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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 224 of 326

This practice set contains high-yield board review questions covering key concepts in 3. Adult Reconstruction (Hip & Knee). Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 4461

Topic: 3. Adult Reconstruction (Hip & Knee)
A 55-year-old morbidly obese patient (BMI 45 kg/m²) undergoes a primary total hip arthroplasty. What is a commonly cited increased risk specific to the immediate postoperative period in morbidly obese patients undergoing THA compared to non-obese patients?
. Periprosthetic fracture
. Aseptic loosening
. Deep vein thrombosis (DVT)
. Surgical site infection (SSI)
. Heterotopic ossification

Correct Answer & Explanation

. Surgical site infection (SSI)

Explanation

Morbid obesity significantly increases the risk of several complications after THA, but certain risks are particularly elevated in the immediate postoperative period. While DVT risk (C) is generally increased in obese patients, surgical site infection (SSI) (D) is arguably the most significantly and consistently cited increased risk specific to the immediate postoperative period for THA in morbidly obese individuals. The increased subcutaneous tissue thickness, poor vascularity of adipose tissue, difficulty with wound care, and impaired immune function contribute to higher rates of superficial and deep SSI. Periprosthetic fracture (A) and aseptic loosening (B) are typically longer-term complications, and heterotopic ossification (E) is a general risk but not disproportionately higher in obesity compared to SSI.

Question 4462

Topic: Total Hip Arthroplasty (THA)

A 70-year-old female presents with progressive groin pain 3 years after primary uncemented THA. Radiographs show superior migration of the uncemented acetabular component by 5 mm, without gross instability or signs of infection. The femoral component is well-fixed. The acetabular defect is classified as Paprosky Type IIA. What is the most appropriate surgical management for the acetabulum?

. Observation with activity modification and pain management
. Liner exchange only, without revising the acetabular shell
. Revision of the acetabular component with a larger uncemented cup, potentially utilizing supplemental screws and bone graft
. Cementing a new polyethylene liner directly into the migrated metal shell
. Explantation of all components and conversion to a Girdlestone arthroplasty

Correct Answer & Explanation

. Revision of the acetabular component with a larger uncemented cup, potentially utilizing supplemental screws and bone graft

Explanation

Superior migration of an uncemented acetabular component, even if mild (Paprosky Type IIA, involving a superior rim defect), indicates failure of ingrowth and mechanical loosening. Observation (A) is inappropriate for a failed component. A liner exchange (B) only addresses the articulation, not the failed fixation of the shell to the bone. Cementing a new liner into a loose metal shell (D) would not provide durable fixation. Explantation (E) is a salvage procedure. The most appropriate treatment for a loose uncemented acetabular component with a Paprosky IIA defect is revision of the acetabular component (C). This involves removing the loose shell, debriding any fibrous tissue, bone grafting the superior defect, and implanting a new, often larger, uncemented porous-coated cup that gains purchase in healthy bone and fills the defect. Supplemental screws are commonly used to enhance primary stability and promote ingrowth.

Question 4463

Topic: 3. Adult Reconstruction (Hip & Knee)
A 72-year-old male presents with persistent groin pain and instability four years after undergoing revision total hip arthroplasty (THA) for aseptic loosening of a cemented femoral stem. Radiographs reveal a Paprosky Type IIIB femoral defect with a well-fixed, extensively porous-coated acetabular component. He has a positive Girdlestone sign on physical exam. What is the most appropriate next step in surgical management for this patient?
. Exchange of the femoral stem with a longer, tapered fluted modular revision stem, maintaining the existing acetabular component.
. Two-stage revision for periprosthetic joint infection (PJI) with an antibiotic spacer, followed by definitive reconstruction.
. Conversion to a Girdlestone resection arthroplasty given his age and extensive bone loss.
. Revision of the femoral stem using an allograft-prosthesis composite with a modular stem.
. Placement of a constrained acetabular liner with irrigation and debridement of the femoral side without stem revision.

