Orthopedic Adult Reconstructiv Review | Dr Hutaif Hip & -...

Question 1

In the manufacturing of highly cross-linked polyethylene (HXLPE) for total hip arthroplasty, what is the primary consequence of the remelting process performed after gamma irradiation?

Explanation

Gamma irradiation is used to cross-link polyethylene, which significantly decreases its wear rate. However, irradiation creates free radicals that can react with oxygen, leading to oxidation and degradation over time. To eliminate these free radicals, the polyethylene undergoes either remelting (heating above the melting point) or annealing (heating below the melting point). Remelting successfully eliminates all free radicals, making it highly oxidation-resistant, but it decreases crystallinity, which reduces the material's mechanical properties, such as fatigue strength and yield strength.

Question 2

During a total hip arthroplasty, the surgeon decides to medialize the acetabular component to the true floor of the acetabulum. How does this modification alter the biomechanics of the hip joint in the coronal plane?

Explanation

Medializing the center of rotation of the hip decreases the moment arm of the body weight (the distance from the symphysis to the hip center). Because the body weight moment arm is shortened, the abductor muscles need to generate less force to maintain a level pelvis during single-leg stance. Consequently, the overall joint reaction force (which is the sum of the body weight and the abductor force) is decreased. This is a fundamental principle of hip biomechanics described by Pauwels.

Question 3

A 68-year-old woman presents with an inability to actively extend her knee 3 years after a primary total knee arthroplasty. Radiographs show a high-riding patella indicating a complete patellar tendon rupture. Given the chronicity and setting of TKA, what is the most reliable surgical reconstruction option yielding the best long-term outcomes?

Explanation

Patellar tendon rupture following TKA is a devastating complication. Direct primary repair in the chronic setting or over a TKA is associated with unacceptably high failure rates due to poor tissue quality and a compromised vascular envelope. The gold standard treatments for chronic extensor mechanism disruption in the setting of a TKA are an extensor mechanism allograft (tibial tubercle, patellar tendon, patella, and quadriceps tendon) or synthetic mesh (e.g., Marlex mesh) reconstruction. These provide the necessary structural integrity.

Question 4

The direct anterior approach (Smith-Petersen) for total hip arthroplasty is gaining popularity due to its internervous plane. Which of the following describes the correct superficial internervous plane utilized in this approach?

Explanation

The direct anterior approach to the hip utilizes a true superficial internervous and intermuscular plane between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (TFL) (innervated by the superior gluteal nerve). The deep plane lies between the rectus femoris (femoral nerve) and the gluteus medius (superior gluteal nerve).

Question 5

A 72-year-old male presents with a painful total knee arthroplasty 4 years postoperatively. Erythrocyte sedimentation rate (ESR) is 45 mm/hr and C-reactive protein (CRP) is 22 mg/L. Joint aspiration yields a synovial white blood cell count of 4,500 cells/µL with 85% polymorphonuclear (PMN) leukocytes. What is the next best step in management?

Explanation

Based on the 2018 Musculoskeletal Infection Society (MSIS) / International Consensus Meeting (ICM) criteria, a synovial fluid WBC count > 3,000 cells/µL and > 80% PMNs in a chronic setting (>90 days post-op) is diagnostic for a periprosthetic joint infection (PJI). The gold standard treatment for chronic PJI in North America is a two-stage exchange arthroplasty, which involves explantation, placement of an antibiotic spacer, a course of IV antibiotics, and subsequent reimplantation.

Question 6

In conventional mechanical alignment for total knee arthroplasty, the goal is to create a neutral mechanical axis. How are the femoral and tibial component bone cuts classically oriented relative to their respective mechanical axes?

Explanation

In classic mechanical alignment for TKA, both the distal femoral cut and the proximal tibial cut are made strictly perpendicular (90 degrees, or 0 degrees of deviation) to their respective mechanical axes. This results in an overall mechanical axis that is neutral (0 degrees). It is important not to confuse the anatomic axis with the mechanical axis; the femoral mechanical axis is generally 5-7 degrees valgus to the femoral anatomic axis.

Question 7

A 65-year-old woman experiences recurrent posterior dislocations of her total hip arthroplasty. Radiographic evaluation demonstrates the acetabular component is placed in 5 degrees of retroversion and 45 degrees of inclination. The femoral stem is in neutral version. What is the most appropriate surgical intervention?

Explanation

The patient has recurrent posterior dislocations driven by a malpositioned (retroverted) acetabular component. The "safe zone" described by Lewinnek suggests an acetabular anteversion of 15 ± 10 degrees. A cup placed in 5 degrees of retroversion will cause posterior impingement and instability. The most anatomic and reliable solution is to revise the acetabular component to the correct anteversion. Constrained liners should be reserved for cases of abductor deficiency or cognitive issues where anatomic alignment cannot restore stability.

