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Total Hip Arthroplasty (THA) MCQs

Practice Set 28 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 541

Topic: Total Hip Arthroplasty (THA)

Which of the following surgical approaches to the hip is most commonly associated with a higher risk of sciatic nerve injury?

. Direct anterior approach
. Anterolateral approach
. Posterior approach
. Transtrochanteric approach
. Hardinge approach

Correct Answer & Explanation

. Posterior approach

Explanation

The posterior approach to the hip is most commonly associated with a higher risk of sciatic nerve injury compared to other approaches. The sciatic nerve lies posterior to the short external rotators and is exposed during this approach, making it vulnerable during muscle release, retraction, or instrument placement. The direct anterior and anterolateral approaches generally have a lower risk of sciatic nerve injury but may pose risks to the lateral femoral cutaneous nerve (DAA) or superior gluteal nerve (Anterolateral). The Hardinge approach is an older term for a variation of the anterolateral approach. Transtrochanteric approaches are less common for primary THA but involve osteotomy of the greater trochanter.

Question 542

Topic: Total Hip Arthroplasty (THA)

A 65-year-old man presents with groin pain 5 years after a metal-on-polyethylene total hip arthroplasty. Aspiration yields fluid with numerous macrophages containing metallic debris. Which of the following implant factors most significantly increases the risk of mechanically assisted crevice corrosion (trunnionosis)?

. Increased femoral head size
. Decreased femoral offset
. Use of a ceramic femoral head
. Shorter femoral neck length
. Use of a highly cross-linked polyethylene liner

Correct Answer & Explanation

. Increased femoral head size

Explanation

Increased femoral head size increases the frictional torque and toggling forces at the head-neck junction (trunnion). This excess mechanical stress disrupts the passivation layer of the metal, leading to mechanically assisted crevice corrosion.

Question 543

Topic: Total Hip Arthroplasty (THA)

During a posterior approach to the hip for total hip arthroplasty, the preservation or meticulous repair of which of the following structures has been shown in the literature to be most critical in minimizing the risk of postoperative posterior dislocation?

. Gluteus maximus tendon
. Piriformis, obturator internus, and posterior capsule
. Quadratus femoris and adductor magnus
. Tensor fasciae latae and iliotibial band
. Gluteus medius and minimus

Correct Answer & Explanation

. Piriformis, obturator internus, and posterior capsule

Explanation

Enhanced posterior soft tissue repair, which specifically involves the reattachment of the short external rotators (piriformis, obturator internus, and gemelli) along with the posterior capsule to the greater trochanter, has been consistently demonstrated to dramatically reduce the rate of posterior dislocation following a posterior approach THA.

Question 544

Topic: Total Hip Arthroplasty (THA)

Which of the following statements best describes the mechanical design principle of a 'taper-slip' cemented femoral stem (e.g., Exeter stem)?

. It is designed with a broad collar to load the medial calcar directly.
. It has a roughened or matte surface finish to mechanically interlock with the cement.
. It relies on controlled subsidence into the cement mantle to increase radial compressive forces.
. It is designed to be fully unbonded to allow toggling in the sagittal plane.
. It transfers load primarily through proximal shear forces at the cement-bone interface.

Correct Answer & Explanation

. It relies on controlled subsidence into the cement mantle to increase radial compressive forces.

Explanation

Taper-slip cemented stems are collarless, highly polished, and double-tapered. They are engineered to slightly subside within the cement mantle under axial load. This subsidence acts like a wedge, creating radial compressive forces that strengthen the cement-bone interface and transform shear forces into more favorable compressive forces on the surrounding bone.

Question 545

Topic: Total Hip Arthroplasty (THA)

A 75-year-old patient with Parkinson's disease and a history of recurrent hip dislocations after a primary THA is undergoing revision surgery. The surgeon decides to use a dual mobility articulation. What is the primary biomechanical advantage of this bearing design in preventing dislocation?

. It restricts hip range of motion to prevent impingement.
. It increases the functional jump distance.
. It uses a constrained locking ring to hold the femoral head.
. It increases the coefficient of friction to stabilize the joint.
. It lateralizes the center of rotation to increase abductor tension.

Correct Answer & Explanation

. It increases the functional jump distance.

