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Total Hip Arthroplasty (THA) MCQs

Practice Set 26 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 501

Topic: Total Hip Arthroplasty (THA)

A 65-year-old man undergoes a right total hip arthroplasty. During preoperative templating, the surgeon plans to use a high-offset femoral stem to increase the femoral offset by 8 mm without changing the vertical height or leg length. What is the primary biomechanical effect of this modification?

. Increased overall joint reaction force.
. Decreased abductor muscle tension required for pelvic stability.
. Decreased bending moment on the femoral stem.
. Decreased impingement-free range of motion.
. Medialization of the hip center of rotation.

Correct Answer & Explanation

. Decreased abductor muscle tension required for pelvic stability.

Explanation

Correct Answer: Decreased abductor muscle tension required for pelvic stability.Increasing the femoral offset increases the lever arm of the abductor musculature. According to the biomechanics of the hip, the joint reaction force is a balance between the body weight (and its lever arm) and the abductor force (and its lever arm). By increasing the abductor lever arm (offset), less abductor force is required to counteract the body weight and maintain a level pelvis. Consequently, this decreases the overall joint reaction force across the hip. Increasing offset also increases the impingement-free range of motion and soft tissue tension, reducing the risk of dislocation. However, a negative consequence of increasing femoral offset is that it increases the bending moment (stress) on the femoral stem, potentially increasing the risk of stem fatigue failure or loosening if extreme.

Question 502

Topic: Total Hip Arthroplasty (THA)

During a posterior approach to the hip for a hemiarthroplasty, the surgeon identifies and protects the main blood supply to the adult femoral head. Which of the following arteries provides the predominant blood supply to the weight-bearing dome of the adult femoral head?

. Artery of the ligamentum teres (foveal artery)
. Ascending branch of the lateral circumflex femoral artery
. Lateral epiphyseal branch of the medial circumflex femoral artery
. Inferior gluteal artery
. First perforating artery of the profunda femoris

Correct Answer & Explanation

. Lateral epiphyseal branch of the medial circumflex femoral artery

Explanation

Correct Answer: Lateral epiphyseal branch of the medial circumflex femoral arteryThe predominant blood supply to the adult femoral head is the medial circumflex femoral artery (MCFA). Specifically, the lateral epiphyseal branches of the MCFA supply the critical weight-bearing superior and lateral portions of the femoral head. The lateral circumflex femoral artery supplies the anterior and inferior portions of the head and neck but is less critical. The artery of the ligamentum teres (a branch of the obturator artery) provides a negligible amount of blood supply in the adult, though it is more significant in the pediatric population.

Question 503

Topic: Total Hip Arthroplasty (THA)

During a posterior approach to the hip (Kocher-Langenbeck), the surgeon releases the short external rotators. While releasing the quadratus femoris from its femoral insertion, brisk arterial bleeding is encountered. Which of the following vessels is most likely injured?

. Ascending branch of the medial circumflex femoral artery
. Descending branch of the lateral circumflex femoral artery
. Inferior gluteal artery
. First perforating artery
. Superior gluteal artery

Correct Answer & Explanation

. Ascending branch of the medial circumflex femoral artery

Explanation

Correct Answer: Ascending branch of the medial circumflex femoral arteryDuring the posterior approach to the hip, the short external rotators are detached from the femur. The ascending branch of the medial circumflex femoral artery (MCFA) consistently runs near the superior border of the quadratus femoris. If the quadratus femoris is released too far medially or without prior identification and coagulation of this vessel, brisk bleeding can occur. To avoid this, many surgeons leave the quadratus femoris intact or only partially release its superior edge while carefully cauterizing the ascending branch of the MCFA.

Question 504

Topic: Total Hip Arthroplasty (THA)

A 68-year-old male sustains an anterior dislocation of his primary THA 3 years postoperatively. Fluoroscopic evaluation during reduction reveals the dislocation consistently occurs with hip extension and external rotation. Radiographs demonstrate well-fixed components with optimal femoral offset. Which of the following is the most likely etiology of this specific pattern of instability?

. Excessive acetabular and femoral combined anteversion
. Inadequate femoral offset
. Excessive acetabular retroversion
. Impingement secondary to anterior retained osteophytes
. Abductor muscle deficiency

Correct Answer & Explanation

. Excessive acetabular and femoral combined anteversion

Explanation

Anterior dislocation typically occurs when the hip is subjected to extension and external rotation. This is most frequently caused by excessive combined anteversion of the acetabular and femoral components, causing posterior impingement that levers the head anteriorly.

