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Total Hip Arthroplasty (THA) MCQs

Practice Set 35 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 681

Topic: Total Hip Arthroplasty (THA)

A 55-year-old male who underwent a ceramic-on-ceramic total hip arthroplasty three years ago presents complaining of a reproducible squeaking noise from his hip during specific movements. What is the most frequently cited biomechanical cause for this auditory phenomenon?

. Third-body wear from retained cement debris
. Galvanic corrosion at the trunnion
. Edge loading due to component malposition, causing loss of fluid film lubrication
. Impingement of the greater trochanter on the ilium
. Delamination of the titanium plasma spray from the acetabular shell

Correct Answer & Explanation

. Edge loading due to component malposition, causing loss of fluid film lubrication

Explanation

Squeaking in ceramic-on-ceramic THA is a notable complication. It is heavily correlated with edge loading, which typically occurs due to component malposition (e.g., a steep acetabular cup with an inclination angle >50 degrees or excessive anteversion). Edge loading results in stripe wear on the ceramic head, localized loss of fluid-film lubrication, and generation of the high-frequency auditory squeak during hip motion.

Question 682

Topic: Total Hip Arthroplasty (THA)

A patient experiences recurrent posterior dislocations following a primary Total Hip Arthroplasty (THA). CT scan evaluation reveals the acetabular cup is placed in 10 degrees of anteversion and 40 degrees of abduction. The femoral stem is in 5 degrees of anteversion. What is the most likely cause of the instability?

. Acetabular cup over-abduction
. Insufficient combined anteversion
. Excessive combined anteversion
. Cam impingement
. Leg length discrepancy

Correct Answer & Explanation

. Insufficient combined anteversion

Explanation

Combined anteversion in THA (cup anteversion + stem anteversion) should ideally fall between 25 and 45 degrees (typically calculated by the Widmer formula or safely assumed around 15 degrees cup + 15 degrees stem) to minimize impingement and dislocation risk. A combined anteversion of 15 degrees (10 cup + 5 stem) is severely insufficient and predisposes the patient to posterior dislocation due to early anterior impingement during internal rotation and flexion.

Question 683

Topic: Total Hip Arthroplasty (THA)

During total hip arthroplasty, increasing the femoral offset without significantly altering the leg length yields which of the following biomechanical outcomes?

. Decreases the resting tension of the abductor musculature
. Increases the global joint reactive force acting across the hip
. Increases the moment arm of the hip abductor muscles
. Increases the inherent risk of bony impingement during abduction
. Decreases the bending stress placed upon the femoral stem

Correct Answer & Explanation

. Increases the moment arm of the hip abductor muscles

Explanation

Increasing femoral offset directly increases the lever arm (moment arm) of the abductor muscles, thereby optimizing their mechanical advantage. This reduces the required abductor force to stabilize the pelvis, which in turn effectively decreases the overall joint reactive force.

Question 684

Topic: Total Hip Arthroplasty (THA)

During a posterior approach to the hip (Kocher-Langenbeck), the surgeon takes care to protect the primary blood supply to the adult femoral head. Which of the following describes the anatomical course of the main branch of the medial femoral circumflex artery (MFCA)?

. Anterior to the quadratus femoris and posterior to the obturator externus
. Posterior to the piriformis and superior to the superior gemellus
. Superior to the obturator internus and anterior to the gluteus medius
. Between the pectineus and the adductor longus
. Inferior to the adductor brevis and anterior to the vastus lateralis

Correct Answer & Explanation

. Anterior to the quadratus femoris and posterior to the obturator externus

Explanation

The deep branch of the medial femoral circumflex artery (MFCA) is the predominant blood supply to the femoral head. It runs anterior to the quadratus femoris muscle and posterior to the obturator externus before ascending along the femoral neck.

Question 685

Topic: Total Hip Arthroplasty (THA)

Fretting and crevice corrosion are most commonly observed at which specific interface in modern total hip arthroplasty?

