Orthopedic MCQs: Hip Fractures & Arthroplasty Prep

Question 1

Figure 9 shows the radiograph of a 75-year-old woman who reports the sudden onset of disabling medial knee pain. What is the most likely diagnosis?

Explanation

Idiopathic osteonecrosis of the medial femoral condyle occurs predominantly in women older than age 60 years. It is characterized by pain centered in the medial anterior aspect of the knee, and onset is sudden. Flattening, sclerosis, and the radiolucent crescent sign are radiographic indicators of osteonecrosis. The radiographs show no narrowing of the joint space or osteophyte formation to indicate osteoarthritis, and there are no loose bodies to indicate synovial osteochondromatosis. A meniscal tear is not consistent with the radiographic findings shown here. Meniscal tears can coexist with osteonecrosis, but the pain is not eliminated merely by partial meniscectomy. Metastatic lesions to the distal femoral epiphysis are exceedingly rare. Urbaniak JR, Jones JP Jr (eds): Osteonecrosis: Etiology, Diagnosis, and Treatment. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1997, pp 413-418.

Question 2

Which of the following statements best characterizes polymethylmethacrylate (PMMA) when it is used to secure joint components in bone and to distribute the forces evenly across the bone-implant interface?

Explanation

PMMA has no adhesive properties and can be more accurately described as grout than glue. It does not chemically bond to bone or implants; however, mechanical bonding is accomplished with porous or coated components and with cancellous bone. PMMA is approximately three times stronger in compression than in tension. Peak blood levels of monomer are usually seen approximately 3 minutes after the cement is placed. The monomer is cleared by the lungs. Associated hypotension is more closely related to diminished blood volume than to circulating monomer levels. High porosity decreases the tensile and fatigue properties of cement. Manually mixed cement may have porosity as high as 27%. Porosity may be reduced to less than 1% through vacuum mixing or centrifugation of the cement. When adding antibiotics to cement, the compressive and tensile forces are not appreciably decreased, but the overall fatigue strength may be reduced. Canale ST (ed): Campbell's Operative Orthopaedics, ed 9. St Louis, MO, Mosby, 1998, pp 221-224.

Question 3

During primary total knee arthroplasty, the trial components are in place. The extensor space is tight, but the flexion space is normal. What is the best gap balancing solution?

Explanation

The first rule of total knee arthroplasty is to restore the joint line to its original location. This will ensure optimal patellofemoral biomechanics and will facilitate ligament balancing. Changes on the tibial side affect both the flexion and extension gaps equally. Changes in femoral component sizing or position affect the flexion gap only. Tibial changes affect both the flexion and extension gaps. To convert a tight extension gap to a normal flexion gap, more distal femur needs to be resected. Vince KG: Revision knee arthroplasty technique. Instr Course Lect 1993;42:325-339.

Question 4

Which of the following methods is considered effective in decreasing the dislocation rate following a total hip arthroplasty using a posterior approach to the hip?

Explanation

A total hip arthroplasty using the posterior approach has resulted in hip dislocation under certain circumstances. Reconstruction of the external rotator/capsular complex is recognized as a stability-enhancing mechanism for the posterior approach. During the procedure, the acetabular component should be placed in 15 to 20 degrees of anteversion and approximately 45 degrees of abduction. Relative retroversion is a risk factor for posterior dislocation. High abduction angles result in edge loading of the polyethylene and possible early failure, as well as an increased risk of dislocation. Smaller diameter heads and skirted neck extensions used together decrease the range of motion that is allowed before impingement occurs, and this can result in dislocation. Shorter neck lengths generally result in soft-tissue envelope laxity. If laxity occurs, increased offset, neck length, or both can improve stability. Pellicci PM, Bostrom M, Poss R: Posterior approach to total hip replacement using enhanced posterior soft tissue repair. Clin Orthop 1998;355:224-228.

Question 5

Which of the following treatments of polyethylene results in the highest amount of oxidative degradation?

Explanation

Oxidative degradation of polyethylene occurs as a function of time in an air environment. In an environment such as argon, nitrogen, or a vacuum, the process is reduced. Ethylene oxide is an alternative for sterilization in which the cross-link degradation is minimized because of the absence of oxidative interactions. Gamma sterilization or use of ethylene oxide gas is the industry standard; however, oxygen concentrations are now reduced to a minimal level to retard the oxidation phenomenon. Sanford WM, Saum KA: Accelerated oxidative aging testing of UHMWPE. Trans Orthop Res Soc 1995;20:119. Sun DC, Schmidig G. Stark C, et al: On the origins of a subsurface oxidation maximum and its relationship to the performance of UHMWPE implants. Trans Soc Biomater 1995;18:362. Callaghan JJ, Dennis DA, Paprosky WA, Rosenberg AG (eds): Orthopaedic Knowledge Update: Hip and Knee Reconstruction. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1995, pp 35-41.

Question 6

Figures 10a through 10c show the radiographs of an 85-year-old man who underwent a revision total knee arthroplasty for loosening of the tibial component 6 months ago. He now reports a mildly uncomfortable mass on the anterior part of the knee joint. Examination reveals 95 degrees of motion and good quadriceps strength, and he can ambulate with minimal pain with a walker. History reveals chronic lymphocytic leukemia for which he is taking antineoplastic medication. Culture of the mass aspirate grew Candida albicans on two separate occasions. The patient and the family strongly prefer nonsurgical management. If long-term suppression is chosen as treatment, what advice should be given to the patient and family?

Explanation

In patients with infected implants, treatment usually involves debridement and exchange of the infected components. In rare cases, when there is severe comorbidity and immune system compromise, as there is with this patient, a form of chronic suppression is indicated. This patient's function is quite satisfactory and, even though there is only a 21% to 38% chance of success (Hirawaka as quoted by Mulvey and Thornhill), an attempt at suppression therapy is indicated. The patient must be followed closely to monitor the potential complications of long-term antifungal therapy and to monitor the integrity of the joint, looking for bone or soft-tissue destruction. Because the patient has satisfactory motion and quadriceps strength, no bracing or other assistive device (except for the walker he is now using) is indicated.

Question 7

Consider the theoretic articulation shown in Figure 11 as femoral and tibial components of a total knee prosthesis in which the components fit like a "roller in trough." Which of the following best describes the articulation?

Explanation

The theoretic total knee components will resist anteroposterior motion by making the femoral component "climb the walls" of the tibial component. As drawn, there is no constraint to medial-lateral translation. The cylinder is not rounded on the edges, so varus-valgus motion will impart load from the cylinder to the trough over a small area, thus having a high contact stress.

