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3. Adult Reconstruction (Hip & Knee) MCQs

Practice Set 18 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 341

Topic: Total Hip Arthroplasty (THA)

A 58-year-old male undergoes a direct anterior approach (DAA) total hip replacement. Intraoperatively, the surgeon notes excellent stability on trial reduction, with no impingement throughout a full range of motion. The acetabular component is placed at 45° inclination and 20° anteversion, and a 36mm femoral head is used. Post-operatively, the patient is advised to avoid extreme hip hyperextension and external rotation for 6 weeks. Which of the following statements best explains the rationale for this specific post-operative precaution in a DAA?

. To prevent posterior dislocation due to disruption of the posterior capsule.
. To protect the healing abductor mechanism from excessive tension.
. To avoid anterior impingement and potential anterior dislocation.
. To minimize the risk of sciatic nerve irritation from excessive stretch.
. To prevent periprosthetic fracture of the femoral neck.

Correct Answer & Explanation

. To avoid anterior impingement and potential anterior dislocation.

Explanation

Correct Answer: CThe teaching case states under 'Anterior/Anterolateral Approach Precautions': 'Historically, anterior dislocations are less common. However, some surgeons may advise caution with: Avoid Hip Hyperextension and Extreme External Rotation: To prevent anterior impingement or dislocation, especially in the early post-operative period.' The direct anterior approach (DAA) preserves the posterior capsule and external rotators, making posterior dislocation less common. However, the anterior capsule is typically incised or released, and the anterior soft tissues are retracted. Excessive hip hyperextension and external rotation can cause anterior impingement (e.g., between the anterior aspect of the femoral neck/stem and the anterior acetabular rim or anterior capsule repair) or stress the healing anterior soft tissues, leading to an anterior dislocation.A. To prevent posterior dislocation due to disruption of the posterior capsule:This is incorrect. The DAA preserves the posterior capsule, making posterior dislocation less likely. This precaution is more relevant for a posterior approach.B. To protect the healing abductor mechanism from excessive tension:While abductor integrity is important, this specific precaution (hyperextension/external rotation) is not primarily aimed at protecting the abductors. Abductor protection is more relevant for lateral approaches where the abductors are detached/split.D. To minimize the risk of sciatic nerve irritation from excessive stretch:The sciatic nerve is located posteriorly. Hyperextension and external rotation of the hip are not typically positions that stretch the sciatic nerve.E. To prevent periprosthetic fracture of the femoral neck:While periprosthetic fractures can occur, this specific precaution is not directly aimed at preventing them. Femoral fractures during DAA are more often associated with femoral preparation or broaching.

Question 342

Topic: Total Hip Arthroplasty (THA)

A 68-year-old male with a history of recurrent posterior dislocations after a primary total hip replacement performed via a posterior approach, despite two closed reductions and a period of bracing, is scheduled for revision surgery. Pre-operative CT scan reveals appropriate acetabular component inclination (40°) but significant femoral component retroversion (-5°). The patient also has mild abductor weakness. Which of the following revision strategies would most directly address the identified primary mechanical cause of his recurrent dislocations?

. Exchange of the acetabular liner to a posterior-lipped liner.
. Revision of the femoral component to correct its version.
. Placement of a constrained acetabular liner.
. Abductor repair and augmentation with an allograft.
. Exchange to a larger femoral head (e.g., 40mm).

Correct Answer & Explanation

. Revision of the femoral component to correct its version.