Explanation

A dual mobility bearing consists of a small metallic or ceramic femoral head that articulates within a large mobile polyethylene liner, which in turn articulates within a highly polished metal acetabular shell. This design effectively increases the functional head size. A larger head size directly increases the 'jump distance' (the distance the femoral head must travel to dislocate over the rim of the cup) and improves the impingement-free range of motion.

Question 546

Topic: Total Hip Arthroplasty (THA)

During a primary Total Hip Arthroplasty (THA), restoring the center of rotation is critical. If the surgeon increases the femoral offset without altering the vertical height of the femoral head or leg length, what is the expected biomechanical effect on the abductor mechanism and the joint reaction force?

. Decreased abductor tension and increased joint reaction force
. Increased abductor moment arm and decreased joint reaction force
. Decreased abductor moment arm and decreased joint reaction force
. Increased abductor tension and increased joint reaction force
. No change in abductor moment arm but increased joint reaction force

Correct Answer & Explanation

. Increased abductor moment arm and decreased joint reaction force

Explanation

Increasing femoral offset lateralizes the greater trochanter, which increases the moment arm of the abductor muscles. This provides a mechanical advantage, requiring less abductor muscle force to balance the pelvis, which in turn significantly decreases the overall joint reaction force across the hip.

Question 547

Topic: Total Hip Arthroplasty (THA)
A revision THA is planned for an aseptic loose cup. Preoperative radiographs demonstrate superior migration of the hip center by 3.5 cm, complete destruction of the teardrop, and medial migration of the hip center past Kohler's line. What is the Paprosky classification and most appropriate reconstruction strategy?
. Type IIA; hemispherical cup with multiple screws
. Type IIB; hemispherical cup with particulate graft
. Type IIIA; hemispherical cup with a superior metal augment
. Type IIIB; custom triflange, cup-cage construct, or structural allograft
. Type IIC; jumbo cup with inferior screw fixation

Correct Answer & Explanation

. Type IIIB; custom triflange, cup-cage construct, or structural allograft

Explanation

The defect described involves >3 cm of superior migration, teardrop destruction, and medial migration past Kohler's line, indicating severe combined superior and medial bone loss with a nonsupportive rim. This represents a Paprosky Type IIIB defect (or potential pelvic discontinuity). Reconstruction typically requires a custom triflange, cup-cage construct, or an anti-protrusio cage with structural allograft.

Question 548

Topic: Total Hip Arthroplasty (THA)

A 58-year-old female presents with persistent anterior groin pain 1 year after a primary THA. The pain is strongly exacerbated by active hip flexion against resistance and when lifting her leg to get into a car. Radiographs show a well-fixed, ingrown acetabular component with 15 degrees of anteversion. The anterior edge of the cup projects 4 mm beyond the native anterior acetabular rim. What is the most appropriate initial diagnostic/therapeutic step?

. Intra-articular hip injection of local anesthetic
. Image-guided injection of local anesthetic and corticosteroid into the iliopsoas bursa
. Electromyography (EMG) of the femoral nerve
. Revision of the acetabular component to increase retroversion
. Revision of the femoral stem to increase lateral offset

Correct Answer & Explanation

. Image-guided injection of local anesthetic and corticosteroid into the iliopsoas bursa

Explanation

The clinical presentation is classic for iliopsoas impingement against the anterior rim of the acetabular component. An image-guided diagnostic injection into the iliopsoas bursa is the most appropriate next step. It can confirm the diagnosis (via pain relief) and may provide lasting therapeutic benefit. If it fails, surgical release (tenotomy) is considered for mild prominences (<8-10 mm).

Question 549

Topic: Total Hip Arthroplasty (THA)

A 65-year-old active male underwent a total hip arthroplasty with a ceramic-on-ceramic bearing. Three years postoperatively, he complains of an audible squeaking sound from the hip during walking, but denies pain. What is the most significant risk factor for this phenomenon?

. Component malposition leading to edge loading
. Large femoral head size
. Use of a highly cross-linked polyethylene liner
. Patient's body mass index (BMI)
. Leg length discrepancy

Correct Answer & Explanation

. Component malposition leading to edge loading

Explanation

Squeaking in ceramic-on-ceramic bearings is primarily associated with edge loading due to component malposition, particularly excessive acetabular cup anteversion or abduction.

