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Total Hip Arthroplasty (THA) MCQs

Practice Set 2 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 21

Topic: Total Hip Arthroplasty (THA)
For the acetabular reconstruction in this Paprosky Type IIIA defect, a modular trabecular metal dome augment was selected. What is the primary advantage of using such an augment in this specific scenario?
. To increase the overall diameter of the acetabular component for primary press-fit fixation.
. To prevent medial wall perforation during screw placement.
. To provide structural support for the deficient superior dome, restore the hip center, and allow for stable screw fixation into host bone.
. To reduce the risk of heterotopic ossification around the acetabulum.
. To facilitate the use of a smaller femoral head for increased jump distance.

Correct Answer & Explanation

. To provide structural support for the deficient superior dome, restore the hip center, and allow for stable screw fixation into host bone.

Explanation

The case describes a Paprosky Type IIIA defect with extensive superior segmental and cavitary bone loss, with a deficient superior dome. The rationale for augment selection states: 'This construct allows for immediate stability through screw fixation in healthy host bone (ilium/ischium) and biological ingrowth, while the augment addresses the significant superior segmental bone loss, providing scaffolding and restoring the hip center.' Option A is incorrect; while it might increase the overall construct size, the primary purpose is not just diameter but structural support. Option B is incorrect; while medial wall perforation is a concern, a dome augment primarily addresses superior defects. Option D is incorrect; augments do not directly reduce heterotopic ossification. Option E is incorrect; a larger femoral head (36 mm) was chosen to maximize jump distance, not a smaller one. Therefore, providing structural support for the deficient superior dome, restoring the hip center, and allowing for stable screw fixation into host bone is the primary advantage.

Question 22

Topic: Total Hip Arthroplasty (THA)

Following the successful removal of the femoral component and cement, the surgeon performed cancellous allograft bone chip impaction grafting into the proximal femur. What is the main objective of this technique in the context of a Paprosky Type IIB femoral defect?

. To create a smooth, reamed canal for a standard cemented stem.
. To provide immediate, rigid fixation for a short, proximally coated stem.
. To reconstruct the metaphyseal bone loss, provide a biological scaffold for bone healing, and support trochanteric reattachment.
. To prevent stress shielding of the distal femur.
. To reduce the risk of periprosthetic infection by filling dead space.

Correct Answer & Explanation

. To reconstruct the metaphyseal bone loss, provide a biological scaffold for bone healing, and support trochanteric reattachment.

Explanation

Correct Answer: CThe case states that for the Paprosky IIB defect, 'cancellous allograft bone chips were carefully impacted into the proximal femur around a sizing trial, creating a contained bed for the modular stem. This technique provides mechanical support and promotes biological integration.' It further clarifies that this was done 'to address the proximal femoral bone loss and provide support for the proximal stem and greater trochanteric reattachment.' Option A is incorrect as a modular, uncemented stem was used. Option B is incorrect as a long, distally fixing stem was used, and impaction grafting provides biological support, not necessarily immediate rigid fixation for a short stem. Option D is incorrect; impaction grafting is primarily for bone reconstruction, not stress shielding prevention. Option E is incorrect; while filling dead space can be beneficial, the primary objective is bone reconstruction and biological integration, not infection prevention. Therefore, reconstructing the metaphyseal bone loss, providing a biological scaffold for bone healing, and supporting trochanteric reattachment is the main objective.

Question 23

Topic: Total Hip Arthroplasty (THA)

When performing an extended trochanteric osteotomy (ETO) for femoral stem removal during revision THA, what is the recommended length of the osteotomy to ensure adequate healing and avoid diaphyseal fracture?

. 5-7 cm from the tip of the greater trochanter
. 10-15 cm, maintaining at least a 5 cm intact diaphyseal bridge distal to the stem
. At least 15 cm from the tip of the trochanter, extending past the stem tip
. Just distal to the lesser trochanter
. 3-5 cm distal to the stem tip

Correct Answer & Explanation

. 10-15 cm, maintaining at least a 5 cm intact diaphyseal bridge distal to the stem

Explanation

An ETO should typically be 10-15 cm in length, leaving at least 1-2 diaphyseal diameters (approximately 5-6 cm) of intact bone distal to the tip of the existing stem. This prevents fracture and provides adequate fixation for the new stem.