Correct Answer & Explanation

. Revision of the femoral stem using an allograft-prosthesis composite with a modular stem.

Explanation

The patient presents with a Paprosky Type IIIB femoral defect, which signifies significant metaphyseal and diaphyseal bone loss requiring extensive reconstruction. While a tapered fluted modular stem can be used for Type IIIA defects, Type IIIB often necessitates more substantial support like an allograft-prosthesis composite (APC). An APC provides structural support and bone stock replacement, allowing for biological incorporation and stable fixation of the new stem, which is crucial for such a large defect. The 'Girdlestone sign' suggests significant instability and likely a functional Girdlestone, but converting to a permanent Girdlestone is generally reserved for frail, non-ambulatory patients or those with insurmountable infection. A two-stage revision for PJI is indicated if infection is suspected; however, the clinical scenario primarily describes aseptic loosening and bone loss, with no explicit signs of infection given. A constrained liner addresses instability but does not resolve the underlying issue of severe femoral bone loss and loosening, and a debridement without stem revision is insufficient for a Type IIIB defect.

Question 4464

Topic: 3. Adult Reconstruction (Hip & Knee)

A 65-year-old female with a history of recurrent dislocations after a primary total hip arthroplasty (THA) undergoes revision with a constrained acetabular liner. Three months post-revision, she presents with severe acute groin pain and inability to bear weight. Radiographs show no obvious dislocation but reveal a fracture of the acetabular rim surrounding the constrained liner. What is the most likely diagnosis and appropriate initial management?

. Periprosthetic joint infection; initiate broad-spectrum antibiotics and prepare for two-stage revision.
. Component impingement causing liner failure; plan for further revision with component repositioning.
. Constrained liner dissociation from the shell; consider closed reduction under anesthesia followed by open reduction if unsuccessful.
. Constrained liner failure due to polyethylene wear and particle disease; plan for liner exchange.
. Pelvic stress fracture or fracture through the construct; immobilize and evaluate for stability with possible surgical repair.

Correct Answer & Explanation

. Pelvic stress fracture or fracture through the construct; immobilize and evaluate for stability with possible surgical repair.

Explanation

The scenario describes a patient with acute severe groin pain and inability to bear weight after revision THA with a constrained liner, with radiographs showing a fracture of the acetabular rim. This is highly suggestive of a pelvic stress fracture or a fracture through the constrained construct itself, which can occur due to the increased forces transmitted to the bone by a constrained liner, especially in patients with compromised bone quality. Initial management (Option E) would involve immobilization to prevent further displacement and a thorough evaluation, potentially including CT scan, to assess the fracture pattern and determine the need for surgical stabilization. While infection (Option A) should always be considered, the immediate finding of a fracture on imaging makes it less likely to be the primary diagnosis. Impingement (Option B) or polyethylene wear (Option D) typically cause more gradual symptoms or different radiographic findings, and liner dissociation (Option C) would typically present with frank dislocation or gross instability rather than a fracture of the surrounding bone.

Question 4465

Topic: 3. Adult Reconstruction (Hip & Knee)

A 45-year-old male with a history of long-standing ankylosing spondylitis presents for bilateral total hip arthroplasty due to severe pain and bilateral hip ankylosis in a flexion-adduction-internal rotation deformity. What is the most significant perioperative challenge specific to this patient population undergoing THA?

. Increased risk of heterotopic ossification (HO).
. Difficulty with patient positioning and surgical exposure.
. Higher incidence of periprosthetic joint infection (PJI).
. Increased risk of deep vein thrombosis (DVT) and pulmonary embolism (PE).
. Challenge in achieving full range of motion post-operatively.

Correct Answer & Explanation

. Increased risk of heterotopic ossification (HO).

