resistant to wear. Severity of oxidation and a decrease in mechanical properties have been shown to be related to the length of time that the component is exposed to air (the shelf life). Currier and associates studied the clinical performance of gamma irradiated in air polyethylene components that had been shelf aged. They demonstrated that for the first 5 years of shelf life, polyethylene oxidized rather slowly. However, polyethylene components with a shelf life of more than 5 years would be expected to have minimal mechanical toughness and would likely fail rapidly if implanted. Bohl and associates evaluated 135 patients who had undergone total knee arthroplasty. Survivorship at 5 years was 100% for components with a shelf life of less than 4 years, 89% for components with a shelf life of 4 to 8 years, and 79% for components with a shelf life of more than 8 years. Sychterz and associates reported no correlation between shelf life and true wear rates for components with a shelf life of less than 3 years. In summary, both in vivo and in vitro data suggest that shelf life in excess of 3 to 5 years has a direct effect on wear of polyethylene. Currier BH, Currier JH, Collier JP, et al: Shelf life and in vivo duration: Impacts on performance of tibial bearings. Clin Orthop 1997;342:111-122. Bohl JR, Bohl WR, Postak PD, et al: The Coventry Award: The effects of shelf life on clinical outcome for gamma sterilized polyethylene tibial components. Clin Orthop 1999;367:28-38.

Question 26

During a primary total knee arthroplasty trial reduction, the knee is well-balanced and stable in full extension but is excessively tight at 90 degrees of flexion. Which of the following intraoperative interventions is the most appropriate next step to specifically address the tight flexion gap?

Explanation

Downsizing the femoral component (using an anterior referencing guide) reduces the posterior condylar offset, thereby increasing and loosening the flexion gap without altering the extension gap.

Question 27

A 68-year-old man undergoes primary total knee arthroplasty. Intraoperatively, with trial components in place, the knee is appropriately balanced and tight in extension but opens 4 mm symmetrically both medially and laterally when assessed at 90 degrees of flexion. What is the most appropriate next step to achieve a balanced knee?

Explanation

A knee that is stable in extension but symmetrically loose in flexion has an isolated loose flexion gap. Increasing the femoral component size and using posterior referencing adds posterior condylar offset, tightening the flexion gap without altering the extension gap.

Question 28

A 65-year-old man presents with progressive groin pain 5 years after receiving a metal-on-polyethylene total hip arthroplasty. Radiographs demonstrate well-fixed components with no osteolysis. Serum cobalt is 8.5 ppb and chromium is 1.2 ppb. MARS MRI shows a mixed solid and cystic mass in the abductor musculature. What is the most likely etiology?

Explanation

Trunnionosis, or mechanically assisted crevice corrosion at the modular head-neck junction, can occur in metal-on-polyethylene THAs. It classically presents with an elevated cobalt-to-chromium ratio and adverse local tissue reactions (ALTR) such as pseudotumors.

Question 29

A 70-year-old woman presents with a painful "catching" sensation anteriorly when extending her knee from 45 degrees of flexion to full extension, 1 year after a posterior-stabilized total knee arthroplasty. What is the most likely diagnosis?

Explanation

Patellar clunk syndrome is a complication of posterior-stabilized knees where a fibrous nodule forms at the superior pole of the patella. The nodule engages the intercondylar notch in flexion and "clunks" out during active extension.

Question 30

During a direct anterior (Smith-Petersen) approach to the hip for a primary total hip arthroplasty, the superficial surgical dissection passes between which of the following internervous muscle intervals?

Explanation

The direct anterior approach utilizes the superficial internervous plane between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve).

Question 31

According to current evidence and criteria for periprosthetic joint infection (PJI), which of the following synovial fluid biomarkers provides the highest sensitivity and specificity for diagnosing PJI?

Explanation

Alpha-defensin is an antimicrobial peptide released by neutrophils in response to pathogens. It has demonstrated extremely high sensitivity and specificity for diagnosing periprosthetic joint infection, functioning well even in the setting of concurrent antibiotic use.

Question 32

To recreate a neutral mechanical axis during a primary total knee arthroplasty in a patient with a normal femoral bow, the distal femoral cut should typically be made at what angle relative to the anatomic axis of the femur?

Explanation

The mechanical axis of the femur typically intersects the anatomic axis at an angle of 5 to 7 degrees. Making the distal femoral resection at 5 to 7 degrees of valgus relative to the intramedullary alignment rod ensures a neutral mechanical axis for the lower extremity.