Question 24

Topic: Total Hip Arthroplasty (THA)
A patient requires revision of a loose cemented femoral stem. Radiographs demonstrate complete loss of metaphyseal cancellous bone and diaphyseal bone loss down to the isthmus, with less than 4 cm of intact diaphyseal bone remaining for fixation. What is the Paprosky femoral defect classification?
. Type I
. Type II
. Type IIIA
. Type IIIB
. Type IV

Correct Answer & Explanation

. Type IIIB

Explanation

Paprosky Type IIIB defects are characterized by severe metaphyseal and diaphyseal bone loss with less than 4 cm of intact diaphyseal isthmus available for fixation. They often require a fully coated cylindrical stem, modular fluted tapered stem, or allograft-prosthesis composite.

Question 25

Topic: Total Hip Arthroplasty (THA)

In revision THA, a "jumbo" acetabular cup is often used to achieve stability in Paprosky Type II defects. Which of the following defines a jumbo cup?

. >54 mm in females and >58 mm in males
. >62 mm in females and >66 mm in males
. >50 mm in both genders
. >66 mm in females and >70 mm in males
. Any cup size that is at least 10 mm larger than the primary cup

Correct Answer & Explanation

. >62 mm in females and >66 mm in males

Explanation

A jumbo cup is traditionally defined as >62 mm in females and >66 mm in males. It allows for a large surface area of porous coating to achieve biologic fixation in the presence of mild to moderate bone loss.

Question 26

Topic: Total Hip Arthroplasty (THA)

A 75-year-old female with a history of recurrent dislocations following primary THA is undergoing revision surgery. The abductor mechanism is noted to be severely deficient and fatty infiltrated on preoperative MRI. Which of the following components offers the most reliable stability?

. Elevated rim liner
. Standard highly cross-linked polyethylene liner with a 36mm head
. Dual mobility construct or constrained liner
. Larger femoral offset stem
. Prophylactic abductor repair with allograft

Correct Answer & Explanation

. Dual mobility construct or constrained liner

Explanation

In the setting of severe abductor deficiency and recurrent instability, standard liners carry a high failure rate. A constrained liner or a dual mobility articulation provides the highest degree of mechanical stability.

Question 27

Topic: Total Hip Arthroplasty (THA)

During revision THA for a superiorly migrated and loose acetabular component, restoring the anatomic hip center of rotation is crucial. Placing the hip center of rotation superiorly and laterally rather than at its anatomic position will result in which of the following biomechanical effects?

. Decreased joint reaction force
. Increased abductor moment arm
. Increased joint reaction force and decreased abductor efficiency
. Decreased risk of dislocation
. Improved leg length equality

Correct Answer & Explanation

. Increased joint reaction force and decreased abductor efficiency

Explanation

A superior and lateral hip center decreases the abductor moment arm and increases the body weight moment arm. This leads to a significantly increased joint reaction force, accelerating wear and decreasing abductor efficiency.

Question 28

Topic: Total Hip Arthroplasty (THA)

A 28-year-old male suffers a T11 fracture-dislocation with complete paraplegia (ASIA A) 24 hours post-injury. During surgical stabilization, what is the most important factor in determining the likelihood of his neurologic recovery?

. The timing of surgery within 8 hours
. The initial severity of the neurologic deficit (complete vs incomplete)
. The choice of anterior versus posterior approach
. Administration of high-dose methylprednisolone
. The type of bone graft used for fusion

Correct Answer & Explanation

. The initial severity of the neurologic deficit (complete vs incomplete)

Explanation

In spinal cord injury, the most significant prognostic factor for neurologic recovery is the completeness of the initial injury. Patients with a complete deficit (ASIA A) have a very low probability of significant functional motor recovery.

