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

Question 1

A 72-year-old female is undergoing revision total hip arthroplasty for aseptic loosening. Intraoperative assessment of the acetabulum reveals superior migration of the cup of 3.5 cm, medial migration past the Kohler line, and an ischiolytic lesion. There is severe superior bone loss with less than 40% host bone contact available for the new component, but the anterior and posterior columns remain intact. What is the most appropriate acetabular reconstruction strategy?

Explanation

The scenario describes a Paprosky 3B acetabular defect (superior migration >3cm, medial migration, ischiolytic lesion, and <40% host bone contact), without pelvic discontinuity (columns intact). The gold standard for this level of severe uncontained bone loss is a highly porous (e.g., trabecular metal) cup with metal augments to substitute for the massive structural bone loss. A cup-cage is typically reserved for pelvic discontinuity, while standard hemispherical cups will fail due to lack of adequate biological fixation (<50% host bone contact).

Question 2

A 65-year-old male is evaluated for a painful total knee arthroplasty (TKA) 2 years postoperatively. Serum CRP is 18 mg/L and ESR is 45 mm/hr. Synovial fluid aspiration demonstrates a WBC count of 4,800 cells/µL with 75% PMNs. An alpha-defensin test is positive. According to the 2018 International Consensus Meeting (ICM) criteria, what is the most appropriate next step in management?

Explanation

According to the 2018 ICM criteria, the diagnosis of periprosthetic joint infection (PJI) is definitively confirmed based on the scoring system. A positive alpha-defensin (3 points), elevated synovial WBC/PMN (3 points), and elevated serum inflammatory markers (2 points) yield a score well above the threshold for definitive PJI (score ≥6). The standard of care for a chronic PJI (>4 weeks post-op) is revision arthroplasty, most commonly a two-stage exchange in North America, or single-stage in highly selected cases. Liner exchange with retention of components (DAIR) is contraindicated for chronic infections.

Question 3

During a primary TKA, the surgeon uses spacer blocks to assess gap kinematics. The extension gap is symmetric and well-balanced. However, the flexion gap is symmetric but significantly tight, preventing adequate knee flexion with the trial components. Which of the following technical adjustments is the most appropriate next step to balance the knee?

Explanation

The scenario describes a 'balanced extension, tight flexion' gap mismatch. Modifying the distal femoral cut or the overall polyethylene thickness will affect BOTH gaps. Releasing the PCL primarily affects the flexion gap but often necessitates switching to a posterior stabilized (PS) construct if not already planned, and upsizing poly would tighten extension. Downsizing the femoral component (which decreases the AP dimension of the femur) removes more posterior femoral condyle bone, thereby opening the flexion gap without altering the extension gap. Increasing (not decreasing) tibial slope would also open the flexion gap, but downsizing the femur is the most direct and standard adjustment.

Question 4

A 60-year-old male with a metal-on-polyethylene THA presents with an 8-month history of progressive groin pain. Radiographs show a well-fixed stem and cup. MRI reveals a large, thick-walled cystic fluid collection surrounding the hip joint. Aspiration yields yellow fluid, negative cultures, and a WBC count of 500 cells/µL. Serum cobalt is 18 ppb and chromium is 2 ppb. What is the primary pathophysiologic mechanism driving this complication?

Explanation

The clinical presentation (cystic pseudotumor, groin pain, negative cultures) combined with dramatically elevated cobalt levels relative to chromium (Co > Cr) in a metal-on-polyethylene THA is pathognomonic for trunnionosis. This is driven by mechanically assisted crevice corrosion (MACC) at the modular head-neck taper junction. Polyethylene wear osteolysis (Option A) would not elevate serum metal ions or typically present with an ALVAL-type pseudotumor.

Question 5

In planning a revision total hip arthroplasty, the surgeon evaluates the femoral bone stock. There is complete loss of metaphyseal cancellous bone, and diaphyseal bone loss extends 2 cm distal to the lesser trochanter. However, the diaphyseal isthmus remains intact with 5 cm of scratch fit available. What is the correct Paprosky Femoral classification and the most appropriate reconstructive strategy?

Explanation

This describes a Paprosky Type 3A femoral defect. Type 3A defects have severe metaphyseal damage and diaphyseal bone loss extending past the lesser trochanter, but crucially retain >4 cm of intact diaphyseal bone at the isthmus to achieve reliable distal fixation. The recommended implant is a fully porous-coated cylindrical stem (6-8 inches) or a tapered fluted modular stem. Type 3B defects have <4 cm of intact diaphyseal scratch fit.

Question 6

A 72-year-old female is scheduled for a primary THA. She has a history of a multi-level lumbar spinal fusion (L2-S1). Preoperative lateral pelvic radiographs demonstrate a sacral slope of 35 degrees standing and 33 degrees sitting. Recognizing this spinopelvic pathology, how should the surgeon adjust the target acetabular cup positioning to minimize the risk of posterior dislocation?

Explanation

The patient has a stiff spinopelvic construct (change in sacral slope from standing to sitting is <10 degrees). In a normal spine, sitting causes posterior pelvic tilt, which functionally increases acetabular anteversion, protecting against posterior dislocation during hip flexion. A stiff spine fails to tilt posteriorly when sitting, leaving the cup relatively retroverted and risking anterior bony impingement with subsequent posterior dislocation. Therefore, the surgeon must compensate by increasing the target cup anteversion and inclination.

Question 7

During a complex primary TKA for a severe fixed valgus deformity, the medial collateral ligament (MCL) is inadvertently transected mid-substance and is deemed completely incompetent and irreparable. Which of the following implant constraints is required to provide adequate stability?

Explanation

A completely incompetent, absent, or irreparable MCL in total knee arthroplasty necessitates a rotating hinge construct. A Constrained Condylar Knee (CCK) utilizes a tall tibial post to provide varus/valgus stability, but it relies on functional collateral ligaments to act as checkreins; it will fail early or subluxate if the primary stabilizer (MCL) is completely deficient. CR and PS implants offer no coronal plane constraint.