Question 550

Topic: Total Hip Arthroplasty (THA)

When exposing the hip via the posterior approach (Moore), which of the following vascular structures is at greatest risk of injury during the release of the short external rotators and the quadratus femoris?

. Medial femoral circumflex artery
. Lateral femoral circumflex artery
. Inferior gluteal artery
. Superior gluteal artery
. Obturator artery

Correct Answer & Explanation

. Medial femoral circumflex artery

Explanation

The ascending branch of the medial femoral circumflex artery crosses the upper border of the quadratus femoris. It is at high risk of injury during the release of the short external rotators and must be carefully coagulated.

Question 551

Topic: Total Hip Arthroplasty (THA)

When cementing a femoral stem during THA, what is the optimal thickness of the cement mantle to ensure long-term survivorship and limit the risk of cement fracture?

. 2 to 3 mm
. Less than 1 mm
. 5 to 7 mm
. 10 mm
. Line-to-line fit with no gap

Correct Answer & Explanation

. 2 to 3 mm

Explanation

Biomechanical studies show that an optimal PMMA cement mantle thickness is between 2 to 3 mm. Mantles thinner than this are prone to brittle fracture under load, while thicker mantles can undergo excessive shrinkage and thermal necrosis of bone.

Question 552

Topic: Total Hip Arthroplasty (THA)

A 65-year-old male with end-stage hip osteoarthritis is being templated for a THA. It is critical to restore the femoral offset. If the surgeon selects a femoral stem with a high offset option (standard vs high offset neck), what is the primary biomechanical effect on the hip joint?

. It increases the lever arm of the abductor mechanism, decreasing the joint reaction force
. It increases the leg length by exactly the amount of offset added
. It decreases the tension on the abductor muscles, increasing the risk of dislocation
. It shifts the center of rotation medially
. It directly decreases the risk of sciatic nerve stretch

Correct Answer & Explanation

. It increases the lever arm of the abductor mechanism, decreasing the joint reaction force

Explanation

Increasing femoral offset (the horizontal distance from the center of the femoral head to the anatomical axis of the femur) increases the moment arm of the abductor muscles. This allows the abductors to stabilize the pelvis with less force, which consequently decreases the overall joint reaction force pressing into the acetabulum, reducing wear.

Question 553

Topic: Total Hip Arthroplasty (THA)

A 55-year-old female presents with bilateral osteoarthritis of the hip secondary to developmental dysplasia. She undergoes a THA. The acetabular cup is placed in the "safe zone" defined by Lewinnek. What are the specific angular parameters of the Lewinnek safe zone?

. 10° ± 5° inclination and 5° ± 5° anteversion
. 50° ± 10° inclination and 30° ± 10° anteversion
. 40° ± 10° inclination and 15° ± 10° anteversion
. 30° ± 5° inclination and 0° anteversion
. 45° ± 10° inclination and 45° ± 10° anteversion

Correct Answer & Explanation

. 10° ± 5° inclination and 5° ± 5° anteversion

Explanation

The historical Lewinnek "safe zone" for acetabular component placement to minimize dislocation risk is 40° ± 10° of inclination (abduction) and 15° ± 10° of anteversion.

Question 554

Topic: Total Hip Arthroplasty (THA)

A surgeon is performing a direct anterior approach for a THA. Postoperatively, the patient notes numbness and a burning sensation over the anterolateral aspect of the operative thigh. Which surgical maneuver most likely caused this complication?

. Aggressive medial retraction of the sartorius muscle
. Aggressive lateral retraction of the tensor fasciae latae
. Placement of an anterior retractor over the pelvic brim
. Releasing the short external rotators
. Reaming the acetabulum too deeply

Correct Answer & Explanation

. Aggressive medial retraction of the sartorius muscle

Explanation

The lateral femoral cutaneous nerve (LFCN) is at risk during the direct anterior approach to the hip. Aggressive medial retraction of the sartorius or rectus femoris can stretch or directly injure the LFCN.