Question 29

Topic: Total Hip Arthroplasty (THA)

A 70-year-old female with recurrent THA dislocations due to abductor deficiency is planned for revision. The existing acetabular shell is a well-fixed, correctly positioned multi-hole titanium cup. Which of the following is the most appropriate surgical intervention to restore stability?

. Cementation of a dual mobility liner into the existing well-fixed shell
. Use of a standard constrained liner in the existing shell without cement
. Extraction of the well-fixed shell and placement of a tri-flange component
. Placement of a 36-mm cobalt-chrome head directly into the titanium shell
. Use of a standard polyethylene liner with an elevated 10-degree rim

Correct Answer & Explanation

. Cementation of a dual mobility liner into the existing well-fixed shell

Explanation

Cementing a dual mobility liner into a well-fixed compatible titanium shell provides excellent stability for recurrent instability and avoids the morbidity of extracting a well-ingrown cup.

Question 30

Topic: Total Hip Arthroplasty (THA)

A surgeon is utilizing a posterior approach to the humerus for open reduction and internal fixation of a midshaft fracture. To properly access the posterior humerus while minimizing damage to the triceps innervation, the superficial dissection utilizes an internervous or intermuscular plane. Which of the following describes the correct superficial interval for this approach?

. Between the brachialis and the brachioradialis
. Between the medial head and lateral head of the triceps
. Between the long head and lateral head of the triceps
. Between the anconeus and the extensor carpi ulnaris
. Between the brachioradialis and the extensor carpi radialis longus

Correct Answer & Explanation

. Between the long head and lateral head of the triceps

Explanation

The superficial interval in the posterior approach to the humerus is between the lateral and long heads of the triceps. Deep to this, the medial head is split longitudinally to expose the humeral shaft, avoiding the radial nerve which spirals proximally.

Question 31

Topic: Total Hip Arthroplasty (THA)

A 62-year-old male undergoes a total hip arthroplasty (THA) via a direct anterior approach. Postoperatively, he complains of numbness and burning pain over the lateral aspect of his thigh. Physical examination reveals diminished sensation in this distribution. Motor strength is intact. Which of the following nerves was most likely injured during the procedure?

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

Correct Answer & Explanation

. Lateral femoral cutaneous nerve

Explanation

Correct Answer: CThe patient's symptoms of numbness and burning pain over the lateral aspect of the thigh, without motor weakness, are classic for meralgia paresthetica, which is caused by compression or injury to the lateral femoral cutaneous nerve (LFCN). The direct anterior approach (DAA) to the hip is known to have a higher risk of LFCN injury due to the nerve's superficial course and its proximity to the surgical incision and retractors. While the DAA is associated with a lower dislocation rate and potentially faster recovery, this specific nerve injury is a recognized complication. The sciatic nerve (A) injury would typically cause weakness in the posterior thigh and leg muscles, and sensory loss in the posterior leg and foot. The femoral nerve (B) injury would cause weakness in hip flexion and knee extension, and sensory loss over the anterior thigh. The obturator nerve (D) injury would cause weakness in hip adduction and sensory loss over the medial thigh. The superior gluteal nerve (E) injury would cause weakness in hip abduction (Trendelenburg gait).

Question 32

Topic: Total Hip Arthroplasty (THA)

During a posterior approach to the knee for open reattachment of a PCL avulsion, the popliteal vessels are displaced laterally. Which of the following neurovascular structures is most directly at risk of injury during this maneuver, particularly if ligation of the middle geniculate and superior medial geniculate vessels is required?

. Common peroneal nerve
. Sural nerve
. Tibial nerve
. Small saphenous nerve
. Popliteal artery

Correct Answer & Explanation

. Popliteal artery

Explanation

Correct Answer: EThe case states, "Popliteal vessels are displaced laterally and this usually requires ligation of middle geniculate and superior medial geniculate vessels." The middle and superior medial geniculate vessels are branches of the popliteal artery. Therefore, the maneuver of displacing the popliteal vessels and ligating these specific branches directly involves the popliteal artery, placing it at the most direct risk of injury during this particular step. While the tibial nerve (which lies posterior to the popliteal vein) and other nerves (common peroneal, sural, small saphenous) are generally at risk during a posterior approach, the question specifically highlights the manipulation of the popliteal vessels and ligation of its branches, making the popliteal artery the most pertinent answer in this context.