Explanation

Correct Answer: BThe teaching case states under 'Indications for Revision THR for Recurrent Dislocation': 'Component Malposition: Acetabular component malalignment (excessive anteversion/retroversion, inclination), or femoral component malversion.' And under 'Femoral Component Positioning': 'The femoral component should be implanted with appropriate anteversion, typically matching the native femoral version (10-20°). Excessive retroversion significantly increases posterior dislocation risk.' The vignette explicitly identifies 'significant femoral component retroversion (-5°)' as a finding on the CT scan. This is a direct mechanical cause for recurrent posterior dislocations. Therefore, revision of the femoral component to correct its version (Option B) would most directly address this primary mechanical issue.A. Exchange of the acetabular liner to a posterior-lipped liner:While a posterior-lipped liner can augment posterior stability, it is a compensatory measure. It does not correct the underlying femoral component malversion, which is the primary mechanical issue identified.C. Placement of a constrained acetabular liner:Constrained liners are reserved for severe instability due to irreversible soft tissue laxity or neuromuscular dysfunction, or when other measures have failed. While it would prevent dislocation, it has higher mechanical failure rates and is not the most direct solution for a correctable component malposition.D. Abductor repair and augmentation with an allograft:The patient has mild abductor weakness, which can contribute to instability, but the primary mechanical cause identified is femoral retroversion. Addressing the femoral version would be more impactful for posterior dislocation.E. Exchange to a larger femoral head (e.g., 40mm):A larger femoral head increases the jump distance and improves stability. This is a good general strategy for instability, but again, it does not correct the fundamental malposition of the femoral component, which is the root cause in this scenario. Correcting the femoral version would be a more definitive solution.

Question 343

Topic: 3. Adult Reconstruction (Hip & Knee)

A 78-year-old male with a history of Parkinson's disease and mild cognitive impairment undergoes a primary total hip replacement via a direct lateral approach. Intraoperatively, the surgeon notes that despite meticulous abductor repair and optimal component positioning, the hip feels somewhat lax on trial reduction, and the 'shuck test' is positive. Given the patient's comorbidities and intraoperative findings, which of the following liner options would be most appropriate to consider for enhancing stability?

. Standard polyethylene liner.
. Posterior-lipped polyethylene liner.
. Constrained acetabular liner.
. Highly cross-linked polyethylene liner with a smaller femoral head.
. Metal-on-metal bearing with a large femoral head.

Correct Answer & Explanation

. Constrained acetabular liner.

Explanation

Correct Answer: CThe teaching case states under 'Liner Options': 'Constrained Liner: Reserved for specific indications, such as recurrent dislocations due to severe abductor insufficiency, neuromuscular disorders, or in revision settings where other measures have failed. Constrained liners physically lock the head within the liner...' The patient has Parkinson's disease (a neuromuscular disorder) and mild cognitive impairment, both of which are risk factors for dislocation due to impaired motor control, balance, and compliance with precautions. The intraoperative finding of a 'somewhat lax' hip and a positive 'shuck test' (suggesting inadequate soft tissue tension) further indicates inherent instability despite optimal component positioning and abductor repair. In this high-risk scenario, a constrained acetabular liner (Option C) is the most appropriate choice to physically prevent dislocation, acknowledging its higher mechanical failure rates but accepting them due to the severe instability risk.A. Standard polyethylene liner:This would be used for a stable hip, which is not the case here.B. Posterior-lipped polyethylene liner:This is primarily used to augment posterior stability, typically with a posterior approach, and would not address the generalized laxity or the patient's high-risk profile for overall instability.D. Highly cross-linked polyethylene liner with a smaller femoral head:While highly cross-linked polyethylene is excellent for wear, a smaller femoral head would decrease the jump distance and further compromise stability, which is the opposite of what is needed.E. Metal-on-metal bearing with a large femoral head:While large femoral heads improve stability, metal-on-metal bearings have fallen out of favor due to concerns about metal ion release and pseudotumor formation. It's not the primary solution for a mechanically unstable hip in a high-risk patient.

Question 344

Topic: 3. Adult Reconstruction (Hip & Knee)

A 55-year-old active male undergoes a primary total hip replacement for avascular necrosis. The surgeon utilizes a posterior approach and meticulously repairs the posterior capsule and short external rotators. Intraoperative assessment confirms excellent stability. Post-operatively, the patient is advised on standard posterior hip precautions. Which of the following activities, if performed incorrectly, would most likely lead to a posterior dislocation in this patient?

. Sleeping on the back with legs straight.
. Walking with a cane on level ground.
. Sitting in a high-backed chair with feet flat on the floor.
. Bending forward to tie shoelaces while seated on a low stool.
. Performing gentle hip abduction exercises in supine.

Correct Answer & Explanation

. Bending forward to tie shoelaces while seated on a low stool.