Explanation

Patients with ankylosing spondylitis undergoing total hip arthroplasty (THA) have a significantly increased risk of heterotopic ossification (HO) compared to the general THA population, often requiring prophylactic measures like NSAIDs, radiation therapy, or both. While difficulty with patient positioning and surgical exposure (Option B) can be challenging due to severe deformities and spinal rigidity, it's a technical challenge addressed by experienced surgeons. The incidence of PJI (Option C) and DVT/PE (Option D) are general risks of THA but not specifically higher in AS patients compared to HO. Achieving full range of motion (Option E) is a goal, but HO is a major impediment to this, making its prevention critical. The increased HO risk is a very specific and well-documented perioperative challenge in this patient group.

Question 4466

Topic: 3. Adult Reconstruction (Hip & Knee)

A 32-year-old female presents with groin pain and stiffness following a metal-on-metal (MoM) hip resurfacing arthroplasty performed five years prior. Serum cobalt and chromium levels are elevated, and advanced imaging (MARS-MRI) reveals a large periprosthetic pseudotumor. She is asymptomatic apart from mild pain. What is the most appropriate management strategy?

. Observation with serial monitoring of metal ion levels and imaging, as she is largely asymptomatic.
. Aspiration of the pseudotumor for cytology and metal particle analysis, followed by local corticosteroid injection.
. Revision THA with exchange of both femoral and acetabular components to a non-MoM bearing surface.
. Surgical debridement of the pseudotumor with retention of the existing MoM implants if they appear well-fixed.
. Medical therapy with chelation agents to reduce metal ion levels and shrink the pseudotumor.

Correct Answer & Explanation

. Revision THA with exchange of both femoral and acetabular components to a non-MoM bearing surface.

Explanation

Despite being largely asymptomatic, the presence of elevated metal ion levels and a large periprosthetic pseudotumor identified on MARS-MRI after a metal-on-metal (MoM) hip resurfacing (or THA) is an indication for revision surgery. These pseudotumors can be progressive, lead to osteolysis, and cause significant tissue damage, even in the absence of severe pain. Revision THA (Option C) with removal of both MoM components and exchange to a non-MoM bearing (e.g., ceramic-on-polyethylene or metal-on-polyethylene) is the recommended treatment to address the source of metal ion release and prevent further adverse local tissue reactions (ALTR). Observation (Option A) is not appropriate given the documented pseudotumor and elevated ions. Aspiration and corticosteroid injection (Option B) or debridement with implant retention (Option D) do not address the fundamental issue of ongoing metal wear and release. Medical chelation (Option E) is not an established or effective treatment for periprosthetic metal ion toxicity.

Question 4467

Topic: 3. Adult Reconstruction (Hip & Knee)
A 58-year-old male undergoes revision THA for recurrent dislocation. Intraoperatively, after removal of the previously well-fixed cementless acetabular component, a large cavitary defect with an intact rim and deficient medial wall is encountered, consistent with Paprosky Type IIIA acetabular bone loss. The femoral stem is stable. What is the most appropriate reconstruction strategy for the acetabulum?
. Re-reaming to a larger size and placement of an oversized conventional cementless hemispheric cup with screws.
. Placement of a jumbo hemispheric cup with screws and impaction bone grafting of the cavitary defect.
. Use of a custom triflange acetabular component.
. Placement of a modular cage or reconstruction ring with impaction bone grafting and a cemented liner.
. Application of an acetabular reinforcement device (e.g., a cage) combined with bulk allograft reconstruction of the medial wall.

Correct Answer & Explanation

. Re-reaming to a larger size and placement of an oversized conventional cementless hemispheric cup with screws.

Explanation

For a Paprosky Type IIIA defect, characterized by a cavitary defect with an intact rim and deficient medial wall, a common and effective reconstruction strategy is to re-ream to a larger size and place an oversized conventional cementless hemispheric cup with adjunctive screw fixation. This allows for stable fixation in the remaining host bone. Impaction bone grafting can be used to fill the defect and promote bone ingrowth but an oversized conventional cup can often achieve stability. Custom triflange components are typically reserved for more severe, uncontained defects or pelvic discontinuity (Type IV). Modular cages or reconstruction rings are often used in conjunction with impaction grafting for Type IIIB or IIIc defects, or Type IV. Bulk allograft reconstruction might be considered for more extensive defects or when the rim is also compromised, but for a contained cavitary defect with an intact rim (Type IIIA), an oversized conventional cup is often sufficient.

