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Total Hip Arthroplasty (THA) MCQs

Practice Set 12 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 221

Topic: Total Hip Arthroplasty (THA)

A 78-year-old male with a history of recurrent posterior THA dislocations undergoes revision surgery. Intraoperative evaluation reveals an extremely deficient abductor mechanism. The acetabular shell is well-fixed and in appropriate anteversion and inclination. Which intervention will best restore stability in this patient?

. Use of an elevated rim liner placed in the anterior superior position
. Increasing horizontal femoral offset alone
. Revision to a dual-mobility articulation or a constrained liner
. Conversion to a bipolar hemiarthroplasty
. Distal advancement of the greater trochanter

Correct Answer & Explanation

. Revision to a dual-mobility articulation or a constrained liner

Explanation

In the setting of severe abductor deficiency leading to recurrent instability where components are well-positioned, optimizing soft tissue tension is often impossible. Therefore, an implant with high intrinsic stability is required. A dual-mobility construct or a constrained acetabular liner is indicated. Dual-mobility is typically preferred due to a better range of motion and lower risk of mechanical failure.

Question 222

Topic: Total Hip Arthroplasty (THA)

A patient presents 6 months after a right THA complaining that the right leg feels too long. On examination, the true leg length (measured from the ASIS to the medial malleolus) is equal bilaterally. However, the apparent leg length (measured from the umbilicus to the medial malleolus) is 2 cm longer on the right. What is the most likely etiology of this discrepancy?

. The femoral neck cut was made too high during surgery
. The acetabular component was placed too inferiorly
. Abductor weakness and an adduction contracture of the operative hip
. An abduction contracture of the operative hip
. Excessive femoral offset of the implanted stem

Correct Answer & Explanation

. An abduction contracture of the operative hip

Explanation

If the true leg lengths (ASIS to medial malleolus) are equal, the actual bony lengths of the lower extremities are identical. An apparent leg length discrepancy (umbilicus to medial malleolus) is caused by pelvic obliquity. An abduction contracture of the right hip forces the patient to tilt the right side of the pelvis downward to bring the legs parallel for standing/walking. This downward tilt of the right hemipelvis makes the right leg appear longer when measured from a central point (the umbilicus). Conversely, an adduction contracture results in an apparent shortening of the limb.

Question 223

Topic: Total Hip Arthroplasty (THA)

A 65-year-old male presents with groin pain 5 years after a primary metal-on-polyethylene total hip arthroplasty. Joint aspiration yields fluid with a high cobalt-to-chromium ratio and negative cultures. Which of the following implant characteristics most increases the risk of this specific complication?

. Use of a 28-mm femoral head
. Standard offset femoral stem
. Increased femoral head diameter (e.g., 36-mm or larger)
. Use of a ceramic femoral head
. Highly cross-linked polyethylene liner

Correct Answer & Explanation

. Increased femoral head diameter (e.g., 36-mm or larger)

Explanation

The patient is experiencing trunnionosis (taper corrosion). Utilizing larger diameter metal femoral heads increases the frictional torque at the head-neck junction, exacerbating fretting and corrosion at the trunnion.

Question 224

Topic: Total Hip Arthroplasty (THA)
During a complex revision total hip arthroplasty, the surgeon identifies a complete structural separation of the ilium from the ischium and pubis. Which of the following terms best describes this specific pattern of acetabular bone loss?
. Paprosky Type I defect
. Paprosky Type IIIA defect
. Paprosky Type IIIB defect
. Pelvic discontinuity
. Protrusio acetabuli

Correct Answer & Explanation

. Pelvic discontinuity

Explanation

Pelvic discontinuity is defined by a complete separation of the superior hemipelvis (ilium) from the inferior hemipelvis (ischium and pubis). It requires specialized fixation techniques, such as a cup-cage construct, custom triflange, or distraction plating.

Question 225

Topic: Total Hip Arthroplasty (THA)

A patient suffers a recurrent anterior dislocation of their total hip arthroplasty, which was placed via a posterior approach. CT scan reveals an acetabular cup with 45 degrees of inclination and 30 degrees of anteversion. The femoral stem is placed in 20 degrees of anteversion. What is the primary cause of instability?