Question 505

Topic: Total Hip Arthroplasty (THA)

A surgeon is performing a primary THA utilizing a direct lateral (Hardinge) approach. To gain adequate exposure, the splitting of the gluteus medius is extended proximally. To minimize the risk of denervating the anterior portion of the gluteus medius and the tensor fascia lata, the proximal split should not extend beyond what distance from the tip of the greater trochanter?

. 1 cm
. 3 cm
. 5 cm
. 8 cm
. 10 cm

Correct Answer & Explanation

. 5 cm

Explanation

The superior gluteal nerve courses approximately 5 cm proximal to the tip of the greater trochanter. Extending the split of the gluteus medius beyond 5 cm during a direct lateral approach risks transecting the nerve, leading to abductor weakness and a Trendelenburg gait.

Question 506

Topic: Total Hip Arthroplasty (THA)
A 72-year-old male presents with severe thigh pain 12 years after a primary total hip arthroplasty. Radiographs reveal a loose femoral stem with substantial metaphyseal and diaphyseal bone loss. The bone defect extends to the diaphyseal isthmus, and there is less than 3 cm of diaphyseal scratch fit available. According to the Paprosky classification (Type IIIB), which of the following femoral components is the most appropriate choice for revision?
. Cemented standard length stem
. Fully porous-coated cylindrical uncemented stem
. Impaction bone grafting with a short cemented stem
. Modular fluted tapered uncemented stem
. Proximal femoral replacement

Correct Answer & Explanation

. Modular fluted tapered uncemented stem

Explanation

Paprosky IIIB femoral defects are characterized by extensive metaphyseal and diaphyseal bone loss with less than 4 cm of diaphyseal scratch fit available. A modular fluted tapered stem provides rigid distal fixation in the remaining healthy diaphyseal bone, whereas fully porous stems require at least 4 cm of intact isthmus.

Question 507

Topic: Total Hip Arthroplasty (THA)

A surgeon is evaluating operative variables to minimize dislocation rates after primary THA using a conventional posterior approach. Based on current orthopedic literature, which of the following surgical techniques most significantly reduces the rate of early postoperative posterior dislocation?

. Utilizing a 28 mm instead of a 32 mm femoral head
. Routine use of an elevated rim (lipped) polyethylene liner
. Meticulous capsulorrhaphy and repair of the short external rotators
. Reaming the acetabulum line-to-line
. Retaining the piriformis tendon while releasing the remaining rotators

Correct Answer & Explanation

. Meticulous capsulorrhaphy and repair of the short external rotators

Explanation

Enhanced soft tissue repair, specifically the meticulous reattachment of the posterior capsule and short external rotators to the greater trochanter, has been robustly shown to significantly reduce the risk of posterior dislocation following a posterior approach to the hip.

Question 508

Topic: Total Hip Arthroplasty (THA)

An 8-year-old boy with OI Type IV underwent bilateral femoral rodding with Fassier-Duval telescoping rods 4 years ago. He now presents with a 3 cm leg length discrepancy and recurrent bowing of the left femur. Radiographs show the left rod has failed to elongate, and the distal femur has grown past the end of the rod. What is the most appropriate management?

. Observation until skeletal maturity.
. Revision surgery to exchange the jammed rod and correct the deformity.
. Epiphysiodesis of the contralateral distal femur.
. Application of a circular external fixator for lengthening.
. Initiation of high-dose bisphosphonate therapy to halt bowing.

Correct Answer & Explanation

. Revision surgery to exchange the jammed rod and correct the deformity.

Explanation

Correct Answer: BFassier-Duval rods are designed to telescope and accommodate longitudinal bone growth. A known complication is failure of the rod to expand (jamming). When this occurs, the bone continues to grow around and past the rod, leading to recurrent deformity (bowing), loss of internal splinting, and leg length discrepancy. The most appropriate management for a symptomatic, jammed rod with recurrent deformity is revision surgery to remove the failed hardware, perform corrective osteotomies if necessary, and insert a new telescoping rod.

Question 509

Topic: Total Hip Arthroplasty (THA)

A 5-year-old girl with active, untreated oligoarticular JIA affecting solely her left knee is evaluated in the orthopedic clinic. Which of the following growth disturbances is most likely to be observed in the affected limb during the active inflammatory phase?

