Orthopedic Board MCQs: Arthroplasty & Osteoporosis

Question 1

Which factor is most highly associated with the clinical phenomenon of 'squeaking' in a ceramic-on-ceramic total hip arthroplasty?

Explanation

Squeaking in ceramic-on-ceramic THA is highly associated with edge loading, which typically results from component malposition (such as excessive acetabular cup inclination or anteversion outliers). Edge loading causes a loss of fluid film lubrication and stripe wear, ultimately leading to audible squeaking.

Question 2

A 68-year-old female complains of instability particularly when descending stairs 1 year following a primary total knee arthroplasty. On examination, her knee is completely stable in full extension, but demonstrates 15 degrees of varus/valgus laxity at 90 degrees of flexion. Which intraoperative technical error most likely caused this specific pattern of instability?

Explanation

The patient presents with flexion instability (a loose flexion gap with a stable extension gap). This is classically caused by over-resection of the posterior femoral condyles, undersizing the femoral component in the anteroposterior plane, or excessive posterior slope of the tibial cut.

Question 3

A 72-year-old female with severe osteoporosis has a T-score of -3.5 and a recent fragility fracture of the lumbar spine. Her endocrinologist recommends romosozumab. What is the primary mechanism of action of this medication?

Explanation

Romosozumab is a humanized monoclonal antibody that targets and inhibits sclerostin. By inhibiting sclerostin, it produces a dual effect: it increases osteoblastic bone formation while simultaneously decreasing osteoclastic bone resorption, making it highly effective for severe osteoporosis.

Question 4

A 65-year-old male, 3 weeks status-post primary THA, presents with 3 days of increasing hip pain, erythema, and drainage from the incision. His CRP is 150 mg/L. Aspiration reveals an elevated WBC count with 95% PMNs. Radiographs show stable, well-fixed implants. What is the most appropriate management?

Explanation

DAIR is indicated for early postoperative periprosthetic joint infections (typically defined as < 4 weeks from the index surgery) or acute hematogenous infections (< 3 weeks of symptoms) when the implants are radiographically stable and the soft-tissue envelope is adequate. Exchanging modular components (e.g., femoral head and polyethylene liner) is critical to reduce the biofilm burden.

Question 5

Which design modification in posterior-stabilized (PS) total knee arthroplasty components has most significantly reduced the incidence of patellar clunk syndrome?

Explanation

Patellar clunk syndrome occurs primarily in posterior-stabilized (PS) knees due to scar tissue formation in the superior pole of the patella catching in the intercondylar notch. Modern femoral component designs have largely mitigated this by lowering the profile of the intercondylar box, smoothing the transition, and lengthening the trochlear groove.

Question 6

A 65-year-old female on alendronate for 8 years presents with progressive, activity-related lateral thigh pain. Radiographs of the femur demonstrate lateral cortical thickening and a transverse, incomplete radiolucent line in the subtrochanteric region. What is the most appropriate next step in management?

Explanation

This patient has an impending atypical femur fracture (AFF) associated with long-term bisphosphonate use, characterized by clinical pain and radiographic evidence (lateral cortical beaking and a radiolucent line). Because she has pain and an incomplete fracture line, prophylactic surgical fixation (intramedullary nailing) is the standard of care to prevent a catastrophic complete fracture.

Question 7

During a total hip arthroplasty, the surgeon decides to switch from a standard neck stem (131-degree neck-shaft angle) to a high-offset stem (121-degree neck-shaft angle) of the exact same size. Assuming the depth of insertion remains identical, what is the primary biomechanical effect?

Explanation

Changing from a standard neck-shaft angle to a lower 'varus' angle (high-offset) stem directs the femoral head further laterally. This maneuver primarily increases the horizontal femoral offset without significantly changing the vertical leg length, allowing the surgeon to tension the abductors without lengthening the leg.

Question 8

In a kinematically aligned total knee arthroplasty compared to a traditional mechanically aligned TKA, the femoral component is typically placed in what position relative to the mechanical axis?

Explanation

Kinematic alignment aims to restore the pre-arthritic joint lines and the natural cylindrical axis of the knee. Because the normal native distal femur has about 3 degrees of joint line valgus (which equates to varus relative to the mechanical axis perpendicular cut) and less external rotation than classic mechanical alignment cuts, the component is placed in more varus and internal rotation compared to a strictly mechanically aligned knee.

Question 9

Which of the following laboratory profiles is most characteristic of severe osteomalacia, helping to differentiate it from primary postmenopausal osteoporosis?

Explanation

Osteomalacia is a defect in bone mineralization commonly caused by severe Vitamin D deficiency. It typically presents with low or low-normal serum calcium and phosphate, accompanied by elevated alkaline phosphatase and secondary hyperparathyroidism (elevated PTH). Primary osteoporosis features normal serum calcium, phosphate, and alkaline phosphatase.

Question 10

A 62-year-old male with a metal-on-polyethylene THA placed 8 years ago presents with new-onset hip pain and swelling. A large periarticular cystic mass is noted on MRI. Joint aspiration is negative for infection. Bloodwork shows a markedly elevated serum cobalt level with a normal chromium level. What is the most likely diagnosis?

Explanation

The clinical presentation describes trunnionosis, or mechanically assisted crevice corrosion (MACC), which occurs at the modular head-neck junction. It can happen even in metal-on-polyethylene bearings, particularly with large head sizes. It is characterized by adverse local tissue reactions (ALTR/pseudotumors) and elevated serum cobalt levels, often with a disproportionately high cobalt-to-chromium ratio.

Question 11

A 70-year-old female sustains a complete patellar tendon rupture 2 years after a primary TKA. She undergoes reconstruction using a full extensor mechanism allograft (tibial tubercle, patellar tendon, patella, and quadriceps tendon). To optimize outcomes and prevent a postoperative extensor lag, how should the allograft be tensioned during fixation?

Explanation

When using an extensor mechanism allograft for a disruption post-TKA, it is imperative to tension the graft very tightly in full extension. The graft inherently stretches out postoperatively, and any laxity introduced at the time of surgery will inevitably result in a permanent and debilitating extensor lag.

Question 12

The FRAX (Fracture Risk Assessment Tool) algorithm is used to calculate the 10-year probability of a major osteoporotic fracture. Which of the following is NOT included as a discrete risk factor variable in the FRAX tool?

Explanation

Despite a history of falls being one of the most significant clinical predictors of future fracture risk, it is notably absent from the FRAX algorithm. FRAX variables include age, sex, weight, height, prior fracture, parental hip fracture, current smoking, glucocorticoid use, rheumatoid arthritis, secondary osteoporosis, and excessive alcohol intake.

Question 13

A 79-year-old patient sustains a periprosthetic femur fracture around a cemented total hip arthroplasty stem. Radiographs demonstrate the fracture extending from the mid-stem to just distal to the tip. The stem is radiographically loose, but there is excellent proximal femoral bone stock. According to the Vancouver classification, what is the fracture type and appropriate treatment?

