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Total Hip Arthroplasty (THA) MCQs

Practice Set 27 of 36

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

Question 521

Topic: Total Hip Arthroplasty (THA)
A 55-year-old female undergoes revision THA for recurrent dislocation. Intraoperatively, she is found to have a significant acetabular bone defect (Paprosky Type IIIB) with pelvic discontinuity. The surgeon plans to use a custom triflange acetabular component. What is the primary indication for using such a component in this scenario?
. To achieve biological ingrowth for long-term fixation.
. To bypass acetabular bone defects and provide stable fixation to intact pelvic bone.
. To allow for future liner exchange without full component revision.
. To reduce the risk of metal ion release from the acetabular shell.
. To provide increased jump distance and reduce dislocation risk.

Correct Answer & Explanation

. To bypass acetabular bone defects and provide stable fixation to intact pelvic bone.

Explanation

Custom triflange acetabular components are highly specialized implants used in complex revision THA cases, particularly for massive acetabular bone loss (Paprosky Type IIIB, sometimes Type III with pelvic discontinuity) where standard cages or conventional uncemented shells cannot provide stable fixation. The primary indication for these components is their ability to achieve stable, peripheral fixation to intact pelvic bone (e.g., ischium, ilium, pubis) bypassing the central acetabular defect and discontinuity. They are custom-designed from preoperative CT scans to perfectly match the patient's unique pelvic anatomy, providing a durable solution in otherwise unreconstructible acetabular defects. While they aim for biological ingrowth, their primary strength is mechanical stability in areas of severe bone loss, distributing load to healthy bone. The other options describe general benefits of THA components or are not the main indication for a triflange design.

Question 522

Topic: Total Hip Arthroplasty (THA)

During a primary THA, a significant leg length discrepancy (LLD) of 3 cm is noted intraoperatively with the ipsilateral limb being shorter. The surgeon has already reduced the hip and achieved stable component fixation. What is the most appropriate next step to address this LLD while minimizing complications?

. Accept the current LLD and counsel the patient on a shoe lift postoperatively.
. Perform a femoral shaft lengthening osteotomy to equalize limb length.
. Increase the neck-length of the femoral component by exchanging to a longer neck or a different stem version.
. Decrease the size of the acetabular component to lower the hip center.
. Perform a controlled release of the ipsilateral adductor and psoas muscles.

Correct Answer & Explanation

. Increase the neck-length of the femoral component by exchanging to a longer neck or a different stem version.

Explanation

Intraoperative leg length discrepancy >2-2.5 cm can lead to complications such as sciatic nerve palsy, lower back pain, and gait abnormalities. While accepting LLD with a shoe lift is an option for smaller discrepancies, 3 cm is significant. A femoral shaft lengthening osteotomy (option B) is a major procedure generally reserved for very large discrepancies or reconstructive needs outside of typical THA. Decreasing the acetabular component size (option D) would likely compromise stability and fixation. Controlled release of adductors and psoas (option E) is used to prevent impingement or to facilitate reduction in cases of severe contracture, but it doesn't directly lengthen the limb. The most practical and common intraoperative solution to address a short limb after initial stable reduction is to increase the effective neck length of the femoral component. This can be achieved by using a longer modular neck, a different femoral head length (e.g., +4, +8mm offset), or, if necessary, revising to a stem that allows for more lengthening, provided it doesn't compromise stability or risk neurovascular injury. This increases the offset and length without disturbing the established fixation of the stem or acetabulum.

Question 523

Topic: Total Hip Arthroplasty (THA)

Which of the following statements most accurately reflects the current understanding of robotic-assisted total hip arthroplasty (THA) compared to conventional manual THA?

. Robotic-assisted THA consistently results in significantly improved long-term clinical outcomes and implant survival compared to manual THA.
. Robotic-assisted THA universally leads to shorter operative times and reduced blood loss.
. Robotic-assisted THA has been shown to achieve more reproducible and accurate component positioning, particularly for acetabular inclination and anteversion.
. The learning curve for robotic-assisted THA is typically shorter than for conventional manual THA.
. Robotic-assisted THA eliminates the need for intraoperative fluoroscopy or conventional radiographic templating.

Correct Answer & Explanation

. Robotic-assisted THA has been shown to achieve more reproducible and accurate component positioning, particularly for acetabular inclination and anteversion.