Question 8

A 58-year-old male with a metal-on-metal total hip arthroplasty presents with new-onset groin pain and a palpable mass. Serum cobalt levels are elevated at 15 ppb. MRI demonstrates a large cystic fluid collection around the hip joint.

Histological analysis of the periprosthetic tissue during revision surgery is most likely to show which of the following?

Explanation

The patient is presenting with an adverse local tissue reaction (ALTR) or pseudotumor secondary to metal-on-metal bearing wear. The hallmark histological finding in this condition is ALVAL (aseptic lymphocyte-dominated vasculitis-associated lesion), which is a Type IV delayed hypersensitivity reaction characterized by perivascular lymphocytic infiltrates, tissue necrosis, and macrophages containing fine metallic debris. Birefringent particles (Option C) are characteristic of polyethylene wear.

Question 9

During a posterior-stabilized total knee arthroplasty, trial reduction reveals that the knee is symmetric and stable in full extension but excessively tight in 90 degrees of flexion, causing lift-off. Which of the following adjustments is the most appropriate next step to balance the knee?

Explanation

A knee that is balanced in extension but tight in flexion has an isolated tight flexion gap. Since it is a posterior-stabilized knee, the PCL has already been sacrificed. Downsizing the femoral component (using a smaller AP size) translates the posterior condyles anteriorly, which increases the flexion gap without affecting the distal femoral surface, thus leaving the extension gap unchanged. Resecting more distal femur would increase the extension gap. Releasing the posterior capsule increases the extension gap.

Question 10

A 78-year-old female sustains a fall and presents with thigh pain. Radiographs reveal a spiral fracture around the tip of her cementless femoral stem. The stem is visibly subsided and loose, but the proximal femoral bone stock remains adequate.

According to the Vancouver classification, what is the recommended treatment?

Explanation

This is a Vancouver B2 periprosthetic femur fracture. The fracture occurs around the stem or just distal to it (Type B), the stem is loose (2), but the proximal bone stock is adequate. The standard of care for a Vancouver B2 fracture is revision arthroplasty using a long, diaphyseal-engaging stem to bypass the fracture by at least 2 cortical diameters. ORIF alone (Option A) is reserved for Vancouver B1 fractures (well-fixed stem). Proximal femoral replacement is indicated for Vancouver B3 fractures (loose stem, poor proximal bone stock).

Question 11

In the pathogenesis of aseptic loosening secondary to polyethylene wear debris in total joint arthroplasty, which of the following cell types is primarily responsible for the initial phagocytosis of the submicron wear particles and subsequent release of pro-inflammatory cytokines such as TNF-α and IL-1?

Explanation

The biological cascade of particle disease (osteolysis) begins when submicron polyethylene wear debris is generated. These particles are phagocytosed by macrophages. The macrophages cannot digest the polyethylene and subsequently release a cascade of pro-inflammatory cytokines, including TNF-α, IL-1, and IL-6. This leads to the upregulation of RANKL, which activates osteoclasts, culminating in periprosthetic bone resorption (osteolysis) and eventual aseptic loosening.

Question 12

A patient presents with persistent anterior knee pain and lateral patellar subluxation 6 months following a primary total knee arthroplasty. A CT scan protocol is obtained to evaluate component rotation. Which of the following errors in component positioning is the most likely cause of lateral patellar maltracking?

Explanation

Lateral patellar maltracking is frequently caused by component malrotation. Internal rotation of the tibial component effectively lateralizes the tibial tubercle relative to the trochlear groove, increasing the Q-angle and causing a lateral pull on the patella. Similarly, internal rotation of the femoral component medializes the trochlear groove, also increasing the Q-angle. External rotation of the tibial or femoral components tends to improve patellar tracking. Medialization of the patellar button improves tracking by lateralizing the patellar bone.

Question 13

During single-leg stance, the hip abductor muscles must generate sufficient force to maintain a level pelvis. In a normal adult hip, the ratio of the body weight moment arm to the abductor moment arm is approximately 2.5 to 1. If a patient weighs 800 N, what is the approximate joint reaction force across the hip during single-leg stance?

Explanation

To maintain a level pelvis in single-leg stance, the torque generated by the abductors must equal the torque of the body weight. Given the moment arm ratio is 2.5:1, Abductor Force × 1 = Body Weight × 2.5. Therefore, Abductor Force = 800 N × 2.5 = 2000 N. The total joint reaction force (JRF) across the hip is the sum of the body weight and the abductor force pulling the femur into the acetabulum. JRF = 800 N + 2000 N = 2800 N (which is 3.5 times body weight).