. Premature physeal closure resulting in severe shortening of the left leg
. Longitudinal overgrowth of the left leg due to chronic hyperemia
. Progressive varus deformity of the left knee
. Severe patella alta with extensor mechanism rupture
. Posterior subluxation of the left tibia

Correct Answer & Explanation

. Longitudinal overgrowth of the left leg due to chronic hyperemia

Explanation

In the early, active phase of JIA involving a large joint like the knee, chronic inflammation and hyperemia stimulate the adjacent physes. This frequently leads to accelerated longitudinal bone growth and an ipsilateral leg length discrepancy (affected leg is longer).

Question 510

Topic: Total Hip Arthroplasty (THA)

When planning a deformity correction, the surgeon places the osteotomy at a different level than the Center of Rotation of Angulation (CORA), but the Axis of Correction of Angulation (ACA) passes directly through the CORA. Which of the following describes the resultant alignment according to Paley's rules?

. Pure angular correction without translation
. Angular correction with a necessary translation at the osteotomy site
. Angular correction with persistent translation of the mechanical axis
. Pure translation without angular correction
. Worsening of the angular deformity with an iatrogenic leg length discrepancy

Correct Answer & Explanation

. Angular correction with a necessary translation at the osteotomy site

Explanation

According to Paley's osteotomy Rule 2, when the ACA is at the CORA but the osteotomy is at a different level, the mechanical axis will realign correctly. However, a predictable and necessary translation of the bone ends will occur at the osteotomy site.

Question 511

Topic: Total Hip Arthroplasty (THA)

A patient is undergoing deformity correction for a mid-diaphyseal tibial varus deformity. If the osteotomy is performed at a level proximal to the Center of Rotation of Angulation (CORA), but the Axis of Correction of Angulation (ACA) is maintained exactly at the CORA, what is the expected geometric outcome of the limb?

. Angulation correction without any translation
. Pure translation without angulation correction
. Angulation correction with secondary translation at the osteotomy site
. Correction of angulation but creation of a leg length discrepancy
. Complete failure of deformity correction

Correct Answer & Explanation

. Angulation correction with secondary translation at the osteotomy site

Explanation

According to Osteotomy Rule 2, if the ACA is at the CORA but the osteotomy is at a different level, the angulation will correct, but secondary translation of the bone ends will unavoidably occur at the osteotomy site.

Question 512

Topic: Total Hip Arthroplasty (THA)

A 25-year-old female with severe systemic JIA is undergoing bilateral total hip arthroplasties. Which of the following is the most likely intraoperative finding or technical challenge?

. Coxa valga
. A large medullary canal requiring oversized stems
. Excessive anteversion of the femoral neck
. Subchondral bone sclerosis with massive osteophytes
. Valgus knee deformity causing sciatic nerve palsy post-op

Correct Answer & Explanation

. Excessive anteversion of the femoral neck

Explanation

Patients with JIA commonly exhibit hypoplastic, narrow medullary canals (stovepipe appearance) and excessive femoral neck anteversion. Custom or modular small-sized implants are often required to accommodate the distorted anatomy.

Question 513

Topic: Total Hip Arthroplasty (THA)

A 75-year-old female, 3 weeks post-posterior approach total hip arthroplasty, presents to the ER after a fall with sudden, severe hip pain and inability to bear weight. Physical examination reveals a shortened, internally rotated, and adducted left lower extremity. Radiographs confirm posterior dislocation of the prosthetic femoral head. After successful closed reduction under sedation, what is the most appropriate next step in management to prevent recurrence?

. Immediate revision surgery of the femoral head and acetabular liner.
. Application of a hip abduction brace for 6-8 weeks.
. Initiation of physical therapy focusing on strengthening hip abductors.
. Prescribe extended bed rest.
. Observation with strict non-weight bearing.

Correct Answer & Explanation

. Application of a hip abduction brace for 6-8 weeks.

Explanation

This patient experienced an acute, first-time posterior dislocation after THA. Following successful closed reduction, the immediate priority is to prevent recurrence while soft tissues heal. A hip abduction brace (B) is commonly used for 6-8 weeks to restrict extreme hip flexion, adduction, and internal rotation, which are the positions of instability for a posterior approach. Immediate revision surgery (A) is typically reserved for recurrent dislocations, component malposition, or failed non-operative management. While physical therapy (C) is important, it needs to be protected in the immediate post-reduction period. Bed rest (D) is not beneficial and can lead to complications. Observation with non-weight bearing (E) alone is insufficient to prevent recurrence.