. Impingement due to excessive combined anteversion
. Insufficient posterior soft tissue repair
. Retroversion of the acetabular component
. Abductor musculature deficiency
. Excessive femoral offset

Correct Answer & Explanation

. Impingement due to excessive combined anteversion

Explanation

The combined anteversion in this patient is 50 degrees (30 cup + 20 stem), which is excessively high. High combined anteversion predisposes the hip to anterior dislocation, particularly in extension and external rotation, due to anterior uncoverage.

Question 226

Topic: Total Hip Arthroplasty (THA)

When comparing the direct anterior approach to the posterior approach for primary total hip arthroplasty, the direct anterior approach is associated with a higher risk of iatrogenic injury to which of the following nerves?

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

Correct Answer & Explanation

. Lateral femoral cutaneous nerve

Explanation

The direct anterior approach utilizes the internervous plane between the sartorius (femoral nerve) and the tensor fasciae latae (superior gluteal nerve). The lateral femoral cutaneous nerve crosses the surgical field anteriorly and is at the highest risk for neuropraxia or transection during this approach.

Question 227

Topic: Total Hip Arthroplasty (THA)

A 40-year-old male with a ceramic-on-ceramic total hip arthroplasty complains of a highly audible 'squeaking' sound coming from his hip during ambulation. Radiographic evaluation of component positioning is most likely to reveal which of the following?

. Excessive retroversion and low inclination
. Excessive anteversion and high inclination
. Decreased femoral offset
. Excessive leg length
. Use of a 32 mm ceramic head instead of 36 mm

Correct Answer & Explanation

. Excessive anteversion and high inclination

Explanation

Squeaking in ceramic-on-ceramic THA is a phenomenon strongly linked to edge loading, stripe wear, and micro-separation. Edge loading occurs when the femoral head articulates against the rim of the acetabular liner rather than the dome. This is most strongly associated with component malpositioning, particularly when the acetabular cup is placed in excessive anteversion combined with excessive (steep) inclination.

Question 228

Topic: Total Hip Arthroplasty (THA)

A 45-year-old active male underwent a ceramic-on-ceramic total hip arthroplasty 2 years ago. He now complains of a squeaking noise with deep flexion. Which of the following component factors is most strongly associated with this phenomenon?

. Acetabular component retroversion
. Increased femoral stem anteversion
. Acetabular component placed in >50 degrees of abduction
. Use of a 36-mm rather than 32-mm femoral head
. Excessive inferior placement of the acetabular component

Correct Answer & Explanation

. Acetabular component placed in >50 degrees of abduction

Explanation

Squeaking in ceramic-on-ceramic bearings is strongly associated with edge loading. This typically occurs when the acetabular component is placed in excessive abduction (>50 degrees) or malversion, leading to concentrated contact stresses and fluid film disruption.

Question 229

Topic: Total Hip Arthroplasty (THA)

A 55-year-old male with a ceramic-on-ceramic total hip arthroplasty presents with a high-pitched squeaking sound during hip flexion. Which of the following factors is most strongly associated with this phenomenon?

. Acetabular cup retroversion
. Femoral stem subsidence
. Use of a 36-mm femoral head instead of 28-mm
. Short neck length
. Edge loading due to component malposition

Correct Answer & Explanation

. Edge loading due to component malposition

Explanation

Squeaking in ceramic-on-ceramic THA is predominantly associated with edge loading. This often results from acetabular cup malposition, such as excessive steepness or anteversion, which leads to stripe wear and microseparation.

Question 230

Topic: Total Hip Arthroplasty (THA)

During a revision THA, the surgeon notes massive acetabular bone loss with superior migration of the hip center by 4 cm, but the teardrop and Kohler's line remain intact. According to the Paprosky classification, what type of defect is this, and what is the preferred management?

. Paprosky 2B; hemispherical cup with screws
. Paprosky 3A; hemispherical cup with structural allograft or metal augment
. Paprosky 3B; custom triflange component or cage
. Paprosky 2C; jumbo cup
. Paprosky 1; primary uncemented cup

Correct Answer & Explanation

. Paprosky 3A; hemispherical cup with structural allograft or metal augment

Explanation

A Paprosky 3A defect is characterized by greater than 3 cm of superior migration with intact medial wall structures (Kohler's line). Management typically involves a hemispherical cup supplemented with structural allograft or highly porous metal augments to address the superior defect.