Question 14

A 65-year-old diabetic male is evaluated in the clinic prior to an elective total hip arthroplasty. Which of the following preoperative hemoglobin A1c (HbA1c) levels is the generally accepted strict upper threshold above which the risk of periprosthetic joint infection (PJI) is significantly elevated, typically prompting delay of elective arthroplasty?

Explanation

Tight glycemic control is paramount in preventing surgical site infections and PJI. Extensive orthopedic literature and consensus guidelines generally cite an HbA1c threshold of > 7.5% to 8.0% as a significant inflection point where the risk of postoperative complications, including infection, dramatically increases. Most institutional protocols delay elective joint arthroplasty if the HbA1c is 8.0% or higher, optimizing the patient prior to surgery.

Question 15

During a total knee arthroplasty, the surgeon is performing the proximal tibial resection. Injury to the popliteal artery is a rare but catastrophic complication. Anatomically, at what level is the popliteal artery most tethered and vulnerable during the standard tibial cut?

Explanation

The popliteal artery is located directly posterior to the posterior joint capsule. It is most vulnerable to injury during the proximal tibial bone cut because it runs in close proximity to the posterior capsule just behind the tibial attachment of the posterior cruciate ligament (PCL). Careful retractor placement and awareness of saw blade depth in this exact region are critical to avoid vascular injury.

Question 16

Which of the following procedural steps is a defining characteristic of a "third-generation" cementing technique in total hip arthroplasty, aimed at maximizing the mechanical interlock and longevity of the cemented stem?

Explanation

Third-generation cementing techniques significantly improve the survivorship of cemented femoral stems. Key components include: thorough pulsatile lavage of the cancellous bone to remove fat and marrow, insertion of a distal medullary restrictor (plug), vacuum mixing or centrifugation of the cement to reduce porosity, retrograde filling of the canal using a cement gun, and pressurization of the cement prior to stem insertion to ensure micro-interlock with the cancellous bone bed.

Question 17

A patient with a history of long-segment lumbar fusion (L2-Pelvis) is planned for a total hip arthroplasty. Because of spinopelvic stiffness, how does the pelvis normally respond when transitioning from standing to sitting, and what specific instability is this patient at highest risk for due to their fusion?

Explanation

In a normal spinopelvic relationship, when a person transitions from standing to sitting, the lumbar spine flexes and the pelvis tilts posteriorly. This posterior pelvic tilt functionally increases acetabular anteversion, allowing the anterior femur to clear the acetabulum during deep hip flexion. A patient with a fusion to the pelvis has a stiff spine and cannot posteriorly tilt the pelvis when sitting. Therefore, the functional anteversion does not increase, leading to anterior bony/component impingement and subsequent posterior dislocation.

Question 18

Tranexamic acid (TXA) is routinely administered in total joint arthroplasty to reduce perioperative blood loss. What is the primary pharmacologic mechanism of action of TXA?

Explanation

Tranexamic acid (TXA) is a synthetic analog of the amino acid lysine. It acts as an antifibrinolytic agent by reversibly and competitively binding to the lysine receptor sites on plasminogen. This prevents plasminogen from activating into plasmin, thereby inhibiting the degradation of fibrin clots (fibrinolysis). It does not affect the primary coagulation cascade or platelet function.

Question 19

A 55-year-old female is scheduled for a primary total knee arthroplasty. She reports a history of severe localized blistering rash when wearing cheap jewelry or metal watch bands. Dermatological patch testing confirms a severe Nickel allergy. Which of the following femoral component materials is most appropriate for this patient?

Explanation

Nickel is a common sensitizing agent in metal allergies. Standard Cobalt-Chromium-Molybdenum (CoCr) alloys and stainless steel both contain small but significant amounts of nickel, which can elicit an allergic response in highly sensitized individuals leading to aseptic failure. Oxidized Zirconium (Oxinium) and pure Titanium alloys do not contain nickel and are the preferred bearing surfaces for the femoral component in patients with severe, confirmed metal hypersensitivities. Tantalum is used for ingrowth surfaces, not articular surfaces. Polyethylene is a plastic bearing insert, not a femoral component.

Question 20

During a total knee arthroplasty for a severe fixed varus deformity, the surgeon performs sequential medial soft tissue releases to balance the extension gap. After removing medial osteophytes and releasing the deep medial collateral ligament (MCL) and the posteromedial corner, the knee remains tight medially in full extension. What is the next most appropriate structure to release?

Explanation

The standard step-wise medial release for a varus knee deformity begins with the removal of medial and posterior tibial osteophytes. If the medial side remains tight, the deep MCL is released, followed by the posteromedial capsule. If further release is necessary, the superficial MCL is progressively released (often subperiosteally elevated off the proximal tibia). If profound deformity exists, a final step may involve releasing the pes anserinus. Releasing lateral structures (LCL, IT band, popliteus) is indicated for valgus knees, not varus knees.