Question 4468

Topic: 3. Adult Reconstruction (Hip & Knee)

A 70-year-old female presents with persistent pain and a limp three years after revision THA for aseptic loosening. Imaging reveals a well-fixed acetabular component and a stable, extensively porous-coated femoral stem. A bone scan shows mild uptake around the tip of the femoral stem but is otherwise unremarkable. Lab work (ESR, CRP) is normal. She has a history of opioid use and significant psychosocial distress. What is the most appropriate next step in her management?

. Proceed with explantation of the femoral stem for presumed subtle infection or aseptic loosening.
. Referral for pain management, psychological evaluation, and physical therapy with careful observation.
. Order a comprehensive infectious workup including hip aspiration, leukocyte esterase, and alpha-defensin testing.
. Perform a diagnostic arthroscopy to evaluate for intra-articular pathology.
. Prescribe a trial of non-steroidal anti-inflammatory drugs (NSAIDs) and activity modification.

Correct Answer & Explanation

. Referral for pain management, psychological evaluation, and physical therapy with careful observation.

Explanation

This patient presents with chronic pain after revision THA with a well-fixed acetabular and stable femoral component, normal inflammatory markers, and a history of psychosocial distress. This scenario is highly suggestive of 'painful hip arthroplasty with no obvious cause' or 'unexplained chronic pain' after THA. In such cases, and after ruling out mechanical issues, the focus shifts to non-operative management. Referral for pain management, psychological evaluation, and physical therapy (Option B) is the most appropriate next step. These measures aim to address the multifactorial nature of chronic pain and improve functional outcomes without resorting to unnecessary surgery. Explantation (Option A) is a drastic measure, especially with normal labs and stable components, and should be considered only after exhausting non-operative options and if a clear diagnosis still eludes. An infectious workup (Option C) is warranted if there's any suspicion of PJI, but normal ESR/CRP make it less likely, and should typically be done before considering explantation. Diagnostic arthroscopy (Option D) is rarely indicated in THA. NSAIDs (Option E) may offer symptomatic relief but do not address the underlying psychosocial and chronic pain issues.

Question 4469

Topic: Total Hip Arthroplasty (THA)

During a primary THA via a direct anterior approach, the surgeon encounters significant difficulty in achieving adequate exposure of the acetabulum due to obesity and muscular build. After release of the rectus femoris and capsular structures, visualization remains suboptimal, leading to concerns about accurate cup placement. Which of the following is the most appropriate next step?

. Proceed with cup placement using fluoroscopy guidance to ensure proper alignment.
. Convert to a posterolateral approach to gain better visualization.
. Utilize a specialized table (e.g., a traction table) to improve exposure.
. Perform a limited trochanteric osteotomy to enhance exposure.
. Utilize an intraoperative navigation system for acetabular component positioning.

Correct Answer & Explanation

. Convert to a posterolateral approach to gain better visualization.

Explanation

When faced with inadequate acetabular exposure during a direct anterior approach due to patient anatomy (obesity, muscular build), the most appropriate and safest next step to ensure accurate cup placement is often to convert to an approach that provides better visualization (Option B), such as a posterolateral or direct lateral approach. This prioritizes patient safety and optimal implant positioning over adhering strictly to the initial approach. While fluoroscopy (Option A) and navigation (Option E) can aid in positioning, they do not fundamentally solve the issue of inadequate visualization, which can still lead to soft tissue impingement, unrecognized pathology, or difficulties with reaming. A traction table (Option C) can improve femoral exposure but is less effective for acetabular exposure, and it's generally used from the start of the case. A limited trochanteric osteotomy (Option D) is not part of the direct anterior approach and is typically reserved for complex revision cases or specific primary situations via different approaches, not for simple exposure issues in a primary DAA.