Explanation

A fracture around or just distal to the stem is a Vancouver Type B. Because the stem is loose but the proximal bone stock is adequate, it is classified as a Vancouver B2 fracture. The standard of care for a B2 fracture is revision arthroplasty utilizing a long stem (often uncemented, fluted, and tapered) that bypasses the fracture by at least two cortical diameters.

Question 14

A 74-year-old female on denosumab therapy for 5 years suddenly discontinues the medication due to a planned dental procedure. Eight months later, she presents with severe back pain, and radiographs reveal three new acute vertebral compression fractures. What is the primary pathophysiological mechanism for this rapid deterioration?

Explanation

Discontinuation of denosumab leads to a rapid 'rebound' effect characterized by an immense surge in osteoclastogenesis. The removal of the RANKL inhibitor allows unopposed RANKL to rapidly activate osteoclasts, leading to accelerated bone loss and a significantly increased risk of multiple vertebral compression fractures. A bisphosphonate must be administered when stopping denosumab to prevent this phenomenon.

Question 15

A 65-year-old male is 8 weeks post-uncomplicated primary TKA and complains of significant stiffness. His range of motion is 15 to 75 degrees despite excellent compliance with aggressive physical therapy. Radiographs confirm appropriate component sizing and alignment without loosening. What is the most appropriate next step in management?

Explanation

Manipulation under anesthesia (MUA) is the treatment of choice for post-TKA arthrofibrosis (stiffness) that has failed to improve with aggressive physical therapy. The optimal window for MUA is generally between 6 and 12 weeks postoperatively. Waiting beyond 12 weeks decreases the success rate and increases the risk of complications such as supracondylar femur fracture or extensor mechanism disruption during the manipulation.

Question 16

During a direct anterior approach (DAA) to the hip, a consistent crossing arterial branch is routinely encountered within the internervous plane and must be ligated to prevent postoperative hematoma. This vessel is a branch of which major artery?

Explanation

The ascending branches of the lateral femoral circumflex artery reliably cross the surgical field in the direct anterior approach (DAA) to the hip, specifically within the internervous plane between the tensor fasciae latae (superior gluteal n.) and the sartorius/rectus femoris (femoral n.). These vessels must be identified, cauterized, or ligated to prevent hematoma.

Question 17

When balancing a total knee arthroplasty in a patient with a severe fixed valgus deformity, isolated release or 'pie-crusting' of the iliotibial (IT) band will primarily affect which gap?

Explanation

The iliotibial (IT) band is a strong lateral structure that is tight in extension and relatively relaxed in flexion. Therefore, isolated release or pie-crusting of the IT band will primarily open the lateral extension gap, with minimal effect on the lateral flexion gap. To affect the lateral flexion gap, release of the popliteus tendon is required.

Question 18

What is the optimal timing for the first dose of zoledronic acid following surgical fixation of an osteoporotic hip fracture to maximize the reduction in mortality and subsequent fracture risk?

Explanation

The HORIZON Recurrent Fracture Trial demonstrated that administering zoledronic acid between 2 and 6 weeks postoperatively resulted in significant reductions in new clinical fractures and mortality. Administration within the first 2 weeks was less effective and did not show the same mortality benefit, likely due to interference with the early acute-phase reaction or early fracture healing physiology.

Question 19

A 78-year-old male with a history of recurrent posterior THA dislocations undergoes revision surgery. Intraoperative evaluation reveals an extremely deficient abductor mechanism. The acetabular shell is well-fixed and in appropriate anteversion and inclination. Which intervention will best restore stability in this patient?

Explanation

In the setting of severe abductor deficiency leading to recurrent instability where components are well-positioned, optimizing soft tissue tension is often impossible. Therefore, an implant with high intrinsic stability is required. A dual-mobility construct or a constrained acetabular liner is indicated. Dual-mobility is typically preferred due to a better range of motion and lower risk of mechanical failure.

Question 20

During a total knee arthroplasty, 'overstuffing' the patellofemoral joint by using a patellar component that is too thick can predictably lead to which of the following postoperative complications?

Explanation

Overstuffing the patellofemoral joint (restoring an anteroposterior dimension that is greater than the native patella) increases the tension on the extensor mechanism. This reliably leads to increased patellofemoral contact forces (presenting as anterior knee pain) and restricts terminal knee flexion due to early impingement and tightness of the quadriceps mechanism.

Question 21

A 68-year-old female with severe hip osteoarthritis and severe osteoporosis is scheduled for an elective total hip arthroplasty (THA). She is currently on denosumab therapy, receiving subcutaneous injections every 6 months. Her last injection was 3 months ago. What is the most appropriate recommendation regarding her denosumab therapy and the timing of surgery?

Explanation

Denosumab is a RANKL inhibitor with a rapid offset of action. Delaying a scheduled dose of denosumab by even 1 to 2 months past the 6-month window can lead to a rebound increase in bone turnover, resulting in a significantly elevated risk of multiple spontaneous vertebral fractures. Orthopedic and rheumatologic guidelines strongly recommend that elective surgeries be scheduled mid-cycle (e.g., month 3 or 4) to avoid missing a dose due to perioperative complications, and that the regular 6-month dosing interval be strictly maintained regardless of the surgical date.

Question 22

A 65-year-old female presents with anterior knee pain and a reproducible "popping" sensation when extending her knee from a flexed position. She underwent a primary total knee arthroplasty (TKA) 18 months ago. Examination reveals a palpable catch at approximately 30 to 45 degrees of flexion as the knee extends. Which of the following implant design features is most strongly associated with this specific complication?

Explanation

The patient's presentation is classic for "patellar clunk syndrome," which is predominantly associated with posterior-stabilized (PS) TKA designs. It occurs due to the formation of a fibrous nodule at the superior pole of the patella. As the knee extends from a flexed position (usually around 30-45 degrees), this nodule catches in the intercondylar box of the femoral component and then snaps out, causing a painful clunk. Implant designs with a high intercondylar box ratio (a sharp, anteriorly placed box) have historically demonstrated a higher incidence of this complication.

Question 23

A 70-year-old male presents with progressively worsening anterior groin pain 5 years after an uncomplicated primary THA. He has a highly cross-linked polyethylene liner, a 36-mm cobalt-chromium femoral head, and a titanium alloy femoral stem. Radiographs show a well-fixed stem and cup. An MRI with metal artifact reduction sequence (MARS) reveals a 4-cm cystic periarticular mass. Serological workup is notable for elevated cobalt levels and normal chromium levels. What is the primary pathophysiologic mechanism for this failure?

Explanation

The clinical picture describes trunnionosis (mechanically assisted crevice corrosion and fretting) at the modular head-neck junction. This is classically seen when a cobalt-chromium head is placed on a titanium stem, particularly with larger diameter heads (e.g., 36 mm or larger) which increase frictional torque on the trunnion. This process releases cobalt ions out of proportion to chromium ions (unlike metal-on-metal bearings where Co and Cr are elevated symmetrically), leading to an adverse local tissue reaction (ALTR) presenting as a cystic pseudotumor and groin pain.