Question 8

A 45-year-old man underwent unipolar hemiarthroplasty reconstruction using cementless fixation for nontraumatic osteonecrosis of the femoral head 5 years ago. He now reports buttock and groin pain that is associated with loading activities. What is the most likely cause of his pain?

Explanation

One of the most common complications of hemiarthroplasty is acetabular cartilage degeneration, resulting in increasing pain. Conversion total hip arthroplasty generally is successful with placement of an acetabular cup. Additionally, many patients with osteonecrosis already have degenerative changes of the acetabular cartilage even though radiographic findings may appear normal. Steinberg ME, Corces A, Fallon M: Acetabular involvement in osteonecrosis of the femoral head. J Bone Joint Surg Am 1999;81:60-65.

Question 9

Which of the following factors is associated with decreases in active periprosthetic osteolysis in total hip arthroplasty?

Explanation

A 32-mm head design results in less linear wear but more volumetric wear particles. Modular components that allow motion between the polyethylene insert and the shell can result in backside wear. The oxidative degradation of gamma-irradiated polyethylene stored in air leads to increased wear. All of these factors lead to a greater particulate load and more osteolysis. Circumferential porous coating blocks ingrowth of particle-laden fluid and decreases osteolysis. Bartel DL, Bicknell VL, Wright TM: The effect of conformity, thickness, and material on stresses in ultra-high molecular weight components for total joint replacement. J Bone Joint Surg Am 1986;68:1041-1051. Fisher J, Hailey JL, Chan KL, et al: The effect of aging following irradiation on the wear of UHMWPE. Trans Orthop Res Soc 1995;20:12.

Question 10

When using highly cross-linked ultra-high molecular weight polyethylene as an articulating surface for total knee arthroplasty, what property of the material raises concern?

Explanation

The decreased mobility of the polymer chains from cross-linking leads to decreased volumetric wear but also to decreases in ductility and fatigue resistance. Stresses at the knee are higher and varied in the point of application, leading to the concern for fatigue resistance and fracture.

Question 11

The diagnosis of an infection after total knee arthroplasty is most reliably proven based on what single study?

Explanation

In a study of 52 patients with infected total knee arthroplasties, Windsor and associates showed that the average leukocyte count was 8,300/mm3 and that aspirated knee fluid was positive in all patients except one. Knee radiographs can be unclear in showing infection, which may be present without radiographic signs of loosening. Technetium Tc 99m and gallium bone scans may not conclusively show the presence of infection, particularly in the first 3 years after knee arthroplasty. Windsor RE, Bono JV: Infected total knee replacements. J Am Acad Orthop Surg 1994;2:44-53.

Question 12

A 48-year-old woman has knee pain that is worse with weight bearing. She reports no night pain or pain at rest. History reveals that she underwent total knee arthroplasty with cementless components 2 years ago. Examination reveals tenderness along the medial joint line. Figures 12a through 12c show radiographs and a bone scan. What is the most likely cause of the patient's pain?

Explanation

The radiographs show a halo-like sclerotic margin around the tibial stem and lucency under the baseplate. The bone scan shows markedly increased uptake under the tibial component, particularly on the medial side (not diffusely through the knee as seen with infection). These studies indicate lack of bone ingrowth fixation of the cementless porous-coated tibial component. The recent report of Fehring and associates has identified failure of ingrowth of a porous-coated implant as a dominant mode of early failure of total knee arthroplasties. Fehring TK, Odum S, Griffin WL, Mason B, Nadaud M: Early failures of total knee arthroplasty. Clin Orthop 2001;392:315-318.

Question 13

A 65-year-old man who underwent cemented right total hip arthroplasty 6 years ago now reports acute pain for the past week. He denies any trauma, recent illnesses, or symptoms other than pain. Plain radiographs show possible loosening of the femoral component. A normal result from which of the following studies will most specifically rule out infection?

Explanation

A patient with an infected total hip arthroplasty may lack the symptoms of fever, chills, redness, or increased warmth typical of septic arthritis. Sensitivity for ESR and CRP ranges from 61% to 96%, and specificity ranges from 85% to 100%. Technetium Tc 99m bone scans are costly and time-consuming and will not differentiate between septic and aseptic loosening. Hip aspiration has a false-positive rate of up to 15%, although it may be useful in this patient to further complement the clinical picture if the ESR and CRP are elevated. The WBC count is rarely elevated in infected total hip arthroplasty. MRI is expensive and is not indicated for the diagnosis; however, it can aid in identifying intrapelvic extension of a periprosthetic abscess. Beaty JH (ed): Orthopaedic Knowledge Update 6. Rosemont, IL, American Academy of Orthopaedic Surgeons, 1999, pp 455-492.

Question 14

Which of the following procedures is included in third-generation cement technique?

Explanation

The so-called third-generation cement technique adds porosity reduction techniques, centralization devices, and surface modifications to the femoral component. The surgeon must be aware of the meaning of the various generations of cement technique when interpreting the results presented at meetings and in the literature. 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 181-193.

Question 15

Which of the following acetabular cup designs has shown the greatest survivorship at 10 years in patients younger than age 60 years?

Explanation

Poor survivorship of cemented sockets in young patients has lead to the development of a variety of cementless designs. Of these, smooth metal-backed sockets have not performed as well as porous-coated designs. Threaded metal-backed sockets showed a 6% to 25% revision rate secondary to aseptic loosening at a mean follow-up of 4.5 to 6 years. Despite some early failed designs, cementless porous-coated metal-backed sockets have shown the best survivorship in long-term studies. Smith SE, Harris WH: Total hip arthroplasty performed with insertion of the femoral component with cement and the acetabular component without cement: Ten to thirteen-year study. J Bone Joint Surg Am 1997;79:1827-1833.

Question 16

What is the most common donor site complication following a free vascularized fibular graft for osteonecrosis of the femoral head?

Explanation

Urbaniak and Harvey reported donor site morbidity following free vascularized fibular graft in 198 consecutive patients. At a 5-year follow-up, they reported overall complications in 24% of the patients. The most common complication was a sensory deficit (11.8%), followed by motor weakness (2.7%), flexor hallucis longus contracture (2%), and deep venous thrombosis (less than 1%).

Question 17

A 77-year-old woman who underwent a cemented total hip arthroplasty 10 years ago now reports groin pain. Examination reveals a loosened acetabular component and a well-fixed femoral component. Treatment should consist of revision of

Explanation

Recent literature supports retention of well-fixed cemented femoral components when revising loosened cemented acetabular components. Current literature also supports the use of cementless components for revision of loosened cemented acetabular components. Peters CL, Kull L, Jacobs JJ, Rosenberg AG, Galante JO: The fate of well fixed cemented femoral components left in place at the time of revision of the acetabular component. J Bone Joint Surg Am 1997;79:701-706. Poon ED, Lachiewicz PF: Results of isolated acetabular revisions: The fate of the unrevised femoral component. J Arthroplasty 1998;13:42-49. Moskal JT, Shen FH, Brown TE: The fate of stable femoral components retained during isolated acetabular revision: A six- to twelve-year follow-up study. J Bone Joint Surg Am 2002;84:250-255.