Question 4470

Topic: 3. Adult Reconstruction (Hip & Knee)
A 68-year-old female presents with severe groin pain and a leg length discrepancy following an uncemented THA performed 10 years ago. Radiographs show a well-fixed acetabular component, but the femoral stem has subsided significantly, with extensive osteolysis around the stem extending distally. There are no signs of infection. The Paprosky femoral defect is classified as Type IIIB. What is the most appropriate surgical strategy for femoral reconstruction?
. Exchange with a longer, extensively porous-coated stem engaging distally in healthy bone.
. Impaction bone grafting with a cemented polished taper-slip stem.
. Use of a modular tapered fluted stem with cortical strut allografts.
. Proximal femoral allograft-prosthesis composite.
. Revision with a calcar-replacing stem.

Correct Answer & Explanation

. Exchange with a longer, extensively porous-coated stem engaging distally in healthy bone.

Explanation

A Paprosky Type IIIB femoral defect signifies significant metaphyseal and diaphyseal bone loss, requiring a stem that can achieve stable diaphyseal fixation distally. An extensively porous-coated stem that bypasses the defect and obtains fixation in healthy bone distally is a common and effective solution for Type IIIB defects. It relies on scratch fit and subsequent bone ingrowth for stability. Impaction bone grafting is typically used for Type IIA/B defects, or in conjunction with stems for Type III defects, but not as the sole reconstruction method for significant diaphyseal loss. Modular tapered fluted stems are also excellent for Type IIIB defects but often used in conjunction with screws or for more complex defects; without specific mention of modularity or other features, the extensively porous-coated stem is a strong general option. A proximal femoral allograft-prosthesis composite is generally reserved for massive bone loss (Type IV) or cases where diaphyseal fixation is not achievable. A calcar-replacing stem addresses only proximal medial bone loss and is insufficient for extensive diaphyseal osteolysis.

Question 4471

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following scenarios in a total hip arthroplasty (THA) patient is most indicative of early, acute periprosthetic joint infection (PJI) rather than aseptic loosening or other complications?

. Gradual onset of groin pain over several months with normal inflammatory markers.
. Sudden onset of severe hip pain, warmth, erythema, and purulent drainage from the surgical site within 4 weeks post-op.
. Chronic thigh pain with radiographic evidence of progressive lucency at the cement-bone interface years after THA.
. Recurrent dislocation without signs of infection, responsive to closed reduction.
. Clicking sensation and mild pain with activity, found to have polyethylene wear on imaging.

Correct Answer & Explanation

. Sudden onset of severe hip pain, warmth, erythema, and purulent drainage from the surgical site within 4 weeks post-op.

Explanation

Acute periprosthetic joint infection (PJI) typically presents with an early, sudden onset of severe pain, warmth, erythema, and often purulent drainage from the surgical site, usually within weeks of surgery (Option B). This clinical picture, especially with purulent drainage, is highly suggestive of acute infection. Gradual onset of pain with normal inflammatory markers (Option A) is more consistent with aseptic loosening or other mechanical issues. Chronic thigh pain with lucency at the cement-bone interface years after THA (Option C) is classical for aseptic loosening. Recurrent dislocation (Option D) and polyethylene wear (Option E) are mechanical complications, not indicative of infection unless superinfected.

Question 4472

Topic: 3. Adult Reconstruction (Hip & Knee)

A 40-year-old male with a history of sickle cell disease and avascular necrosis (AVN) of the femoral head undergoes THA. One year post-op, he develops persistent pain, elevated inflammatory markers, and a lucent line around the femoral stem on radiographs. Aspiration confirms PJI with coagulase-negative Staphylococcus. What is the most significant long-term complication risk in this patient population following revision for PJI?