Question 33

To minimize the risk of dislocation following a primary total hip arthroplasty, the acetabular component should ideally be placed in which of the following "safe zone" target orientations?

Explanation

The classic Lewinnek safe zone for acetabular cup placement to minimize dislocation risk is 40 +/- 10 degrees of abduction (inclination) and 15 +/- 10 degrees of anteversion.

Question 34

In a cruciate-retaining total knee arthroplasty, over-resection of the posterior tibial slope can lead to which of the following kinematic abnormalities?

Explanation

Over-resecting the posterior tibial slope increases the flexion gap and renders the posterior cruciate ligament (PCL) relatively loose. This PCL insufficiency leads to paradoxical anterior translation of the femur on the tibia during flexion.

Question 35

A 72-year-old woman requires revision THA for aseptic loosening.

Radiographs demonstrate a Paprosky Type IIIA acetabular defect with superior migration of the hip center by 2.5 cm and intact Kohler's line. Which of the following is the most appropriate reconstruction technique?

Explanation

Paprosky Type IIIA defects feature severe bone loss with 10-30% host bone contact and >2 cm superior migration. Reconstruction typically requires a hemispherical multi-hole highly porous cup supplemented with a highly porous metal augment to support the construct.

Question 36

A 75-year-old woman sustains a displaced supracondylar femur fracture (Rorabeck Type II) directly proximal to a well-fixed posterior-stabilized total knee arthroplasty. The femoral component has a closed-box design. What is the most appropriate surgical management?

Explanation

A well-fixed TKA with a periprosthetic femur fracture is typically treated with internal fixation. A closed-box PS femoral component precludes the insertion of a retrograde intramedullary nail, making lateral locked plating the treatment of choice.

Question 37

A 78-year-old man falls and sustains a periprosthetic femur fracture around his THA. Radiographs show a fracture at the tip of the stem. The stem is radiographically loose, but the proximal femoral bone stock remains robust (Vancouver B2). What is the standard of care?

Explanation

Vancouver B2 periprosthetic fractures involve a loose stem with adequate surrounding bone stock. The standard of care is revision arthroplasty using a cementless, distally fixing long stem that bypasses the most distal fracture line by at least two cortical diameters.

Question 38

A 69-year-old man presents with an inability to actively extend his knee 3 years after a primary total knee arthroplasty. Ultrasound confirms a complete mid-substance rupture of the patellar tendon. What is the most reliable surgical option for restoring extensor function?

Explanation

Chronic or complete patellar tendon ruptures in the setting of a TKA have unacceptably high failure rates with direct repair. Extensor mechanism allograft reconstruction (or synthetic mesh) provides the most reliable and durable restoration of active extension.

Question 39

A 60-year-old woman complains of new-onset, sharp groin pain with active hip flexion, such as getting into a car, 6 months after an uncomplicated THA. Radiographs show the acetabular cup is retroverted and prominent anteriorly. What is the most appropriate initial management?

Explanation

The clinical presentation is highly consistent with iliopsoas impingement secondary to a prominent anterior acetabular rim. Initial management is nonoperative, consisting of physical therapy and a diagnostic/therapeutic corticosteroid injection into the iliopsoas bursa.

Question 40

During a two-stage exchange arthroplasty for a chronic periprosthetic joint infection of the knee, an articulating antibiotic spacer is placed. What is the primary advantage of an articulating spacer over a static spacer?

Explanation

Articulating spacers maintain joint mobility between stages. This preserves soft tissue compliance, minimizes extensor mechanism scarring, and facilitates the secondary re-implantation procedure, ultimately leading to better final postoperative range of motion.

Question 41

Following a total hip arthroplasty via a posterior approach, a patient exhibits a foot drop and inability to extend the great toe, but plantar flexion and foot inversion remain intact. Which specific nerve division is most likely injured?

Explanation

The common peroneal division of the sciatic nerve runs laterally and is securely tethered at the fibular head, making it highly susceptible to stretch injury during hip lengthening or retractor placement. It innervates the dorsiflexors and toe extensors.

Question 42

During a primary total knee arthroplasty, failure to adequately resect the native patella before placing the patellar component results in an "overstuffed" patellofemoral joint. This technical error is most likely to cause which of the following complications?