Question 18

Which of the following findings is a relative contraindication to primary total knee arthroplasty?

Explanation

Contraindications to primary total knee arthroplasty include active infection, an incompetent extensor mechanism, compromised vascularity in the extremity, and local neurologic disruption affecting the competence of the musculature about the knee. Anterior cruciate, posterior cruciate, or lateral ligament incompetence can be managed with primary total knee arthroplasty. Mild flexion contracture and previous high tibial valgus osteotomy are not contraindications to primary total knee arthroplasty.

Question 19

Risk of fat embolism is greatest during what step of total hip arthroplasty?

Explanation

Embolization of fat and bone marrow elements during total hip arthroplasty has been studied intraoperatively using transesophageal echocardiography. These studies showed the occurrence of a large number of embolic events during the insertion of a cemented femoral stem. Embolic events were rare during insertion of a cementless stem. Femoral broaching caused some embolic events, but they were not nearly as significant as those that occurred following insertion of a cemented stem. Additionally, relocation of the cemented hip was accompanied by significant embolic events. This may be related to the untwisting of blood vessels, with the subsequent release of emboli that were most likely generated during insertion of a cemented femoral stem. Pitto RP, Koessler M, Kuehle JW: Comparison of fixation of the femoral component without cement and fixation with use of a bone-vacuum cementing technique for the prevention of fat embolism during total hip arthroplasty. J Bone Joint Surg Am 1999;81:831-843.

Question 20

Venous thrombolembolism is a common complication following total hip and total knee arthroplasty; therefore, prophylaxis is deemed efficacious. Several studies on low-molecular-weight heparin (LMWH) have shown which of the following findings?

Explanation

Prophylactic LMWH is associated with a risk of bleeding complications, especially if administered too soon after surgery. The risk of major bleeding is 0.3% for control, 0.4% for aspirin, 1.3% for warfarin, 1.8% for LMWH, and 2.6% for unfractionated heparin. Colwell and associates conducted a prospective, randomized trial on over 1,500 total hip arthroplasty patients. Overall, the risk of clinically apparent venous thrombolembolism was 3.6% for LMWH and 3.7% for warfarin. LMWH acts in several sites of the coagulation cascade, with its principal action being inhibition of factor 10a. Thrombocytopenia is less common with LMWH than with unfractionated heparin. The use of LMWH is a relative contraindication with indwelling epidural anesthesia. Colwell CW Jr, Collis DK, Paulson R, et al: Comparison of enoxaparin and warfarin for the prevention of venous thromboembolic disease after total hip arthroplasty:. Evaluation during hospitalization and three months after discharge. J Bone Joint Surg Am 1999;81:932-940.

Question 21

Wear particles of ultra-high molecular weight polyethylene that are generated by total hip implants are predominantly of what diameter?

Explanation

Multiple studies have shown that the size of an ultra-high molecular weight polyethylene particle generated by total hip implants is typically less than 1 micron. This finding is significant in that particles of that size are readily phagocytized by macrophages. Campbell P, Ma S, Yeom B, McKellop H, Schmalzried TP, Amstutz HC: Isolation of predominantly submicron-sized UHMWPE wear particles from periprosthetic tissues. J Biomed Mater Res 1995;29:127-131. Shanbhag AS, Jacobs JJ, Glant TT, Gilbert JL, Black J, Galante JO: Composition and morphology of wear debris in failed uncemented total hip replacement. J Bone Joint Surg Br 1994;76:60-67.

Question 22

Osteoporosis is best diagnosed by

Explanation

Risk factors can suggest the existence of osteoporosis. However, definitive testing, based on the use of bone densitometry measurements, uses the T score in which an average score is taken from a normal population of young women. The presence of increased osteoid in lamellar bone is seen in osteomalacia but not osteoporosis. The presence of fractures is evidence of a risk factor for osteoporosis and can predict future fractures, but it does not definitively confirm the diagnosis. The Singh index is a radiographic finding that is not as accurate as bone mineral density scores.

Question 23

When compared to patients with osteoarthritis, patients with ankylosing spondylitis undergoing total hip arthroplasty can expect a

Explanation

Joshi and associates reported a 96% incidence of pain relief in 181 total hip arthroplasties in patients with ankylosing spondylitis. Only 65% of patients had good to excellent functional results, primarily the result of associated systemic diseases and spinal deformity. The incidence of infection was slightly higher, and the incidence of heterotopic ossification was higher in this group of patients.

Question 24

What postoperative complication occurs at a significantly higher rate in patients undergoing bilateral simultaneous total knee arthroplasty than in patients undergoing unilateral total knee arthroplasty?

Explanation

Parvizi and associates studied the 30-day mortality rate after more than 22,000 total knee arthroplasties and found that the rate after bilateral total knee arthroplasty was significantly higher than after unilateral total knee arthroplasty. Aseptic loosening, bleeding, and range of motion have not been shown to be statistically different between patients who had unilateral and simultaneous bilateral total knee arthroplasty.

Question 25

Metal-on-metal articulation has been reintroduced because of concern about polyethylene wear. This type of articulation is considered favorable because

Explanation

The improvements in metal-on-metal bearing surfaces come from the nonlinear wear rate and smaller particle size of the high carbon wrought material. Extremely low rates of wear have been demonstrated with high carbon metal-on-metal implants. There is no significant electrochemical effect of mating two like materials in vivo.

Question 26

What is the primary advantage of highly cross-linked polyethylene (HXLPE) compared to conventional polyethylene in total hip arthroplasty?

Explanation

Highly cross-linked polyethylene significantly reduces volumetric wear compared to conventional polyethylene, thus decreasing the incidence of wear debris osteolysis. However, the cross-linking and subsequent thermal treatments can decrease the mechanical toughness of the material.

Question 27

A 72-year-old man sustains a reverse obliquity intertrochanteric femur fracture. Which of the following fixation constructs provides the highest biomechanical stability for this fracture pattern?

Explanation

Cephalomedullary nails provide superior biomechanical stability for reverse obliquity intertrochanteric fractures due to their intramedullary load-sharing design. Sliding hip screws are contraindicated as they allow the femoral shaft to medialize excessively in this fracture pattern.