Question 24

A 74-year-old female with severe postmenopausal osteoporosis is started on romosozumab. What is the specific mechanism of action of this medication?

Explanation

Romosozumab is a monoclonal antibody that binds to and inhibits sclerostin. Sclerostin (produced by osteocytes) normally inhibits the Wnt signaling pathway, decreasing osteoblastogenesis. By inhibiting sclerostin, romosozumab promotes Wnt signaling, resulting in a dual effect: substantially increasing bone formation (anabolic) while simultaneously decreasing bone resorption (antiresorptive). Bisphosphonates inhibit farnesyl pyrophosphate synthase; denosumab targets RANKL; calcimimetics target the calcium-sensing receptor; and raloxifene is a SERM.

Question 25

A 62-year-old male requires a THA for end-stage osteoarthritis. He has a history of an instrumented lumbar fusion from L2 to the sacrum. Given the stiffness in his lumbopelvic segment, how does his pelvic dynamics alter his risk profile, and how should the acetabular component positioning be adjusted?

Explanation

In a patient with a stiff lumbopelvic junction (e.g., L-spine fusion to the sacrum), the pelvis cannot dynamically adjust to position changes. Normally, when moving from a standing to a sitting position, the lumbar spine flexes and the pelvis tilts posteriorly, which functionally increases acetabular anteversion and clears the anterior acetabular rim from the proximal femur. A stiff spine prevents this posterior tilt, leaving the acetabulum functionally retroverted relative to the flexed femur. This leads to anterior impingement and an increased risk of posterior dislocation. To compensate, the surgeon should aim for increased operative anteversion and inclination.

Question 26

During trialing in a primary posterior-stabilized total knee arthroplasty utilizing a measured resection technique, the surgeon finds that the knee is well-balanced and fully extends to 0 degrees symmetrically. However, upon testing flexion, the joint is symmetrically tight at 90 degrees and cannot achieve full flexion. What is the most appropriate next step to balance the knee?

Explanation

An isolated tight flexion gap with a symmetric, well-balanced extension gap usually indicates that the anteroposterior (AP) dimension of the femoral component is too large, or the posterior tibial slope is inadequate. Decreasing the AP size of the femur (downsizing) utilizing an anterior referencing guide will selectively remove more posterior condylar bone, thereby enlarging the flexion gap without altering the extension gap. Upsizing or increasing the AP dimension would worsen the tightness. Changing the polyethylene thickness would affect both gaps equally. Distal femoral resection affects only the extension gap.

Question 27

A 75-year-old female presents with an atraumatic dull ache in her left thigh. She has been taking alendronate for 9 years for osteoporosis. Plain radiographs of the left femur reveal localized lateral cortical thickening in the subtrochanteric region with a subtle transverse radiolucent line, consistent with an incomplete atypical femur fracture (AFF). What is the most critical next step in her imaging workup?

Explanation

Atypical femur fractures (AFFs) are strongly associated with prolonged bisphosphonate use (usually >5 years) due to severe suppression of bone turnover. They characteristically present with an insidious onset of thigh pain and characteristic radiographic features (transverse fracture pattern originating at the lateral cortex, focal lateral cortical thickening/beaking, medial spiking). AFFs are frequently bilateral (occurring in up to 28-60% of cases). Therefore, whenever an AFF is identified, it is critical to obtain full-length radiographs of the contralateral femur to evaluate for an asymptomatic or symptomatic contralateral impending fracture.

Question 28

Which of the following physical examination or radiographic findings is considered a strict contraindication to performing a medial unicompartmental knee arthroplasty (UKA) using standard traditional criteria?

Explanation

According to the classic Kozinn and Scott criteria for unicompartmental knee arthroplasty (UKA), absolute contraindications include inflammatory arthropathy, fixed varus deformity > 15 degrees, fixed valgus deformity > 20 degrees, flexion contracture > 15 degrees, and ACL deficiency (though modern criteria with fixed-bearing designs have challenged the ACL deficiency rule). A flexion contracture of 20 degrees exceeds the accepted threshold and requires a total knee arthroplasty (TKA) for adequate soft tissue balancing and bone resection.

Question 29

Based on the 2018 International Consensus Meeting (ICM) criteria for Periprosthetic Joint Infection (PJI), which of the following findings is considered a definitive "Major Criteria," establishing the diagnosis of PJI independently?

Explanation

The 2018 ICM criteria dictate that the presence of either of two Major Criteria definitively establishes the diagnosis of PJI. These are: 1) Two positive periprosthetic cultures with phenotypically identical organisms, or 2) A sinus tract communicating with the joint or visualizing the prosthesis. The other options (elevated synovial WBC, positive alpha-defensin, single positive culture, elevated CRP/D-dimer) are minor criteria that contribute to an aggregate scoring system but do not diagnose PJI independently.

Question 30

During a revision total knee arthroplasty, the surgeon encounters massive metaphyseal bone loss on both the femoral and tibial sides. Furthermore, the medial collateral ligament (MCL) epicondylar origin has been completely compromised by the osteolysis. According to the Anderson Orthopaedic Research Institute (AORI) classification, this is a Type III defect. What is the most appropriate reconstructive strategy?

Explanation

AORI Type III bone defects are defined by severe bone loss that compromises a major portion of the condyles/metaphysis and is occasionally accompanied by collateral ligament detachment or complete structural incompetence. In revision TKA where the MCL or LCL is absent or non-functional, an unlinked constrained device (like CCK) cannot provide adequate coronal stability. A linked, rotating hinge knee (RHK) prosthesis with long diaphyseal engaging stems is required to substitute for the global ligamentous incompetence and provide intrinsic stability.

Question 31

Bisphosphonates are the most commonly prescribed first-line therapy for osteoporosis. By which of the following specific cellular mechanisms do nitrogen-containing bisphosphonates (e.g., alendronate) primarily exert their antiresorptive effect?

Explanation

Nitrogen-containing bisphosphonates (like alendronate, zoledronic acid, and risedronate) are internalized by osteoclasts and inhibit farnesyl pyrophosphate (FPP) synthase, a key enzyme in the mevalonate pathway. This prevents the prenylation of small GTPase proteins (such as Ras, Rho, and Rab) which are essential for osteoclast function, ruffled border formation, and cell survival, ultimately leading to osteoclast apoptosis.

Question 32

The Fracture Risk Assessment Tool (FRAX) is widely used to calculate the 10-year probability of a major osteoporotic fracture and a hip fracture. Which of the following clinical variables is NOT included in the FRAX calculation model?

Explanation

The FRAX tool calculates a 10-year fracture risk based on clinical risk factors and femoral neck BMD. The specific clinical risk factors included are: Age, Sex, Weight, Height, Prior fracture, Parental history of hip fracture, Current smoking, Glucocorticoid use, Rheumatoid arthritis, Secondary osteoporosis, and Alcohol intake (>3 units/day). History of falls, despite being a major independent risk factor for fractures, is notably NOT included in the FRAX algorithm.