Question 555

Topic: Total Hip Arthroplasty (THA)

A 75-year-old male with a history of recurrent THA dislocations secondary to severe abductor deficiency is planned for revision surgery. His acetabular cup is well-fixed and correctly positioned. Which of the following is the most appropriate reconstructive option?

. Exchange to a larger diameter conventional femoral head
. Revision to a constrained acetabular liner
. Revision to a dual-mobility construct
. Advancement of the greater trochanter
. Application of an abduction brace for 12 weeks

Correct Answer & Explanation

. Exchange to a larger diameter conventional femoral head

Explanation

A dual-mobility construct provides excellent stability for patients with recurrent instability and abductor deficiency, boasting lower failure rates than constrained liners. It increases the effective head size and jump distance.

Question 556

Topic: Total Hip Arthroplasty (THA)

In total hip arthroplasty, increasing the femoral offset without changing the leg length or neck-shaft angle has which of the following biomechanical effects?

. Increases the joint reaction force
. Decreases the tension on the abductor musculature
. Decreases the risk of sciatic nerve palsy
. Increases the risk of component impingement
. Decreases the bending moment on the femoral stem

Correct Answer & Explanation

. Increases the joint reaction force

Explanation

Increasing femoral offset increases the lever arm of the abductor muscles, thereby decreasing the force required by the abductors and reducing the overall joint reaction force. However, it does increase the bending moment on the femoral stem.

Question 557

Topic: Total Hip Arthroplasty (THA)

A 75-year-old patient with Parkinson's disease and abductor deficiency experiences recurrent posterior dislocations following a primary THA. A revision to a constrained acetabular liner is planned. What is the most critical prerequisite for the successful use of a constrained liner?

. Use of a highly cross-linked polyethylene liner
. Use of a 36-mm or larger femoral head
. Excellent bone ingrowth and stable fixation of the acetabular shell
. Preservation of the short external rotators
. Use of a dual-mobility construct

Correct Answer & Explanation

. Excellent bone ingrowth and stable fixation of the acetabular shell

Explanation

Constrained liners transfer significant forces to the bone-implant interface. Therefore, a well-fixed, osseointegrated acetabular shell is an absolute prerequisite to prevent catastrophic failure and cup loosening.

Question 558

Topic: Total Hip Arthroplasty (THA)

A patient complains of the operative leg feeling "too long" immediately following a THA. Radiographs show the tip of the greater trochanter is perfectly aligned with the center of the femoral head, but the lesser trochanter is 15 mm distal to the ischial tuberosity compared to the contralateral side. The femoral offset is symmetric. What error occurred intraoperatively?

. The femoral neck cut was made too low
. An excessively long modular head was chosen
. The acetabular cup was placed too far superiorly
. The acetabular cup was placed too inferiorly
. The femoral stem was placed in varus

Correct Answer & Explanation

. The acetabular cup was placed too inferiorly

Explanation

If the relationship between the greater trochanter and the center of rotation is maintained, but the femur is distally displaced relative to the pelvis (lesser trochanter to ischial tuberosity), the acetabular component was placed too inferiorly, lowering the center of rotation and lengthening the leg.

Question 559

Topic: Total Hip Arthroplasty (THA)

During a posterior approach to the hip (Kocher-Langenbeck), the main blood supply to the femoral head must be protected. The deep branch of the medial femoral circumflex artery (MFCA) is most at risk during the surgical release of which of the following structures?

. Piriformis tendon
. Obturator internus tendon
. Quadratus femoris muscle
. Gluteus maximus insertion
. Superior gemellus

Correct Answer & Explanation

. Piriformis tendon

Explanation

The MFCA runs deep to the quadratus femoris muscle. When releasing the quadratus femoris, the surgeon must leave a cuff of muscle attached to the femur or stay superficial to avoid injury to the MFCA, which is the predominant blood supply to the femoral head.

Question 560

Topic: Total Hip Arthroplasty (THA)

A direct lateral (Hardinge) approach to the hip requires splitting the gluteus medius. To avoid iatrogenic denervation, 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

. 1 cm

Explanation

The superior gluteal nerve supplies the gluteus medius, gluteus minimus, and tensor fasciae latae. Splitting the gluteus medius more than 5 cm proximal to the tip of the greater trochanter places this nerve at significant risk of transection.

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