Question 8

A surgeon is performing a primary THA using a direct anterior (Smith-Petersen) approach. Which of the following neurologic structures is at highest risk during the superficial dissection, and what is its expected sensory distribution if injured?

Explanation

The direct anterior approach utilizes the internervous plane between the sartorius (femoral n.) and tensor fasciae latae (superior gluteal n.). The lateral femoral cutaneous nerve (LFCN) is highly vulnerable during the superficial dissection as it courses over or near the sartorius muscle just distal to the ASIS. Injury results in lateral/anterolateral thigh numbness (meralgia paresthetica).

Question 9

A 78-year-old female presents with a periprosthetic femur fracture around a cemented polished taper slip stem, 10 years post-op. Radiographs show a spiral fracture extending to the distal tip of the stem. The stem cement mantle is debonded and the implant has subsided, but the proximal femoral bone stock remains robust. What is the Vancouver classification and the recommended standard of care?

Explanation

This is a Vancouver B2 fracture: fracture around the stem (B), loose implant (2), with adequate proximal bone stock. The standard of care for Vancouver B2 fractures is revision arthroplasty using a long uncemented diaphyseal engaging stem (extensively porous-coated or fluted tapered), bypassing the most distal fracture line by at least two cortical diameters. B1 fractures (well-fixed stem) are treated with ORIF. B3 fractures (loose stem, poor bone stock) require proximal femoral replacement.

Question 10

What is the primary cellular cascade responsible for aseptic loosening and periprosthetic osteolysis in a total hip arthroplasty?

Explanation

Periprosthetic osteolysis is primarily a macrophage-mediated biologic response to particulate wear debris (most commonly polyethylene). Macrophages phagocytose these particles but cannot digest them, leading to activation and the release of pro-inflammatory cytokines such as TNF-alpha, IL-1, IL-6, and PGE2. These cytokines increase the expression of RANKL, which strongly activates osteoclasts, leading to bone resorption and eventual implant loosening.

Question 11

A 66-year-old patient undergoes revision TKA. The surgeon utilizes thick tibial and femoral augments to manage bone loss. Postoperatively, the patient reports a painful catch and mid-flexion instability. Lateral radiographs show the inferior pole of the patella is abnormally close to the tibial plateau. What intraoperative technical error most likely led to this complication?

Explanation

Elevating the joint line is a common complication in revision TKA when distal femoral bone loss is not adequately compensated with distal femoral augments, and a thicker polyethylene is used instead. This elevates the tibiofemoral joint line relative to the patella. Because the patellar tendon length remains fixed to the tibial tubercle, the patella sits lower relative to the joint line (patella baja/infra). This alters patellofemoral tracking, causes anterior knee pain, limits flexion, and can lead to mid-flexion instability.

Question 12

In a revision THA setting, a patient presents with massive acetabular osteolysis. Preoperative radiographs reveal a distinct transverse fracture line through the acetabular fossa and medial translation of the inferior hemipelvis relative to the superior hemipelvis. What is the diagnosis, and what is the most appropriate intraoperative implant consideration?

Explanation

The clinical description of a transverse fracture line through the fossa with independent movement/translation of the superior and inferior hemipelvis is the definition of pelvic discontinuity. To bridge and stabilize this defect, constructs that secure the ilium to the ischium/pubis are required. A cup-cage construct, custom triflange component, or a highly porous cup with half-pin distraction are the standard of care.

Question 13

A 75-year-old male with Parkinson's disease and a history of recurrent posterior hip dislocations is scheduled for revision THA. A dual mobility construct is selected. What is the primary biomechanical advantage of a dual mobility bearing that reduces dislocation risk?

Explanation

A dual mobility bearing features a small inner metal or ceramic head that articulates within a larger unconstrained mobile polyethylene head, which in turn articulates within the metallic acetabular shell. The primary advantage is an increased effective head diameter (the size of the large poly head), which drastically increases the jump distance required for dislocation. The dual articulation minimizes wear compared to a traditional monolithic large head design.

Question 14

Intravenous Tranexamic Acid (TXA) is routinely utilized in total joint arthroplasty to reduce perioperative blood loss. Which of the following accurately describes its pharmacological mechanism of action?

Explanation

Tranexamic acid is an antifibrinolytic agent. It works by reversibly and competitively binding to the lysine receptor sites on plasminogen. This prevents plasminogen from binding to fibrin and subsequently being activated into plasmin, thereby inhibiting the degradation of fibrin clots (fibrinolysis).

Question 15

A 55-year-old patient underwent the first stage of a two-stage exchange for a chronic MRSA periprosthetic hip infection. An articulating antibiotic spacer was placed. According to established protocols, when is the optimal time to evaluate the patient for the second-stage reimplantation?

Explanation

The standard protocol for two-stage exchange arthroplasty for PJI requires completion of culture-directed systemic antibiotic therapy (typically 4-6 weeks of IV antibiotics), followed by an 'antibiotic holiday' (often 2-4 weeks) off all antibiotics. If the joint remains clinically quiescent and inflammatory markers trend down or normalize, the patient is cleared for reimplantation. Aspiration may be performed to ensure negative cultures prior to stage 2.

Question 16

A 68-year-old female presents 3 years post-TKA with the sudden inability to actively extend her knee after a fall. Examination reveals a palpable gap at the superior pole of the patella. For this chronic, full-thickness quadriceps tendon tear in the setting of a TKA, what is the most reliable surgical treatment option to restore extensor mechanism continuity?

Explanation

Extensor mechanism disruption in the setting of a TKA is a devastating complication. Primary repair of chronic tears or poor quality tissue in this setting has a notoriously high failure rate. The most reliable and durable surgical options are reconstruction with an allograft (entire extensor mechanism: tibial tubercle, patella, quadriceps tendon) or synthetic mesh (e.g., Marlex mesh), which has gained significant popularity due to high success rates and lack of disease transmission risk.

Question 17

A 45-year-old female is scheduled for a TKA. She reports a history of severe localized blistering and eczematous rash whenever she wears inexpensive jewelry or metal watch bands. Which of the following pre-operative steps and implant choices represents the most appropriate evidence-based management?