Question 33

A 78-year-old female sustains a periprosthetic femur fracture around her cemented total hip arthroplasty stem. Radiographs demonstrate a fracture located around the distal tip of the stem with extension into the diaphysis. The cement mantle is fractured, indicating a loose stem, and there is severe osteolysis and comminution of the proximal femur, leaving inadequate bone stock for proximal fixation. What is the correct Vancouver classification and the recommended treatment?

Explanation

The Vancouver classification for periprosthetic femur fractures relies on fracture location, stem stability, and bone stock. This fracture is at/around the stem (Type B). The stem is loose (rules out B1). The proximal bone stock is severely deficient/comminuted, making it a B3 fracture. The recommended treatment for a Vancouver B3 fracture in an elderly patient with poor bone stock is typically a proximal femoral replacement (megaprosthesis) to bypass the un-reconstructible proximal bone and allow for immediate weight-bearing.

Question 34

The direct anterior approach (DAA) to the hip utilizes the internervous plane between the tensor fasciae latae (TFL) and the sartorius. During the superficial dissection, careful retractor placement is necessary to avoid injury to a nerve that typically courses distally over the sartorius muscle. Which of the following nerves is at greatest risk during this part of the exposure?

Explanation

The direct anterior approach (Smith-Petersen) utilizes the internervous plane between the femoral nerve (sartorius, rectus femoris) and the superior gluteal nerve (TFL). During the superficial dissection, the lateral femoral cutaneous nerve (LFCN) is at significant risk as it typically exits the pelvis medial to the ASIS and courses distally over the sartorius muscle. Injury to the LFCN can lead to meralgia paresthetica (numbness, dysesthesia over the anterolateral thigh).

Question 35

A 65-year-old female with severe rheumatoid arthritis presents for a primary THA. Preoperative radiographs demonstrate severe protrusio acetabuli (Kohler's line is crossed by the femoral head). When preparing the acetabulum during surgery, what is the most appropriate technique to achieve a stable, biomechanically sound reconstruction?

Explanation

In protrusio acetabuli, the center of rotation is pathologically medialized, and the medial wall is extremely thin or absent. The biomechanical goal of THA in this setting is to restore the normal, anatomic center of rotation by lateralizing the cup. This is achieved by reaming peripherally to achieve an interference rim fit on the strong peripheral bone, and using impaction bone grafting (autograft from the femoral head or allograft) to fill the medial defect and prevent the cup from medializing.

Question 36

A 71-year-old male with a T-score of -3.5 and multiple recent fragility fractures requires aggressive medical management for osteoporosis. You are considering starting teriparatide. Which of the following elements in his past medical history represents an absolute contraindication to teriparatide therapy?

Explanation

Teriparatide is a recombinant parathyroid hormone (PTH) analog that acts as a potent anabolic agent. Historically, it carried a black box warning (which has since been modified but the clinical contraindication remains for high-risk patients) due to an increased incidence of osteosarcoma observed in rat studies. Absolute contraindications include conditions that predispose to osteosarcoma, including prior skeletal radiation therapy, Paget's disease of bone, unexplained elevated alkaline phosphatase, or open epiphyses.

Question 37

A 60-year-old female presents for a primary total knee arthroplasty. She has a documented severe hypersensitivity reaction to nickel, confirmed by a dermatologist via patch testing. Which of the following femoral component materials is the most appropriate alternative to minimize her risk of a delayed hypersensitivity reaction?

Explanation

Standard total knee arthroplasty femoral components are predominantly made of Cobalt-Chromium (CoCr) alloy, which invariably contains trace amounts of nickel and can elicit a Type IV hypersensitivity reaction in susceptible patients. In patients with severe, confirmed nickel allergy, alternative bearing surfaces must be used. Oxidized zirconium (Oxinium) or an all-titanium component (often titanium-nitride coated) are the standard alternatives, as they lack nickel. Stainless steel (316L) also contains a significant amount of nickel (10-14%).

Question 38

During a complex revision TKA, the surgeon notes that the joint line has been inadvertently elevated by 8 mm compared to its pre-disease anatomic location. If left uncorrected, which of the following complications is most likely to occur postoperatively?

Explanation

Elevation of the joint line in revision TKA is a common error resulting from excessive distal femoral resection without adequate augmentation. Because the patellar tendon length remains constant from the tibial tubercle, elevating the joint line moves the femoral trochlea proximally relative to the patella, creating a "pseudo-patella baja" (the patella sits abnormally low relative to the joint line, causing impingement and decreased ROM). Additionally, because the collateral ligaments originate on the epicondyles, moving the joint line proximally without altering the AP dimension introduces slack into the ligaments in mid-flexion, leading to mid-flexion instability. The solution is using distal femoral augments to restore the joint line distally.

Question 39

Stress shielding in cementless total hip arthroplasty leads to proximal femoral bone resorption over time due to the transfer of mechanical load distally. Which of the following femoral stem designs is associated with the highest degree of proximal stress shielding?

Explanation

According to Wolff's Law, bone remodels in response to mechanical stress. Stress shielding occurs when the stiff femoral stem bypasses the proximal femur and transfers load directly to the diaphysis. This is most pronounced with fully porous-coated stems (which achieve rigid diaphyseal fixation), large-diameter stems (which have a very high bending stiffness), and cobalt-chromium alloys (which possess a much higher modulus of elasticity than titanium). A fully porous-coated, large-diameter CoCr stem provides rigid distal fixation, completely unloading the proximal femur and leading to significant proximal cortical osteolysis/stress shielding.

Question 40

When performing patellar resurfacing during a primary TKA, careful attention must be paid to the remaining thickness of the native patellar bone after the resection. To minimize the risk of a catastrophic postoperative patellar fracture, what is the generally accepted absolute minimum composite thickness of the remaining native anterior patellar bone shell?

Explanation

The native, unresurfaced patella is typically 22 to 26 mm thick in adults. When resurfacing the patella, the goal is to resect an amount of bone equal to the thickness of the polyethylene button being implanted to restore the native patellar composite thickness. However, if the native patella is thin or asymmetric, the surgeon must prioritize leaving an adequate residual bony shell. The established biomechanical threshold to prevent catastrophic patellar fracture is leaving an absolute minimum of 12 to 15 mm of native anterior patellar bone.

Question 41

An 80-year-old female with severe osteoporosis and a recent femoral neck fracture is placed on romosozumab. What is the precise mechanism of action of this medication?

Explanation

Romosozumab is a humanized monoclonal antibody that targets and binds to sclerostin. Sclerostin is a glycoprotein secreted by osteocytes that naturally inhibits the Wnt signaling pathway, thereby inhibiting bone formation. By blocking sclerostin, romosozumab provides a dual effect: it significantly stimulates bone formation (anabolic) while concurrently decreasing bone resorption (antiresorptive).

Question 42

In modern total hip arthroplasty, highly cross-linked polyethylene (HXLPE) is frequently doped with Vitamin E (alpha-tocopherol). What is the primary biochemical purpose of adding Vitamin E to the polyethylene prior to or after irradiation?