Question 28

A patient undergoes a primary total hip arthroplasty via a direct anterior approach. If this patient experiences a postoperative dislocation, in which position is the hip most likely to be unstable?

Explanation

Dislocation following a direct anterior approach typically occurs with the hip in extension, adduction, and external rotation due to the anterior capsular defect. This contrasts with the posterior approach, which generally dislocates in flexion, adduction, and internal rotation.

Question 29

During preoperative templating for a total hip arthroplasty, increasing the femoral neck offset without changing the neck resection level or stem length will result in which of the following?

Explanation

Increasing the femoral neck offset lateralizes the femur, which increases abductor tension and mechanical advantage without altering the vertical leg length. This enhanced abductor lever arm effectively decreases the overall joint reaction force on the hip.

Question 30

A 35-year-old man sustains a vertically oriented (Pauwels type III) displaced femoral neck fracture. What is the most appropriate internal fixation construct to minimize shear forces and prevent varus collapse?

Explanation

For young patients with vertically oriented (Pauwels type III) femoral neck fractures, a dynamic hip screw (fixed-angle device) provides superior biomechanical resistance to shear forces compared to multiple cancellous screws. A derotational screw is often added for additional rotational control.

Question 31

A 68-year-old woman presents with persistent groin pain 2 years after a primary total hip arthroplasty. Aspiration of the hip joint yields synovial fluid with a white blood cell (WBC) count of 4,500 cells/mcL and 85% polymorphonuclear neutrophils (PMNs). What is the most appropriate next step in management?

Explanation

The synovial fluid analysis (WBC > 3,000 cells/mcL and >80% PMNs) is highly diagnostic for a chronic periprosthetic joint infection in a hip. The standard of care for a chronic PJI in the United States remains a two-stage revision arthroplasty.

Question 32

In a proximal third subtrochanteric femur fracture, the proximal fragment is typically displaced into which of the following positions?

Explanation

In a subtrochanteric fracture, the proximal fragment is flexed by the iliopsoas, abducted by the gluteus medius and minimus, and externally rotated by the short external rotators. Recognition of these deforming forces is critical for achieving a successful closed reduction prior to nailing.

Question 33

A 65-year-old man presents with progressive groin pain 5 years after receiving a total hip arthroplasty utilizing a 40-mm cobalt-chromium femoral head on a titanium stem. MRI with metal artifact reduction sequence (MARS) shows a solid cystic mass in the abductor musculature. Blood metal ion testing shows significantly elevated serum cobalt with normal chromium. What is the most likely diagnosis?

Explanation

Trunnionosis (mechanically assisted crevice corrosion) occurs at the head-neck junction, classically presenting with an elevated cobalt-to-chromium ratio and adverse local tissue reactions. The use of large-diameter, heavy CoCr heads on titanium tapers significantly increases this risk.

Question 34

During acetabular component fixation in total hip arthroplasty, screw placement in the anterosuperior quadrant places which of the following structures at greatest risk of injury?

Explanation

The anterosuperior quadrant is considered the "danger zone" because aberrant screw placement places the external iliac artery and vein at high risk. The safest region for screw placement is the posterosuperior quadrant, which has excellent bone stock and the lowest risk to neurovascular structures.

Question 35

A 40-year-old woman undergoes closed reduction and percutaneous pinning for a displaced femoral neck fracture. Which of the following factors is most predictive of subsequent osteonecrosis of the femoral head?

Explanation

The initial degree of displacement (Garden classification) is the most significant prognostic factor for the development of osteonecrosis after a femoral neck fracture. While an anatomic reduction is crucial to prevent nonunion, initial vascular disruption is tied directly to the trauma's severity.

Question 36

Which of the following nerves is at greatest risk of injury during a direct lateral (Hardinge) approach to the hip?

Explanation

The superior gluteal nerve innervates the gluteus medius, minimus, and tensor fasciae latae. Proximal splitting of the gluteus medius during the direct lateral approach beyond 3 to 5 cm from the greater trochanter places this nerve at significant risk for denervation.

Question 37

A 78-year-old woman presents with thigh pain and inability to bear weight after a mechanical fall. Radiographs demonstrate a fracture around her cemented femoral stem just distal to the lesser trochanter. The stem has subsided 1.5 cm and there is a visible cement mantle fracture. What is the most appropriate surgical treatment?

Explanation

This is a Vancouver B2 periprosthetic fracture, defined as a fracture around the stem with a loose implant but good bone stock. The standard treatment is revision of the femoral component using a long cementless stem that bypasses the fracture by at least two cortical diameters.

Question 38

A patient experiences recurrent posterior dislocations after a total hip arthroplasty. Radiographs and CT scans reveal the acetabular component is placed in 10 degrees of anteversion and 35 degrees of inclination. The femoral stem is in 15 degrees of anteversion. What is the most appropriate definitive management?

Explanation

Recurrent posterior instability is commonly caused by inadequate combined anteversion. Normal acetabular anteversion is 15-20 degrees; revising the under-anteverted cup will correct the underlying mechanical cause of the posterior dislocations.

Question 39

During a primary total knee arthroplasty, the trial components are evaluated. The knee is tight in both flexion and extension. What is the most appropriate next step to balance the gaps?

Explanation

When the knee is symmetrically tight in both flexion and extension, the tibial component (or polyethylene insert) is the common denominator. Decreasing the thickness of the polyethylene insert will equally increase both the flexion and extension gaps.

Question 40

In an active, community-dwelling 70-year-old patient with a displaced femoral neck fracture, what is the primary advantage of total hip arthroplasty (THA) over bipolar hemiarthroplasty?

Explanation

THA provides superior long-term functional outcomes and eliminates the risk of acetabular cartilage wear (erosion) and subsequent groin pain compared to hemiarthroplasty in active, older patients. However, THA does carry a higher risk of postoperative dislocation.

Question 41

What is the predominant blood supply to the adult femoral head?

Explanation

The medial femoral circumflex artery (MFCA), specifically its lateral epiphyseal branches, provides the predominant blood supply to the adult femoral head. Injury to this vessel during trauma or surgery significantly increases the risk of avascular necrosis.

Question 42

According to the AAOS clinical practice guidelines on venous thromboembolic disease prophylaxis after elective total hip arthroplasty, which of the following regimens is recommended for patients with standard risk profiles?

Explanation

Current AAOS guidelines support the use of pharmacologic agents, such as aspirin, combined with mechanical compressive devices for VTE prophylaxis in standard-risk patients undergoing elective THA. This balances efficacy in preventing DVT/PE with a lower risk of bleeding complications.

Question 43

A 72-year-old woman sustains a fall. Radiographs reveal a displaced femoral neck fracture.

