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Total Hip Arthroplasty (THA) MCQs

Practice Set 3 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 41

Topic: Total Hip Arthroplasty (THA)

A 72-year-old female undergoes a primary total hip replacement (THR) via a posterior approach for severe osteoarthritis. Three weeks post-operatively, she presents to the emergency department with acute hip pain and inability to bear weight after attempting to pick up an object from the floor, resulting in a posterior dislocation. Radiographs confirm a posterior dislocation without periprosthetic fracture. After successful closed reduction, the surgeon reviews the case. Which of the following factors is LEAST likely to be the primary contributing cause of this early dislocation?

. Inadequate repair of the posterior capsule and short external rotators.
. Acetabular component malposition outside the Lewinnek safe zone.
. Patient non-compliance with post-operative hip precautions.
. Progressive soft tissue laxity due to implant wear.
. Use of a smaller femoral head (e.g., 28mm) leading to reduced jump distance.

Correct Answer & Explanation

. Progressive soft tissue laxity due to implant wear.

Explanation

Correct Answer: DThe case describes anearly dislocation(three weeks post-operatively). The teaching case states: 'Early dislocations typically occur within the first three months post-operatively and are frequently attributed to surgical technique, component malposition, or early non-compliance with precautions. Late dislocations, occurring beyond three months, are more often associated with factors such as soft tissue laxity, component wear, neuromuscular dysfunction, or trauma.' Progressive soft tissue laxity due to implant wear (Option D) is a characteristic oflate dislocations, as significant wear typically takes a longer period to develop and contribute to laxity. Therefore, it is the least likely primary contributing cause for an early dislocation.Options A, B, C, and E are all well-established risk factors for early dislocation:A. Inadequate repair of the posterior capsule and short external rotators:The posterior approach, if not meticulously repaired, is associated with higher posterior dislocation risk. The case specifically mentions a posterior approach.B. Acetabular component malposition:Deviations from the safe zone (e.g., excessive anteversion or retroversion, high inclination) are a leading cause of early dislocation due to impingement or reduced stability.C. Patient non-compliance with post-operative hip precautions:The patient's action of bending at the waist to pick up an object is a classic violation of posterior hip precautions (avoiding hip flexion > 90° and internal rotation), which can directly lead to posterior dislocation.E. Use of a smaller femoral head:Smaller femoral heads inherently have a shorter 'jump distance,' making the hip less stable and more prone to dislocation, especially in the early post-operative period before full soft tissue healing and strength are achieved. The case emphasizes that larger femoral heads significantly enhance stability.

Question 42

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 43

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 44

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 45

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 46

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 47

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 48

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 49

Topic: Total Hip Arthroplasty (THA)

A 55-year-old male presents with audible squeaking from his right ceramic-on-ceramic total hip arthroplasty two years postoperatively. Radiographs show a well-fixed cup with 55 degrees of inclination. What is the most likely biomechanical cause of this squeaking phenomenon?

. Stripe wear from edge loading due to component malposition
. Third-body wear from retained cement mantle fragments
. Galvanic corrosion at the head-neck junction
. Fatigue failure of the ceramic head
. Impingement of the femoral neck on the anterior capsule

Correct Answer & Explanation

. Stripe wear from edge loading due to component malposition

Explanation

Squeaking in ceramic-on-ceramic THA is highly associated with edge loading caused by component malposition, such as excessive cup inclination or version. Edge loading leads to stripe wear and loss of fluid-film lubrication, producing the audible squeak.

Question 50

Topic: Total Hip Arthroplasty (THA)

During a total hip arthroplasty, the surgeon increases the femoral offset by 5 mm without altering the vertical leg length. What is the primary biomechanical effect of this modification?

. Increases the joint reactive force across the hip
. Decreases the moment arm of the abductor musculature
. Increases the resting tension of the abductor musculature
. Increases the risk of posterior dislocation
. Decreases the varus bending moment on the femoral stem

Correct Answer & Explanation

. Increases the resting tension of the abductor musculature

Explanation

Increasing femoral offset lateralizes the femur, which increases the moment arm and resting tension of the abductor musculature. This improves abductor mechanical advantage, thereby decreasing the overall joint reactive force while increasing the bending moment on the stem.

Question 51

Topic: Total Hip Arthroplasty (THA)

A 77-year-old female presents with a new dislocation of her dual mobility total hip arthroplasty. Radiographs reveal an 'intra-prosthetic' dislocation. What is the defining mechanical failure in this type of dislocation?