. Between the acetabular shell and the polyethylene liner
. At the modular head-neck taper junction
. Between the femoral stem and the bone cement
. At the articulating surface of a ceramic-on-ceramic bearing
. Between the acetabular shell and the host bone

Correct Answer & Explanation

. At the modular head-neck taper junction

Explanation

Mechanically assisted crevice corrosion (MACC), also known as trunnionosis, occurs at modular junctions such as the head-neck taper of a femoral stem. Micro-motion (fretting) at this interface disrupts the protective passivation layer, leading to corrosion and adverse local tissue reactions.

Question 686

Topic: Total Hip Arthroplasty (THA)

A patient undergoes a posterior-approach total hip arthroplasty. Postoperatively, the patient experiences recurrent posterior dislocations. Which of the following component malpositions is most likely responsible?

. Excessive anteversion of the acetabular cup
. Excessive retroversion of the acetabular cup
. Excessive valgus of the femoral stem
. Insufficient femoral offset
. Excessive anterior tilt of the pelvis

Correct Answer & Explanation

. Excessive retroversion of the acetabular cup

Explanation

Excessive retroversion of the acetabular component in a THA is a primary cause of posterior instability and dislocation. Proper anteversion (usually 15-20 degrees) and inclination (40-45 degrees) are crucial for dynamic stability.

Question 687

Topic: Total Hip Arthroplasty (THA)

A 58-year-old male with a ceramic-on-ceramic total hip arthroplasty presents with an audible squeaking noise from his hip during certain movements. There is no pain, and radiographs show well-fixed components. Which of the following technical factors during the index surgery most likely contributed to this issue?

. Increased femoral offset
. Excessive anteversion of the femoral stem
. Excessive cup inclination
. Use of a large diameter femoral head
. Placement of a constrained liner

Correct Answer & Explanation

. Excessive cup inclination

Explanation

Squeaking in ceramic-on-ceramic THA is often associated with component malposition, specifically excessive acetabular cup inclination or anteversion. This malpositioning leads to edge loading, disrupting the fluid film lubrication and causing the audible squeak.

Question 688

Topic: Total Hip Arthroplasty (THA)

A 65-year-old female presents with recurrent posterior hip dislocations 2 months after a primary total hip arthroplasty via a posterior approach. CT imaging shows a well-fixed acetabular component with 20 degrees of abduction and 5 degrees of retroversion. What is the most appropriate definitive management?

. Application of an abduction brace for 6 weeks
. Revision of the femoral stem to increase offset
. Exchange to a constrained polyethylene liner
. Revision of the acetabular component to increase anteversion
. Conversion to a dual-mobility construct without component revision

Correct Answer & Explanation

. Revision of the acetabular component to increase anteversion

Explanation

Acetabular component retroversion is a primary structural cause of posterior instability after THA. The most appropriate definitive treatment is revision of the cup to achieve the safe zone of 15-20 degrees of anteversion.

Question 689

Topic: Total Hip Arthroplasty (THA)

The Paley multiplier method provides accurate predictions of leg length discrepancy (LLD) at skeletal maturity. At what specific age is the skeletal multiplier for girls exactly 2.0?

. Birth
. 1 year
. 2 years
. 3 years
. 4 years

Correct Answer & Explanation

. 2 years

Explanation

For girls, the Paley multiplier is approximately 2.0 at exactly 2 years of age, meaning they have achieved half of their mature limb length. For boys, the multiplier is 2.0 closer to 3 years of age.

Question 690

Topic: Total Hip Arthroplasty (THA)

A 16-year-old patient presents with a combined leg length discrepancy and complex femoral deformity. A proximal femoral osteotomy and external fixation are performed.

When distracting a fixator over a newly formed regenerate in the proximal femur, what soft tissue structure is at highest risk of causing an apex-anterior (procurvatum) and varus bowing of the regenerate?