Explanation

While long-term clinical superiority of robotic-assisted THA over conventional THA (A) is still being investigated, current evidence strongly supports that robotic systems achieve more reproducible and accurate component positioning, especially for acetabular inclination and anteversion (C). This precision can potentially reduce complications like dislocation and impingement. Operative times may initially be longer during the learning curve (B, D) and blood loss is not consistently reduced. Robotic assistance often complements, rather than eliminates, conventional templating and sometimes requires intraoperative imaging for registration (E).

Question 524

Topic: Total Hip Arthroplasty (THA)

A 65-year-old active female undergoes primary THA. She has a high-riding greater trochanter and significant hip abductor weakness despite no overt abductor tear. The surgeon performs a direct anterior approach. What is a potential unique advantage of a modified direct anterior approach, specifically related to abductor function, in this patient compared to a standard posterior or lateral approach?

. It allows for better visualization of the sciatic nerve, reducing nerve injury risk.
. It facilitates a more accurate leg length assessment during surgery.
. It preserves the abductor muscles by working between the sartorius and tensor fascia lata, potentially aiding in quicker recovery of abductor strength.
. It avoids the need for external rotation of the leg, reducing femoral head fracture risk.
. It provides superior exposure for acetabular reconstruction in complex revision cases.

Correct Answer & Explanation

. It preserves the abductor muscles by working between the sartorius and tensor fascia lata, potentially aiding in quicker recovery of abductor strength.

Explanation

The direct anterior approach (DAA) is unique in that it is an intermuscular and internervous interval approach, typically done between the tensor fascia lata (innervated by superior gluteal nerve) and the sartorius (innervated by femoral nerve). This approach largely preserves the hip abductor mechanism (gluteus medius and minimus) and their insertions, as well as the external rotators (C). This can be particularly advantageous in patients with pre-existing abductor weakness, potentially leading to quicker recovery of abductor strength and reduced risk of postoperative limp or abductor tears, compared to approaches that involve detaching or splitting these muscles (e.g., transtrochanteric, direct lateral, or posterior approach with repair). Visualization of the sciatic nerve (A) is typically better with a posterior approach. Leg length assessment (B) can be achieved with various approaches, often with aids. External rotation (D) is typically performed for femoral preparation in a DAA. Superior exposure for complex revision (E) is often better achieved with extensile posterior or lateral approaches.

Question 525

Topic: Total Hip Arthroplasty (THA)
A 60-year-old patient with rheumatoid arthritis presents with severe bilateral protrusio acetabuli, graded as Paprosky Type IIIA defects, with significant loss of the medial wall. Which of the following reconstructive strategies is most appropriate for the acetabulum?
. Standard uncemented hemispheric cup placed more medially to gain coverage
. Placement of a small-diameter cemented cup within the protruded region without bone graft
. Resection of the protruded bone to achieve a flush fit for a standard cup
. Medialization of the cup combined with a structural autograft or allograft and reinforcement plate/cage
. A custom triflange acetabular component

Correct Answer & Explanation

. Medialization of the cup combined with a structural autograft or allograft and reinforcement plate/cage

Explanation

Protrusio acetabuli involves medial displacement of the femoral head and acetabulum. For severe protrusio (Paprosky IIIA), characterized by significant medial wall bone loss, merely placing a standard cup or resecting bone will not adequately restore hip mechanics or provide durable fixation. A small cemented cup without grafting is insufficient for significant bone loss. The ideal approach often involves restoring the medial wall with a structural bone graft (autograft or allograft) to support the acetabular component, followed by medialization of the cup into a more anatomical position and often supported by an anti-protrusio cage or reinforcement plate to prevent further medial migration and achieve stability. Custom triflange implants (Option E) are typically reserved for much more complex and irregular defects than a Paprosky IIIA protrusio, though they could technically address it, they are often an overkill and more expensive option for this scenario. Medializing the cup into the true hip center with graft support is the reconstructive principle.

Question 526

Topic: Total Hip Arthroplasty (THA)

During a primary total hip arthroplasty via a posterior approach, the patient is noted to have a preoperative leg length discrepancy of 2.5 cm, with the operative leg being shorter. The surgeon plans to restore leg length to within 5 mm of the contralateral side. What is a crucial intraoperative maneuver or consideration to minimize the risk of sciatic nerve injury during this limb lengthening?