Explanation

Overstuffing the patellofemoral joint increases tension on the extensor mechanism. This reliably leads to anterior knee pain, restricted postoperative flexion, and an increased risk of patellar maltracking or lateral subluxation.

Question 43

During a posterior-stabilized total knee arthroplasty, trial reduction reveals that the knee is perfectly balanced in extension but significantly tight in flexion. Which of the following is the most appropriate surgical step to balance the gaps?

Explanation

A knee that is tight in flexion and balanced in extension requires an increase in the flexion gap. Downsizing the femoral component using an anterior referencing system reduces the posterior condylar offset, thereby increasing the flexion gap without affecting extension.

Question 44

Highly cross-linked polyethylene (HXLPE) is widely used in total hip arthroplasty to reduce wear. Which of the following manufacturing processes is critical to eliminate free radicals and reduce in vivo oxidation of HXLPE?

Explanation

Irradiation creates cross-links to improve wear resistance but also generates free radicals. Melting or annealing the polyethylene post-irradiation quenches these free radicals, significantly reducing the risk of in vivo oxidation and subsequent degradation.

Question 45

A 62-year-old female presents with groin pain and a palpable mass five years after a metal-on-metal total hip arthroplasty. Aspiration of the hip yields aseptic fluid, and serum cobalt and chromium levels are elevated. Histological examination of the periprosthetic tissue is most likely to show which of the following?

Explanation

Adverse local tissue reaction (ALTR/ALVAL) to metal wear debris in metal-on-metal hips is characterized histologically by a diffuse perivascular infiltrate of T-lymphocytes and macrophages. This represents a delayed-type hypersensitivity reaction.

Question 46

A 75-year-old male sustains a fall and suffers a periprosthetic fracture around his cemented total hip arthroplasty.

Radiographs demonstrate a fracture around the tip of the stem with evidence of cement mantle fragmentation and subsidence of the femoral component. Which of the following is the most appropriate management?

Explanation

The clinical and radiographic presentation is consistent with a Vancouver B2 periprosthetic fracture (fracture around a loose stem with adequate bone stock). The standard of care is revision arthroplasty using a long cementless stem that bypasses the fracture to achieve diaphyseal fixation.

Question 47

According to the 2018 International Consensus Meeting on Periprosthetic Joint Infection, which of the following synovial fluid profiles strongly supports the diagnosis of an acute periprosthetic joint infection (within 4 weeks of surgery)?

Explanation

Acute periprosthetic joint infections generally present with significantly higher synovial fluid WBC counts. A WBC > 10,000 cells/uL and > 90% PMNs is highly suggestive of an acute PJI within the first 6 weeks postoperatively.

Question 48

A 68-year-old male presents with a painful catching sensation and an audible clunk as his knee extends from 40 degrees of flexion to full extension, 18 months after a posterior-stabilized total knee arthroplasty. What is the most common cause of this phenomenon?

Explanation

Patellar clunk syndrome is caused by the formation of a fibrosynovial nodule at the superior pole of the patella that catches in the intercondylar notch of a posterior-stabilized femoral component during active extension. Arthroscopic debridement of the nodule is the definitive treatment.

Question 49

A surgeon is performing a total hip arthroplasty via the direct anterior approach. When preparing the femur, excessive retraction is applied to the medial soft tissues. Which of the following structures is at greatest risk of injury?

Explanation

During the direct anterior approach, the femoral nerve is at risk if excessive medial retraction is applied over the iliopsoas muscle. The lateral femoral cutaneous nerve is also at risk but usually from the superficial dissection rather than deep medial retraction.

Question 50

A 70-year-old female presents with an inability to actively extend her knee 3 years following a total knee arthroplasty. Evaluation confirms a chronic, massive rupture of the patellar tendon with severe tissue retraction and poor host tissue quality. Which of the following is the most reliable reconstructive option?

Explanation

Chronic extensor mechanism disruptions post-TKA with poor tissue quality require robust reconstruction. Extensor mechanism allograft or synthetic mesh (Marlex) reconstruction has been shown to provide the most reliable outcomes in restoring active extension.

Question 51

During a primary total knee arthroplasty, the surgeon finds the joint is perfectly balanced in flexion but tight in extension. Which of the following is the most appropriate surgical step to correct this mismatch?