Explanation

Irradiation is used to cross-link polyethylene to improve wear resistance, but it creates free radicals that can oxidize over time, leading to degradation and embrittlement. Historically, post-irradiation thermal treatment (remelting or annealing) was used to eliminate free radicals, but remelting reduces mechanical strength. Vitamin E acts as an antioxidant (free radical scavenger) that neutralizes these free radicals, preventing oxidation while avoiding the mechanical property loss associated with remelting.

Question 43

A modern total knee arthroplasty utilizes a 'medial pivot' design. In a normal native knee during active flexion from 0 to 90 degrees, how does the kinematics of the femoral condyles on the tibia typically behave to justify this implant design?

Explanation

Native knee kinematics involve a 'medial pivot' mechanism. During knee flexion, the medial femoral condyle exhibits minimal anteroposterior translation (acting as a pivot point), while the lateral femoral condyle rolls and translates posteriorly. This differential translation results in the internal rotation of the tibia relative to the femur during flexion.

Question 44

A 65-year-old woman is scheduled for a total hip arthroplasty. Standing and sitting lateral spinopelvic radiographs reveal a stiff lumbar spine with a pelvic tilt change of 5 degrees between standing and sitting, and a significantly decreased standing sacral slope. What is the most appropriate modification in acetabular cup positioning to minimize the risk of dislocation?

Explanation

A stiff lumbar spine (change in pelvic tilt < 10 degrees) combined with a decreased standing sacral slope indicates a 'flatback' deformity where the pelvis is already retroverted and does not retrovert further normally upon sitting. This puts the patient at a high risk for anterior impingement and subsequent posterior dislocation during sitting. To compensate for the lack of dynamic functional pelvic retroversion in flexion, the cup should be placed in more anteversion and slightly more inclination (abduction).

Question 45

A 72-year-old female on alendronate for 10 years presents with 3 months of progressive anterior thigh pain. Radiographs reveal focal lateral cortical thickening and a transverse radiolucent line involving 30% of the lateral cortex of the subtrochanteric femur. There is moderate varus bowing of the femur. What is the most appropriate next step in management?

Explanation

This clinical picture represents an impending atypical femur fracture (AFF) associated with prolonged bisphosphonate use, characterized by a transverse radiolucent line (incomplete fracture) in the lateral cortex, cortical thickening, and a prodrome of thigh pain. Given the presence of the radiolucent line and symptomatic pain in a biologically altered bone with mechanical disadvantage (varus bowing), prophylactic intramedullary nailing is highly recommended to prevent completion of the fracture. Nonsurgical management has a high failure rate in the presence of a visible fracture line and pain.

Question 46

A 70-year-old male presents with an inability to perform a straight leg raise 4 years after a primary TKA. Ultrasound confirms a massive distal patellar tendon rupture with poor tissue quality. An extensor mechanism allograft reconstruction is planned. Which of the following technical principles is considered critical for optimizing the success of this procedure?

Explanation

When performing an extensor mechanism reconstruction with a complete allograft (e.g., extensor mechanism allograft including the tibial tubercle, patellar tendon, patella, and quadriceps tendon), the graft must be tensioned under maximal tension in full, absolute extension (or even slight hyperextension). Over time, the allograft will inevitably stretch; if it is tensioned in any amount of flexion, it will stretch out and result in a debilitating permanent extensor lag.

Question 47

Which of the following combinations of implant characteristics confers the highest risk for mechanically assisted crevice corrosion (trunnionosis) at the head-neck junction in total hip arthroplasty?

Explanation

Trunnionosis (mechanically assisted crevice corrosion) is most heavily associated with mixed-metal modular junctions, particularly a titanium alloy stem paired with a cobalt-chromium head. The risk is significantly amplified by the use of larger femoral heads (>36 mm), which increase the frictional torque and the resultant lever arm forces transmitted to the trunnion, leading to micromotion, fretting, and corrosion.

Question 48

A 68-year-old female sustains a fragility fracture of the pelvis. A DXA scan reveals a T-score of -3.2 at the femoral neck. An incidental finding on the pelvic radiograph is an asymptomatic area characteristic of Paget's disease involving her right hemipelvis. Which of the following medical treatments for her osteoporosis is strictly contraindicated?

Explanation

Teriparatide (a recombinant human PTH analog) is contraindicated in patients with Paget's disease of bone, prior skeletal radiation therapy, unexplained elevations in alkaline phosphatase, or open epiphyses. This contraindication is due to a theoretical increased risk of osteosarcoma, which was observed in long-term, high-dose rat studies.

Question 49

A 65-year-old male complains of a sense of giving way and recurrent effusions one year after a primary posterior-stabilized total knee arthroplasty. On examination, the knee is perfectly stable in full extension but exhibits excessive anteroposterior laxity at 90 degrees of flexion. Radiographs show well-fixed components with no loosening. What is the most appropriate surgical management to address this specific instability pattern?

Explanation

The patient presents with isolated flexion instability, indicating that the flexion gap is unacceptably loose while the extension gap is stable. Placing a thicker polyethylene insert would tighten the flexion gap but would simultaneously over-tighten the extension gap, causing a flexion contracture. Increasing the tibial slope would paradoxically increase the flexion gap, making the instability worse. The correct management is to increase the anteroposterior dimension of the femur by upsizing the femoral component or adding posterior femoral augments; this tightens the flexion gap exclusively without affecting the extension gap.

Question 50

Intra-prosthetic dislocation (IPD) is a unique and major complication associated with dual mobility total hip arthroplasty constructs. Which of the following best describes the pathomechanics of this specific complication?

Explanation

Intra-prosthetic dislocation (IPD) is unique to dual mobility bearings and refers specifically to the failure of the retentive rim of the large polyethylene component, causing the small inner metal or ceramic head to dislocate from within the polyethylene liner. The patient typically presents with sudden pain and limp. Radiographs will show the inner head eccentrically located or articulating directly with the metal acetabular shell.

Question 51

A 74-year-old woman with severe osteoporosis has been receiving denosumab injections every 6 months for the past 4 years. She missed her last two appointments and is now 12 months since her last dose. She presents to the emergency department with acute back pain, and radiographs reveal three new acute vertebral compression fractures. What underlying physiological mechanism best explains this clinical presentation?

Explanation

Denosumab is a potent monoclonal antibody against RANK ligand (RANKL). When denosumab is discontinued, there is a well-documented 'rebound phenomenon.' As the drug clears, the uninhibited RANKL leads to a massive and rapid increase in the formation, function, and survival of osteoclasts. This results in a period of profoundly accelerated bone resorption, severe bone density loss, and a high risk of multiple spontaneous vertebral compression fractures. Patients stopping denosumab must be immediately transitioned to a bisphosphonate to prevent this rebound.

Question 52

During a primary total knee arthroplasty, the surgeon notes severe lateral patellar tracking requiring a lateral retinacular release. Postoperatively, the patient continues to experience anterior knee pain. A CT scan is obtained to evaluate component rotation. Internal rotation of which of the following component pairs is the most frequent surgical cause of this patellar maltracking?