. Performing a staged lengthening over several weeks with an external fixator
. Intraoperative neuromonitoring (e.g., somatosensory evoked potentials or electromyography)
. Positioning the hip in extreme external rotation during reduction
. Administering a bolus of intravenous steroids immediately prior to lengthening
. Avoiding any soft tissue releases around the hip capsule

Correct Answer & Explanation

. Intraoperative neuromonitoring (e.g., somatosensory evoked potentials or electromyography)

Explanation

Restoring significant leg length discrepancy (e.g., >2-3 cm) during THA carries a notable risk of sciatic nerve palsy due to excessive tension. While a femoral shortening osteotomy (not an option here) is a definitive way to prevent excessive lengthening, in this scenario, options to mitigate risk are crucial. Intraoperative neuromonitoring (B) is a critical tool to detect impending nerve compromise. It provides real-time feedback on nerve function, allowing the surgeon to adjust lengthening or perform additional soft tissue releases if nerve signals diminish. Staged lengthening (A) is for very extreme cases or where nerve function cannot be monitored or salvaged. Extreme external rotation (C) may temporarily reduce tension but is not a primary protective maneuver. Steroids (D) are not proven prophylactic. Avoiding soft tissue releases (E) increases nerve tension. Therefore, neuromonitoring is key for safe lengthening.

Question 527

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 528

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 529

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 530

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 531

Topic: Total Hip Arthroplasty (THA)

During a primary THA, the surgeon inadvertently decreases the patient's femoral offset by 10 mm. Which of the following is the most likely clinical consequence of this technical error?

. Decreased joint reactive forces across the hip
. Increased risk of postoperative dislocation and a Trendelenburg gait
. Increased mechanical advantage of the abductor musculature
. Significant leg length discrepancy with a lengthened operative leg
. Reduced volumetric wear of the polyethylene liner

Correct Answer & Explanation

. Increased risk of postoperative dislocation and a Trendelenburg gait

Explanation

Decreasing femoral offset reduces the moment arm of the abductor muscles, leading to weakness and a Trendelenburg gait. It also decreases soft tissue tension, thereby significantly increasing the risk of instability and postoperative dislocation.

Question 532

Topic: Total Hip Arthroplasty (THA)

A 55-year-old female presents with persistent anterior groin pain 1 year post-THA. Pain is elicited with an active straight leg raise. Cross-sectional imaging reveals the acetabular component overhangs the anterior bone edge by 12 mm. What is the most appropriate definitive management?

. Arthroscopic iliopsoas tenotomy
. Open iliopsoas tenotomy
. Revision of the acetabular component
. Revision of the femoral component
. Ultrasound-guided corticosteroid injection into the psoas sheath

Correct Answer & Explanation

. Revision of the acetabular component

Explanation

While iliopsoas impingement is often treated with tenotomy, significant anterior cup overhang (generally >8 mm) provides a mechanical block that will cause tenotomy to fail. Acetabular component revision is the definitive treatment in this scenario.

Question 533

Topic: Total Hip Arthroplasty (THA)

During a Kocher-Langenbeck approach for a posterior wall acetabular fracture, the short external rotators of the hip are tagged and tenotomized near their femoral insertion. Which muscle should be preserved or have its femoral insertion left intact to protect the main blood supply to the femoral head?

. Piriformis
. Superior gemellus
. Obturator internus
. Quadratus femoris
. Inferior gemellus

Correct Answer & Explanation

. Quadratus femoris

Explanation

The deep branch of the medial femoral circumflex artery (MFCA) provides the primary blood supply to the adult femoral head. It runs anterior to the quadratus femoris and posterior to the obturator externus. To protect the MFCA during a posterior approach, the quadratus femoris (or at least its inferior half) and the obturator externus should be preserved. Tenotomizing the piriformis and the triceps coxae (superior gemellus, obturator internus, inferior gemellus) is standard and safe.

Question 534

Topic: Total Hip Arthroplasty (THA)

During a posterior approach to the hip, aggressive release of the quadratus femoris muscle insertion on the proximal femur puts which of the following vascular structures at greatest risk?

. Superior gluteal artery
. Inferior gluteal artery
. Ascending branch of the lateral circumflex femoral artery
. Medial circumflex femoral artery
. First perforating branch of the profunda femoris

Correct Answer & Explanation

. Medial circumflex femoral artery

Explanation

The deep branch of the medial circumflex femoral artery runs anterior to the quadratus femoris and posterior to the obturator externus. Aggressive release or division of the quadratus femoris too close to its femoral insertion can easily sever this vital artery, jeopardizing the femoral head blood supply.

Question 535

Topic: Total Hip Arthroplasty (THA)

The main blood supply to the adult femoral head is derived from the deep branch of the medial femoral circumflex artery (MFCA). At what key anatomical location does the MFCA cross the obturator externus muscle?