Question 21

A 70-year-old man undergoes a primary total hip arthroplasty. He has a history of a solid instrumented lumbar fusion from L2 to the sacrum. How does this spinal pathology affect his spinopelvic biomechanics and subsequent dislocation risk during sitting?

Explanation

In patients with lumbar fusion to the sacrum, the pelvis becomes stiff and cannot retrovert during sitting. This failure to increase functional acetabular anteversion upon sitting leads to anterior bony impingement and a high risk of posterior dislocation.

Question 22

During a posterior-stabilized total knee arthroplasty, trial reduction reveals a joint that is balanced in flexion but excessively tight in extension. Which of the following is the most appropriate intraoperative step to achieve a balanced gap?

Explanation

An isolated tight extension gap is managed by removing more distal femoral bone, which enlarges the extension gap without affecting the flexion gap. Recutting the proximal tibia would enlarge both the flexion and extension gaps symmetrically.

Question 23

A 76-year-old woman presents with acute thigh pain after a fall. She underwent a total hip arthroplasty 8 years ago. Radiographs demonstrate a fracture around the tip of the femoral stem. The stem appears to be subsided and loose, but there is adequate proximal diaphyseal bone stock.

According to the Vancouver classification, what is the most appropriate surgical management?

Explanation

This represents a Vancouver B2 periprosthetic fracture (loose stem, adequate bone stock). The standard of care is revision of the femoral component using a long uncemented diaphyseal-engaging stem that bypasses the most distal fracture line by at least two cortical diameters.

Question 24

A 65-year-old female undergoes a primary total hip arthroplasty. The surgeon opts to use a high-offset femoral stem rather than a standard-offset stem, maintaining the identical neck length and seating depth within the medullary canal. What is the expected biomechanical outcome of this modification?

Explanation

A high-offset stem lateralizes the femoral shaft, which increases the lever arm of the abductor mechanism (increasing tension and efficiency) without altering the vertical height or leg length. Increased offset aids in hip stability and minimizes impingement.

Question 25

During a primary total knee arthroplasty using a measured resection technique, trial reduction reveals a symmetric but excessively tight extension gap, while the flexion gap is perfectly balanced. Which of the following is the most appropriate next step to balance the knee?

Explanation

A tight extension gap with a well-balanced flexion gap is managed by resecting additional bone from the distal femur. Resecting more proximal tibia would inappropriately widen both the extension and flexion gaps.

Question 26

A 70-year-old male presents with chronic pain 2 years following a total hip arthroplasty. Serology reveals an ESR of 45 mm/hr and a CRP of 25 mg/L. Hip aspiration yields synovial fluid with a WBC count of 3,500 cells/uL and 75% neutrophils. Which of the following synovial biomarkers offers the highest specificity for confirming a periprosthetic joint infection (PJI)?

Explanation

Synovial alpha-defensin is an antimicrobial peptide released by neutrophils that has demonstrated extremely high sensitivity and specificity (often >95%) for diagnosing periprosthetic joint infections, making it highly reliable in ambiguous cases.

Question 27

A 60-year-old female with advanced knee osteoarthritis is scheduled for a total knee arthroplasty. She has a documented, severe, delayed-type hypersensitivity reaction to nickel. Which of the following femoral component biomaterials is most appropriate to minimize the risk of a hypersensitivity reaction?

Explanation

Oxidized zirconium (Oxinium) components have virtually zero nickel content and possess excellent wear characteristics, making them the implant of choice for patients with documented severe nickel or metal hypersensitivity in total knee arthroplasty. Standard CoCr implants contain trace amounts of nickel.

Question 28

A 55-year-old male who underwent a ceramic-on-ceramic total hip arthroplasty 2 years ago presents complaining of an audible squeaking sound during ambulation. Radiographs show secure components. Which of the following factors is most strongly associated with the development of this phenomenon?

Explanation

Squeaking in ceramic-on-ceramic hips is highly associated with component malposition, particularly excessive acetabular inclination (>50 degrees) or anteversion. This leads to edge loading, disruption of the fluid film lubrication, and stripe wear.

Question 29

A 65-year-old female presents with anterior knee pain and a painful catching sensation when actively extending her knee from 40 to 30 degrees of flexion. She underwent a posterior-stabilized total knee arthroplasty one year ago. What is the most likely underlying etiology of her symptoms?

Explanation

This presentation is classic for patellar clunk syndrome, a complication specific to posterior-stabilized TKA designs. It occurs when a fibrous nodule develops at the superior pole of the patella and catches in the intercondylar box of the femoral component during extension.

Question 30

The direct anterior approach (Smith-Petersen) for total hip arthroplasty utilizes a superficial internervous plane. Which of the following best describes the nerve supplies to the muscles bounding this plane?