Explanation

Correct Answer: DThe teaching case states under 'Posterior Approach Precautions': 'Avoid Hip Flexion > 90°,' 'Avoid Adduction Past Midline,' and 'Avoid Internal Rotation.' It also lists 'Activities to Avoid: Crossing legs, sleeping on the side without a pillow between knees, low chairs, bending at the waist to pick things up.' Bending forward to tie shoelaces while seated on a low stool (Option D) combines several high-risk movements for a posterior approach: significant hip flexion (likely >90°), adduction (if the leg crosses the midline), and internal rotation. This combination creates a lever-out mechanism that can lead to posterior dislocation.A. Sleeping on the back with legs straight:This position does not violate posterior hip precautions.B. Walking with a cane on level ground:This is a recommended activity for early mobilization and does not typically place the hip at risk for dislocation.C. Sitting in a high-backed chair with feet flat on the floor:A high-backed chair helps maintain hip flexion below 90°, and feet flat on the floor prevents excessive adduction or internal rotation. This is a safe activity.E. Performing gentle hip abduction exercises in supine:Gentle hip abduction is a common and safe exercise in the acute phase of rehabilitation, helping to strengthen the abductors without violating posterior precautions.

Question 345

Topic: 3. Adult Reconstruction (Hip & Knee)

A 62-year-old female undergoes a revision total hip replacement for recurrent dislocations. During the procedure, the surgeon identifies a significant posterior acetabular wall deficiency. After addressing component malposition and ensuring adequate soft tissue tension, the surgeon needs to augment the posterior stability. Which of the following options is specifically mentioned in the case as a salvage strategy for severe posterior wall defects?

. Iliopsoas release.
. Use of a larger femoral head.
. Augmentation with a posterior acetabular cage or allograft.
. Girdlestone resection arthroplasty.
. Arthrodesis of the hip.

Correct Answer & Explanation

. Augmentation with a posterior acetabular cage or allograft.

Explanation

Correct Answer: CThe teaching case, under 'Complications & Management' and 'Salvage Strategies (Revision Surgery) for Recurrent Dislocation,' explicitly states: 'Augmentation: Use of a posterior acetabular cage or allograft for severe posterior wall defects.' A posterior acetabular wall deficiency directly compromises the bony containment of the femoral head posteriorly, making the hip highly susceptible to posterior dislocation. Augmenting this defect with a cage or allograft provides structural support and helps restore the acetabular anatomy, thereby enhancing stability.A. Iliopsoas release:This is rarely considered for anterior impingement and is not relevant for a posterior wall deficiency.B. Use of a larger femoral head:While a larger femoral head increases the jump distance and improves overall stability, it does not directly address a structural bony defect like a posterior wall deficiency. It's a general measure, not specific to this defect.D. Girdlestone resection arthroplasty:This is a salvage procedure for recalcitrant infection and instability in medically infirm patients, involving removal of the femoral head and neck, resulting in a flail hip. It is not a reconstructive option for a posterior wall defect in a patient undergoing revision for recurrent dislocation.E. Arthrodesis of the hip:This is an extremely rare salvage procedure for young, active patients with persistent pain and instability where other options are exhausted, fusing the hip joint. It is not a solution for a posterior wall defect in a revision THR.

Question 346

Topic: Total Hip Arthroplasty (THA)

A 70-year-old male undergoes a primary total hip replacement via a direct lateral approach. Post-operatively, he develops a persistent Trendelenburg gait and complains of hip weakness, despite diligent physical therapy. This abductor insufficiency increases his risk for superior dislocation. Which of the following intraoperative steps is most critical in preventing this specific complication with a direct lateral approach?

. Ensuring adequate femoral anteversion.
. Meticulous repair of the abductor mechanism to the greater trochanter.
. Thorough removal of peripheral osteophytes.
. Placement of a posterior-lipped acetabular liner.
. Restoration of the native femoral neck-shaft angle.

Correct Answer & Explanation

. Meticulous repair of the abductor mechanism to the greater trochanter.