Question 33

Topic: Total Hip Arthroplasty (THA)

When performing a posterior approach to the knee, the candidate describes the relative anatomical positions of key neurovascular structures in the popliteal fossa. From deepest to most superficial, what is the correct order of the popliteal artery, popliteal vein, and tibial nerve?

. Popliteal artery, Popliteal vein, Tibial nerve
. Tibial nerve, Popliteal vein, Popliteal artery
. Popliteal vein, Popliteal artery, Tibial nerve
. Popliteal artery, Tibial nerve, Popliteal vein
. Tibial nerve, Popliteal artery, Popliteal vein

Correct Answer & Explanation

. Popliteal artery, Popliteal vein, Tibial nerve

Explanation

Correct Answer: AThe case describes the anatomical relationship of these structures in the popliteal fossa: "The tibial nerve lies posterior to the popliteal vein which in turn is superficial to popliteal artery." This means the popliteal artery is the deepest structure, followed by the popliteal vein, and then the tibial nerve is the most superficial of these three structures.

Question 34

Topic: Total Hip Arthroplasty (THA)

A 28-year-old male presents with a terrible triad injury. During the surgical approach, the surgeon utilizes the 'utility posterior approach' as described in the case. Which of the following anatomical structures is typically incised or elevated to gain access to the radial head and coronoid fractures via this approach?

. A. The common flexor origin from the medial epicondyle.
. B. The triceps tendon, which is then reflected distally.
. C. The anconeus muscle, which is elevated off the ulna.
. D. The anterior bundle of the medial collateral ligament.
. E. The brachialis muscle, which is split longitudinally.

Correct Answer & Explanation

. C. The anconeus muscle, which is elevated off the ulna.

Explanation

Correct Answer: CThe utility posterior approach, often referred to as the Kocher approach or a modification thereof, involves an incision centered over the lateral epicondyle. To access the radial head and coronoid (which is anterior), the interval between the anconeus and extensor carpi ulnaris (ECU) is typically utilized. The anconeus muscle is elevated off the ulna, and the lateral collateral ligament complex is identified and often repaired. This provides access to the radial head and, by flexing the elbow and pronating the forearm, allows visualization of the coronoid.Option A (The common flexor origin from the medial epicondyle)is incorrect. This is on the medial side and is not part of the utility posterior (lateral) approach.Option B (The triceps tendon, which is then reflected distally)is incorrect. While the triceps is posterior, reflecting it distally is part of a direct posterior approach, not typically the utility posterior approach which focuses on the lateral side for terrible triads.Option D (The anterior bundle of the medial collateral ligament)is incorrect. This is a medial structure and is not incised or elevated during a lateral-based utility posterior approach.Option E (The brachialis muscle, which is split longitudinally)is incorrect. The brachialis muscle is anterior to the elbow joint. Splitting it is part of an anterior approach, not a utility posterior approach.

Question 35

Topic: Total Hip Arthroplasty (THA)
A 68-year-old male presents with a two-year history of worsening left hip pain, progressive instability, and a 3.5 cm leg length discrepancy following a revision THA 5 years prior. Clinical examination reveals a profound Trendelenburg gait, severely restricted range of motion, and an audible/palpable mechanical clunk. Preoperative radiographs demonstrate catastrophic failure of the left acetabular construct with significant superior and medial migration, violation of Kohler's line, and extensive periacetabular osteolysis. The previously placed bulk femoral head allograft shows signs of advanced resorption and structural collapse. Based on these findings, which of the following is the most appropriate initial classification of the acetabular defect, prior to advanced imaging?
. Paprosky Type I
. Paprosky Type IIA
. Paprosky Type IIB
. Paprosky Type IIC
. Paprosky Type IIIB