Explanation

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

Question 31

A 75-year-old female sustains a distal femur fracture just superior to a well-fixed posterior-stabilized total knee arthroplasty component.

The fracture is displaced but the joint line is maintained. What is the most appropriate surgical management?

Explanation

This is a Lewis-Rorabeck Type II periprosthetic fracture (displaced fracture, well-fixed components). The standard of care is open reduction internal fixation (ORIF) with a lateral locking plate or a retrograde intramedullary nail.

Question 32

A 68-year-old male with a metal-on-polyethylene total hip arthroplasty utilizing a large-diameter cobalt-chromium head presents with progressive groin pain. Radiographs show well-fixed components. Aspiration yields sterile, low-WBC fluid. MRI demonstrates a large pseudotumor. What is the primary pathophysiologic mechanism?

Explanation

This scenario describes trunnionosis, or adverse local tissue reaction (ALTR) resulting from mechanically assisted crevice corrosion (MACC) at the modular head-neck junction. It is particularly associated with large metal heads on distinct metal alloy stems.

Question 33

In kinematic alignment principles for total knee arthroplasty, the primary goal for orienting the femoral component is to align its transverse axis with which of the following native anatomical axes?

Explanation

Kinematic alignment aims to restore the patient's pre-arthritic constitutional alignment. For the femur, this involves aligning the component with the primary transverse axis of the knee, which is the cylindrical axis of the posterior femoral condyles.

Question 34

A patient experiences recurrent posterior dislocations of a total hip arthroplasty. CT evaluation reveals a combined anteversion (Widmer technique) of 15 degrees, with the acetabular cup at 5 degrees and the femoral stem at 10 degrees. What is the most appropriate revision strategy?

Explanation

The normal target for combined anteversion in THA is roughly 25 to 45 degrees. A combined anteversion of 15 degrees is too low and predisposes the patient to posterior dislocation. Revising the acetabular component to increase its version will restore appropriate stability.

Question 35

During a total knee arthroplasty for a severe, fixed valgus deformity, standard releases are performed. Which structure is typically tightest and may require targeted release to effectively balance the extension gap laterally?

Explanation

In a fixed valgus knee, the lateral structures are contracted. The tightest structures typically requiring release to balance the extension gap include the iliotibial band (ITB), lateral collateral ligament (LCL), and posterolateral capsule.

Question 36

An 80-year-old male sustains a fall resulting in a periprosthetic femur fracture around a previously asymptomatic THA.

Radiographs demonstrate a fracture pattern localized around the femoral stem. The stem exhibits obvious subsidence and loosening, but the proximal femoral bone stock remains adequate. What is the Vancouver classification and standard treatment?

Explanation

A fracture around the stem with a loose implant but good proximal bone stock is classified as Vancouver B2. The gold standard treatment is revision arthroplasty utilizing a long, fluted, tapered stem to bypass the fracture and achieve diaphyseal fixation.

Question 37

If the femoral component in a total knee arthroplasty is inadvertently placed in excessive internal rotation relative to the surgical transepicondylar axis, what is the most likely biomechanical consequence?

Explanation

Internal rotation of the femoral component elevates the anterolateral flange, pushing the patella medially and causing relative lateral maltracking. It also shifts the medial posterior condyle distally and posteriorly, causing a tight medial flexion gap.

Question 38

In strictly controlled in-vitro simulator studies, which of the following bearing surface combinations demonstrates the lowest linear and volumetric wear rates per million cycles?

Explanation

Ceramic-on-ceramic articulations provide the highest scratch resistance and best fluid-film lubrication, resulting in the lowest wear rates of all available bearing surfaces (<1 micron/year in simulator testing).

Question 39

A patient with a midshaft femoral malunion presenting with 20 degrees of coronal varus requires a total knee arthroplasty. If standard intra-articular bone cuts perpendicular to the mechanical axis are performed without addressing the extra-articular deformity, what major intraoperative complication is most likely?

Explanation

Correcting a severe extra-articular deformity (>10-15 degrees) purely with intra-articular cuts leads to extreme asymmetric bone resection. This often cuts into the origin of the collateral ligaments, resulting in profound instability that standard implants cannot address.

Question 40

A surgeon decides to increase the femoral offset during a primary total hip arthroplasty (THA) using a high-offset femoral stem. Assuming leg length remains unchanged, what is the primary biomechanical effect of this modification?

Explanation

Increasing femoral offset lateralizes the greater trochanter, which lengthens the abductor moment arm. This improved mechanical advantage reduces the force required by the abductors, thereby significantly decreasing the overall joint reaction force across the hip.

Question 41

A 65-year-old patient presents with a 'clunking' sensation and recurrent instability in deep flexion 2 years after a posterior-stabilized (PS) total knee arthroplasty (TKA). What is the most likely biomechanical cause of this cam-post jump phenomenon?