She is an active community ambulator and cognitively intact. Which of the following treatments provides the lowest rate of reoperation?

Explanation

In an active, cognitively intact elderly patient with a displaced femoral neck fracture, total hip arthroplasty provides better functional outcomes and lower reoperation rates compared to internal fixation or hemiarthroplasty. Hemiarthroplasty carries a higher risk of acetabular wear and subsequent revision.

Question 44

A 68-year-old man presents with an unstable intertrochanteric femur fracture.

A cephalomedullary nail is planned. To minimize the risk of hardware cut-out, what is the ideal tip-apex distance (TAD)?

Explanation

A tip-apex distance (TAD) of less than 25 mm is the most critical biomechanical and radiographic factor in preventing lag screw cut-out. This rule applies to both sliding hip screws and cephalomedullary nails used for intertrochanteric fractures.

Question 45

During a direct anterior approach for a total hip arthroplasty, the surgeon dissects between the tensor fasciae latae and the sartorius. Which of the following nerves is at greatest risk of injury during this superficial dissection?

Explanation

The lateral femoral cutaneous nerve courses anteriorly over the sartorius and is at significant risk of injury during the superficial internervous plane of the direct anterior approach (Smith-Petersen). Injury can lead to meralgia paresthetica.

Question 46

An 80-year-old woman with a history of severe osteoporosis undergoes a cemented total hip arthroplasty. During cement pressurization and stem insertion, her blood pressure drops precipitously. What is the primary pathophysiologic mechanism for bone cement implantation syndrome (BCIS)?

Explanation

Bone cement implantation syndrome is primarily caused by fat, marrow, and air embolization to the pulmonary circulation during intramedullary pressurization. This shower of emboli leads to increased pulmonary vascular resistance and subsequent right ventricular failure.

Question 47

A 55-year-old woman presents with persistent anterior groin pain one year after a primary total hip arthroplasty. The pain is exacerbated by rising from a seated position and active straight leg raising. Radiographs demonstrate the acetabular component is placed in 15 degrees of anteversion, but the anterior edge extends 8 mm beyond the native anterior acetabular rim. What is the most likely diagnosis?

Explanation

Iliopsoas impingement commonly presents as anterior groin pain exacerbated by active straight leg raise or resisted hip flexion. An oversized or malpositioned acetabular component overhanging the anterior rim mechanically irritates the psoas tendon.

Question 48

A 30-year-old male sustains a high-energy Pauwels type III (vertical) femoral neck fracture. He is medically stable. Which of the following biomechanical constructs provides the most stable fixation for this specific fracture pattern?

Explanation

Pauwels type III (vertical) fractures experience high shear forces and have higher failure rates with traditional cannulated screws. A sliding hip screw combined with a derotational screw provides superior biomechanical stability and higher loads to failure for highly vertical femoral neck fractures.

Question 49

A 75-year-old patient falls and sustains a periprosthetic femur fracture around a fully porous-coated cementless stem.

Radiographs show a fracture at the tip of the stem. The stem is definitively loose, but there is excellent proximal bone stock. According to the Vancouver classification, what is the fracture subtype and optimal treatment?

Explanation

A Vancouver B2 fracture occurs around or just below the stem tip with a loose implant but adequate bone stock. The standard treatment is bypass of the fracture by at least two cortical diameters using a longer fully porous-coated or fluted tapered cementless stem.

Question 50

A 65-year-old man is scheduled for primary total hip arthroplasty. He is healthy with no history of prior DVT, pulmonary embolism, or bleeding disorders. According to the latest AAOS guidelines, what is the most appropriate routine venous thromboembolism (VTE) prophylaxis postoperatively?

Explanation

Recent AAOS guidelines and consensus statements support the use of Aspirin for routine VTE prophylaxis in standard-risk patients undergoing elective total joint arthroplasty. It is highly effective and significantly reduces the risk of major bleeding compared to stronger anticoagulants.

Question 51

A patient with a metal-on-metal total hip arthroplasty presents with increasing pain and a large, sterile fluid collection around the hip. MRI with metal artifact reduction shows a solid and cystic mass. A biopsy is obtained. What is the most likely histologic finding of the periprosthetic tissue?

Explanation

Adverse local tissue reactions (ALTR) or pseudotumors in metal-on-metal hips are histologically characterized by an aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL). This represents a delayed type IV hypersensitivity response to metal ions.

Question 52

During a posterior approach to the hip for total hip arthroplasty, the short external rotators are detached. The primary blood supply to the native adult femoral head, which is sacrificed during the femoral neck osteotomy, arises from which of the following vessels?

Explanation

The medial femoral circumflex artery (MFCA) provides the predominant blood supply to the adult femoral head via the lateral epiphyseal vessels. It courses posterior to the obturator externus and is at risk during the posterior approach.

Question 53

A 65-year-old man sustains recurrent posterior dislocations following a primary total hip arthroplasty. Radiographs demonstrate an acetabular component in 10 degrees of retroversion and 40 degrees of abduction. Which of the following is the most appropriate definitive management?

Explanation

Posterior instability due to a retroverted acetabular cup requires revision to correct the malposition. A constrained liner or larger head does not correct the underlying mechanical malalignment and will likely fail.

Question 54

A 25-year-old man sustains a vertically oriented (Pauwels type III) femoral neck fracture. Biomechanical studies indicate which of the following constructs provides the greatest stability against shear forces for this fracture pattern?

Explanation

Pauwels type III fractures have high shear forces. A fixed-angle device, such as a sliding hip screw with a derotation screw, provides superior biomechanical stability compared to multiple cancellous screws.

Question 55

A 78-year-old woman with an intertrochanteric hip fracture is found to have a highly comminuted lateral wall on pre-operative imaging. Which fixation method is most appropriate?

Explanation

An intact lateral wall is critical for the success of a sliding hip screw. When the lateral wall is comminuted or fractured, a cephalomedullary nail is indicated to prevent excessive lateral slide and medialization of the femoral shaft.

Question 56

In a direct anterior approach for total hip arthroplasty, the superficial internervous plane is utilized. Which two nerves supply the muscles defining this plane?

Explanation

The direct anterior (Smith-Petersen) approach exploits the internervous plane between the sartorius (femoral nerve) and the tensor fasciae latae (superior gluteal nerve).

Question 57

A 70-year-old man presents with a Vancouver B2 periprosthetic femur fracture 10 years after a cemented total hip arthroplasty. The fracture is located around the tip of the stem, and the stem is demonstrably loose. What is the recommended treatment?