Explanation

Patients with a strong clinical history of severe metal hypersensitivity (most commonly Nickel or Cobalt) are at risk for complications if standard Cobalt-Chromium (CoCr) implants are used. While routine patch testing or Lymphocyte Transformation Testing (LTT) is debated and often unreliable, the standard of care for a patient with a compelling history of metal allergy is to bypass testing and utilize hypoallergenic implants, such as oxidized zirconium (Oxinium) or Titanium alloy components.

Question 18

Which of the following intraoperative variables most significantly increases the risk of posterior dislocation following a primary THA performed via a posterior approach?

Explanation

The posterior approach disrupts the posterior soft tissue envelope (capsule and short external rotators). Failure to perform a robust posterior soft-tissue repair significantly increases the risk of early posterior dislocation. Conversely, increased acetabular anteversion, larger femoral head size (increases jump distance), increased leg length, and increased offset all serve to increase soft tissue tension and mechanical stability, thereby decreasing dislocation risk.

Question 19

A 62-year-old male is evaluated 8 weeks after a primary TKA complaining of severe stiffness. His active range of motion is 15 to 75 degrees. Radiographs demonstrate well-fixed and well-positioned components. Inflammatory markers (CRP/ESR) are strictly within normal limits, and pain is minimal at rest. Supervised physical therapy has reached a plateau over the last 3 weeks. What is the most appropriate next step in management?

Explanation

The patient is presenting with arthrofibrosis after TKA. He is in the optimal window (6-12 weeks post-op) for Manipulation Under Anesthesia (MUA). Infection has been ruled out (normal markers), components are mechanically sound, and conservative measures (PT) have failed. Delaying beyond 12 weeks drastically reduces the efficacy of MUA due to mature collagen cross-linking. Arthroscopic or open lysis is reserved for refractory cases after a failed MUA.

Question 20

A patient presents 6 months after a right THA complaining that the operative leg feels longer. On physical examination, the distance from the anterior superior iliac spine (ASIS) to the medial malleolus is strictly equal bilaterally. However, the distance from the umbilicus to the medial malleolus is 2 cm greater on the right. Anteroposterior pelvic radiographs demonstrate that the lesser trochanters are perfectly level relative to the ischial tuberosities. What is the most likely etiology of the patient's symptoms?

Explanation

The patient has an apparent (functional) leg length discrepancy, not a true (anatomic) leg length discrepancy. True leg length is measured from ASIS to medial malleolus, which is equal here, and confirmed radiographically by level lesser trochanters. Apparent leg length is measured from the umbilicus to the medial malleolus. A discrepancy in apparent length with equal true length is caused by pelvic obliquity, often driven by lumbar scoliosis, fixed spinal deformity, or adductor/abductor contractures.

Question 21

A 55-year-old active male is undergoing total hip arthroplasty. The surgeon chooses a highly cross-linked polyethylene (HXLPE) liner. Which of the following is an expected trade-off compared to conventional ultra-high-molecular-weight polyethylene (UHMWPE)?

Explanation

Cross-linking of polyethylene significantly reduces adhesive and abrasive wear, decreasing the volumetric wear rate. However, the irradiation process decreases the mechanical properties of the material, specifically reducing its fracture toughness, yield strength, ultimate tensile strength, and fatigue crack propagation resistance.

Question 22

In total hip arthroplasty, the 'jump distance' is defined as the distance the femoral head center must travel to dislocate over the rim of the acetabular component. Which of the following modifications most significantly increases the jump distance without altering the component position?

Explanation

The jump distance is the distance the center of the femoral head must translate to dislocate from the acetabular socket. Increasing the femoral head size increases the radius of the head, thereby proportionally increasing the jump distance and providing greater stability against dislocation.

Question 23

During a total knee arthroplasty (TKA), the surgeon decides to use a posterior-stabilized (PS) design instead of a cruciate-retaining (CR) design. Which of the following biomechanical phenomena is exclusively facilitated by the cam-and-post mechanism in the PS design?

Explanation

In a normal knee, the posterior cruciate ligament (PCL) facilitates posterior femoral rollback during flexion, which improves clearance and increases the lever arm of the extensor mechanism. In a PS TKA, the PCL is sacrificed, and the cam-and-post mechanism is designed to reproduce this obligatory femoral rollback during deep flexion.

Question 24

Following the initial bone cuts in a cruciate-retaining total knee arthroplasty, the surgeon assesses the gaps with spacer blocks. The knee is tight in flexion and symmetric in extension. Which of the following is the most appropriate next step to balance the knee?

Explanation

A knee that is tight in flexion but balanced in extension indicates an isolated tight flexion gap. In a CR knee, an excessively tight PCL can tether the flexion gap. Appropriate interventions include releasing or recessing the PCL, downsizing the femoral component, or increasing the posterior tibial slope.

Question 25

A 65-year-old female presents with a painful total knee arthroplasty 3 years postoperatively. Her serum CRP is 15 mg/L (normal < 10) and ESR is 40 mm/hr. A joint aspiration is performed. Which of the following synovial fluid profiles is most definitively diagnostic of a chronic periprosthetic joint infection according to the 2018 Evidence-Based International Consensus Meeting criteria?

Explanation

According to the 2018 ICM criteria, a score of >= 6 indicates infection. Elevated CRP (score 1) and ESR (score 1) provide 2 points. A positive leukocyte esterase (++) gives a score of 3, and a PMN% > 80% gives a score of 2. The combination (1+1+3+2 = 7) definitively diagnoses PJI. Alpha-defensin alone gives 3 points.

Question 26

A direct anterior approach to the hip is chosen for a primary total hip arthroplasty. The superficial surgical dissection utilizes an internervous plane between muscles supplied by which two nerves?

Explanation

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

Question 27

A patient presents with aseptic loosening and extensive periprosthetic osteolysis 15 years after a cementless total hip arthroplasty. What is the primary biological mediator responsible for osteoclast activation in this process?

Explanation

Particle wear debris is phagocytosed by macrophages, which release pro-inflammatory cytokines. These cytokines stimulate the expression of RANKL by osteoblasts and fibroblasts. RANKL binds to the RANK receptor on osteoclast precursors, leading to osteoclastogenesis and subsequent osteolysis.