Explanation

Cam-post disengagement (cam jump) in a PS knee typically occurs in deep flexion when the flexion gap is unacceptably loose. This allows the femur to translate anteriorly over the tibial post, leading to instability.

Question 42

A 45-year-old man undergoes THA with a ceramic-on-ceramic (CoC) articulation. Postoperatively, he complains of a loud, high-pitched squeaking noise during gait. Which of the following component positions is most strongly associated with this phenomenon?

Explanation

Squeaking in CoC bearings is heavily linked to stripe wear and edge loading. Edge loading most commonly occurs due to component malposition, specifically excessive cup steepness (inclination) or excessive anteversion.

Question 43

According to the Musculoskeletal Infection Society (MSIS) / International Consensus Meeting (ICM) criteria, which of the following is considered a definitive major criterion for diagnosing a periprosthetic joint infection (PJI)?

Explanation

The two major criteria for PJI are the presence of a sinus tract communicating with the joint, or two distinct positive tissue/fluid cultures yielding the same organism. Biomarkers like ESR, CRP, alpha-defensin, and synovial WBC are considered minor criteria.

Question 44

During trialing of a primary TKA, the surgeon notes that the knee is perfectly balanced and achieves full extension, but it is unacceptably tight in 90 degrees of flexion, preventing full range of motion. Which of the following is the most appropriate next step in management?

Explanation

A knee that is tight in flexion but balanced in extension requires a modification that only increases the flexion gap. Increasing the posterior tibial slope or downsizing the femoral component (with anterior referencing) will selectively open the flexion gap.

Question 45

The direct anterior approach (DAA) to the hip is increasingly popular for primary THA. This approach utilizes a true internervous plane between which two muscles superficially?

Explanation

The superficial internervous plane for the direct anterior approach (Smith-Petersen) lies between the sartorius (femoral nerve) and the tensor fasciae latae (superior gluteal nerve). The deep plane is between the rectus femoris (femoral nerve) and gluteus medius (superior gluteal nerve).

Question 46

A 78-year-old woman presents with a periprosthetic femur fracture around her cemented THA stem after a fall. Radiographs demonstrate a spiral fracture at the tip of the stem with evidence of subsidence and a radiolucent mantle, but excellent proximal and distal bone stock. What is the most appropriate definitive management?

Explanation

This is a Vancouver B2 fracture (fracture around a loose stem with adequate bone stock). The standard of care is revision arthroplasty utilizing a long extensively porous-coated or fluted tapered stem that bypasses the most distal fracture line by at least two cortical diameters.

Question 47

A patient presents with a painful catch and an audible 'clunk' as their knee approaches terminal active extension 1 year after a posterior-stabilized TKA. What is the pathomechanism of this specific complication?

Explanation

Patellar clunk syndrome is strongly associated with posterior-stabilized (PS) knee designs. It occurs when a fibrosynovial nodule develops at the superior pole of the patella and catches within the femoral intercondylar box during active extension from a flexed position.

Question 48

Mechanically assisted crevice corrosion (MACC), or trunnionosis, has been identified as a cause of adverse local tissue reactions in non-metal-on-metal THA. Which combination of implant factors confers the highest risk for trunnionosis?

Explanation

Trunnionosis is exacerbated by increased frictional torque and bending moments at the head-neck junction. Large diameter metallic heads (>36mm) and long/high-offset necks significantly increase these mechanical stresses, accelerating MACC.

Question 49

Adverse local tissue reaction (ALTR) and pseudotumor formation in metal-on-metal (MoM) hip arthroplasty (ALVAL) is primarily driven by which immunological mechanism?

Explanation

Aseptic Lymphocytic Vasculitis-Associated Lesion (ALVAL) represents a delayed, cell-mediated Type IV hypersensitivity reaction to metal ions (cobalt and chromium). It is characterized histologically by dense perivascular lymphocytic infiltrates.

Question 50

To minimize the risk of posterior dislocation following a primary THA, surgeons aim for an optimal 'combined anteversion' of the acetabular and femoral components. Based on classic principles, what is the generally accepted target range for combined anteversion?

Explanation

Combined anteversion (acetabular anteversion + femoral anteversion) is targeted between 25 and 45 degrees (often cited as the Ranawat or Widmer safe zones) to optimize stability and prevent both anterior and posterior impingement.

Question 51

During a mechanically aligned primary TKA, the surgeon uses an intramedullary guide for the distal femoral cut. To achieve a neutral mechanical axis, the valgus cut angle set on the distal femoral cutting block is typically based on the angle between which two axes?