Explanation

Vancouver B2 fractures involve a loose stem with adequate distal bone stock. The standard of care is revision arthroplasty utilizing a long cementless stem that bypasses the fracture by at least two cortical diameters, often supplemented with cerclage wiring.

Question 58

A 25-year-old man sustains a completely displaced, vertically oriented femoral neck fracture (Pauwels type III). Which of the following fixation constructs offers the highest biomechanical stability for this specific fracture pattern?

Explanation

For high-shear, vertically oriented (Pauwels type III) femoral neck fractures in young adults, a sliding hip screw with a derotation screw provides superior biomechanical stability. It better resists vertical shear forces compared to three parallel cancellous screws.

Question 59

A 72-year-old woman sustains the fracture shown in the radiograph, characterized as a reverse obliquity intertrochanteric fracture. What is the most appropriate definitive management?

Explanation

Reverse obliquity intertrochanteric fractures are mechanically unstable due to the tendency of the shaft to displace medially. A cephalomedullary nail is biomechanically superior to a sliding hip screw, which has an unacceptably high failure rate for this pattern.

Question 60

A 68-year-old man presents with a painful THA 4 years postoperatively. Synovial fluid analysis reveals a WBC count of 4,500 cells/uL with 85% neutrophils. What is the next most appropriate step in management if a chronic periprosthetic joint infection is confirmed?

Explanation

For chronic periprosthetic joint infections in North America, the gold standard treatment remains a two-stage exchange arthroplasty. Debridement, antibiotics, and implant retention (DAIR) is generally reserved for acute infections (within 4 weeks of surgery or acute hematogenous spread).

Question 61

An 81-year-old woman sustains a periprosthetic fracture around her cementless THA stem. Radiographs show a fracture extending just distal to the stem tip with evidence of stem subsidence and loosening. Based on the Vancouver classification, what is the most appropriate treatment?

Explanation

This is a Vancouver B2 fracture (loose stem with adequate surrounding bone stock). The standard of care is revision arthroplasty using a long, diaphyseal-fitting stem bypassing the fracture by at least two cortical diameters, combined with ORIF.

Question 62

A patient experiences recurrent posterior dislocations of their THA. The acetabular component is evaluated on CT scan and found to be placed in 5 degrees of anteversion and 30 degrees of abduction. Which parameter falls outside the traditional Lewinnek safe zone and is contributing most to the instability?

Explanation

The traditional Lewinnek safe zone for acetabular cup placement is 15 +/- 10 degrees of anteversion and 40 +/- 10 degrees of inclination (abduction). The 5 degrees of anteversion in this patient is too low and strongly contributes to posterior instability.

Question 63

What is the primary biological mechanism responsible for the aseptic loosening and osteolysis commonly seen in older generation polyethylene total hip replacements?

Explanation

Submicron polyethylene wear particles are phagocytosed by local tissue macrophages. This triggers the release of pro-inflammatory cytokines (such as TNF-alpha, IL-1, and IL-6) that activate osteoclasts, ultimately leading to periprosthetic osteolysis.

Question 64

A 55-year-old man with a metal-on-metal THA presents with groin pain and a palpable mass. Serum cobalt and chromium levels are elevated. MARS MRI demonstrates a large solid and cystic mass. What is the most characteristic histological finding of the periprosthetic tissue in this scenario?

Explanation

Adverse local tissue reaction (ALTR) in metal-on-metal hips is histologically characterized by an aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL). This represents a delayed cell-mediated (Type IV) hypersensitivity response to metal ions.

Question 65

A 70-year-old woman on long-term alendronate therapy reports a 3-month history of vague thigh pain. Radiographs reveal lateral cortical thickening and a transverse radiolucent line in the subtrochanteric region. What is the most appropriate prophylactic surgical management for this impending fracture?

Explanation

For impending atypical femoral fractures associated with prolonged bisphosphonate use (manifesting as lateral thigh pain and cortical beaking/radiolucency), prophylactic fixation with a cephalomedullary nail is recommended. The bisphosphonate should also be immediately discontinued.

Question 66

Medical optimization and surgical treatment of an acute hip fracture in a geriatric patient should ideally be completed within what timeframe to most significantly reduce 30-day and 1-year mortality rates?

Explanation

Extensive literature and current AAOS guidelines strongly support that surgical fixation of geriatric hip fractures within 48 hours significantly decreases mortality, complication rates, and length of hospital stay.

Question 67

A 45-year-old active male is undergoing a THA. The surgeon selects a ceramic-on-ceramic bearing surface. What is the most commonly reported specific complication associated with this bearing coupling compared to other options?

Explanation

Ceramic-on-ceramic bearings offer excellent wear properties and no risk of ALTR, making them suitable for young patients. However, they carry unique risks including catastrophic component fracture and audible "squeaking" during movement in up to 10% of patients.

Question 68

During the insertion of a cemented femoral stem for a femoral neck fracture, the patient develops sudden hypoxia, hypotension, and right heart strain. What is the most important step a surgeon can take during canal preparation to minimize the risk of this specific complication?

Explanation

Bone cement implantation syndrome (BCIS) is caused by the embolization of marrow fat and debris due to increased intramedullary pressure. Copious pulsatile lavage, drying the canal, and using a distal restrictor help reduce this pressure and embolization risk.

Question 69

Following a primary THA using a posterior approach, a patient exhibits a foot drop and inability to extend the great toe. Which specific portion of the sciatic nerve is most vulnerable to injury during this procedure?

Explanation

The common peroneal division of the sciatic nerve is much more susceptible to stretch and retractor injury during a posterior THA. This is due to its more lateral, superficial anatomical location and its fixed tethering distally at the fibular head.

Question 70

A 65-year-old man with a history of hypertrophic osteoarthritis and prior contralateral heterotopic ossification (HO) undergoes a THA. What is the most appropriate prophylactic regimen to prevent recurrence of HO in this high-risk patient?

Explanation

Patients at high risk for heterotopic ossification (e.g., prior HO, ankylosing spondylitis, hypertrophic OA) should receive prophylaxis. Effective options include a single dose of localized radiation therapy (700-800 cGy) within 48 hours postoperatively or oral indomethacin.

Question 71

A patient complains of groin pain starting 3 months after a cementless THA. The pain is worst when rising from a seated position. Examination shows pain with active hip flexion against resistance. Radiographs demonstrate an acetabular component in 10 degrees of retroversion with an overhanging anterior edge. What is the most likely diagnosis?

Explanation

Iliopsoas impingement classically presents as groin pain reproduced by active hip flexion or a straight leg raise. It is commonly associated with an oversized, retroverted, or proud anterior acetabular component mechanically irritating the overlying psoas tendon.