Explanation

Correct Answer: BThe teaching case, under 'Direct Lateral/Anterolateral Approaches (Hardinge/Modified Hardinge)' and 'Dislocation Mitigation,' states: 'Meticulous repair of the abductor mechanism to the greater trochanter is critical to prevent post-operative abductor insufficiency and superior dislocation.' The direct lateral approach involves detaching or splitting the abductor muscles (gluteus medius and minimus) from the greater trochanter. Failure to meticulously repair these muscles can lead to abductor insufficiency, resulting in a Trendelenburg gait and increased risk of superior or superolateral dislocation due to the loss of the primary stabilizing force against superior migration.A. Ensuring adequate femoral anteversion:This is crucial for preventing posterior dislocation and impingement, but less directly related to superior dislocation caused by abductor insufficiency.C. Thorough removal of peripheral osteophytes:This prevents impingement and lever-out, which can cause dislocation in various directions, but is not specific to preventing superior dislocation due to abductor weakness.D. Placement of a posterior-lipped acetabular liner:This is used to augment posterior stability, typically with a posterior approach, and is not relevant for preventing superior dislocation in a direct lateral approach.E. Restoration of the native femoral neck-shaft angle:This contributes to overall hip biomechanics and offset, but the direct repair of the abductor mechanism is the most critical step for preventing abductor insufficiency and superior dislocation in a lateral approach.

Question 347

Topic: 3. Adult Reconstruction (Hip & Knee)

A 48-year-old male, an avid golfer, is undergoing a primary total hip replacement. He expresses concern about returning to his sport and wants to minimize any risk of dislocation. The surgeon plans to use a modern uncemented system. Based on current literature and guidelines, which of the following implant choices is most strongly supported by evidence to reduce dislocation rates and would be beneficial for this active patient?

. A 28mm ceramic femoral head with a standard polyethylene liner.
. A 32mm metal femoral head with a metal-on-metal bearing.
. A 36mm ceramic femoral head with a highly cross-linked polyethylene liner.
. A 22mm ceramic femoral head with a constrained liner.
. A 32mm metal femoral head with a standard polyethylene liner.

Correct Answer & Explanation

. A 36mm ceramic femoral head with a highly cross-linked polyethylene liner.

Explanation

Correct Answer: CThe teaching case, under 'Femoral Head Size' and 'Summary of Key Literature / Guidelines,' states: 'A vast body of literature unequivocally supports the use of larger femoral heads (>32mm, preferably 36mm or greater) in reducing dislocation rates. Larger heads increase the 'jump distance' – the linear distance the center of the femoral head must travel before dislocating – effectively enhancing intrinsic stability.' It also notes that 'advancements in polyethylene technology (e.g., highly cross-linked polyethylene) have mitigated these wear concerns, making larger heads the standard for most bearing surfaces.'Therefore, a 36mm ceramic femoral head with a highly cross-linked polyethylene liner (Option C) is the optimal choice. This combination provides the benefits of a large femoral head for increased stability (larger jump distance) and the excellent wear characteristics of ceramic-on-highly cross-linked polyethylene, which is crucial for an active patient.A. A 28mm ceramic femoral head with a standard polyethylene liner:A 28mm head is considered smaller and offers less stability (shorter jump distance) compared to larger heads. Standard polyethylene has higher wear rates than highly cross-linked polyethylene.B. A 32mm metal femoral head with a metal-on-metal bearing:While 32mm is better than 28mm, metal-on-metal bearings have significant concerns regarding metal ion release and pseudotumor formation, and are generally avoided in modern practice.D. A 22mm ceramic femoral head with a constrained liner:A 22mm head is very small and inherently unstable. While a constrained liner would prevent dislocation, it is reserved for specific high-risk cases due to higher mechanical failure rates and is not the primary choice for a healthy, active patient where intrinsic stability can be achieved with larger heads.E. A 32mm metal femoral head with a standard polyethylene liner:Similar to option A, a 32mm head is good, but standard polyethylene has higher wear rates, and a 36mm head offers even greater stability.

Question 348

Topic: 3. Adult Reconstruction (Hip & Knee)

A 67-year-old male with a history of severe rheumatoid arthritis and chronic steroid use undergoes a primary total hip replacement via a posterior approach. During the procedure, the surgeon notes that the soft tissues, including the posterior capsule and external rotators, are attenuated and difficult to repair robustly. Despite using a 36mm femoral head and achieving optimal component positioning, the hip feels somewhat lax on trial reduction. Which of the following intraoperative strategies, beyond what has already been done, would be the most appropriate next step to enhance stability in this specific scenario?