Explanation

In mechanical alignment, the goal is a femoral cut perpendicular to the mechanical axis. Because the intramedullary guide follows the femoral anatomical axis, the valgus cut angle (usually 5-7 degrees) compensates for the natural divergence between the anatomical and mechanical axes of the femur.

Question 52

A 72-year-old female presents for revision THA. Radiographs demonstrate severe acetabular osteolysis with a fracture line separating the superior and inferior halves of the hemipelvis, indicating pelvic discontinuity.

What is the most appropriate reconstructive option to achieve long-term stability?

Explanation

Pelvic discontinuity occurs when there is a complete dissociation between the ilium and the ischium/pubis. Stable fixation requires bridging the defect, best achieved with a cup-cage construct, custom triflange, or an ilioischial plate combined with a trabecular metal shell.

Question 53

During a TKA, a surgeon inadvertently uses a patellar button that is significantly thicker than the native resected patella, leading to an 'overstuffed' anterior compartment. What is the most likely clinical consequence of this error?

Explanation

Overstuffing the patellofemoral joint increases tension on the extensor mechanism. This leads to increased retropatellar contact forces, resulting in anterior knee pain, and a mechanical block that reduces terminal knee flexion.

Question 54

Highly cross-linked polyethylene (HXLPE) has significantly reduced wear rates in THA. What is the primary biological and mechanical advantage of doping HXLPE with Vitamin E rather than performing post-irradiation remelting?

Explanation

Remelting HXLPE eliminates free radicals but decreases its mechanical properties (fatigue strength). Blending with Vitamin E (an antioxidant) neutralizes free radicals without the need for remelting, thereby maintaining the material's structural fatigue resistance while preventing oxidation.

Question 55

Tranexamic acid (TXA) is widely used in adult reconstruction to minimize perioperative blood loss. What is the precise pharmacological mechanism of action of this medication?

Explanation

Tranexamic acid is a synthetic analog of the amino acid lysine. It reversibly binds to the lysine-binding sites on plasminogen, competitively inhibiting its activation to plasmin, thereby preventing the degradation of fibrin clots (antifibrinolytic effect).

Question 56

A surgeon is performing a primary TKA on a patient with a severe fixed valgus deformity (Krackow Type II). After bone cuts, the lateral compartment remains excessively tight in extension but is adequately balanced in flexion. Which structure should be selectively released to correct this specific imbalance?

Explanation

The iliotibial band (ITB) acts as a primary lateral tether in extension but relaxes in flexion. Therefore, a tight extension gap with a balanced flexion gap on the lateral side dictates selective release of the ITB or lateral capsule.

Question 57

During acetabular component fixation in THA, screw placement is targeted to specific anatomic zones to avoid neurovascular injury. According to Wasielewski's quadrant system, which quadrant is considered the 'safe zone' for placing screws?

Explanation

The posterosuperior quadrant is the safe zone for screw placement, providing excellent bone stock (ilium) while avoiding major neurovascular structures. The anterosuperior/anteroinferior quadrants risk injury to the external iliac vessels and obturator nerve.

Question 58

Increasing femoral offset during a total hip arthroplasty has what primary biomechanical effect on the hip joint?

Explanation

Increasing femoral offset increases the abductor moment arm. This mechanically reduces the required force generated by the abductor muscles to maintain pelvic stability, thereby decreasing the overall joint reaction force.

Question 59

Review the provided imaging.

During a total knee arthroplasty, the surgeon notes that the extension gap is perfectly balanced, but the flexion gap is excessively tight. Which of the following is the most appropriate step to balance the knee?

Explanation

A tight flexion gap with a balanced extension gap can be addressed by increasing the posterior tibial slope, downsizing the femoral component, or recessing the PCL (in CR knees). Resecting more distal femur only loosens the extension gap.

Question 60

A 65-year-old male presents with persistent groin pain 4 years after a metal-on-polyethylene total hip arthroplasty. Aspiration is negative for infection, but serum cobalt levels are significantly elevated while chromium levels are normal. What is the most likely diagnosis?

Explanation

Elevated cobalt with normal or mildly elevated chromium in a metal-on-polyethylene THA is classic for mechanically assisted crevice corrosion (trunnionosis) at the modular head-neck taper. Metal-on-metal bearing wear typically presents with elevations of both ions.

Question 61

When performing a direct anterior approach for total hip arthroplasty, the superficial internervous plane utilizes the interval between which two muscles?

Explanation

The superficial internervous plane in the direct anterior (Smith-Petersen) approach is between the sartorius (innervated by the femoral nerve) and the tensor fasciae latae (innervated by the superior gluteal nerve). The deep plane is between the rectus femoris and gluteus medius.

Question 62

Review the radiograph.