Explanation

A knee that is tight in extension but balanced in flexion requires additional resection of the distal femur. Resecting more of the proximal tibia or changing the polyethylene thickness would affect both the flexion and extension gaps equally.

Question 52

A 65-year-old man presents with progressive groin pain 5 years after receiving a metal-on-polyethylene total hip arthroplasty. Aspiration is negative for infection. Blood tests reveal serum cobalt levels that are significantly higher than chromium levels. What is the most likely etiology of his symptoms?

Explanation

Elevated serum cobalt levels that are disproportionately higher than chromium in a metal-on-polyethylene THA are highly indicative of trunnionosis (fretting and crevice corrosion at the modular head-neck junction). Metal-on-metal bearing wear typically produces more equal elevations of cobalt and chromium.

Question 53

A 78-year-old woman presents with thigh pain after a ground-level fall. Radiographs demonstrate a fracture around her cemented polished taper-slip femoral stem. The fracture occurs at the level of the stem tip, and the stem is clearly loose within the cement mantle, but the proximal bone stock remains adequate. According to the Vancouver classification, what is the most appropriate management?

Explanation

This is a Vancouver B2 periprosthetic fracture, characterized by a fracture around the stem, a loose stem, and adequate remaining bone stock. The gold standard treatment is revision to a long, cementless, diaphyseal-engaging stem that bypasses the fracture by at least two cortical diameters.

Question 54

A 60-year-old man presents with a painful total knee arthroplasty 3 years postoperatively. His ESR is 45 mm/hr and CRP is 25 mg/L. Joint aspiration yields a white blood cell count of 3,500 cells/uL with 85% neutrophils. Synovial alpha-defensin testing is positive. Based on the 2018 ICM criteria, what is the definitive diagnosis?

Explanation

According to the 2018 International Consensus Meeting (ICM) criteria, a positive alpha-defensin test, combined with elevated inflammatory markers and a synovial WBC > 3,000 cells/uL with > 80% PMNs, firmly establishes the diagnosis of periprosthetic joint infection.

Question 55

When converting a standard offset femoral stem to a high offset femoral stem of the exact same neck angle during total hip arthroplasty, what is the expected biomechanical effect on the hip joint?

Explanation

Increasing femoral offset laterally translates the femur without changing the vertical height (leg length). This effectively increases the abductor moment arm, which subsequently decreases the overall joint reaction force across the hip.

Question 56

During a trial reduction for a posterior-stabilized total knee arthroplasty, the surgeon notes significant lateral patellar subluxation. Which of the following component positioning errors is the most likely cause of this maltracking?

Explanation

Internal rotation of either the femoral or tibial components increases the Q-angle, leading to lateral patellar maltracking. Proper external rotation of these components optimizes patellar tracking and flexion gap symmetry.

Question 57

A 45-year-old active man with a ceramic-on-ceramic total hip arthroplasty reports an audible squeaking noise from his hip when bending over. Which of the following factors is most strongly associated with the development of this phenomenon?

Explanation

Squeaking in ceramic-on-ceramic total hip arthroplasty is highly associated with edge loading of the bearing surface. This typically occurs due to acetabular component malposition, such as excessive inclination or malversion, which disrupts the fluid film lubrication.

Question 58

A 70-year-old woman is 1 year status post a posterior-stabilized total knee arthroplasty. She reports a sensation of giving way, especially when descending stairs. On examination, the knee is completely stable in full extension but exhibits excessive anterior-posterior laxity at 90 degrees of flexion. What is the most likely intraoperative cause of her symptoms?

Explanation

Instability when descending stairs with laxity at 90 degrees of flexion but stability in extension indicates an isolated loose flexion gap. This is classically caused by utilizing an undersized femoral component in the anteroposterior dimension.

Question 59

A 68-year-old woman is undergoing revision total hip arthroplasty for aseptic loosening. Preoperative imaging

demonstrates superior migration of the hip center by 4 cm and medial migration past Kohler's line. Severe osteolysis of the ischium and teardrop is noted. What is the Paprosky classification of this acetabular defect?

Explanation

A Paprosky Type 3B defect is characterized by severe bone loss with >3 cm of superior migration and medial migration past Kohler's line. This indicates massive destruction of the supportive inferior and medial column structures.

Question 60

Highly cross-linked polyethylene was introduced to drastically reduce wear rates in total joint arthroplasty. Which of the following thermal processing steps is specifically performed to eliminate residual free radicals, but results in a slight decrease in the material's mechanical yield strength?