. The outer polyethylene bearing dislocates from the metal acetabular shell
. The entire acetabular shell dislocates from the pelvis
. The inner metal head dislocates out of the larger polyethylene bearing
. The femoral stem dissociates from the inner metal head
. The femoral stem subsides into the femoral canal

Correct Answer & Explanation

. The inner metal head dislocates out of the larger polyethylene bearing

Explanation

An intra-prosthetic dislocation is specific to dual mobility cups. It occurs when the small inner head escapes the captive larger polyethylene liner due to wear or impingement at the retentive rim of the polyethylene.

Question 52

Topic: Total Hip Arthroplasty (THA)

A 50-year-old male presents with severe hip pain. Radiographs demonstrate an advanced cam-type femoroacetabular impingement (FAI) leading to end-stage osteoarthritis. If a total hip arthroplasty is performed, which aspect of component positioning is most critical to prevent impingement and dislocation given his history of cam morphology?

. Increasing cup inclination beyond 50 degrees
. Ensuring adequate combined anteversion of the cup and stem
. Placing the femoral stem in relative retroversion
. Using a constrained liner
. Decreasing femoral offset

Correct Answer & Explanation

. Ensuring adequate combined anteversion of the cup and stem

Explanation

Restoring appropriate combined anteversion (typically 25-35 degrees) is critical to preventing component impingement and dislocation in THA. Proper combined version provides clearance during functional ranges of motion, which is crucial in patients with pre-existing impingement anatomy.

Question 53

Topic: Total Hip Arthroplasty (THA)

Which of the following surgical approaches to the hip carries the highest risk of injury to the superior gluteal nerve?

. Direct anterior approach
. Posterior approach
. Direct lateral approach (Hardinge)
. Anterolateral approach (Watson-Jones)
. Transtrochanteric approach

Correct Answer & Explanation

. Direct lateral approach (Hardinge)

Explanation

Correct Answer: CThe direct lateral approach (Hardinge approach) involves incising the fascia lata and splitting the gluteus medius abductor insertion, which places the superior gluteal nerve at risk. The superior gluteal nerve innervates the gluteus medius, gluteus minimus, and tensor fascia lata. Injury to this nerve can lead to a Trendelenburg gait. While all approaches have specific nerve risks, the direct lateral approach is particularly known for this risk due to its dissection plane. The posterior approach risks the sciatic nerve, the direct anterior approach risks the lateral femoral cutaneous nerve, and the anterolateral approach carries a lower risk of superior gluteal nerve injury compared to the direct lateral but still involves the abductors.

Question 54

Topic: Total Hip Arthroplasty (THA)

A 65-year-old male presents with groin pain 4 years after a total hip arthroplasty utilizing a titanium stem and a 36-mm cobalt-chromium head. Inflammatory markers are normal, but metal ion levels (cobalt) are elevated. What is the most likely source of the elevated metal ions?

. Femoral stem loosening
. Acetabular component wear
. Corrosion at the head-neck junction
. Polyethylene debris
. Third-body wear

Correct Answer & Explanation

. Corrosion at the head-neck junction

Explanation

Trunnionosis (fretting and corrosion at the modular head-neck junction) is associated with large-diameter cobalt-chromium heads on titanium stems. It leads to elevated serum cobalt levels and adverse local tissue reactions.

Question 55

Topic: Total Hip Arthroplasty (THA)

While VTE rates are similar across total hip arthroplasty (THA) approaches, the direct anterior approach carries a unique risk of injury to which of the following structures?

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

Correct Answer & Explanation

. Lateral femoral cutaneous nerve

Explanation

The direct anterior approach to the hip utilizes the internervous plane between the sartorius and tensor fasciae latae. It uniquely places the lateral femoral cutaneous nerve at risk, which can lead to meralgia paresthetica.

Question 56

Topic: Total Hip Arthroplasty (THA)

A patient with a Vancouver Type C periprosthetic femur fracture (fracture well distal to a solidly fixed femoral stem) undergoes open reduction and internal fixation with a lateral locking plate. To minimize the risk of a subsequent stress riser and peri-implant failure, what is the minimum recommended plate overlap of the existing femoral stem?

. The plate must span entirely to the greater trochanter
. The plate should stop exactly at the tip of the stem
. The plate must overlap the stem by at least two cortical diameters
. The plate must overlap the stem by at least six cortical diameters
. Overlap is unnecessary if bicortical screws are used distal to the stem

Correct Answer & Explanation

. The plate must overlap the stem by at least two cortical diameters

Explanation

When treating a Vancouver C periprosthetic fracture with a plate, the hardware must overlap the existing intramedullary stem by at least two cortical diameters (or approximately 2 to 3 bone widths). Stopping the plate at or near the tip of the stem creates a severe stress riser, significantly increasing the risk of subsequent fracture.