. Perform an iliopsoas release to reduce anterior impingement.
. Exchange the standard liner for a posterior-lipped liner.
. Increase the femoral offset by using a longer neck option.
. Perform a Girdlestone resection arthroplasty.
. Switch to a smaller femoral head to reduce impingement.

Correct Answer & Explanation

. Exchange the standard liner for a posterior-lipped liner.

Explanation

Correct Answer: BThe teaching case, under 'Liner Options,' states: 'A posterior-lipped liner can be used in posterior approaches to augment posterior stability by increasing the posterior jump distance, especially if soft tissue repair is compromised or the patient is at higher risk. The lip must be oriented correctly (posteriorly).' In this scenario, the patient has attenuated soft tissues (due to rheumatoid arthritis and chronic steroid use), making robust repair difficult. This directly compromises the soft tissue envelope's contribution to stability. Despite optimal component positioning and a large femoral head, the hip still feels lax. A posterior-lipped liner (Option B) is specifically designed to compensate for posterior soft tissue laxity in a posterior approach by increasing the effective posterior jump distance, thereby enhancing stability.A. Perform an iliopsoas release to reduce anterior impingement:Iliopsoas release is for anterior impingement and would not address posterior laxity.C. Increase the femoral offset by using a longer neck option:While restoring offset is crucial for abductor tension, the vignette implies that component positioning (including offset) was already optimized. Further increasing offset might lead to leg lengthening or impingement.D. Perform a Girdlestone resection arthroplasty:This is a salvage procedure for severe, recalcitrant problems, not a primary strategy to enhance stability in a primary THR.E. Switch to a smaller femoral head to reduce impingement:Switching to a smaller femoral head would decrease the jump distance and further compromise stability, which is the opposite of what is needed.

Question 349

Topic: 3. Adult Reconstruction (Hip & Knee)

A 68-year-old female with a metal-on-highly-crosslinked-polyethylene THA presents with new-onset groin pain. Radiographs show a well-fixed implant. Aspiration is negative for infection, but MRI demonstrates a solid/cystic pseudotumor. What is the most likely etiology?

. Polyethylene wear
. Mechanically assisted crevice corrosion at the head-neck junction
. Undiagnosed indolent infection
. Psoas impingement
. Galvanic corrosion at the stem-cement interface

Correct Answer & Explanation

. Mechanically assisted crevice corrosion at the head-neck junction

Explanation

Mechanically assisted crevice corrosion (trunnionosis) can occur at the head-neck modular junction, even in metal-on-polyethylene bearings. It leads to adverse local tissue reactions (ALTR) and pseudotumor formation.

Question 350

Topic: Total Hip Arthroplasty (THA)

A 70-year-old male sustains a recurrent posterior dislocation of his THA. Radiographs reveal the acetabular component is placed in 5 degrees of retroversion and 40 degrees of abduction. The stem has 15 degrees of anteversion. What is the most appropriate surgical management?

. Revision of the femoral stem to increase anteversion
. Revision of the acetabular component to increase anteversion
. Exchange of the modular head to a longer neck length
. Application of a constrained polyethylene liner
. Trochanteric advancement

Correct Answer & Explanation

. Revision of the acetabular component to increase anteversion

Explanation

The acetabular component is in retroversion, predisposing the patient to posterior dislocation. The most appropriate treatment is revision of the cup to achieve the target 15-20 degrees of anteversion.

Question 351

Topic: Total Hip Arthroplasty (THA)

A 55-year-old female complains of start-up groin pain when transitioning from seated to standing 1 year after an uncemented THA. Pain is reproduced with active hip flexion against resistance. Radiographs show a well-fixed cup with anterior overhang. What is the next best step in management if conservative treatment fails?