Question 28

A surgeon aims to increase femoral offset during a total hip arthroplasty without increasing leg length. Which of the following techniques will best achieve this goal?

Explanation

A lateralized or high-offset femoral stem is designed specifically to increase the offset (the perpendicular distance from the center of rotation to the anatomical axis of the femur) without changing the vertical height (leg length). Increasing the femoral head length or decreasing stem insertion depth would inadvertently increase leg length.

Question 29

Following trial reduction in a total knee arthroplasty, the patella is found to track laterally and tilts during flexion.

Which of the following component position errors is the most likely cause?

Explanation

Internal rotation of the femoral component medially translates the trochlear groove, effectively increasing the Q-angle. This alters the extensor mechanism vector, leading to lateral tracking and tilting of the patella.

Question 30

During a total knee arthroplasty for a severe varus deformity, the medial compartment remains tight in both flexion and extension after initial bone resections. Which of the following is the most appropriate sequence of soft tissue release?

Explanation

For a tight medial compartment (varus knee) in both flexion and extension, standard releases proceed sequentially: 1. Osteophyte removal; 2. Deep MCL release; 3. Posteromedial capsule and semimembranosus (to address extension tightness); 4. Superficial MCL subperiosteal stripping; 5. Pes anserinus.

Question 31

A 72-year-old female presents with thigh pain following a fall. Radiographs demonstrate a transverse fracture entirely distal to the tip of her well-fixed cementless femoral stem.

According to the Vancouver classification, what is the type and the most appropriate treatment?

Explanation

A fracture distal to the tip of the stem is a Vancouver Type C fracture. The treatment of choice is open reduction and internal fixation, typically utilizing a plate that overlaps the stem proximally to prevent a stress riser at the transition zone.

Question 32

A patient with ankylosing spondylitis is scheduled for a bilateral total hip arthroplasty. To prevent heterotopic ossification (HO), the surgeon plans to administer localized radiation therapy. When is the optimal timing for this prophylaxis?

Explanation

Radiation therapy is highly effective for preventing heterotopic ossification. The optimal window for administration is either within 24 hours preoperatively or within 72 hours postoperatively (typically 700-800 cGy in a single fraction). Efficacy drops significantly outside this window.

Question 33

A 62-year-old male presents with groin pain and swelling 6 years after a metal-on-polyethylene total hip arthroplasty. Serum cobalt and chromium levels are elevated. Aspiration yields sterile fluid with a high macrophage count. Which of the following implant characteristics is most associated with this condition?

Explanation

This presentation describes mechanically assisted crevice corrosion (trunnionosis) at the modular head-neck junction. Risk factors include large diameter metal heads, which increase the torsional forces on the taper, mixed metal couples, and certain taper designs.

Question 34

Which of the following histologic findings is considered the hallmark of an adverse local tissue reaction (ALTR) secondary to metal hypersensitivity (ALVAL) in a patient with a modular total hip arthroplasty?

Explanation

Aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) is characterized histologically by a dense perivascular infiltrate of lymphocytes (predominantly T-cells), plasma cells, and macrophages, often accompanied by tissue necrosis. This indicates a Type IV hypersensitivity reaction.

Question 35

A 68-year-old female sustains a complete patellar tendon rupture 4 years after a primary total knee arthroplasty. The components are well-fixed and appropriately positioned. What is the most reliable surgical option to restore active extension?

Explanation

Complete patellar tendon ruptures in the setting of a TKA have very poor outcomes with primary repair. Extensor mechanism allograft reconstruction (involving the tibial tubercle, patellar tendon, patella, and quadriceps tendon) or synthetic mesh reconstruction are the most reliable salvage options.

Question 36

A 55-year-old male presents with isolated medial compartment knee osteoarthritis. He is being evaluated for a medial unicompartmental knee arthroplasty (UKA). Which of the following is considered an absolute contraindication to a mobile-bearing UKA?

Explanation

An intact anterior cruciate ligament (ACL) is considered an absolute prerequisite for a mobile-bearing UKA. ACL deficiency leads to excessive anterior tibial translation, resulting in abnormal kinematics, bearing spin-out, and accelerated wear.

Question 37

In revision total knee arthroplasty, the Anderson Orthopaedic Research Institute (AORI) classification is used to describe bone defects. A femoral defect characterized by metaphyseal bone damage isolated to the medial condyle requiring metal augments, but with an intact joint line and functional collaterals, is classified as:

Explanation

The AORI classification defines Type 2 as damaged metaphyseal bone requiring augments or bone graft. Type 2A involves one condyle (femur) or plateau (tibia), whereas Type 2B involves both. Type 1 is intact metaphysis, and Type 3 involves deficient metaphysis compromising ligaments.

Question 38

A 65-year-old female is undergoing total hip arthroplasty. Preoperative standing and sitting lateral spine radiographs demonstrate that her sacral slope decreases by 5 degrees when moving from standing to sitting. She has no history of spinal fusion. This condition is best described as:

Explanation

Normal spinopelvic mobility involves the sacral slope decreasing (pelvis retroverting) by 10 to 30 degrees when transitioning from standing to sitting. A change of less than 10 degrees defines a stiff spine, placing the patient at higher risk for impingement and dislocation.

Question 39

During a cemented total hip arthroplasty, which of the following techniques is most important to maximize the fatigue strength of the polymethylmethacrylate (PMMA) bone cement?

Explanation

Vacuum mixing significantly reduces the porosity of PMMA bone cement by eliminating air bubbles trapped during mixing. Reduced porosity decreases stress risers within the cement mantle, thereby maximizing its intrinsic fatigue strength.

Question 40

According to the American Academy of Orthopaedic Surgeons (AAOS) clinical practice guidelines, which of the following patients undergoing an elective primary total hip arthroplasty is best suited for aspirin alone as a venous thromboembolism (VTE) prophylaxis?

Explanation

Current AAOS guidelines support the use of aspirin for VTE prophylaxis in standard-risk patients undergoing primary THA and TKA. Patients with a high risk for VTE (prior history, known coagulopathy, active malignancy) should receive more potent pharmacologic prophylaxis.