Correct Answer & Explanation

. Paprosky Type IIIB

Explanation

Correct Answer: E. The AP pelvis radiograph clearly demonstrates significant superior migration of the acetabular component exceeding 3 cm, violation of Kohler's line (indicating medial wall deficiency), and extensive periacetabular osteolysis in all three DeLee and Charnley zones. The superior dome is entirely deficient, and the previously placed bulk allograft has failed. These findings are characteristic of a Paprosky Type IIIB defect, which involves severe bone loss with a non-supportive rim and significant column compromise, specifically superior bone loss greater than 3 cm, severe destruction of the teardrop, Kohler's line, and both columns. Paprosky Type I defects have minimal bone loss and an intact rim. Type IIA involves superior bone loss but intact columns. Type IIB involves superior and lateral bone loss. Type IIC involves a medial wall defect. None of these adequately describe the catastrophic bone loss and superior migration seen in the image and described in the vignette.

Question 36

Topic: Total Hip Arthroplasty (THA)
During the cup-cage reconstruction, a jumbo, highly porous trabecular metal multi-hole acetabular shell was selected and impacted into the prepared defect. Due to the massive bone loss, host bone contact was estimated at approximately 30-40%, primarily located superiorly against the ilium and inferiorly against the ischium. Multiple locking and non-locking screws were placed through the cup into the superior ilium and the posterior column to achieve initial press-fit stability. Despite the screws, the cup alone did not provide sufficient rigidity to neutralize the pelvic discontinuity, necessitating the cage construct. What is the primary biomechanical role of the highly porous trabecular metal cup in this specific cup-cage construct for a Paprosky IIIB defect with pelvic discontinuity?
. To provide immediate, rigid mechanical fixation across the pelvic discontinuity.
. To serve as a scaffold for biological ingrowth and long-term osseointegration.
. To act as a spacer, filling the void created by the bone defect.
. To provide a smooth articulating surface for the femoral head.
. To prevent medialization of the femoral component into the true pelvis.

Correct Answer & Explanation

. To serve as a scaffold for biological ingrowth and long-term osseointegration.

Explanation

Correct Answer: B. The case explicitly states that the highly porous trabecular metal cup is impacted into the remaining viable host bone, and its high coefficient of friction and osteoconductive properties promote rapid biological ingrowth, eventually providing long-term, durable fixation. This is the primary role of the porous cup: to achieve biological fixation and osseointegration with the host bone. The cage, not the cup, provides the immediate mechanical stability across the discontinuity. Option A is incorrect; the cage provides the immediate rigid mechanical fixation across the discontinuity, protecting the cup. Option C is a secondary effect, but not its primary biomechanical role. Option D is incorrect; the polyethylene liner, cemented into the cage, provides the articulating surface, not the metal cup itself. Option E is a function of the entire construct, but the specific role of the porous cup is biological fixation.

Question 37

Topic: Total Hip Arthroplasty (THA)

Digital templating was performed using a calibrated AP pelvis radiograph. The goals for acetabular component placement included maximizing coverage (80-90%), achieving appropriate inclination (40-45°) and anteversion (15-20°). For the femoral component, templating aimed to restore femoral offset, leg length, and potential for restoration of femoral anteversion. The lesser trochanter was used as a key landmark for stem depth and leg length adjustments.

Which of the following biomechanical parameters, when optimally restored during THA, is most critical for improving abductor muscle efficiency and minimizing the risk of a post-operative Trendelenburg gait?

. Acetabular component inclination of 40-45 degrees.
. Restoration of femoral offset.
. Achieving 15-20 degrees of acetabular anteversion.
. Using a 36mm femoral head diameter.
. Ensuring a 10-20 degree femoral stem anteversion.

Correct Answer & Explanation

. Restoration of femoral offset.