Explanation

Patellar maltracking (lateral tracking and subluxation) in TKA is frequently caused by errors in component rotation that increase the Q-angle. Internal rotation of the femoral component medializes the trochlear groove relative to the extensor mechanism. Internal rotation of the tibial component externally rotates the tibial tubercle relative to the rest of the knee. Both of these specific technical errors effectively lateralize the tibial tubercle relative to the trochlear groove, increasing the Q-angle and causing lateral patellar maltracking.

Question 53

An 82-year-old female presents with a periprosthetic femur fracture around a cemented polished taper-slip stem placed 15 years ago. Radiographs reveal a fracture extending just distal to the tip of the stem. The stem is frankly loose. Furthermore, there is severe proximal bone loss with marked cortical thinning, rendering the proximal femur mechanically nonsupportive. According to the Vancouver classification, what is the standard recommended surgical management?

Explanation

This is a Vancouver B3 fracture, defined by a fracture around or just below the stem, a loose stem, and poor proximal bone stock. Because the proximal bone cannot provide adequate initial fixation or support, the surgical solution must bypass this area. Standard of care relies on obtaining stable diaphyseal fixation using a distally fixing modular fluted tapered stem, or in cases of extreme comminution and elderly/low-demand patients, utilizing a proximal femoral replacement (megaprosthesis) to allow immediate weight-bearing.

Question 54

A 45-year-old premenopausal woman with a history of celiac disease undergoes a dual-energy x-ray absorptiometry (DXA) scan. The report indicates a lumbar spine T-score of -2.6 and a Z-score of -2.8. How should her bone density status be formally classified according to the International Society for Clinical Densitometry (ISCD) guidelines?

Explanation

According to the ISCD guidelines, in premenopausal women, men under the age of 50, and children, the Z-score should be used rather than the T-score. A Z-score of -2.0 or lower is defined strictly as 'below the expected range for age.' The diagnostic terminology of 'osteoporosis' based on T-score criteria (≤ -2.5) is reserved for postmenopausal women and men aged 50 and older.

Question 55

During a primary total knee arthroplasty for a severe fixed varus deformity, the surgeon resects the proximal tibia and distal femur. The knee remains tight medially in both flexion and extension. After releasing the deep medial collateral ligament (MCL) and removing all medial osteophytes, what is the most appropriate next step in the standard stepwise medial release to balance the knee?

Explanation

The standard step-wise medial soft-tissue release for balancing a varus TKA begins with comprehensive osteophyte resection. The deep MCL is then released. If the knee remains tight, particularly in extension, the next structure in the sequence is the posteromedial capsule (and semimembranosus insertion). Releasing the superficial MCL completely off its distal tibial insertion is reserved as a last resort, as it can lead to catastrophic medial instability requiring constrained inserts.

Question 56

A 60-year-old male complains of persistent groin pain 1 year following an uncemented total hip arthroplasty. The pain is worst when initiating movement, specifically when actively lifting his leg to get into a car. Examination reveals pain with an active straight leg raise. Radiographs demonstrate an acetabular cup with 10 degrees of anteversion and 12 mm of anterior overhang beyond the bony anterior acetabular rim. What is the most definitive surgical management?

Explanation

This patient is suffering from classic iliopsoas impingement after THA, characterized by start-up groin pain and pain with active hip flexion. It is mechanically caused by a prominent anterior edge of the acetabular component. While an iliopsoas tenotomy can be considered for minor overhang, significant anterior cup overhang (>8 mm) combined with relative retroversion (10 degrees anteversion) represents a gross mechanical block. The definitive treatment with the lowest recurrence rate for this degree of mechanical impingement is revision of the acetabular cup to sink it completely into the bone and correct the version.

Question 57

A 55-year-old female is scheduled for a primary total knee arthroplasty. She reports a severe, blistering skin reaction to cheap jewelry, and a formal patch test is intensely positive for nickel and cobalt hypersensitivity. To minimize the risk of a hypersensitivity reaction, what is the best combination of implant materials for her TKA?

Explanation

In a patient with documented severe metal hypersensitivity, particularly to cobalt or nickel, standard cobalt-chromium implants must be avoided. Stainless steel also contains nickel. Oxidized zirconium (Oxinium) is an ideal femoral component material for these patients; it consists of a zirconium alloy core with a transformed ceramic-like surface of zirconium oxide, virtually eliminating metal ion exposure. This should be paired with a titanium or all-polyethylene tibial component to avoid cobalt entirely.

Question 58

The Fracture Risk Assessment Tool (FRAX) is utilized to estimate the 10-year probability of a major osteoporotic fracture and a hip fracture. Which of the following clinical variables is NOT explicitly included as a risk factor input in the calculation of the FRAX score?

Explanation

The FRAX tool includes inputs for age, sex, weight, height, prior fracture, parental history of hip fracture, current smoking, glucocorticoid use, rheumatoid arthritis, secondary osteoporosis, alcohol intake (≥3 units/day), and femoral neck BMD. Although Type 2 Diabetes Mellitus is recognized as a significant risk factor for poor bone quality and fractures, it is not explicitly included as a discrete variable in the standard FRAX calculation, which can sometimes lead to underestimating fracture risk in diabetic patients.

Question 59

A patient presents 6 months after a right THA complaining that the right leg feels too long. On examination, the true leg length (measured from the ASIS to the medial malleolus) is equal bilaterally. However, the apparent leg length (measured from the umbilicus to the medial malleolus) is 2 cm longer on the right. What is the most likely etiology of this discrepancy?

Explanation

If the true leg lengths (ASIS to medial malleolus) are equal, the actual bony lengths of the lower extremities are identical. An apparent leg length discrepancy (umbilicus to medial malleolus) is caused by pelvic obliquity. An abduction contracture of the right hip forces the patient to tilt the right side of the pelvis downward to bring the legs parallel for standing/walking. This downward tilt of the right hemipelvis makes the right leg appear longer when measured from a central point (the umbilicus). Conversely, an adduction contracture results in an apparent shortening of the limb.

Question 60

Which of the following specific design modifications in modern posterior-stabilized total knee arthroplasty systems has been most instrumental in reducing the incidence of 'patellar clunk syndrome'?

Explanation

Patellar clunk syndrome occurs in posterior-stabilized (PS) knee designs when a fibrotic nodule forms at the superior pole of the patella or deep quadriceps tendon, which drops into the femoral intercondylar box during flexion and catches as the knee extends, causing a painful 'clunk.' Modern PS implants have significantly reduced this complication by lengthening the trochlear groove more proximally and lowering/smoothing the anterior lip of the intercondylar box, allowing the patella to track smoothly over the box without impingement.

Question 61

During a posterior-stabilized total knee arthroplasty, the knee is found to be tight in extension and loose in flexion after the initial bone cuts. Which of the following is the most appropriate technical adjustment to balance the gaps?

Explanation

A tight extension gap with a loose flexion gap requires increasing the extension gap without affecting the flexion gap. Recutting the distal femur achieves this, whereas resecting the proximal tibia would affect both gaps equally.