Question 41

In a total knee arthroplasty for a patient with a long-standing fixed valgus deformity, the surgeon utilizes a gap-balancing technique. After the initial bone cuts, the lateral side is tight in extension but symmetric and balanced in flexion. Release of which of the following structures is most appropriate as the first step to balance this specific mismatch?

Explanation

The iliotibial (IT) band is the primary lateral stabilizer in extension and becomes relatively lax in flexion. Therefore, isolated tightness in the lateral extension gap with a balanced flexion gap is best addressed by releasing or pie-crusting the IT band. Releasing the popliteus or LCL would inappropriately affect the flexion gap.

Question 42

A 55-year-old male with a metal-on-metal total hip arthroplasty presents with progressive groin pain and a palpable anterior mass. MRI reveals a solid and cystic periprosthetic collection. Histological analysis of the tissue in this condition (ALVAL) is most likely to demonstrate:

Explanation

Aseptic Lymphocytic Vasculitis-Associated Lesion (ALVAL) is a delayed type IV hypersensitivity reaction to metal ions (cobalt and chromium) seen in metal-on-metal implants. Histologically, it is characterized by a dense perivascular lymphocytic infiltrate, plasma cells, and macrophage accumulation, distinguishing it from particulate-induced foreign-body granulomatous osteolysis.

Question 43

A 45-year-old active male underwent a THA with a ceramic-on-ceramic bearing. Three years postoperatively, he complains of an audible squeaking sound from his hip when walking or bending. Which of the following component positions is most strongly associated with the biomechanical phenomenon causing this sound?

Explanation

Squeaking in ceramic-on-ceramic bearings is strongly associated with edge loading, which disrupts the fluid lubrication film between the articular surfaces. Edge loading is often caused by malpositioning of the acetabular cup, particularly increased inclination (steep cup) or retroversion, which leads to stripe wear and subsequent squeaking.

Question 44

A 62-year-old male with a primary metal-on-polyethylene THA presents with a 6-month history of worsening hip pain. Blood tests reveal elevated serum cobalt and chromium levels. Radiographs demonstrate a well-fixed modular titanium stem and acetabular cup. What is the most likely source of the metal ion elevation in this specific clinical scenario?

Explanation

In a metal-on-polyethylene bearing with elevated metal ions, the most common source of cobalt and chromium is mechanically assisted crevice corrosion (trunnionosis) at the modular head-neck taper junction. This is increasingly recognized with large diameter metal heads on titanium stems.

Question 45

In revision total knee arthroplasty, management of severe metaphyseal bone defects (AORI Type III) often requires highly porous metaphyseal cones or sleeves. A major biomechanical difference of metaphyseal sleeves compared to traditional unlinked cones is that sleeves:

Explanation

Metaphyseal sleeves are modular components that link directly to the revision stem and articular components via a Morse taper, allowing them to directly transfer loads to the metaphysis. Traditional porous cones are independent of the implant; they fill the bone defect, and the stem is subsequently cemented through the cone.

Question 46

A 72-year-old female presents with a chronic patellar tendon rupture 3 years after a primary TKA. Her components are radiographically well-fixed. She has an active extensor lag of 40 degrees. According to recent clinical evidence, which of the following techniques offers the lowest rate of re-rupture and clinical failure for chronic extensor mechanism disruption in TKA?

Explanation

Chronic extensor mechanism disruption post-TKA is a devastating complication. Recent literature strongly supports the use of synthetic mesh (such as Marlex) over traditional Achilles allografts, as mesh reconstruction has demonstrated significantly lower rates of mechanical failure, re-rupture, and infection.

Question 47

Kinematic alignment in total knee arthroplasty aims to restore the patient's pre-arthritic, native joint lines in all three planes. Compared to traditional mechanical alignment, kinematic alignment typically results in which of the following component positions?

Explanation

Traditional mechanical alignment cuts the tibia perpendicular (0 degrees) to the mechanical axis. Kinematic alignment aims to replicate the native anatomy, which typically features a joint line with about 3 degrees of varus. Therefore, the tibial component is placed in slight varus relative to the mechanical axis. The femur is aligned parallel to the posterior condylar axis (0 degrees of rotation), rather than externally rotated as in mechanical alignment.

Question 48

A 75-year-old male requires a revision THA. Preoperative radiographs reveal a loose femoral stem with severe diaphyseal bone loss, a completely absent isthmus, and less than 4 cm of intact diaphyseal bone for distal fixation.

According to the Paprosky classification, this is a Type IIIB defect. Which of the following femoral components is the most appropriate workhorse for this reconstruction?

Explanation

A Paprosky IIIB defect implies inadequate diaphyseal bone (<4 cm of 'scratch fit') to reliably support a fully porous-coated cylindrical stem. Modular fluted tapered titanium stems are the preferred choice, as their flutes provide rotational stability and the taper provides axial stability in the distal diaphyseal bone, bypassing the deficient proximal bone.

Question 49

Performing a total hip arthroplasty in a patient with active Paget's disease of the pelvis and proximal femur is associated with a significantly increased risk of which of the following specific perioperative complications?

Explanation

Active Paget's disease is characterized by markedly increased osteoclastic and osteoblastic activity, leading to highly vascularized bone. Surgery during the active phase (elevated alkaline phosphatase) is associated with massive intraoperative hemorrhage. Preoperative administration of bisphosphonates is recommended to decrease disease activity and bleeding risk.

Question 50

During a mechanically aligned primary TKA using a measured resection and gap balancing technique, the surgeon evaluates the gaps after the distal femoral and proximal tibial cuts. The extension gap measures 12 mm, while the flexion gap measures 18 mm. What is the most appropriate surgical step to balance the knee?

Explanation

The knee is tight in extension (12 mm) and loose in flexion (18 mm). To equalize the gaps, the extension gap must be enlarged without affecting the flexion gap. Resecting an additional 6 mm of the distal femur will increase the extension gap to 18 mm. The surgeon can then use an 18 mm polyethylene insert to balance both gaps perfectly.