A 72-year-old female sustains a periprosthetic femur fracture around a cemented total hip arthroplasty. Radiographs reveal a fracture at the tip of the stem. The stem is loose, but there is adequate proximal femoral bone stock. What is the appropriate Vancouver classification and standard management?

Explanation

A periprosthetic fracture around the stem with a loose implant but adequate bone stock is a Vancouver B2 fracture. The gold standard treatment is revision to a longer stem (usually uncemented, diaphyseal-engaging) that bypasses the fracture by at least two cortical diameters.

Question 63

A patient presents with a palpable and audible clunk at 30 to 40 degrees of knee extension 1 year after a posterior-stabilized total knee arthroplasty. What is the primary etiology of this complication?

Explanation

Patellar clunk syndrome is caused by the formation of a fibrous nodule at the superior pole of the patella. During active extension, this nodule catches in the intercondylar notch/box of a posterior-stabilized femoral component and then pops out, producing a clunk.

Question 64

In a posterior-stabilized total knee arthroplasty, the interaction between the femoral cam and the tibial post is designed to replicate the function of the posterior cruciate ligament (PCL). What specific kinematic function does this mechanism provide?

Explanation

The cam-post mechanism in a posterior-stabilized TKA forces posterior femoral rollback during deep flexion. This mimics the native PCL, preventing posterior impingement of the tibia on the femur and thereby optimizing knee flexion.

Question 65

According to the Musculoskeletal Infection Society (MSIS) criteria, which of the following is considered a major (absolute) criterion for diagnosing a periprosthetic joint infection?

Explanation

A sinus tract communicating directly with the prosthesis is one of the major absolute criteria for periprosthetic joint infection. The other major criterion is two positive periprosthetic cultures with phenotypically identical organisms.

Question 66

A 55-year-old active male with a ceramic-on-ceramic total hip arthroplasty reports an audible squeaking sound during certain activities. Which of the following component factors is most strongly associated with this phenomenon?

Explanation

Squeaking in ceramic-on-ceramic bearings is strongly associated with edge loading. This phenomenon typically results from component malposition, specifically excessive cup inclination or anteversion, as well as microseparation during the swing phase of gait.

Question 67

Review the radiograph.

A patient experiences recurrent posterior dislocations of their total hip arthroplasty. On radiographic evaluation, the acetabular component is found to have 5 degrees of anteversion and 30 degrees of inclination. What is the most appropriate acetabular revision strategy?

Explanation

The Lewinnek safe zone for an acetabular cup is 15 +/- 10 degrees of anteversion and 40 +/- 10 degrees of inclination. This patient's cup is under-anteverted and under-inclined, predisposing to posterior instability; therefore, both should be increased.

Question 68

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

Explanation

Inflammatory arthropathies like rheumatoid arthritis involve the entire synovial lining and typically progress to pan-compartmental disease, making them absolute contraindications for UKA. An intact ACL is a strict prerequisite for UKA.

Question 69

Following total hip arthroplasty, a patient at high risk for heterotopic ossification (HO) is prescribed prophylactic radiation therapy. To be maximally effective, within what timeframe relative to the surgery should the radiation be administered?

Explanation

Prophylactic radiation for heterotopic ossification is most effective when administered within 24 hours preoperatively or up to 72 hours postoperatively. It works by inhibiting the differentiation of mesenchymal stem cells into osteoblasts.

Question 70

Review the intraoperative image.

During a revision total knee arthroplasty, restoring the native joint line is critical for optimal outcome. What is the most reliable bony landmark to determine the native joint line level?

Explanation

The native knee joint line is typically located 2.5 to 3 cm distal to the medial epicondyle and approximately 1.5 cm proximal to the fibular head. Restoring this level is essential for optimizing patellofemoral tracking and mid-flexion kinematics.

Question 71

Intraoperatively during a THA, the surgeon tests the hip and notes it is stable in all positions, but the leg is 15 mm longer than the contralateral side, and the surrounding soft tissues are extremely tight. What is the most appropriate surgical adjustment?

Explanation

If the hip is stable but the leg is too long with tight soft tissues, the center of rotation has been elevated too far superiorly. The appropriate step is to lower the stem by recutting the femoral neck more distally, decreasing leg length while maintaining stability.

Question 72

In total knee arthroplasty, which of the following design characteristics of the polyethylene insert most significantly increases the risk of accelerated wear and osteolysis?

Explanation

Flat or low-conformity polyethylene designs lead to point contact rather than surface contact, drastically increasing focal contact stresses. This predisposes the polyethylene to accelerated subsurface damage, delamination, wear, and subsequent osteolysis.

Orthopedic Ob Reconstru Review | Dr Hutaif Hip & Knee R -...

Orthopedic Adult Reconstructiv Review | Dr Hutaif Hip & -...

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Orthopedic Adult Reconstructiv Review | Dr Hutaif Hip & -...

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