Question 231

Topic: Total Hip Arthroplasty (THA)

A lateral opening wedge distal femoral osteotomy (DFO) is planned for a young patient with symptomatic valgus osteoarthritis. Compared to a medial closing wedge DFO, what is the expected effect on leg length?

. Decreases overall leg length
. Increases overall leg length
. Causes no change in overall leg length
. Medializes the mechanical axis without leg length changes
. Consistently causes a leg length discrepancy greater than 3 cm

Correct Answer & Explanation

. Increases overall leg length

Explanation

An opening wedge osteotomy adds volume to the bone segment, thereby increasing overall leg length. In contrast, a closing wedge osteotomy removes a bone segment and decreases leg length.

Question 232

Topic: Total Hip Arthroplasty (THA)

A 68-year-old woman underwent a ceramic-on-ceramic total hip arthroplasty 2 years ago. She now complains of a squeaking noise coming from the hip during walking, though she denies significant pain. Radiographs show a well-fixed stem and a cup with 55 degrees of inclination and 30 degrees of anteversion. What is the most likely biomechanical cause of the squeaking?

. Allergic reaction to the ceramic material
. Impingement of the iliopsoas tendon
. Edge loading of the articular surface
. Fracture of the ceramic liner
. Trunnionosis at the Morse taper

Correct Answer & Explanation

. Edge loading of the articular surface

Explanation

Squeaking in ceramic-on-ceramic THA is heavily correlated with edge loading, which typically occurs due to component malposition, microseparation, or impingement. The cup inclination of 55 degrees (excessive) in this vignette strongly predisposes to edge loading.

Question 233

Topic: Total Hip Arthroplasty (THA)

A 62-year-old woman complains of groin pain 1 year after an uncomplicated THA. The pain is worst when getting out of a car and actively lifting her leg into bed. Resisted active hip flexion reproduces the pain. Radiographs show the acetabular component in 40 degrees of abduction and 20 degrees of anteversion, but the anterior rim protrudes 4 mm beyond the anterior acetabular wall. What is the most appropriate initial treatment?

. Revision of the acetabular component
. Revision of the femoral stem to increase offset
. CT-guided iliopsoas bursa corticosteroid injection and physical therapy
. Immediate arthroscopic iliopsoas release
. Open iliopsoas release and capsulotomy

Correct Answer & Explanation

. CT-guided iliopsoas bursa corticosteroid injection and physical therapy

Explanation

This patient's symptoms and radiographic findings are highly consistent with iliopsoas impingement secondary to a prominent anterior acetabular rim. Initial management should be conservative, consisting of rest, NSAIDs, and a corticosteroid injection, before considering surgical release or component revision.

Question 234

Topic: Total Hip Arthroplasty (THA)

A 60-year-old man sustained a posterior dislocation of his primary THA 3 weeks postoperatively while bending over. Closed reduction was successful. Radiographs demonstrate the acetabular cup is positioned in 10 degrees of anteversion and 40 degrees of abduction. The femoral stem is in 5 degrees of retroversion. What is the primary cause of his dislocation?

. Inadequate combined anteversion
. Abductor muscle deficiency
. Impingement from heterotopic ossification
. Excessive offset of the femoral stem
. Vertical cup placement

Correct Answer & Explanation

. Inadequate combined anteversion

Explanation

The patient has a combined anteversion of only 5 degrees (10 degrees cup + -5 degrees stem), which is significantly lower than the target safe zone of 25 to 35 degrees. This lack of combined anteversion strongly predisposes the hip to posterior dislocation.

Question 235

Topic: Total Hip Arthroplasty (THA)

A 45-year-old man who underwent a ceramic-on-ceramic THA 3 years ago complains of a high-pitched squeaking noise coming from his hip when walking. He denies pain. Radiographs show a well-fixed cup in 60 degrees of abduction and a well-fixed stem. What is the most likely etiology of the squeaking?

. Edge loading due to vertical cup placement
. Impingement of the iliopsoas tendon
. Microfracture of the ceramic liner
. Femoral stem subsidence
. Metal ion release from the trunnion

Correct Answer & Explanation

. Edge loading due to vertical cup placement

Explanation

Squeaking in ceramic-on-ceramic hips is often associated with component malposition, particularly a vertically placed cup (abduction angle > 50 degrees). This verticality leads to edge loading, disruption of fluid-film lubrication, and subsequent noise generation.