Question 51

A 65-year-old female with long-standing rheumatoid arthritis presents with progressive hip pain. Radiographs demonstrate severe protrusio acetabuli with the femoral head migrated medially past the Kohler line. During THA, which of the following is the most appropriate technique to reconstruct the acetabulum and restore biomechanics?

Explanation

In protrusio acetabuli, the center of rotation is pathologically medialized. The goal of surgery is to restore the anatomic center of rotation laterally to its native position. This is best achieved by impacting morselized cancellous bone graft into the medial defect to lateralize the standard hemispherical cup, preventing further medial migration.

Question 52

A 72-year-old male presents with a loose acetabular component. Imaging demonstrates an inferiorly migrated teardrop, a fracture line extending through the posterior column, and complete separation between the superior and inferior halves of the hemipelvis.

What is the preferred contemporary management for this severe defect?

Explanation

Complete separation of the superior and inferior hemipelvis is a pelvic discontinuity. It requires reconstruction that spans and rigidly fixes the superior and inferior segments. Contemporary techniques include custom triflange components, cup-cage constructs, or the acetabular distraction technique utilizing highly porous tantalum cups with augments to bridge the gap.

Question 53

A patient is evaluated for a painful TKA one year post-operatively. Serum labs show an elevated CRP (15 mg/L) and ESR (45 mm/hr). Joint aspiration yields 2,500 WBC/uL with 75% PMNs. The synovial fluid alpha-defensin immunoassay is positive. Using the 2018 MSIS (ICM) criteria scoring system, what is the correct diagnosis?

Explanation

According to the 2018 MSIS/ICM criteria, a score of >= 6 indicates a definite PJI. Points are awarded as follows: Elevated CRP >10 mg/L (2 pts), Elevated ESR >30 mm/hr (1 pt), Positive alpha-defensin (3 pts). Total = 6 points. Even though WBC and PMN% did not meet the classical thresholds (WBC >3000, PMN >80%), the combined score reaches 6, confirming definite PJI.

Question 54

A 60-year-old female presents with a painful 'catch' and an audible popping sensation when extending her knee from 40 degrees of flexion to full extension, occurring one year after a posterior-stabilized (PS) TKA. What is the fundamental pathomechanics of this specific condition?

Explanation

The clinical presentation is classic for Patellar Clunk Syndrome, which occurs almost exclusively in posterior-stabilized (PS) knees. It is caused by the formation of a fibrous nodule at the junction of the superior pole of the patella and the quadriceps tendon. As the knee extends from flexion, this nodule catches in the intercondylar box of the femoral component, then painfully 'clunks' out.

Question 55

Highly cross-linked polyethylene (HXLPE) has become the standard bearing surface in total hip arthroplasty due to its remarkable wear properties. What is the primary mechanical trade-off associated with the increased cross-linking process compared to conventional UHMWPE?

Explanation

Irradiating polyethylene breaks molecular bonds and creates free radicals, which then recombine to form cross-links. While this significantly improves wear resistance, the structural alterations decrease the material's mechanical properties, specifically its fatigue strength, ductility, and fracture toughness, increasing the risk of mechanical failure (e.g., rim fracture) under high stress.

Question 56

An asymptomatic 58-year-old female with a large-head metal-on-metal THA placed 8 years ago presents for a routine follow-up. Her serum cobalt level is 8.5 ppb and chromium is 7.2 ppb. According to consensus regulatory guidelines, what is the most appropriate next step in management?

Explanation

Consensus guidelines (such as MHRA and FDA) recommend cross-sectional imaging (MARS MRI or specialized ultrasound) for any patient with a metal-on-metal hip and elevated metal ions (typically > 7 ppb for Co or Cr), even if asymptomatic. This is to rule out silent adverse local tissue reactions (ALTR) or pseudotumors, which can cause severe, irreversible muscle and tissue destruction.

Question 57

A patient presents with a feeling of the knee 'giving way' when descending stairs one year following a primary TKA. Varus/valgus stress testing is stable in full extension and at 90 degrees of flexion, but there is marked laxity at 30-45 degrees of flexion. Which of the following technical errors is the most likely cause of this mid-flexion instability?

Explanation

Elevation of the joint line (commonly caused by excessive distal femoral resection combined with a thicker tibial insert to restore extension stability) alters the isometry of the collateral ligaments. While the knee may be stable in full extension and 90 degrees of flexion, the elevated joint line creates relative laxity of the collateral ligaments in mid-flexion (30-60 degrees), leading to mid-flexion instability.

Question 58

During a direct anterior approach for a total hip arthroplasty, the surgeon develops the internervous plane superficially between the tensor fasciae latae and the sartorius. Which nerve is anatomically at greatest risk of iatrogenic injury during this superficial dissection?

Explanation

The direct anterior (Smith-Petersen) approach uses the superficial interval between the tensor fasciae latae (superior gluteal n.) and sartorius (femoral n.). The lateral femoral cutaneous nerve (LFCN) courses over the sartorius and can cross the surgical interval, putting it at high risk for stretch or transection during the superficial approach.

Question 59

Tantalum and highly porous titanium constructs are extensively used in revision arthroplasty to manage bone loss due to their excellent biologic fixation properties. What is the approximate porosity of these advanced trabecular metals compared to traditional sintered bead porous coatings?

Explanation

Highly porous metals (like trabecular metal/tantalum) have a porosity of approximately 75-80%, which closely mimics native cancellous bone. Traditional porous coatings (like sintered beads or plasma spray) generally have a lower porosity, ranging from 30% to 50%. The higher porosity allows for greater initial friction and superior biologic bone ingrowth.

Question 60

Early formulations of zirconia ceramic femoral heads in total hip arthroplasty experienced an unacceptably high rate of catastrophic failure in vivo. This mechanical failure was fundamentally attributed to which of the following material properties?

Explanation

Yttria-stabilized zirconia was introduced for its high fracture toughness. However, in the aqueous, warm environment of the human body, the material undergoes a slow phase transformation from the strong tetragonal phase to the weaker monoclinic phase. This transformation is accompanied by a volume expansion that creates microcracks, ultimately leading to catastrophic shattering of the femoral head.