. Tensor fasciae latae
. Hamstrings
. Rectus femoris
. Iliopsoas and hip abductors
. Adductor longus

Correct Answer & Explanation

. Iliopsoas and hip abductors

Explanation

During proximal femoral lengthening, the unopposed pull of the iliopsoas (flexing the proximal fragment) and hip abductors (abducting the proximal fragment) creates a deforming force. This classically results in a varus and procurvatum deformity at the regenerate site.

Question 691

Topic: Total Hip Arthroplasty (THA)

A 35-year-old female presents with a trimalleolar ankle fracture. Preoperative CT scan reveals a large, displaced posterior malleolus fragment involving 35% of the articular surface, necessitating direct visualization and posterior-to-anterior screw fixation with a buttress plate. To optimally facilitate this specific surgical approach, which of the following patient positions is most appropriate?

. Supine with a bump under the ipsilateral hip
. Supine with the leg externally rotated
. Prone or lateral decubitus
. Lithotomy position
. Supine with the knee flexed to 90 degrees over a radiolucent triangle

Correct Answer & Explanation

. Prone or lateral decubitus

Explanation

Correct Answer: CWhen a posterior malleolus fracture requires direct visualization and fixation (e.g., due to a large fragment size, articular comminution, or the need for buttress plating), a direct posterior or posterolateral approach is indicated. The text notes that if a significant posterior malleolus fracture requires a direct posterior approach, the patient may need to be positioned prone or in the lateral decubitus position. The supine position with a bump is standard for lateral and medial malleolus access but does not provide adequate exposure for a direct posterior approach.

Question 692

Topic: Total Hip Arthroplasty (THA)

The Paley multiplier method is used to predict leg length discrepancy at maturity. What demographic variable is the standard multiplier strictly dependent upon?

. Current weight
. Chronological age and sex
. Skeletal age and sex
. Bone age independently
. Height percentiles

Correct Answer & Explanation

. Chronological age and sex

Explanation

The Paley multiplier method is primarily based on chronological age and sex. It is a simple and highly accurate tool for predicting limb length discrepancy at maturity, avoiding the need for bone age calculations in most congenital cases.

Question 693

Topic: Total Hip Arthroplasty (THA)

A 12-year-old boy is undergoing deformity correction for a mid-diaphyseal tibial procurvatum deformity. According to Paley's Rule 1 of osteotomy, if the osteotomy and the axis of correction of angulation (ACA) are both located at the center of rotation of angulation (CORA), what will be the radiographic outcome of the correction?

. Pure angulation occurs without translation of the bone segments.
. Angulation occurs with obligatory translation of the bone segments at the osteotomy site.
. The mechanical axis will remain deviated parallel to the anatomical axis.
. Translation occurs without angulation, creating a bayonet apposition.
. The correction will induce an iatrogenic leg length discrepancy.

Correct Answer & Explanation

. Pure angulation occurs without translation of the bone segments.

Explanation

Osteotomy Rule 1 states that when the osteotomy and the ACA are placed at the CORA, pure angulation occurs. The mechanical and anatomical axes are realigned without any translation at the osteotomy site.

Question 694

Topic: Total Hip Arthroplasty (THA)

An 8-year-old girl presents with a congenital femoral deficiency. Her current leg length discrepancy (LLD) is 3.0 cm. Using the Paley Multiplier method, and knowing the multiplier for a girl at age 8 is approximately 1.5, what is her predicted LLD at skeletal maturity?

. 2.0 cm
. 3.0 cm
. 4.5 cm
. 6.0 cm
. 7.5 cm

Correct Answer & Explanation

. 4.5 cm

Explanation

The Paley Multiplier method predicts limb length discrepancy at maturity by multiplying the current discrepancy by a chronological age- and sex-specific multiplier. In this case, 3.0 cm x 1.5 = 4.5 cm.

Question 695

Topic: Total Hip Arthroplasty (THA)

A 15-year-old patient is undergoing distraction osteogenesis for a 4 cm tibial leg length discrepancy using an Ilizarov circular fixator. At the 4-week clinic visit, radiographs show premature consolidation of the regenerate bone at the osteotomy site. Which of the following technical errors most likely contributed to this complication?