. Revision of the acetabular component
. Iliopsoas tenotomy
. Revision of the femoral stem
. Application of a constrained liner
. Gluteus medius repair

Correct Answer & Explanation

. Iliopsoas tenotomy

Explanation

Iliopsoas impingement is commonly caused by anterior overhang of the acetabular component. If conservative management (NSAIDs, injections, PT) fails, an arthroscopic or open iliopsoas tenotomy is the treatment of choice.

Question 352

Topic: Total Hip Arthroplasty (THA)

Failure to restore femoral offset during a total hip arthroplasty most commonly leads to which of the following clinical findings?

. Increased joint reaction forces and improved abductor mechanical advantage
. Weakness in hip abduction and increased risk of dislocation
. Sciatic nerve palsy
. Leg length discrepancy with over-lengthening
. Trochanteric bursitis

Correct Answer & Explanation

. Weakness in hip abduction and increased risk of dislocation

Explanation

Decreasing femoral offset reduces the lever arm of the abductor musculature. This leads to abductor weakness, increased joint reaction forces, and a higher risk of bony or soft-tissue impingement resulting in instability.

Question 353

Topic: 3. Adult Reconstruction (Hip & Knee)

A 75-year-old female sustains a periprosthetic femur fracture around her cementless THA. Radiographs show a fracture at the tip of the stem. The stem is loose, but the proximal femoral bone stock is adequate. What is the Vancouver classification and appropriate treatment?

. Vancouver B1; ORIF with cables and a laterally applied plate
. Vancouver B2; revision to a long fully porous-coated stem bypassing the fracture
. Vancouver B3; revision to a proximal femoral replacement
. Vancouver C; ORIF with locking plate alone
. Vancouver B2; ORIF with allograft struts alone

Correct Answer & Explanation

. Vancouver B2; revision to a long fully porous-coated stem bypassing the fracture

Explanation

A Vancouver B2 fracture occurs around or just below the stem tip with a loose implant but adequate bone stock. The standard of care is revision to a longer, bypassed diaphyseal engaging stem.

Question 354

Topic: Total Hip Arthroplasty (THA)

Following a posterior approach THA, a patient has a foot drop and diminished sensation over the dorsal foot. Which portion of the sciatic nerve is most vulnerable to injury during this procedure, and why?

. Tibial division, due to its lateral position
. Peroneal division, due to its lateral position and secure tethering at the fibular head
. Tibial division, due to its medial position and lesser epineurium
. Peroneal division, due to its medial position and larger funiculi
. Posterior femoral cutaneous nerve

Correct Answer & Explanation

. Peroneal division, due to its lateral position and secure tethering at the fibular head

Explanation

The peroneal division of the sciatic nerve is more susceptible to injury (stretch or compression) because it lies laterally, has fewer supporting connective tissues, and is securely tethered distally at the fibular neck.

Question 355

Topic: 3. Adult Reconstruction (Hip & Knee)

What is the most common reason for late revision of an anatomic total shoulder arthroplasty?

. Humeral component loosening
. Glenoid component loosening
. Recurrent instability
. Periprosthetic infection
. Rotator cuff failure

Correct Answer & Explanation

. Glenoid component loosening

Explanation

Symptomatic aseptic loosening of the polyethylene glenoid component is the most common long-term complication and the most frequent reason for late revision of an anatomic total shoulder arthroplasty.

Question 356

Topic: 3. Adult Reconstruction (Hip & Knee)

Which of the following patients is the most appropriate candidate for a metal-on-metal hip resurfacing arthroplasty?

. A 60-year-old female with osteoporosis
. A 45-year-old male with severe bilateral avascular necrosis and large femoral head cysts
. A 35-year-old female with childbearing potential and osteoarthritis
. A 50-year-old large-statured male with primary osteoarthritis and good bone stock
. A 65-year-old male with chronic kidney disease

Correct Answer & Explanation

. A 50-year-old large-statured male with primary osteoarthritis and good bone stock

Explanation

Hip resurfacing is best indicated for young, active, large-statured males with primary OA and strong bone stock. Contraindications include females of childbearing age, renal failure, osteoporosis, and large femoral cysts.