Question 514

Topic: Total Hip Arthroplasty (THA)

A 65-year-old male with a history of a cemented total hip arthroplasty (THA) performed 5 years ago presents with his third episode of recurrent posterior dislocation. Radiographs show well-fixed components in satisfactory position. Clinical examination reveals a Trendelenburg gait and weakness in hip abduction. What is the most appropriate next step in surgical management?

. Revision to a larger femoral head.
. Revision to a constrained acetabular liner.
. Revision to a dual mobility acetabular component.
. Abductor repair/reconstruction.
. Femoral stem revision with extended trochanteric osteotomy.

Correct Answer & Explanation

. Revision to a dual mobility acetabular component.

Explanation

For recurrent dislocations in a well-fixed THA where component position is good, a larger femoral head has already failed (or been considered), and abductor insufficiency is present, a dual mobility acetabular component offers enhanced stability. It achieves this by increasing the "jump distance" and allowing for greater range of motion before impingement, thus reducing the risk of dislocation. While abductor repair could be considered if a discrete tear is identified, its success rate can be variable, especially with chronic insufficiency. Dual mobility provides a more mechanically robust solution for persistent instability where soft tissue factors are involved.

Question 515

Topic: Total Hip Arthroplasty (THA)

A patient with severe coxa vara and a functional leg length discrepancy of 4 cm is scheduled for a subtrochanteric osteotomy. To maximally correct both the mechanical axis and the leg length discrepancy simultaneously, which procedure is most appropriate?

. Varus-producing osteotomy with acute shortening
. Valgus-producing osteotomy combined with gradual distraction osteogenesis
. Medial displacement osteotomy of the femoral shaft
. Greater trochanteric advancement only
. Distal femoral lengthening with no proximal correction

Correct Answer & Explanation

. Valgus-producing osteotomy combined with gradual distraction osteogenesis

Explanation

Coxa vara is treated with a valgus-producing osteotomy to restore the neck-shaft angle and abductor mechanics. Combining this with gradual distraction osteogenesis using an external fixator or lengthening nail simultaneously corrects the profound leg length discrepancy.

Question 516

Topic: Total Hip Arthroplasty (THA)

A patient requires correction of a distal tibial procurvatum deformity. The CORA is at the ankle joint line. According to Paley's Rule 3, if a supramalleolar osteotomy is performed proximal to the CORA and the hinge is placed at the osteotomy site, what is the resultant geometric deformity?

. Pure angulation without translation.
. Angulation with collinear realignment of the mechanical axes.
. Angulation with a new translation deformity (parallel axis shift).
. Pure translation without angulation.
. Spontaneous correction of both angulation and leg length discrepancy.

Correct Answer & Explanation

. Angulation with a new translation deformity (parallel axis shift).

Explanation

Paley's Rule 3 states that if the osteotomy and the hinge are both placed at a location different from the CORA, the result is angulation complicated by a new translation deformity. The axes will end up parallel but not collinear.

Question 517

Topic: Total Hip Arthroplasty (THA)

In an irreducible posterior elbow dislocation due to entrapment of the medial epicondyle, what is the MOST appropriate surgical approach to retrieve the entrapped structure and reduce the elbow?

. Posterior approach with olecranon osteotomy.
. Lateral approach (Kocher interval).
. Anterior approach to decompress neurovascular structures.
. Medial approach through the interval between the triceps and brachialis.
. Transarticular external fixator application.

Correct Answer & Explanation

. Medial approach through the interval between the triceps and brachialis.

Explanation

When the medial epicondyle is entrapped, it typically implies that the joint has dislocated laterally. To retrieve the entrapped medial epicondyle and reduce the elbow, a medial approach (Option D) is the most appropriate. This allows direct visualization and retrieval of the entrapped epicondyle. Posterior (Option A) or lateral (Option B) approaches would not provide direct access. An anterior approach (Option C) is for neurovascular decompression, not for retrieving an entrapped epicondyle. External fixator (Option E) is a stabilization method, not for reduction of an entrapped structure.