. Anterior to the obturator externus tendon
. Posterior to the obturator externus tendon
. Superior to the piriformis tendon
. Inferior to the quadratus femoris
. Piercing the iliopsoas tendon

Correct Answer & Explanation

. Posterior to the obturator externus tendon

Explanation

The deep branch of the MFCA travels anterior to the superior gemellus and obturator internus but constantly crosses posterior to the obturator externus tendon. This relationship makes the vessel vulnerable during posterior approaches if the obturator externus is violated.

Question 536

Topic: Total Hip Arthroplasty (THA)

Which surgical approach to the hip is associated with the highest risk of postoperative dislocation, particularly posterior dislocation?

. Direct anterior approach
. Anterolateral approach
. Direct lateral approach
. Posterior approach
. Trochanteric osteotomy approach

Correct Answer & Explanation

. Posterior approach

Explanation

The posterior approach (Moore approach) to total hip arthroplasty is classically associated with a higher risk of posterior dislocation compared to anterior or lateral approaches, primarily due to posterior capsule and short external rotator muscle division. While modern techniques for posterior approach often involve repair of these structures, it historically carries the highest risk. The direct anterior approach and direct lateral approaches generally have lower dislocation rates, particularly for posterior dislocation.

Question 537

Topic: Total Hip Arthroplasty (THA)

During a routine post-operative visit for a patient who had spinal fusion through an anterior approach, the patient complains of a new, subtle bulge and discomfort lateral to their surgical incision. No other GI symptoms are present. What type of hernia, potentially a Richter, is most likely in this context?

. Inguinal hernia
. Femoral hernia
. Obturator hernia
. Spigelian hernia
. Incisional hernia (at the anterior approach site)

Correct Answer & Explanation

. Incisional hernia (at the anterior approach site)

Explanation

An anterior approach spinal fusion involves an abdominal incision, often paramedian or transverse. An incisional hernia at this site is a direct complication of the surgical incision itself. Given the 'subtle bulge and discomfort lateral to their surgical incision' and lack of other GI symptoms, an incisional hernia, potentially with Richter incarceration, is the most likely type. Inguinal, femoral, obturator, and Spigelian hernias occur at distinct anatomical sites unrelated to the spinal fusion incision itself, though they might exist concomitantly. The prompt is specifically about anewbulgelateral to their surgical incision.

Question 538

Topic: Total Hip Arthroplasty (THA)

Which nerve is at greatest risk of injury during anterior surgical approaches to the hip (e.g., direct anterior approach for THA)?

. Sciatic nerve
. Femoral nerve
. Obturator nerve
. Lateral femoral cutaneous nerve
. Superior gluteal nerve

Correct Answer & Explanation

. Lateral femoral cutaneous nerve

Explanation

The lateral femoral cutaneous nerve (LFCN) is particularly vulnerable during direct anterior approaches to the hip, as it crosses the iliac crest and lies superficial within the surgical field. Injury can lead to meralgia paresthetica (numbness, tingling, or burning pain in the lateral thigh). The sciatic nerve is at risk with posterior approaches. The femoral, obturator, and superior gluteal nerves are deeper and less frequently injured during anterior approaches.

Question 539

Topic: Total Hip Arthroplasty (THA)

Which surgical approach for total hip arthroplasty (THA) is most commonly associated with a higher risk of postoperative dislocation?

. Direct anterior approach
. Anterolateral approach
. Posterior approach
. Lateral approach (Hardinge)
. Minimally invasive approach (any type)

Correct Answer & Explanation

. Posterior approach

Explanation

The posterior approach for total hip arthroplasty (THA) has traditionally been associated with a higher risk of postoperative dislocation, primarily due to the necessary division of the short external rotator muscles and posterior capsule. While surgical techniques and repair of the capsule have reduced this risk, it remains a concern compared to anterior or lateral approaches. Direct anterior and lateral approaches are generally considered to have lower dislocation rates, although each approach has its own unique set of potential complications.

Question 540

Topic: Total Hip Arthroplasty (THA)

Which of the following describes the anatomical landmark used to locate the neurovascular bundle during a posterior approach to the knee for meniscal repair or PCL reconstruction?

. Popliteal fossa
. Adductor tubercle
. Gerdy's tubercle
. Medial epicondyle
. Fibular head

Correct Answer & Explanation

. Popliteal fossa

Explanation

The popliteal fossa is the anatomical landmark containing the neurovascular bundle (popliteal artery, vein, and tibial nerve) that must be carefully protected during a posterior approach to the knee. These vital structures are located in the deep aspect of the fossa. The adductor tubercle and medial epicondyle are on the medial aspect of the femur. Gerdy's tubercle is on the lateral tibia. The fibular head is on the lateral aspect of the knee.

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