Question 357

Topic: 3. Adult Reconstruction (Hip & Knee)

A 74-year-old female presents to the emergency department after a ground-level fall. She underwent a cementless total hip arthroplasty 10 years ago. Radiographs reveal a periprosthetic femur fracture extending just distal to the tip of the femoral stem. The stem demonstrates significant subsidence and radiolucencies in zones 1-7, but the proximal femur has good cortical bone stock. According to the Vancouver classification, what is the most appropriate surgical management?

. Open reduction and internal fixation with a lateral locking plate and cables.
. Revision to a standard-length cemented femoral stem with cerclage wiring.
. Revision to a fully porous-coated or fluted tapered cementless stem bypassing the fracture by 2 cortical diameters.
. Cortical strut allografting alone.
. Proximal femoral replacement.

Correct Answer & Explanation

. Revision to a fully porous-coated or fluted tapered cementless stem bypassing the fracture by 2 cortical diameters.

Explanation

This is a Vancouver B2 periprosthetic fracture (fracture around a loose stem with adequate bone stock). The gold standard treatment is revision arthroplasty utilizing a long cementless stem that bypasses the most distal fracture line by at least two cortical diameters.

Question 358

Topic: 3. Adult Reconstruction (Hip & Knee)

A 58-year-old male complains of insidious onset shoulder stiffness and dull pain 18 months following an anatomic total shoulder arthroplasty. Inflammatory markers (ESR, CRP) are within normal limits. Radiographs show progressive radiolucent lines around the glenoid component. Joint aspiration is performed. If Cutibacterium acnes is the causative organism, which of the following is true regarding its microbiologic profile and culture requirements?

. It is a Gram-negative aerobe requiring 48 hours for visible growth.
. It is a Gram-positive anaerobic bacillus that may require cultures to be held for up to 14 days.
. It is an acid-fast bacillus requiring Lowenstein-Jensen medium.
. It is a coagulase-positive coccus that typically presents with a draining sinus tract.
. It is an encapsulated yeast best diagnosed with an India ink stain.

Correct Answer & Explanation

. It is a Gram-positive anaerobic bacillus that may require cultures to be held for up to 14 days.

Explanation

Cutibacterium acnes is a Gram-positive, anaerobic (or aerotolerant) rod commonly implicated in indolent shoulder periprosthetic joint infections. Because it is a slow-growing organism, cultures should routinely be held for up to 14 days to maximize the diagnostic yield.

Question 359

Topic: 3. Adult Reconstruction (Hip & Knee)

A 62-year-old male with a modern cementless total hip arthroplasty presents with new-onset groin pain. His implant utilizes a large-diameter cobalt-chromium head on a standard titanium alloy stem. Radiographs show a well-fixed implant, but serum metal ion testing reveals elevated cobalt levels that are disproportionately higher than chromium levels. What is the most likely diagnosis?

. Ceramic liner fracture.
. Acetabular component loosening.
. Trunnionosis (head-neck taper corrosion).
. Metal-on-metal bearing surface wear.
. Aseptic Lymphocytic Vasculitis-Associated Lesion (ALVAL) from a cross-linked polyethylene liner.

Correct Answer & Explanation

. Trunnionosis (head-neck taper corrosion).

Explanation

Mechanically assisted crevice corrosion at the modular head-neck junction (trunnionosis) typically presents with elevated serum cobalt levels that significantly exceed chromium levels. This is often seen when large-diameter cobalt-chromium heads are used on titanium stems, leading to adverse local tissue reactions.

Question 360

Topic: 3. Adult Reconstruction (Hip & Knee)

During a primary total hip arthroplasty utilizing the direct anterior approach, the surgeon develops the internervous plane between the tensor fasciae latae and the sartorius. To expose the anterior capsule, branches of which of the following vascular structures must typically be identified and ligated?

. Medial circumflex femoral artery
. Inferior gluteal artery
. Superior gluteal artery
. Ascending branches of the lateral circumflex femoral artery
. Descending genicular artery

Correct Answer & Explanation

. Ascending branches of the lateral circumflex femoral artery

Explanation

The direct anterior approach utilizes the internervous plane between the tensor fasciae latae (superior gluteal nerve) and the sartorius (femoral nerve). The ascending branches of the lateral circumflex femoral artery cross this interval and must be ligated to prevent postoperative hematoma and allow adequate capsular exposure.

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