Question 72

A 72-year-old woman with a prior multi-level lumbar spinal fusion (L2-Pelvis) is planned for a THA. How does her spinal fusion alter her spinopelvic mechanics, and what intraoperative adjustment should be considered?

Explanation

Patients with lumbar fusions to the pelvis have a "stiff" spine and lack the normal posterior pelvic tilt that accommodates hip flexion when sitting. This limits functional cup anteversion, increasing the risk of posterior impingement and posterior dislocation, thereby requiring the surgeon to target increased operative cup anteversion.

Question 73

A 28-year-old male sustains a displaced femoral neck fracture in a motor vehicle collision. He is hemodynamically stable. What is the most appropriate surgical management to minimize the risk of avascular necrosis and nonunion?

Explanation

In a young patient with a displaced femoral neck fracture, urgent open reduction and internal fixation is indicated to achieve an anatomic reduction. This reduces the risk of nonunion and avascular necrosis.

Question 74

A 75-year-old female presents with an intertrochanteric femur fracture. Radiographs demonstrate an intact posteromedial cortex but a lateral wall thickness of 18 mm. Which of the following is the most appropriate implant choice to minimize the risk of construct failure?

Explanation

A lateral wall thickness of less than 20.5 mm in an intertrochanteric fracture is a strong predictor for lateral wall fracture during surgery. A cephalomedullary nail is preferred over a sliding hip screw to prevent excessive collapse and construct failure.

Question 75

A 65-year-old male complains of recurrent posterior dislocations following a primary total hip arthroplasty performed via a posterior approach. Radiographs show the acetabular cup is placed in 40 degrees of abduction and 0 degrees of anteversion. What is the most appropriate definitive management?

Explanation

The acetabular cup is retroverted (0 degrees of anteversion), which strongly predisposes the patient to posterior dislocation. The most appropriate definitive treatment is revision of the cup to achieve the safe zone of 15-20 degrees of anteversion.

Question 76

A 68-year-old woman with a 10-year history of alendronate use presents with thigh pain and sustains a low-energy subtrochanteric femur fracture. Radiographs reveal a transverse fracture with lateral cortical beaking. Which of the following surgical principles is critical in her management?

Explanation

Atypical femur fractures associated with bisphosphonate use typically have poor bone healing due to suppressed remodeling. A full-length cephalomedullary nail after reaming is recommended to protect the entire femur and provide stable fixation.

Question 77

A 70-year-old male presents with a painful total hip arthroplasty that has been symptomatic for 18 months. Aspiration reveals 45,000 WBC/mcL with 90% polymorphonuclear cells. Radiographs show circumferential radiolucencies around a loose femoral stem. What is the gold standard surgical management?

Explanation

This is a chronic periprosthetic joint infection (symptoms > 4 weeks). The gold standard treatment in North America is a two-stage revision arthroplasty involving implant removal, antibiotic spacer placement, and delayed reimplantation.

Question 78

A 74-year-old woman sustains a fall around her cemented total hip arthroplasty.

Radiographs demonstrate a periprosthetic fracture around a loose femoral stem, but the proximal femur bone stock remains adequate. According to the Vancouver classification, what is the most appropriate surgical treatment?

Explanation

A Vancouver B2 fracture is characterized by a fracture around a loose stem with adequate remaining bone stock. The standard of care is revision arthroplasty using a long, porous-coated or fluted tapered stem to bypass the fracture.

Question 79

During a direct anterior approach for a total hip arthroplasty, the surgeon utilizes the internervous plane between which of the following muscles?

Explanation

The direct anterior approach (Smith-Petersen) utilizes the true internervous plane between the sartorius (femoral nerve) and the tensor fascia lata (superior gluteal nerve).

Question 80

What is the primary clinical advantage of utilizing highly cross-linked polyethylene (HXLPE) compared to conventional polyethylene in total hip arthroplasty?

Explanation

Highly cross-linked polyethylene significantly decreases volumetric wear and subsequent osteolysis. However, the cross-linking process reduces mechanical strength and resistance to fatigue crack propagation.

Question 81

Current evidence suggests that in elderly patients undergoing hemiarthroplasty for a displaced femoral neck fracture, the use of a cemented femoral stem compared to an uncemented stem is associated with which of the following?

Explanation

Cemented stems in elderly hemiarthroplasty patients have a significantly lower risk of postoperative periprosthetic fractures compared to uncemented stems. While there is a risk of bone cement implantation syndrome, overall survival rates remain comparable.

Question 82

A 60-year-old male with a metal-on-metal total hip arthroplasty presents with increasing groin pain. MRI reveals a large, thick-walled cystic mass. Serum cobalt and chromium levels are significantly elevated. The pathogenesis of this complication is best described as:

Explanation

Adverse local tissue reactions (ALTR) or pseudotumors in metal-on-metal hips are primarily mediated by a Type IV delayed-type hypersensitivity reaction to metal ions (cobalt and chromium).

Question 83

A 52-year-old female complains of a high-pitched squeaking noise coming from her total hip arthroplasty during ambulation. The implant is a ceramic-on-ceramic bearing. Which of the following is the most significant risk factor for this phenomenon?

Explanation

Squeaking in ceramic-on-ceramic THA is heavily correlated with edge loading. This is typically caused by malpositioning of the acetabular cup (steep abduction or inadequate anteversion), microseparation, or impingement.

Question 84

Trunnionosis, or mechanically assisted crevice corrosion, has emerged as a significant mode of failure in modern total hip arthroplasties. Which of the following implant characteristics most increases the risk of this complication?

Explanation

Trunnionosis is associated with large diameter metal heads on small taper trunnions. The larger head increases the lever arm and frictional torque at the head-neck junction, accelerating fretting and corrosion.

Question 85

The main blood supply to the adult femoral head is the lateral epiphyseal artery. This artery is a terminal branch of which of the following vessels?

Explanation

The medial femoral circumflex artery (MFCA) provides the primary blood supply to the adult femoral head via its terminal branches, the lateral epiphyseal arteries.

Question 86

A 55-year-old male complains of numbness and burning over the anterolateral aspect of his thigh following a primary total hip arthroplasty. Which surgical approach was most likely utilized?

Explanation

The lateral femoral cutaneous nerve (LFCN) is at risk during the direct anterior approach to the hip. Injury results in meralgia paresthetica, characterized by numbness or burning in the anterolateral thigh.

Question 87

A 68-year-old female presents with persistent anterior groin pain 6 months after a total hip arthroplasty. The pain is exacerbated by active straight leg raising and getting out of a car. Radiographs reveal the acetabular cup is in 45 degrees of abduction and 20 degrees of anteversion, with slight anterior overhang. What is the most appropriate initial management?