Question 236

Topic: Total Hip Arthroplasty (THA)

A 72-year-old woman experiences her third posterior dislocation 4 months after a primary right THA performed via a posterior approach. Radiographs show the acetabular component is in 30 degrees of inclination and 5 degrees of retroversion. The femoral stem is stable and in 15 degrees of anteversion. What is the most appropriate surgical intervention?

. Prescribe a hip abduction brace for 6 weeks
. Revision of the femoral stem to increase anteversion
. Revision of the acetabular component to increase anteversion
. Placement of a constrained acetabular liner
. Trochanteric advancement

Correct Answer & Explanation

. Revision of the acetabular component to increase anteversion

Explanation

The acetabular component is retroverted (normal target is 15-20 degrees of anteversion). Revision of the malpositioned acetabular component is the definitive treatment for recurrent posterior instability due to cup retroversion.

Question 237

Topic: Total Hip Arthroplasty (THA)

During templating for a primary THA, the surgeon plans to use a high-offset femoral stem instead of a standard-offset stem of the same neck length. How will this change affect the hip biomechanics?

. Increases abductor moment arm and increases leg length
. Increases abductor moment arm without changing leg length
. Decreases abductor tension and decreases leg length
. Increases leg length without changing the abductor moment arm
. Decreases joint reaction force and increases leg length

Correct Answer & Explanation

. Increases abductor moment arm without changing leg length

Explanation

Using a high-offset stem increases femoral offset and the abductor moment arm, which improves abductor mechanical advantage and reduces joint reaction forces. High offset options generally do not affect leg length compared to a standard stem.

Question 238

Topic: Total Hip Arthroplasty (THA)

A 74-year-old woman undergoes a revision THA. Intraoperatively, she is found to have complete absence of the abductor musculature with severe fatty atrophy. Following placement of the revision components, the hip demonstrates significant instability and dislocates with minimal adduction. Which of the following is the most appropriate management?

. Placement of a dual-mobility articulation
. Use of an elevated rim (lipped) polyethylene liner
. Placement of a constrained acetabular liner
. Revision to a larger femoral head size only
. Application of an abduction brace postoperatively

Correct Answer & Explanation

. Placement of a constrained acetabular liner

Explanation

In the setting of severe or complete abductor deficiency causing intraoperative instability, a constrained acetabular liner is indicated to prevent dislocation. Dual mobility relies on dynamic soft-tissue stabilizers and may still fail in the complete absence of abductors.

Question 239

Topic: Total Hip Arthroplasty (THA)

A 62-year-old female with a total hip arthroplasty utilizing a large diameter cobalt-chromium head on a titanium stem presents with thigh pain. MRI with MARS reveals a large cystic mass adjacent to the hip. What biomechanical factor most increases the risk of mechanically assisted crevice corrosion (MACC) at the head-neck junction?

. Use of a ceramic femoral head
. Decreased femoral head diameter
. Increased femoral offset via a longer head-neck taper
. A fully porous-coated titanium stem
. A high clearance between the head and polyethylene liner

Correct Answer & Explanation

. Increased femoral offset via a longer head-neck taper

Explanation

Mechanically assisted crevice corrosion (trunnionosis) is exacerbated by increased bending moments at the head-neck junction. This increased stress typically occurs with increased femoral offset (longer head-neck tapers) and the use of larger diameter metal heads.

Question 240

Topic: Total Hip Arthroplasty (THA)

An 81-year-old, low-demand female sustains a Vancouver B3 periprosthetic femur fracture around a cemented stem. Radiographs demonstrate a loose stem with profound loss of proximal femoral bone stock extending into the subtrochanteric region. What is the most appropriate surgical management?

. ORIF with a locking plate and cortical strut allografts
. Revision THA with a long cemented stem
. Proximal femoral replacement (megaprosthesis)
. Revision THA with a fully porous-coated cylindrical stem
. Impaction bone grafting with a standard length stem

Correct Answer & Explanation

. Proximal femoral replacement (megaprosthesis)

Explanation

A Vancouver B3 fracture is characterized by a loose stem and severely deficient proximal bone stock. In elderly, low-demand patients, a proximal femoral replacement provides immediate stability and allows for early, unrestricted weight-bearing.

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