Explanation

Remelting highly cross-linked polyethylene eliminates residual free radicals, which significantly improves oxidation resistance over time. However, this process alters the crystalline structure, resulting in a measurable decrease in mechanical properties like yield strength and fatigue crack propagation resistance.

Question 61

A 62-year-old man presents with acute onset of severe knee pain, swelling, and a low-grade fever exactly 3 weeks after an uncomplicated primary total knee arthroplasty. Joint aspiration reveals frankly purulent fluid. What is the most appropriate initial surgical management?

Explanation

For acute postoperative periprosthetic joint infections (typically defined as presenting within 4 weeks from the index surgery), Debridement, Antibiotics, and Implant Retention (DAIR) with exchange of modular components is the indicated treatment and offers a high rate of success.

Question 62

A 55-year-old woman with a metal-on-metal total hip arthroplasty presents with new-onset groin pain and a palpable soft tissue mass. Radiographs show well-fixed components.

Metal artifact reduction sequence (MARS) MRI reveals a large cystic fluid collection. What histologic finding is most characteristic of this condition?

Explanation

Adverse local tissue reactions (ALVAL) or pseudotumors in metal-on-metal arthroplasty are characterized histologically by a type IV delayed hypersensitivity reaction. The hallmark feature is a dense, perivascular lymphocytic infiltrate with tissue necrosis.

Question 63

Six months after a posterior-stabilized total knee arthroplasty, a patient reports a painful catching and popping sensation at the anterior knee when extending from a flexed position. The catch typically occurs around 30 to 45 degrees of flexion. What is the most definitive surgical management for this condition if conservative measures fail?

Explanation

This patient is describing patellar clunk syndrome, caused by a fibrosynovial nodule that forms at the superior pole of the patella and catches in the intercondylar box of a posterior-stabilized knee. Arthroscopic debridement of the nodule is the highly successful definitive treatment.

Question 64

During revision total hip arthroplasty for a massive acetabular defect, the surgeon evaluates the remaining bone and notes that the superior hemipelvis moves completely independently from the inferior hemipelvis upon applied stress. Which of the following is an essential biomechanical requirement when reconstructing this specific defect?

Explanation

Independent movement of the superior and inferior hemipelvis indicates a pelvic discontinuity. Successful reconstruction requires rigid bridging of the discontinuity, typically achieved with a cup-cage construct, custom triflange, or a distraction technique using highly porous metal components.

Question 65

A patient presents for total knee arthroplasty with an extra-articular diaphyseal femoral deformity consisting of 15 degrees of varus bowing. According to established alignment principles, what is the best intra-articular adjustment to achieve a neutral postoperative mechanical axis without performing a corrective femoral osteotomy?

Explanation

For a varus extra-articular femoral bowing deformity, the mechanical axis drops medially. To compensate intra-articularly and restore a neutral mechanical axis perpendicular to the floor, the surgeon must increase the valgus angle of the distal femoral cut beyond the standard 5 to 7 degrees.

Question 66

A patient presents with lateral patellar subluxation following a primary total knee arthroplasty. Which of the following component malpositions is the most likely cause?

Explanation

Internal rotation of either the femoral or tibial components increases the Q-angle and leads to lateral patellar tracking. External rotation of these components generally improves patellar tracking.

Question 67

A 72-year-old woman sustains a periprosthetic femur fracture 10 years after a cemented THA. Radiographs show a fracture around the tip of the stem. The stem is loose, but the proximal femoral bone stock is well preserved. According to the Vancouver classification, what is the most appropriate management?

Explanation

This is a Vancouver B2 fracture (fracture around the stem, loose implant, good bone stock). The standard of care is revision arthroplasty bypassing the fracture site with a long, diaphyseal-engaging uncemented stem.

Question 68

What is the primary cellular mechanism of osteolysis induced by polyethylene wear debris in total joint arthroplasty?

Explanation

Wear debris osteolysis is primarily a macrophage-mediated response. Macrophages phagocytose particulate debris and release cytokines (TNF-alpha, IL-1, IL-6), which stimulate osteoclastic bone resorption via the RANK/RANKL pathway.

Question 69

A 55-year-old man who underwent a metal-on-metal THA 6 years ago presents with new-onset groin pain and a palpable anterior mass. Joint aspiration yields sterile fluid with elevated cobalt levels. What is the most likely histological finding of the periprosthetic tissue?