Question 62

A 70-year-old female with severe osteoporosis has been treated with denosumab for 4 years but discontinued it 8 months ago due to a dental procedure. What is the most significant skeletal risk she currently faces due to this cessation?

Explanation

Discontinuation of denosumab leads to a rapid rebound in bone turnover to above-baseline levels. This rebound phenomenon is strongly associated with a high risk of sustaining multiple rapid vertebral compression fractures.

Question 63

A 65-year-old male presents with groin pain 5 years after a primary metal-on-polyethylene total hip arthroplasty. Joint aspiration yields fluid with a high cobalt-to-chromium ratio and negative cultures. Which of the following implant characteristics most increases the risk of this specific complication?

Explanation

The patient is experiencing trunnionosis (taper corrosion). Utilizing larger diameter metal femoral heads increases the frictional torque at the head-neck junction, exacerbating fretting and corrosion at the trunnion.

Question 64

A 75-year-old female with osteoporosis sustains a distal femur periprosthetic fracture. Anabolic bone therapy is considered to aid healing and improve overall bone density. Which of the following represents an absolute contraindication to the use of teriparatide?

Explanation

Teriparatide (recombinant PTH) has a black box warning and is contraindicated in patients with a history of external beam or implant radiation therapy to the skeleton due to a theoretical increased risk of osteosarcoma.

Question 65

A 68-year-old female reports a painful 'catching' sensation at the anterior aspect of her knee when actively extending from a flexed position, 1 year following a total knee arthroplasty. Which of the following component designs is most commonly associated with this complication?

Explanation

Patellar clunk syndrome is most commonly associated with posterior-stabilized (PS) knee designs. It occurs when a fibrous nodule forms in the suprapatellar pouch and catches within the intercondylar box of the femoral component during extension.

Question 66

A 72-year-old male with a prior T10-to-pelvis fusion for degenerative scoliosis is undergoing a primary total hip arthroplasty. Standing lateral radiographs reveal a stiff spine with decreased lumbar lordosis and a fixed posterior pelvic tilt. To minimize dislocation risk, how should the acetabular component orientation be adjusted relative to the standard Lewinnek safe zone?

Explanation

Patients with a stiff spine and a flatback deformity (fixed posterior pelvic tilt) fail to flex their pelvis when sitting, but face a high risk of anterior dislocation in extension. Therefore, the cup should be placed with decreased anteversion and decreased abduction.

Question 67

A 76-year-old female sustains a distal femur fracture superior to her total knee arthroplasty. Radiographs show a displaced fracture, and the femoral component is clinically loose with loss of medial condyle bone stock. What is the most appropriate surgical management?

Explanation

A periprosthetic distal femur fracture with a loose component and poor distal bone stock (Lewis-Rorabeck Type III) requires revision arthroplasty. Distal femoral replacement (tumor prosthesis) is the standard of care to bypass the compromised bone and provide immediate stability.

Question 68

A 55-year-old female complains of persistent groin pain and a catching sensation with active hip flexion 1 year after an uncomplicated primary total hip arthroplasty. An ultrasound-guided injection of local anesthetic into the iliopsoas bursa completely relieves her pain. What radiographic finding is most likely present?

Explanation

Iliopsoas impingement is a common cause of groin pain after THA. It is frequently caused by a prominent anterior edge of the acetabular component, which typically results from cup retroversion, under-seating, or oversizing.

Question 69

A 68-year-old male is initiated on alendronate following a fragility fracture of the femoral neck. What is the primary intracellular molecular mechanism of action of this medication?

Explanation

Nitrogen-containing bisphosphonates (like alendronate) inhibit farnesyl pyrophosphate (FPP) synthase within the mevalonate pathway. This prevents protein prenylation, leading to osteoclast apoptosis and decreased bone resorption.

Question 70

A 79-year-old male sustains a Vancouver B2 periprosthetic femur fracture around a cemented total hip arthroplasty. The stem has subsided 3 cm, but the diaphyseal bone stock distal to the fracture is robust. What is the optimal surgical management?

Explanation

A Vancouver B2 fracture is characterized by a fracture around a loose stem with adequate bone stock. The standard of care is revision arthroplasty utilizing a fluted, tapered, modular titanium stem to achieve diaphyseal bypass fixation.

Question 71

During a total knee arthroplasty for a severe, rigid varus deformity, the deep medial collateral ligament and posteromedial capsule have been released. The knee remains tight medially in both flexion and extension. Which structure should typically be released next to balance the knee?

Explanation

In the stepwise medial release sequence for severe varus deformity, if release of the deep MCL and posteromedial capsule is insufficient, the next structure to be addressed is the superficial medial collateral ligament (sMCL), often performed via a pie-crusting technique or subperiosteal stripping.

Question 72

Which of the following best describes the primary biomechanical advantage of a dual-mobility construct in total hip arthroplasty compared to a standard unipolar construct?

Explanation

Dual-mobility components use a large polyethylene liner that articulates within a metal shell, effectively acting as a massive femoral head. This significantly increases the jump distance to dislocation, making it highly stable.

Question 73

A 62-year-old male with a metal-on-polyethylene total hip arthroplasty presents with new-onset groin pain and swelling 6 years postoperatively. Aspiration yields fluid with markedly elevated cobalt levels and normal chromium levels. An MRI demonstrates a cystic pseudotumor. What is the most likely etiology of this patient's presentation?

Explanation

In a metal-on-polyethylene THA, a pseudotumor coupled with elevated cobalt out of proportion to chromium indicates mechanically assisted crevice corrosion (trunnionosis) at the modular head-neck taper junction.

Question 74

During trialing of a primary total knee arthroplasty, the surgeon notes that the extension gap is perfectly balanced, but the knee is significantly tight in flexion. Which of the following technical adjustments is the most appropriate next step?

Explanation

A tight flexion gap with a balanced extension gap can be addressed by increasing the posterior slope of the tibial cut. Downsizing the femoral component (in an anterior referencing system) or releasing the PCL are also valid options.

Question 75

A 70-year-old female on oral alendronate for 8 years presents with a 3-month history of vague, non-traumatic anterior thigh pain. Radiographs reveal focal lateral cortical thickening and a transverse radiolucent line in the subtrochanteric femur. What is the most appropriate change in her medical management?

Explanation

Long-term bisphosphonate use increases the risk of atypical femur fractures. Management involves immediately discontinuing the bisphosphonate and starting an anabolic agent like teriparatide to stimulate bone formation and fracture healing.

Question 76

A 75-year-old female sustains a periprosthetic femur fracture around a cemented total hip arthroplasty after a fall. Radiographs show a transverse fracture just distal to the tip of the stem. The stem is radiographically loose, but there is excellent diaphyseal bone stock. How is this fracture classified and best treated?

Explanation

A Vancouver B2 fracture involves a loose stem with adequate remaining bone stock. The gold standard treatment is revision arthroplasty bypassing the fracture site with a long, cementless, extensively porous-coated or fluted tapered modular stem.