Question 518

Topic: Total Hip Arthroplasty (THA)

A 60-year-old female undergoes a primary THA via a direct anterior approach. Postoperatively, she complains of numbness and burning pain in the lateral thigh. Sensory examination confirms diminished sensation in the distribution of the lateral femoral cutaneous nerve (LFCN). What is the most appropriate initial management for this iatrogenic complication?

. Immediate surgical exploration and neurolysis of the LFCN.
. Prescription of gabapentin or pregabalin and observation.
. Nerve conduction study and electromyography (NCS/EMG) to assess the extent of injury.
. Local anesthetic injection at the anterior superior iliac spine (ASIS).
. Referral for physical therapy focusing on desensitization.

Correct Answer & Explanation

. Prescription of gabapentin or pregabalin and observation.

Explanation

LFCN neuropathy (meralgia paresthetica) is a known complication of the direct anterior approach due to traction or direct injury to the nerve. While surgical exploration is an option for persistent or severe symptoms, theinitialmanagement for most iatrogenic nerve injuries is conservative, focusing on symptom control and allowing for spontaneous recovery. Medications like gabapentin or pregabalin (option B) are commonly used for neuropathic pain. Observation is crucial as many cases resolve spontaneously over weeks to months. NCS/EMG might be useful if symptoms persist or worsen significantly after an initial conservative period to assess the extent of damage but is not the immediate step. Local anesthetic injection can be diagnostic and therapeutic but typically follows medical management. Immediate surgical exploration is generally reserved for severe, progressive deficits or symptoms that fail extensive conservative management, or if there's suspicion of a transection. Therefore, starting with neuropathic pain medication and observation is the most appropriate initial management.

Question 519

Topic: Total Hip Arthroplasty (THA)
A 67-year-old morbidly obese male (BMI 52 kg/m²) is undergoing primary THA for severe osteoarthritis. What is the most significant specific technical challenge related to his obesity that the surgeon must anticipate and prepare for?
. Increased risk of heterotopic ossification.
. Difficulty with patient positioning and surgical exposure.
. Higher incidence of perioperative anemia.
. Elevated risk of surgical site infection.
. Challenges with adequate pain control postoperatively.

Correct Answer & Explanation

. Difficulty with patient positioning and surgical exposure.

Explanation

Morbid obesity significantly increases the complexity and risks of THA. While all listed options are relevant concerns in obese patients, the 'most significant specific technical challenge' during the actual surgery is often related to patient positioning and achieving adequate surgical exposure. Excess adipose tissue makes standard landmarks difficult to palpate, increases the depth of the surgical field, obscures anatomical structures, and makes retraction challenging. This can lead to longer operative times, increased blood loss, difficulty with component placement, and potential iatrogenic injury. Increased infection risk, DVT, and pain control are all important, but they are general perioperative concerns rather than direct technical challenges of the surgical act itself. Heterotopic ossification is not specifically related to obesity, though overall inflammation might be. Thus, managing the surgical exposure is a predominant intraoperative technical hurdle.

Question 520

Topic: Total Hip Arthroplasty (THA)

A 70-year-old male presents with a persistent Trendelenburg gait and pain over the greater trochanter 1 year after THA. MRI demonstrates discontinuity of the abductor tendons (gluteus medius and minimus) from the greater trochanter. What is the most appropriate surgical intervention?

. Physical therapy focusing on abductor strengthening.
. Corticosteroid injection into the trochanteric bursa.
. Revision THA with a larger femoral head to improve hip stability.
. Surgical repair of the abductor tendon to the greater trochanter.
. Excision of the greater trochanter.

Correct Answer & Explanation

. Surgical repair of the abductor tendon to the greater trochanter.

Explanation

Persistent Trendelenburg gait and pain over the greater trochanter, particularly with MRI evidence of abductor tendon discontinuity, strongly indicate abductor deficiency. This can be due to avulsion, non-healing of a trochanteric osteotomy, or direct injury during surgery (e.g., in a lateral approach). While physical therapy and injections might offer temporary symptomatic relief for bursitis, they do not address the underlying anatomical defect of tendon discontinuity. Revision THA with a larger femoral head primarily addresses instability, not abductor function. Excision of the greater trochanter is a drastic measure not indicated here. The most appropriate and definitive surgical intervention for abductor tendon discontinuity is direct surgical repair of the avulsed tendons to the greater trochanter. This aims to restore the continuity and function of the abductor mechanism, improving gait and reducing pain. Various techniques exist, including direct repair, advancement, or augmentation with allograft/autograft depending on the tissue quality.

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