Explanation

The clinical picture describes an adverse local tissue reaction (ALTR) or ALVAL, common in metal-on-metal implants. Histology typically shows a perivascular infiltrate of T-lymphocytes and macrophages.

Question 70

During a primary TKA, after making the initial bony cuts, the surgeon notices that the knee is tight in flexion but well-balanced in extension. Which of the following maneuvers is most appropriate to balance the knee?

Explanation

A knee that is tight in flexion but balanced in extension requires an increase in the flexion gap without altering the extension gap. Increasing the posterior tibial slope, resecting more posterior femoral condyle, or releasing the PCL will achieve this.

Question 71

A 65-year-old patient presents with a painful total knee arthroplasty 8 weeks postoperatively. The ESR is 45 mm/hr and CRP is 35 mg/L. Knee aspiration yields 45,000 WBC/uL with 92% neutrophils. What is the most appropriate next step in management?

Explanation

This patient has a chronic periprosthetic joint infection, as the symptom onset is >4 weeks postoperatively. The gold standard treatment for chronic PJI in North America is a two-stage exchange arthroplasty.

Question 72

When performing a primary total hip arthroplasty via the direct anterior (Smith-Petersen) approach, the superficial internervous plane lies between muscles supplied by which of the following nerves?

Explanation

The superficial internervous plane for the direct anterior approach is between the tensor fasciae latae (superior gluteal nerve) and the sartorius (femoral nerve).

Question 73

Which of the following is traditionally considered an absolute contraindication for a medial unicompartmental knee arthroplasty (UKA)?

Explanation

Inflammatory arthropathy (e.g., rheumatoid arthritis) is considered an absolute contraindication for UKA due to global joint involvement. Age and BMI are controversial but not absolute contraindications.

Question 74

A patient with a total hip arthroplasty is experiencing recurrent posterior dislocations. Radiographs reveal appropriate cup abduction and anteversion, but the femoral component has inadequate offset. What is the most likely clinical finding on physical examination?

Explanation

Inadequate femoral offset reduces the moment arm of the hip abductors, leading to mechanical disadvantage and abductor weakness. This clinically manifests as a positive Trendelenburg sign and limp.

Question 75

Mechanically assisted crevice corrosion (MACC), or trunnionosis, is most frequently associated with which of the following total hip arthroplasty component combinations?

Explanation

Trunnionosis occurs at the modular head-neck junction. It is most strongly associated with the use of large diameter cobalt-chrome heads on titanium alloy stems due to increased micromotion and galvanic corrosion.

Question 76

During a revision total hip arthroplasty, severe acetabular bone loss is encountered. Radiographs and intraoperative findings demonstrate a complete separation of the superior and inferior halves of the hemipelvis. What is the diagnosis and best reconstruction option?

Explanation

Separation of the superior and inferior hemipelvis defines a pelvic discontinuity. Stable reconstruction typically requires bridging the discontinuity with a cup-cage construct, custom triflange, or a distraction technique.

Question 77

In total knee arthroplasty, the posterior stabilized (PS) design utilizes a cam and post mechanism. Which of the following normal knee kinematics does this mechanism primarily replicate?

Explanation

The cam and post mechanism in a PS knee substitutes for the posterior cruciate ligament (PCL). As the knee flexes, the femoral cam engages the tibial post to drive the femur posteriorly, replicating physiologic femoral rollback.

Question 78

Highly cross-linked polyethylene (HXLPE) was developed to reduce wear in total hip arthroplasty. What is the primary purpose of the post-irradiation remelting or annealing step in the manufacturing process?

Explanation

Irradiation is used to cross-link the polyethylene, but it generates free radicals that can cause oxidative degradation over time. Remelting or annealing the material extinguishes these free radicals, improving oxidation resistance.

Question 79

A 60-year-old male undergoes a ceramic-on-ceramic total hip arthroplasty. Two years postoperatively, he complains of a loud audible squeaking during normal ambulation. What factor is most strongly associated with this complication?

Explanation

Squeaking in ceramic-on-ceramic hips is most commonly associated with component malposition (e.g., vertical cup placement), which leads to stripe wear and edge loading. Loss of fluid film lubrication follows.