Question 61

A 58-year-old male presents with medial compartment knee osteoarthritis. He is being evaluated for a unicompartmental knee arthroplasty (UKA). Which of the following findings is widely considered an absolute contraindication to proceeding with a UKA?

Explanation

Inflammatory arthropathies, such as rheumatoid arthritis, are considered absolute contraindications to unicompartmental knee arthroplasty (UKA) because the systemic and progressive nature of the disease will inevitably involve the preserved compartments. Age, obesity, asymptomatic chondrocalcinosis, and prior meniscectomy are relative or non-contraindications depending on surgeon preference and implant design.

Question 62

In the manufacturing of highly cross-linked polyethylene (HXLPE) for total hip arthroplasty, the polymer is often subjected to a thermal treatment of remelting (heating above its melting point of 135°C). What is the primary advantage of remelting compared to annealing (heating below the melting point)?

Explanation

Remelting highly cross-linked polyethylene above its melting point allows polymer chains enough mobility to recombine and completely eliminate free radicals, which maximizes long-term oxidation resistance. However, it does cause a slight reduction in mechanical properties (like fatigue strength and crystallinity) compared to annealing. Annealing preserves more mechanical strength but leaves residual free radicals.

Question 63

The direct anterior (Smith-Petersen) approach to the hip has gained popularity for total hip arthroplasty. During the superficial dissection, the internervous plane is developed between muscles innervated by which of the following pairs of nerves?

Explanation

The superficial internervous plane in the direct anterior approach to the hip is between the tensor fasciae latae (innervated by the superior gluteal nerve) laterally and the sartorius (innervated by the femoral nerve) medially.

Question 64

A 68-year-old female experiences her third posterior dislocation following a primary total hip arthroplasty. CT scan evaluation of her component positioning reveals an acetabular cup anteversion of 10 degrees and a femoral stem retroversion of 5 degrees. According to the combined anteversion theory (Ranawat/McKee), what is her combined anteversion, and what is its clinical implication?

Explanation

Combined anteversion is the sum of acetabular anteversion and femoral anteversion. In this case, 10 degrees (cup) + (-5 degrees) (stem) = 5 degrees. The normal 'safe zone' for combined anteversion to prevent impingement and dislocation is typically between 25 and 45 degrees. A combined anteversion of 5 degrees is severely deficient and places the patient at a high risk for posterior dislocation due to early anterior bony or component impingement during internal rotation.

Question 65

According to the 2018 International Consensus Meeting on Periprosthetic Joint Infection (PJI), which of the following serves as a major criterion (providing definitive evidence) for the diagnosis of PJI?

Explanation

According to the 2018 MSIS/ICM criteria, definitive evidence (major criteria) for PJI includes either: (1) a sinus tract communicating with the joint, or (2) two positive periprosthetic cultures with phenotypically identical organisms. The other options represent minor criteria or components of the scoring algorithm.

Question 66

A 74-year-old female sustains a catastrophic rupture of the patellar tendon 4 years after a primary posterior-stabilized total knee arthroplasty. Physical examination reveals a palpable 5 cm gap, and she is unable to actively extend the knee. Which of the following is the most reliable surgical management for this chronic, massive defect?

Explanation

Chronic extensor mechanism disruptions in the setting of a TKA, especially with a large gap (>3-4 cm) and poor tissue quality, cannot be reliably treated with primary repair. Extensor mechanism allograft (incorporating the tibial tubercle, patellar tendon, patella, and quadriceps tendon) or synthetic mesh reconstructions are the standard of care for restoring active extension.

Question 67

During preoperative planning for a revision total hip arthroplasty, you classify the acetabular defect as a Paprosky Type IIIB. Which of the following radiographic findings characterizes this specific defect?

Explanation

In the Paprosky classification for acetabular defects, a Type IIIB defect ('up and in') involves superior migration > 3 cm, medial migration past Kohler's line (broken Kohler's), teardrop lysis, and severe ischial bone loss. This contrasts with Type IIIA ('up and out'), where Kohler's line is intact and there is moderate supportive ischial bone remaining.

Question 68

A 55-year-old male with a metal-on-metal total hip arthroplasty presents with progressive groin pain 6 years postoperatively. Radiographs show well-fixed components with a cup abduction angle of 55 degrees. Laboratory testing reveals a serum cobalt level of 14 ppb (normal < 1 ppb). A Metal Artifact Reduction Sequence (MARS) MRI demonstrates a 6 cm thick-walled cystic mass communicating with the joint. What is the most appropriate definitive management?

Explanation

This patient has an Adverse Local Tissue Reaction (ALTR/ALVAL) or pseudotumor due to metal wear debris, exacerbated by the steep cup angle (edge loading). The definitive treatment for a symptomatic pseudotumor with elevated metal ions and malpositioned components is revision surgery to remove the metal-on-metal bearing surfaces, commonly changing to a ceramic-on-polyethylene bearing.

Question 69

To optimize patellofemoral tracking and minimize the risk of patellar subluxation during a total knee arthroplasty, the patellar component should ideally be placed in which position on the resected patellar surface?

Explanation

The native median ridge of the patella is slightly medial to the geometric center. Placing the patellar button slightly medial and superior on the resected bone surface best reproduces the native anatomy, optimizes patellar tracking by lateralizing the remaining bony patella relative to the button, and reduces the risk of patellar clunk or subluxation.

Question 70

In total hip arthroplasty, hard-on-hard bearing surfaces (such as ceramic-on-ceramic) demonstrate exceptionally low wear rates. This is primarily attributed to which of the following lubrication regimes occurring during normal walking?

Explanation

Hard-on-hard bearings (ceramic-on-ceramic, metal-on-metal) rely heavily on fluid-film lubrication. In this regime, the articulating surfaces are completely separated by a thin, continuous layer of synovial fluid, minimizing direct surface asperity contact and resulting in dramatically lower wear rates compared to boundary lubrication (seen more in metal-on-polyethylene).

Question 71

In a posterior-stabilized (PS) total knee arthroplasty design, what is the primary biomechanical function of the femoral cam and tibial post mechanism during knee flexion?