Explanation

The clinical presentation is classic for iliopsoas impingement over a prominent anterior acetabular rim. Initial management should be non-operative, consisting of physical therapy and image-guided corticosteroid injections.

Question 88

During a total hip arthroplasty via a posterior approach, the surgeon meticulously repairs the short external rotators and the posterior capsule to the greater trochanter. What is the primary established clinical benefit of this step?

Explanation

Repair of the posterior capsule and short external rotators (piriformis, obturator internus) significantly reduces the rate of posterior dislocation following THA performed via a posterior approach.

Question 89

A 78-year-old male with multiple medical comorbidities sustains a displaced femoral neck fracture. When counseling the family regarding prognosis, what is the approximate expected 1-year mortality rate for patients over age 65 following a hip fracture?

Explanation

The 1-year mortality rate following a hip fracture in the elderly population is consistently reported in the literature to be between 20% and 30%, largely driven by underlying medical comorbidities.

Question 90

A 72-year-old male with an intertrochanteric femur fracture is treated with a sliding hip screw (DHS). Three months postoperatively, radiographs show cutout of the lag screw through the superior femoral head. Which of the following technical factors is most highly associated with this mode of failure?

Explanation

Baumgaertner et al. demonstrated that a Tip-Apex Distance (TAD) greater than 25 mm is the strongest predictor of lag screw cutout in the treatment of intertrochanteric fractures.

Question 91

A patient requires a revision total hip arthroplasty for massive osteolysis. Preoperative planning suspects pelvic discontinuity. Which of the following radiographic findings is most characteristic of this condition?

Explanation

Pelvic discontinuity is a distinct fracture through the acetabulum separating the superior pelvis (ilium) from the inferior pelvis (ischium and pubis). It is radiographically identified by a transverse lucent line and medial translation of the inferior segment.

Question 92

During surgical fixation of a displaced femoral neck fracture with three cannulated screws, an inverted triangle configuration is utilized. What is the primary biomechanical rationale for placing the inferior screw closely adjacent to the calcar?

Explanation

The inferior screw in the inverted triangle construct should rest on or be immediately adjacent to the calcar (inferior femoral neck cortex) to provide crucial cortical support, which maximizes resistance to varus collapse.

Question 93

A 55-year-old highly active man is undergoing a total hip arthroplasty (THA). He is particularly concerned about the longevity of the implants and volumetric wear. Which of the following bearing surface combinations is biomechanically proven to have the lowest volumetric wear rate?

Explanation

Ceramic-on-ceramic bearing surfaces exhibit the lowest volumetric wear rates of all current THA bearing couples. However, they carry specific clinical risks such as audible squeaking and catastrophic component fracture that must be discussed with the patient.

Question 94

A 72-year-old woman sustains a reverse obliquity intertrochanteric femur fracture (OTA 31-A3). Based on current biomechanical studies and clinical evidence, which of the following constructs provides the most stable fixation with the lowest rate of hardware failure?

Explanation

Reverse obliquity fractures are highly unstable and have high failure rates with sliding hip screws because the fracture line is parallel to the trajectory of the sliding screw. Cephalomedullary nails provide superior biomechanical stability by medially displacing the weight-bearing axis and limiting medial shaft displacement.

Question 95

A 68-year-old man presents with his third posterior dislocation of a primary THA performed 4 months ago. Radiographs demonstrate the acetabular component is in 35 degrees of abduction and 5 degrees of retroversion. The femoral stem is stable and in neutral version. What is the most appropriate definitive management?

Explanation

The acetabular component is retroverted, which mechanically predisposes the patient to posterior impingement and instability. Revision of the malpositioned acetabular component to an ideal 15-20 degrees of anteversion directly addresses the root cause of the recurrent dislocations.

Question 96

A 32-year-old man sustains a completely displaced, vertically oriented femoral neck fracture (Pauwels Type III). What is the optimal fixation construct to minimize the risk of varus collapse, shear failure, and nonunion?

Explanation

Pauwels Type III fractures experience extremely high shear forces, frequently leading to varus collapse and nonunion when treated with simple parallel screws. A sliding hip screw, supplemented with a derotational cancellous screw, provides superior biomechanical resistance against these vertical shear forces.

Question 97

During a direct anterior approach for total hip arthroplasty, the surgeon dissects between the sartorius and the tensor fasciae latae. Which of the following neurologic structures is at highest risk of iatrogenic injury during the exposure of this specific internervous interval?

Explanation

The direct anterior approach utilizes the internervous plane between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve). The lateral femoral cutaneous nerve courses superficially across this operative field and is highly vulnerable to traction or direct transection injury.

Question 98

A 65-year-old woman presents with worsening right hip pain 2 years after a primary THA. Her inflammatory markers are elevated (ESR 45 mm/hr, CRP 3.2 mg/dL). Synovial fluid aspiration reveals a WBC count of 3,500 cells/uL with 75% PMNs. Which of the following synovial fluid biomarkers has the highest specificity for confirming a periprosthetic joint infection?

Explanation

Alpha-defensin is an antimicrobial peptide released by neutrophils and has demonstrated exceptionally high specificity (often >95%) for diagnosing periprosthetic joint infections. Its diagnostic accuracy is notably less affected by prior antibiotic administration than traditional culture methods.

Question 99

During a posterior approach THA, trial reduction reveals that the leg is lengthened by 1.5 cm and the offset is decreased by 1 cm compared to the preoperative template. Shuck testing shows significant soft tissue laxity. Which modular adjustment will best restore proper offset and soft tissue tension while minimizing further leg lengthening?

Explanation

A high-offset stem increases femoral offset (tensioning the abductors) without vertically lengthening the leg. Combining a high-offset stem with a shorter femoral head will appropriately restore the necessary offset while reducing the excessive leg length noted on the trial.

Question 100

A 68-year-old woman on long-term alendronate for osteoporosis presents with a 3-month history of prodromal anterior thigh pain.

Radiographs demonstrate a transverse, nondisplaced radiolucency in the lateral cortex of the subtrochanteric region with localized periosteal "beaking." What is the most appropriate next step in management?

Explanation

The patient exhibits classic clinical and radiographic signs of an impending atypical femoral fracture secondary to prolonged bisphosphonate therapy. Given the presence of prodromal thigh pain and cortical beaking, prophylactic cephalomedullary nailing is indicated to prevent catastrophic completion of the fracture.

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

AAOS & ABOS Orthopedic MCQs (Set 2): Hip Fractures & Arthroplasty | Board Prep

Key Takeaway

AAOS & ABOS Orthopedic MCQs (Set 2): Hip Fractures & Arthroplasty | Board Prep

Chapter Index