Question 80

A 48-year-old female presents with complete disruption of her extensor mechanism 3 months following a primary TKA. Examination shows a palpable gap at the patellar tendon and an inability to actively extend the knee. What is the most reliable surgical treatment?

Explanation

Primary repair of late extensor mechanism ruptures post-TKA has an extremely high failure rate. Reconstruction utilizing a whole extensor mechanism allograft or synthetic mesh (e.g., Marlex) offers the most reliable results.

Question 81

An 80-year-old female with a well-functioning TKA falls and sustains a supracondylar femur fracture. Radiographs show a displaced fracture, but the femoral component remains radiographically well-fixed (Rorabeck Type II). What is the most appropriate management?

Explanation

For Rorabeck Type II fractures (displaced fracture, stable component), surgical fixation using a retrograde intramedullary nail or a lateral locked plate provides stable fixation while preserving the functioning arthroplasty.

Question 82

During preoperative templating for a primary THA, the surgeon identifies a significant leg length discrepancy, with the operative side being 2 cm shorter. To lengthen the leg without excessively increasing the femoral offset, which intraoperative adjustment should be made?

Explanation

A high offset stem (lower neck-shaft angle/more varus) increases offset with minimal effect on leg length. Conversely, a standard offset stem (higher neck-shaft angle/more valgus) gains more vertical length for every unit of offset added.

Question 83

A surgeon is performing a posterior-stabilized total knee arthroplasty. During trialing, the knee is tight in flexion and symmetrically balanced in extension. Which of the following is the most appropriate next step?

Explanation

Downsizing the femoral component translates the posterior femoral condyles anteriorly, which increases the flexion gap. This maneuver successfully addresses a tight flexion gap without altering the extension gap.

Question 84

A 74-year-old woman sustains a fall 6 years after primary total hip arthroplasty. Radiographs reveal a spiral fracture around the tip of the femoral stem. The stem is subsided by 2 cm, but the proximal femoral bone stock remains adequate. According to the Vancouver classification, what is the most appropriate management?

Explanation

This is a Vancouver B2 fracture, characterized by a fracture around a loose stem with adequate bone stock. The gold standard treatment is revision to a longer, diaphyseal-engaging cementless stem to bypass the fracture and achieve stability.

Question 85

A 65-year-old man presents with anterior knee pain and recurrent lateral patellar subluxation 6 months after a primary total knee arthroplasty. Which of the following component malpositions is the most likely cause of his patellar maltracking?

Explanation

Internal rotation of either the femoral or tibial components increases the Q-angle and leads to lateral patellar tracking and potential subluxation. External rotation of the components typically improves patellar tracking.

Question 86

A 58-year-old woman presents with worsening groin pain and swelling 8 years after receiving a metal-on-metal total hip arthroplasty. Laboratory tests show elevated serum cobalt and chromium levels. A MARS MRI demonstrates a large solid and cystic mass communicating with the joint. What is the underlying histologic mechanism of this process?

Explanation

Adverse local tissue reactions (ALTR) or aseptic lymphocytic vasculitis-associated lesions (ALVAL) in metal-on-metal hips are primarily driven by a Type IV delayed hypersensitivity response to metal ions.

Question 87

A 66-year-old man presents with new-onset groin pain 6 years after a primary total hip arthroplasty using a metal-on-polyethylene bearing. Serum metal ion testing reveals a cobalt level of 12 ppb and a chromium level of 1.5 ppb. Which of the following implant characteristics most increases the risk of this condition?

Explanation

Mechanically assisted crevice corrosion (trunnionosis) at the head-neck junction is characterized by elevated serum cobalt disproportionate to chromium. Large diameter metal heads increase torque at the trunnion, heavily exacerbating this risk.

Question 88

A 72-year-old man develops erythema, swelling, and purulent drainage from his incision 14 days after a primary total knee arthroplasty. He is febrile. Joint aspiration yields 65,000 WBCs/mcL with 95% neutrophils. What is the most appropriate surgical management?

Explanation

For acute postoperative periprosthetic joint infections occurring within 4 weeks of the index surgery, DAIR with modular component exchange is the most appropriate and effective initial management strategy.

Question 89

A 70-year-old woman with a history of an L2-pelvis posterior spinal fusion is scheduled for a total hip arthroplasty. Spino-pelvic evaluation reveals a stiff spine with less than 10 degrees of pelvic tilt change from standing to sitting. How should the surgeon adjust the acetabular component positioning to minimize the risk of posterior dislocation?