. Recurrence of periprosthetic joint infection.
. Development of new avascular necrosis in the remaining femoral bone.
. Increased risk of deep vein thrombosis and pulmonary embolism.
. Sickle cell crisis precipitated by surgery.
. Poor bone healing and non-union of osteotomies.

Correct Answer & Explanation

. Recurrence of periprosthetic joint infection.

Explanation

Patients with sickle cell disease (SCD) undergoing THA are at a significantly higher risk for developing periprosthetic joint infection (PJI) and, more importantly, have a higher rate of recurrent PJI (Option A) even after successful initial treatment. This is due to their immunocompromised state, chronic osteomyelitis, and impaired microcirculation. While SCD patients are at increased risk for DVT/PE (Option C) and sickle cell crisis (Option D) during surgery, these are acute perioperative risks. Development of new AVN (Option B) is not a direct complication of PJI treatment. Poor bone healing (Option E) can occur but the most prominent long-term concern after revision for PJI in SCD patients is the high risk of infection recurrence, which can lead to multiple further revisions or limb loss.

Question 4473

Topic: 3. Adult Reconstruction (Hip & Knee)

A 62-year-old male presents with chronic hip pain and progressive leg length discrepancy after a ceramic-on-ceramic (CoC) THA performed 8 years ago. Radiographs show no component loosening or migration, but a 'squeaking' sound is audible with hip motion. What is the most likely cause of his symptoms and potential complication?

. Aseptic loosening of the femoral component.
. Acetabular component malposition causing impingement.
. Ceramic liner fracture.
. Stiffness and impingement due to heterotopic ossification.
. Trunnionosis with release of metal debris.

Correct Answer & Explanation

. Ceramic liner fracture.

Explanation

The combination of chronic hip pain, leg length discrepancy (which can be a subtle sign of collapse), and a 'squeaking' sound in a ceramic-on-ceramic THA, despite no radiographic signs of gross loosening or migration, is highly indicative of a ceramic liner fracture (Option C). While ceramic liners are durable, they are brittle and can fracture due to trauma, edge loading, or material defects. Aseptic loosening (Option A) would usually show radiographic lucency. Acetabular component malposition (Option B) can cause impingement and squeaking but wouldn't typically cause a sudden change in leg length or the specific collapse implied by chronic pain with no obvious loosening. Heterotopic ossification (Option D) can cause stiffness but typically presents with radiographic evidence. Trunnionosis (Option E) is a problem specific to metal-on-metal or ceramic-on-metal bearing surfaces, or when a ceramic head articulates with a metal trunnion, and would not typically present with ceramic squeaking without a significant metal-on-metal component.

Question 4474

Topic: Total Hip Arthroplasty (THA)

In a revision THA for pelvic discontinuity, which surgical approach and fixation strategy is generally preferred to maximize stability and minimize complications?

. Posterolateral approach with a modular cage and screws into the ilium and ischium, supplemented with bulk allograft.
. Direct anterior approach with a custom triflange acetabular component.
. Trochanteric osteotomy and extensive exposure, followed by a jumbo cup with cancellous screws.
. Dual-mobility cup with impaction bone grafting and an anti-protrusio cage.
. Combined anterior and posterior approaches (circumferential fixation) with a reconstruction cage and internal fixation of the pelvic fracture.

Correct Answer & Explanation

. Combined anterior and posterior approaches (circumferential fixation) with a reconstruction cage and internal fixation of the pelvic fracture.

Explanation

Pelvic discontinuity (Paprosky Type IV defect) represents a complete circumferential separation of the acetabulum from the rest of the hemipelvis, requiring robust fixation of both columns. The most stable and preferred strategy is often a combined anterior and posterior approach (circumferential fixation) (Option E) to achieve stable fixation of the pelvic fracture and reconstruct the acetabulum with a reconstruction cage or custom component. This allows for direct visualization and repair of both columns of the pelvis. A posterolateral approach (Option A) alone may not provide adequate access for complete anterior column fixation. A direct anterior approach (Option B) would not allow posterior column fixation. A jumbo cup (Option C) or a dual-mobility cup (Option D) are not sufficient to address the underlying fracture and lack the structural support needed for pelvic discontinuity; cages and rings are typically used in conjunction with these, but the key is the fracture fixation strategy.