Explanation

Correct Answer: BRestoration of femoral offset is most critical for optimizing abductor muscle efficiency and minimizing the risk of a post-operative Trendelenburg gait. Femoral offset refers to the horizontal distance from the center of rotation of the femoral head to the long axis of the femur. Increasing the offset lengthens the abductor lever arm, allowing the gluteus medius and minimus muscles to generate more torque with less force, thereby improving their efficiency and reducing the likelihood of abductor insufficiency (Trendelenburg gait). While acetabular inclination (A) and anteversion (C) are crucial for stability and wear, and femoral stem anteversion (E) is important for preventing impingement and dislocation, they do not directly impact the abductor lever arm as significantly as femoral offset. Femoral head diameter (D) primarily influences range of motion and jump distance for stability, but not directly abductor mechanics.

Question 38

Topic: Total Hip Arthroplasty (THA)

Following an uncemented Total Hip Arthroplasty performed via a posterior approach, the patient is initiated on a post-operative rehabilitation protocol. This protocol includes immediate weight-bearing as tolerated with an assistive device and specific hip precautions.

Which of the following activities should the patient be most strictly instructed to avoid in the immediate post-operative period to minimize the risk of dislocation?

. Immediate weight-bearing as tolerated with a walker.
. Gentle hip abduction exercises in supine.
. Sleeping on the operative side with a pillow between the legs.
. Hip flexion beyond 90 degrees combined with adduction and internal rotation.
. Stationary cycling with appropriate seat height.

Correct Answer & Explanation

. Hip flexion beyond 90 degrees combined with adduction and internal rotation.

Explanation

Correct Answer: DFor a patient who has undergone THA via a posterior approach, the combination of hip flexion beyond 90 degrees, adduction past midline, and internal rotation is the classic position that places the hip at highest risk for posterior dislocation. Therefore, patients are strictly instructed to avoid this combination of movements in the immediate post-operative period. Immediate weight-bearing as tolerated (A) is standard for uncemented components. Gentle hip abduction exercises (B) are encouraged to strengthen abductors. Sleeping on the operative side with a pillow between the legs (C) is often recommended to maintain abduction and prevent adduction. Stationary cycling (E) is a low-impact exercise that can be introduced in early rehabilitation, provided the seat height is adjusted to prevent excessive hip flexion.

Question 39

Topic: Total Hip Arthroplasty (THA)

A 48-year-old male undergoes open reduction for a complex posterior hip dislocation with an incarcerated osteochondral fragment. During the posterior approach, the surgeon is meticulously identifying and protecting structures to minimize the risk of iatrogenic injury and preserve femoral head vascularity. Which of the following arteries is considered the primary blood supply to the adult femoral head and is most vulnerable in this injury?

. Obturator artery (via ligamentum teres)
. Superior gluteal artery
. Medial circumflex femoral artery
. Lateral circumflex femoral artery
. Inferior gluteal artery

Correct Answer & Explanation

. Medial circumflex femoral artery

Explanation

Correct Answer: CThe case highlights the "Medial Circumflex Femoral Artery (MCFA): The primary blood supply to the femoral head in adults, ascending posteriorly and superiorly along the posterior aspect of the femoral neck, deep to the quadratus femoris and obturator externus. Damage to this artery, particularly its retinacular branches, is the main etiology of femoral head AVN following dislocation." The obturator artery via the ligamentum teres provides minimal blood supply in adults. The superior and inferior gluteal arteries supply the gluteal muscles and surrounding structures, while the lateral circumflex femoral artery primarily supplies the greater trochanter and vastus lateralis, not the femoral head itself.

Question 40

Topic: Total Hip Arthroplasty (THA)

During preoperative templating for a total hip arthroplasty, the surgeon plans to use a high-offset femoral stem. Compared to a standard offset stem, what is the primary biomechanical advantage of increasing the femoral offset without changing the leg length?

. Increases the joint reaction force across the hip
. Decreases the tension on the iliotibial band
. Increases the abductor moment arm
. Increases the risk of bony impingement
. Decreases passive external rotation

Correct Answer & Explanation

. Increases the abductor moment arm

Explanation

Increasing femoral offset increases the abductor moment arm, which improves abductor muscle efficiency and decreases the overall joint reaction force. This enhances joint stability and helps prevent a Trendelenburg gait.

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