Explanation

Patients with a stiff lumbar spine fail to increase pelvic retroversion when sitting, increasing the risk of anterior impingement and posterior dislocation. Surgeons should target increased anteversion and inclination to compensate.

Question 90

During a revision total knee arthroplasty for aseptic loosening, removal of the tibial component reveals an uncontained metaphyseal bone defect measuring 4 cm deep, compromising the cortical rim (AORI Type 3). What is the most reliable method for achieving durable fixation?

Explanation

For severe uncontained metaphyseal defects (AORI Type 3) in revision TKA, highly porous metal cones or metaphyseal sleeves provide excellent long-term biologic fixation and construct stability compared to bulk allografts.

Question 91

A 45-year-old man undergoes total hip arthroplasty using a ceramic-on-ceramic bearing. Three years later, he complains of a reproducible squeaking noise during deep flexion. Which of the following biomechanical factors is most strongly associated with this phenomenon?

Explanation

Squeaking in ceramic-on-ceramic THA is heavily associated with edge loading, often caused by acetabular component malposition. This leads to stripe wear and altered fluid lubrication dynamics.

Question 92

A patient presents with mid-flexion instability 1 year after a primary posterior-stabilized total knee arthroplasty. Review of operative notes and radiographs indicates the use of an oversized femoral component and a thick polyethylene insert. What technical error is the most likely cause of this mid-flexion instability?

Explanation

Joint line elevation, often caused by excessive distal femoral resection compensated by a thicker polyethylene insert, alters collateral ligament isometric tension. This mismatch frequently leads to isolated mid-flexion instability.

Question 93

During preoperative templating for a total hip arthroplasty, the surgeon plans to use a high-offset femoral stem. Compared to a standard-offset stem, what is the primary biomechanical advantage of increasing femoral offset?

Explanation

Increasing femoral offset extends the abductor moment arm, which improves the mechanical advantage of the abductor musculature. This reduces the required muscle force and decreases the overall joint reaction force.

Question 94

A 78-year-old woman presents with an inability to actively extend her knee 3 years following a primary total knee arthroplasty. Examination confirms a palpable gap over the patellar tendon. What is the most reliable surgical reconstruction method for this chronic disruption?

Explanation

Chronic patellar tendon ruptures in the setting of TKA respond poorly to primary repair. Reconstruction with a synthetic mesh or a full extensor mechanism allograft offers the most reliable restoration of active extension.

Question 95

A 65-year-old man experiences recurrent anterior dislocations of his total hip arthroplasty. Radiographs reveal the acetabular component is placed in 45 degrees of inclination and 40 degrees of anteversion. The femoral stem is in 25 degrees of anteversion. What is the most appropriate surgical intervention?

Explanation

The patient has excessive combined anteversion, predisposing him to anterior instability. Revising the acetabular cup to a more neutral anteversion (15-20 degrees) is the most appropriate and straightforward management.

Question 96

A 79-year-old woman presents to the emergency department after a fall. Radiographs demonstrate a displaced supracondylar femur fracture above a well-fixed total knee arthroplasty femoral component (Lewis-Rorabeck Type II). What is the preferred definitive treatment?

Explanation

A Lewis-Rorabeck Type II fracture (displaced fracture with a well-fixed implant) is best treated with internal fixation using either a retrograde intramedullary nail or a locked plate to allow early mobilization.

Question 97

A 62-year-old man presents with a painful total knee arthroplasty 3 years postoperatively. Serum CRP and ESR are mildly elevated. Aspiration yields a synovial WBC count of 2,500 cells/mcL with 60% PMNs. Cultures are negative at 5 days. To definitively diagnose periprosthetic joint infection, which synovial fluid biomarker is the most specific next step?

Explanation

Synovial alpha-defensin has demonstrated extremely high sensitivity and specificity for diagnosing periprosthetic joint infection. It is an excellent tie-breaker test in borderline clinical scenarios.

Orthopedic Board Review Set 675: 100 MCQs for ABOS, OITE, FRCS – Hip Focus

AAOS & ABOS Orthopedic MCQs (Set 3): Hip & Knee Arthroplasty & Revision

Key Takeaway

AAOS & ABOS Orthopedic MCQs (Set 3): Hip & Knee Arthroplasty & Revision

Chapter Index