Question 4475

Topic: 3. Adult Reconstruction (Hip & Knee)

A 75-year-old male with a history of previous pelvic radiation therapy for prostate cancer presents with a periprosthetic acetabular fracture (modified Paprosky Type IIB, stable) occurring 6 months after THA. What is the primary concern for surgical management in this patient?

. Increased risk of infection due to compromised tissue vascularity.
. Difficulty achieving biological fixation due to radiation-induced osteonecrosis and poor bone quality.
. Higher rate of nerve injury due to altered anatomy.
. Increased intraoperative blood loss.
. Risk of bladder or bowel injury during acetabular revision.

Correct Answer & Explanation

. Difficulty achieving biological fixation due to radiation-induced osteonecrosis and poor bone quality.

Explanation

Patients who have undergone pelvic radiation therapy present a unique challenge in total hip arthroplasty due to radiation-induced osteonecrosis and severely compromised bone quality. For a periprosthetic acetabular fracture or revision surgery, the primary concern (Option B) is the difficulty in achieving biological fixation and bony ingrowth due to poor bone stock and impaired healing potential. This significantly increases the risk of aseptic loosening and non-union of the fracture. While increased infection risk (Option A) and intraoperative blood loss (Option D) are concerns, the most significant and specific challenge related to radiation is the compromised bone quality and healing capacity. Nerve injury (Option C) and visceral injury (Option E) are general risks in revision THA but are not uniquely exacerbated by prior radiation to the same extent as bone healing. The Paprosky Type IIB fracture, although stable, will still require robust fixation and the compromised bone quality will make it difficult.

Question 4476

Topic: Total Hip Arthroplasty (THA)

A 48-year-old female undergoes a THA for severe osteonecrosis of the femoral head. Postoperatively, she develops a painful sciatic nerve palsy. Which of the following is the most likely intraoperative cause of this complication?

. Excessive leg lengthening exceeding 4 cm.
. Direct trauma from a retracting instrument.
. Heat necrosis during cement polymerization.
. Malpositioning of the acetabular component causing posterior impingement.
. Deep vein thrombosis compressing the nerve.

Correct Answer & Explanation

. Excessive leg lengthening exceeding 4 cm.

Explanation

Sciatic nerve palsy is a known, albeit rare, complication of THA. In the absence of direct trauma from retractors or malpositioning, the most common cause is excessive limb lengthening (Option A), particularly when lengthening exceeds 4 cm. The sciatic nerve, especially if previously scarred or stretched, can be put under significant tension with lengthening, leading to neuropraxia or permanent injury. Direct trauma from retractors (Option B) is possible but less likely if careful technique is used. Heat necrosis from cement (Option C) is more likely to cause femoral nerve palsy in the anterior approach or local tissue damage, but less commonly sciatic nerve palsy, which is more posterior. Malpositioning of the acetabular component (Option D) can cause impingement but typically presents with pain and instability, not nerve palsy unless it causes direct compression. DVT (Option E) can cause leg swelling and pain but not directly a nerve palsy unless it leads to compartment syndrome, which is rare in the context of nerve palsy post-THA.

Question 4477

Topic: 3. Adult Reconstruction (Hip & Knee)

Which factor is considered the strongest independent predictor of recurrent dislocation after primary total hip arthroplasty?

. Surgical approach (e.g., posterolateral vs. direct anterior).
. Patient age (>75 years).
. History of previous hip surgery.
. Female gender.
. Neuromuscular disease (e.g., Parkinson's, stroke).

Correct Answer & Explanation

. Neuromuscular disease (e.g., Parkinson's, stroke).