Question 57

Topic: Total Hip Arthroplasty (THA)

A patient undergoes open reduction and internal fixation for a Vancouver C periprosthetic femur fracture located well below a stable, cemented THA stem. The surgeon utilizes a lateral locking plate. To minimize the biomechanical risk of a subsequent interprosthetic stress fracture, how should the proximal aspect of the plate be positioned?

. Stop exactly at the distal tip of the femoral stem
. Leave a gap of one cortical diameter between the plate and the stem tip
. Overlap the femoral stem by at least two cortical diameters
. Stop at least three cortical diameters distal to the stem tip
. Position the plate entirely on the anterior cortex to avoid lateral stress risers

Correct Answer & Explanation

. Overlap the femoral stem by at least two cortical diameters

Explanation

When plating a Vancouver C fracture, the plate should overlap the existing well-fixed stem by a minimum of two cortical diameters. Ending the plate near the tip of the stem creates a massive stress riser, predisposing the patient to an interprosthetic fracture.

Question 58

Topic: Total Hip Arthroplasty (THA)
During an open posterior approach to the knee for a PCL avulsion fracture, the surgeon must carefully navigate several critical neurovascular structures. Which of the following describes the correct anatomical relationship of the popliteal vein relative to the tibial nerve and popliteal artery in the popliteal fossa?
. A. The popliteal vein lies posterior to the tibial nerve and superficial to the popliteal artery.
. B. The popliteal vein lies anterior to the tibial nerve and deep to the popliteal artery.
. C. The popliteal vein lies posterior to the popliteal artery and superficial to the tibial nerve.
. D. The popliteal vein lies anterior to the popliteal artery and deep to the tibial nerve.
. E. The popliteal vein lies posterior to the tibial nerve and deep to the popliteal artery.

Correct Answer & Explanation

. C. The popliteal vein lies posterior to the popliteal artery and superficial to the tibial nerve.

Explanation

The correct anatomical order from posterior to anterior in the popliteal fossa is Tibial Nerve, Popliteal Vein, Popliteal Artery. Therefore, the popliteal vein is anterior to the tibial nerve and posterior to the popliteal artery. Option C is the most consistent with this anatomical relationship, where 'superficial' in the context of a posterior approach implies being closer to the skin (anterior) relative to the deeper structures.

Question 59

Topic: Total Hip Arthroplasty (THA)

A 62-year-old patient considering total ankle replacement (TAR) asks about the long-term prognosis.

Based on the information provided in the case, what is the approximate 10-year survival rate for total ankle replacements, and how does this compare to hip and knee replacements?

. Approximately 95%, with more extensive data available than for hip and knee replacements.
. Approaching 85%, but with fewer data available than for hip and knee replacements.
. Around 70%, with comparable data to hip and knee replacements.
. Approximately 60%, with significantly better data than for hip and knee replacements.
. Over 90%, but only for fixed-bearing designs.

Correct Answer & Explanation

. Approaching 85%, but with fewer data available than for hip and knee replacements.

Explanation

Correct Answer: BThe candidate's response to the question about TAR longevity is: 'The 10-year survival is approaching 85% but there are fewer data available than for knee and hip replacements. Many series are small.' This directly matches option B.Options A, C, D, and E provide incorrect survival rates or make inaccurate comparisons regarding the availability of data for ankle replacements versus hip and knee replacements.

Question 60

Topic: Total Hip Arthroplasty (THA)

During a posterior approach (Kocher-Langenbeck) to the hip for a posterior wall acetabular fracture, the short external rotators are tagged and released. To prevent profuse bleeding and protect the vascular supply to the femoral head, care must be taken when releasing the quadratus femoris. Which vessel lies within or immediately deep to the quadratus femoris?

. Ascending branch of the medial circumflex femoral artery
. Transverse branch of the lateral circumflex femoral artery
. Inferior gluteal artery
. First perforating branch of the profunda femoris
. Obturator artery

Correct Answer & Explanation

. Ascending branch of the medial circumflex femoral artery

Explanation

The ascending branch of the medial circumflex femoral artery lies deep to the quadratus femoris. It should be identified and protected, or the muscle release should leave a cuff of tissue to avoid vascular injury to the femoral head.

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