Question 77

A 66-year-old male presents 1 year after a posterior-stabilized total knee arthroplasty complaining of a painful catching sensation when extending his knee from a seated position. On examination, a palpable 'pop' is felt at the anterior knee at roughly 35 degrees of flexion. What is the underlying cause?

Explanation

Patellar clunk syndrome occurs in posterior-stabilized TKAs due to the formation of a fibrous nodule at the superior pole of the patella. This nodule gets entrapped in the femoral intercondylar box and pops out as the knee extends.

Question 78

A 65-year-old female with severe osteoporosis is initiated on denosumab therapy by her endocrinologist. What is the precise mechanism of action of this pharmacological agent?

Explanation

Denosumab is a human monoclonal antibody that binds directly to RANKL. This prevents RANKL from binding to the RANK receptor on osteoclast precursors, fundamentally inhibiting osteoclast maturation, function, and survival.

Question 79

A 68-year-old male with a long-standing surgical fusion of his lumbar spine (L2-S1) is scheduled for a total hip arthroplasty. Flexion-extension spine radiographs confirm a completely stiff spinopelvic junction with lack of posterior pelvic tilt when sitting. To minimize the risk of dislocation, how should the acetabular cup be positioned relative to the standard safe zone?

Explanation

A stiff lumbar spine fails to posteriorly tilt during sitting, preventing the natural increase in functional acetabular anteversion. To prevent anterior impingement and posterior dislocation, the cup should be placed in greater anteversion and inclination.

Question 80

A patient presents with a painful total knee arthroplasty 2 years postoperatively. Synovial fluid aspiration reveals a white blood cell count of 4,500 cells/uL with 88% neutrophils. The synovial alpha-defensin test is positive, and serum CRP is 18 mg/L. According to the 2018 MSIS/ICM criteria, what is the diagnosis?

Explanation

Based on the 2018 Evidence-Based Validated Definition for PJI, the combination of elevated CRP, synovial WBC >3000, PMN >80%, and a positive alpha-defensin yields enough points to definitively diagnose a periprosthetic joint infection.

Question 81

A 60-year-old female is evaluated for recurrent fragility fractures. Her DEXA T-score is -3.2. Her physician is considering starting teriparatide. Which of the following in her medical history is an absolute contraindication to this therapy?

Explanation

Teriparatide carries a warning for the potential risk of osteosarcoma. It is strictly contraindicated in patients with a history of skeletal radiation therapy, Paget's disease, or unexplained elevations in alkaline phosphatase.

Question 82

During a complex revision total hip arthroplasty, the surgeon identifies a complete structural separation of the ilium from the ischium and pubis. Which of the following terms best describes this specific pattern of acetabular bone loss?

Explanation

Pelvic discontinuity is defined by a complete separation of the superior hemipelvis (ilium) from the inferior hemipelvis (ischium and pubis). It requires specialized fixation techniques, such as a cup-cage construct, custom triflange, or distraction plating.

Question 83

A 72-year-old male undergoes a full extensor mechanism allograft reconstruction for a chronic patellar tendon rupture following a total knee arthroplasty. To minimize the risk of postoperative extensor lag and ensure a successful outcome, what is the most critical intraoperative technical step?

Explanation

Extensor mechanism allografts inevitably stretch over time. To prevent a debilitating postoperative extensor lag, the graft must be tensioned 'bar-string' tight with the knee in full, absolute extension during fixation.

Question 84

A patient suffers a recurrent anterior dislocation of their total hip arthroplasty, which was placed via a posterior approach. CT scan reveals an acetabular cup with 45 degrees of inclination and 30 degrees of anteversion. The femoral stem is placed in 20 degrees of anteversion. What is the primary cause of instability?

Explanation

The combined anteversion in this patient is 50 degrees (30 cup + 20 stem), which is excessively high. High combined anteversion predisposes the hip to anterior dislocation, particularly in extension and external rotation, due to anterior uncoverage.

Question 85

A 55-year-old postmenopausal female has a DEXA T-score of -1.8 at the femoral neck. Her FRAX tool assessment reveals a 10-year probability of a major osteoporotic fracture of 22% and a hip fracture probability of 4%. What is the most appropriate management according to current guidelines?

Explanation

Pharmacological intervention is recommended for osteopenic patients (T-score -1.0 to -2.5) if the FRAX 10-year risk for a major osteoporotic fracture is >=20% or the risk for a hip fracture is >=3%.

Question 86

A 78-year-old female sustains a distal femur fracture 5 years after a primary total knee arthroplasty. Radiographs show a displaced, comminuted metaphyseal fracture, but the femoral component remains well-fixed. According to the Rorabeck classification, what is the best surgical treatment?

Explanation

A displaced periprosthetic distal femur fracture with a well-fixed femoral component is classified as Rorabeck Type II. The standard of care is open reduction and internal fixation, typically utilizing a lateral locking plate.

Question 87

Modern total hip arthroplasties utilize highly cross-linked polyethylene (HXLPE) to significantly reduce wear rates and subsequent osteolysis. Which manufacturing process is primarily responsible for inducing the cross-linking in the polyethylene?

Explanation

High cross-linking is achieved by exposing the polyethylene to electron beam or gamma irradiation, which breaks molecular chains and allows free radicals to cross-link. Subsequent thermal treatment (melting or annealing) eliminates residual free radicals.

Question 88

During a primary total knee arthroplasty for a severe varus deformity, the surgeon notes symmetric medial tightness in both flexion and extension after making the initial bony cuts. Which soft tissue structure should be sequentially released first to balance the gaps?

Explanation

Symmetric medial tightness in both flexion and extension indicates a contracted superficial medial collateral ligament (sMCL). Releasing the sMCL subperiosteally off its proximal tibial attachment is the primary step to achieve coronal balance.

Question 89

A 58-year-old female presents with persistent groin pain 6 months after an uncemented total hip arthroplasty. The pain is worst when she actively lifts her leg to get into a car. Resisted straight leg raise reproduces her symptoms. Radiographs show the acetabular component is well-fixed but has a prominent anterior edge. What is the most likely diagnosis?

Explanation

Iliopsoas impingement post-THA presents with groin pain exacerbated by active hip flexion against resistance. It is often caused by an oversized, under-anteverted, or laterally prominent acetabular cup irritating the iliopsoas tendon.

Question 90

A 72-year-old female abruptly stops her osteoporosis medication prior to extensive dental surgery. Six months later, she sustains multiple spontaneous vertebral compression fractures. The abrupt cessation of which of the following medications is most notorious for causing this rapid 'rebound' fracture phenomenon?

Explanation

Discontinuation of denosumab leads to a rapid, profound loss of bone mineral density and a well-documented rebound increase in the risk of multiple vertebral fractures. Patients stopping denosumab must be transitioned to a bisphosphonate.

Orthopedic Surgery MCQs: Arthroplasty, Fracture & Hip Exam Prep | Part 18

Orthopedic Board Exam MCQs: Hip & Knee Arthroplasty, Osteoporosis | Part 40

Key Takeaway

Orthopedic Board Exam MCQs: Hip & Knee Arthroplasty, Osteoporosis | Part 40

Chapter Index