Explanation

While all options listed can contribute to the risk of dislocation, neuromuscular diseases (Option E), such as Parkinson's disease, stroke with hemiparesis, or multiple sclerosis, are consistently identified as the strongest independent predictors of recurrent dislocation after primary total hip arthroplasty. These conditions compromise muscle control, coordination, and proprioception, making patients highly susceptible to instability despite technically perfect component placement. Surgical approach (Option A) has been debated, but modern techniques and repair of posterior capsule/short external rotators have minimized differences. Patient age (Option B), previous hip surgery (Option C), and female gender (Option D) are also risk factors but typically secondary to neuromuscular impairment or specific patient activity levels/ligamentous laxity.

Question 4478

Topic: 3. Adult Reconstruction (Hip & Knee)

A 35-year-old male with a history of chronic glucocorticoid use for systemic lupus erythematosus presents with bilateral femoral head osteonecrosis and collapses, requiring THA. What specific complication risk is heightened in this patient population following THA, requiring careful preoperative planning and postoperative monitoring?

. Deep vein thrombosis (DVT).
. Periprosthetic joint infection (PJI).
. Adrenal crisis.
. Aseptic loosening.
. Heterotopic ossification (HO).

Correct Answer & Explanation

. Adrenal crisis.

Explanation

Patients with chronic glucocorticoid use, such as those with systemic lupus erythematosus, are at significant risk of developing adrenal insufficiency. If their steroid regimen is not properly managed perioperatively, they can experience an adrenal crisis (Option C), which is a life-threatening complication characterized by severe hypotension, shock, and electrolyte imbalances. Therefore, careful preoperative endocrinological evaluation and stress-dose steroid administration are crucial. While DVT (Option A), PJI (Option B), aseptic loosening (Option D), and HO (Option E) are general risks of THA, the risk of adrenal crisis is uniquely and significantly heightened in patients on chronic steroids and requires specific preventative measures.

Question 4479

Topic: 3. Adult Reconstruction (Hip & Knee)

What is the primary role of a modular junction failure in a modern total hip arthroplasty (THA) system?

. Providing rotational stability of the femoral head on the stem.
. Allowing customization of femoral head offset and leg length.
. Facilitating the use of various bearing surfaces with a single stem design.
. Enabling the surgeon to select different stem and head sizes independently.
. Reducing the risk of stress shielding in the proximal femur.

Correct Answer & Explanation

. Allowing customization of femoral head offset and leg length.

Explanation

The primary role of a modular junction (e.g., a taper junction between the femoral stem and femoral head) in modern THA systems is to allow customization of femoral head offset and leg length (Option B). This modularity allows the surgeon to independently adjust these critical parameters to optimize soft tissue tension, joint stability, and biomechanics for each individual patient. While it allows selection of different stem and head sizes independently (Option D), this is part of the broader customization goal. It's not primarily for rotational stability (Option A), facilitating various bearing surfaces (Option C) (though different heads can have different bearings), or reducing stress shielding (Option E) (which is more related to stem design and material).

Question 4480

Topic: 3. Adult Reconstruction (Hip & Knee)

A 72-year-old female sustains a minor fall 10 years after a primary total hip arthroplasty. Radiographs reveal a periprosthetic femur fracture extending just distal to the tip of the femoral stem. The stem is loose, but there is excellent proximal and distal bone stock. According to the Vancouver classification, which of the following is the most appropriate surgical treatment?

. Open reduction and internal fixation with a laterally based locking plate and cerclage cables
. Revision to a cemented long stem
. Revision to a cementless long extensively porous-coated or fluted tapered modular stem
. Proximal femoral replacement
. Open reduction and internal fixation with strut allografts alone

Correct Answer & Explanation

. Revision to a cementless long extensively porous-coated or fluted tapered modular stem

Explanation

This is a Vancouver B2 fracture (fracture around a loose stem with adequate bone stock). The gold standard treatment is revision to a cementless long stem (extensively porous-coated or fluted tapered) to bypass the fracture by at least two cortical diameters.

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