Explanation

The cam and post mechanism in a PS TKA is designed to substitute for the resected posterior cruciate ligament (PCL). Its primary function is to engage during flexion and compel the femur to roll back posteriorly on the tibia. This posterior rollback prevents impingement of the posterior femoral cortex on the tibia and maximizes the range of flexion.

Question 72

A 45-year-old male is undergoing revision total hip arthroplasty for aseptic loosening. He has a history of severe Brooker class III heterotopic ossification following his index procedure. What is the most effective prophylactic regimen to prevent recurrence of heterotopic ossification in this high-risk patient?

Explanation

For high-risk patients (e.g., history of severe HO, ankylosing spondylitis, hypertrophic osteoarthritis), prophylaxis is indicated. The most reliable regimens are either a single dose of localized radiation (700-800 cGy) given within 24-48 hours pre- or postoperatively, or a 3-6 week course of NSAIDs like indomethacin. Radiation is often preferred due to compliance and GI side effects of prolonged NSAIDs.

Question 73

The Exeter femoral stem is a classic example of a collarless, polished, double-tapered cemented implant. By which biomechanical principle does this specific stem design achieve long-term stability?

Explanation

Collarless, polished, double-tapered stems (like the Exeter) are designed to function as 'force-closed' devices. Because they are highly polished, they do not bond to the cement. Instead, the double-taper design allows the stem to subside slightly within the intact cement mantle under axial load, effectively acting as a wedge that increases radial compressive forces and stabilizes the implant.

Question 74

Polymethylmethacrylate (PMMA) bone cement is frequently used for component fixation in arthroplasty. What is the primary mechanism by which PMMA secures a prosthesis to the host bone?

Explanation

PMMA bone cement acts strictly as a grout, not an adhesive. It does not chemically bond to bone or the implant. Its primary mechanism of fixation relies on mechanical interdigitation as the liquid cement flows into the trabecular interstices of the prepared cancellous bone bed and subsequently cures and hardens into a solid mantle.

Question 75

A 70-year-old female requires a revision total knee arthroplasty. Preoperative radiographs and intraoperative assessment reveal substantial metaphyseal bone loss involving both the medial and lateral femoral condyles, while the collateral ligament attachments and joint line remain reasonably identifiable. An intraoperative scenario resembling

is encountered. According to the Anderson Orthopaedic Research Institute (AORI) classification, what is her femoral bone defect type?

Explanation

In the AORI classification for revision TKA bone defects, Type 1 denotes intact metaphyseal bone. Type 2 denotes damaged metaphyseal bone necessitating reconstruction (such as augments, cones, or cement): Type 2A involves one condyle (medial or lateral), while Type 2B involves both condyles. Type 3 indicates severe bone loss compromising the collateral ligaments or patellar tendon attachment.

Question 76

An anterior dislocation of a total hip arthroplasty is most likely to occur when the operative limb is placed in which combination of positions?

Explanation

Anterior dislocations typically occur when the hip is subjected to extension and external rotation, often coupled with adduction (which levers the head out of the acetabulum anteriorly). Posterior dislocations typically occur with flexion, adduction, and internal rotation.

Question 77

In the setting of revision total knee arthroplasty, a Constrained Condylar Knee (CCK) prosthesis is best indicated for a patient with which of the following clinical scenarios?

Explanation

A Constrained Condylar Knee (CCK) utilizes a tall, robust tibial post that fits intimately into the femoral box to provide varus-valgus and rotational stability. It is indicated when there is severe attenuation or imbalance of the collateral ligaments (e.g., profound MCL laxity). However, if the collateral ligaments are completely incompetent or absent, a linked rotating hinge prosthesis is required.

Question 78

A 62-year-old female presents with a painful 'catching' and an audible pop in her knee when extending from a flexed position, one year after a primary total knee arthroplasty. This complication, known as patellar clunk syndrome, is primarily associated with which of the following arthroplasty designs?

Explanation

Patellar clunk syndrome is a complication classically seen with posterior-stabilized (PS) TKA designs. It is caused by the formation of a fibrous nodule on the undersurface of the distal quadriceps tendon. During knee extension, this nodule catches in the intercondylar box (cutout for the cam/post mechanism) of the femoral component and then sharply dislodges with a painful 'clunk'.

Question 79

During trial reduction of a primary total hip arthroplasty, the surgeon determines that the hip is stable but the patient's operative leg is 5 mm short and the offset is 5 mm less than the contralateral side. The current trial uses a standard (+0) neck length. If the surgeon changes the modular femoral head to a +5 mm neck length (assuming a standard 135-degree neck angle), what will be the effect on leg length and offset?

Explanation

Because the femoral neck extends superomedially from the shaft (typically at an angle of 125-135 degrees), increasing the neck length via a modular head change will result in a vector increase that adds to both the vertical distance (leg length) and the horizontal distance (femoral offset).

Question 80

A 52-year-old active male who underwent an uncomplicated primary total hip arthroplasty 4 years ago presents with an audible squeaking noise emanating from his hip during deep flexion and normal gait. He denies any pain, and radiographs show well-fixed components in acceptable alignment. Which of the following bearing surface combinations is most commonly associated with this phenomenon?

Explanation

Squeaking is a unique, occasionally audible complication most strongly associated with ceramic-on-ceramic hard bearing surfaces. It is thought to occur due to edge loading, micro-separation, or temporary loss of fluid-film lubrication. While benign in the absence of pain, it can be a source of significant patient dissatisfaction.

Question 81

A 68-year-old male presents with aseptic loosening of a THA. Radiographs show a Paprosky Type IIIB femoral defect. The femoral isthmus has approximately 1.5 cm of diaphyseal scratch fit available. What is the most appropriate femoral revision strategy?

Explanation

A Paprosky Type IIIB femoral defect combined with less than 2-3 cm of diaphyseal scratch fit is highly prone to subsidence with standard diaphyseal-engaging stems. A proximal femoral replacement or an impaction grafting with specialized meshes is indicated when diaphyseal fixation is inadequate.

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

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

Key Takeaway

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

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