. A latency period of 3 days prior to distraction.
. A distraction rate of 1.5 mm per day.
. Performing the osteotomy with a Gigli saw rather than a drill and osteotome.
. A distraction rate of 0.5 mm per day.
. Rhythm of distraction set to 0.25 mm four times a day.

Correct Answer & Explanation

. A distraction rate of 0.5 mm per day.

Explanation

Premature consolidation occurs when the bone heals faster than it is pulled apart, most commonly due to a distraction rate that is too slow (e.g., 0.5 mm/day) or a latency period that is too long. The standard distraction rate is typically 1 mm/day divided into 4 increments.

Question 696

Topic: Total Hip Arthroplasty (THA)

A 9-year-old girl presents with a congenital leg length discrepancy (LLD). Her current discrepancy is 3 cm. According to the Paley Multiplier Method, the multiplier for a girl at age 9 is 1.4. Assuming no surgical intervention, what is her anticipated LLD at skeletal maturity?

. 3.0 cm
. 3.5 cm
. 4.2 cm
. 5.0 cm
. 5.6 cm

Correct Answer & Explanation

. 4.2 cm

Explanation

The Paley Multiplier Method predicts limb length discrepancy at maturity by multiplying the current discrepancy by an age- and gender-specific multiplier. For this patient: 3 cm x 1.4 = 4.2 cm.

Question 697

Topic: Total Hip Arthroplasty (THA)

When using the Paley Multiplier Method to predict leg length discrepancy (LLD) at skeletal maturity, the multiplier coefficient is primarily determined by the patient's:

. Chronological age and gender
. Bone age and current weight
. Skeletal maturity score on a pelvis radiograph (Risser sign)
. Current limb length and desired lengthening amount
. Bone age and gender

Correct Answer & Explanation

. Chronological age and gender

Explanation

The Paley Multiplier Method relies on chronological age and gender to find the specific multiplier coefficient. This coefficient is then multiplied by the current LLD to accurately predict the discrepancy at skeletal maturity.

Question 698

Topic: Total Hip Arthroplasty (THA)

A patient with a ceramic-on-ceramic total hip arthroplasty complains of a new-onset audible 'squeaking' during walking. Radiographic evaluation is most likely to show which of the following component positions?

. Acetabular cup placed in 15 degrees of anteversion
. Acetabular cup placed with an inclination angle of 60 degrees
. Femoral stem placed in excessive anteversion
. Acetabular cup placed in 40 degrees of inclination
. Femoral stem placed in varus alignment

Correct Answer & Explanation

. Acetabular cup placed with an inclination angle of 60 degrees

Explanation

Squeaking in ceramic-on-ceramic THA is highly associated with edge loading, microseparation, and stripe wear. Edge loading typically occurs due to component malposition, such as excessive acetabular inclination (e.g., >50 degrees) or abnormal version.

Question 699

Topic: Total Hip Arthroplasty (THA)

A 15-year-old male presents with a predicted leg length discrepancy of 6.5 cm at skeletal maturity secondary to a physeal arrest of the distal femur. What is the most appropriate definitive management to equalize leg lengths?

. Contralateral distal femoral and proximal tibial epiphysiodesis
. Ipsilateral femoral lengthening
. Contralateral femoral shortening osteotomy
. Use of a permanent 6.5 cm shoe lift
. Ipsilateral proximal tibial lengthening

Correct Answer & Explanation

. Ipsilateral femoral lengthening

Explanation

For predicted leg length discrepancies greater than 5 cm, surgical lengthening of the affected limb is the standard of care. Contralateral epiphysiodesis or shortening is generally reserved for discrepancies of 2-5 cm to avoid unacceptable loss of overall adult height.

Question 700

Topic: Total Hip Arthroplasty (THA)

A 4-year-old girl presents with a congenital short femur resulting in a 2.5 cm leg length discrepancy (LLD). Using the Paley multiplier method, if her age- and gender-specific multiplier is approximately 1.5, what is her predicted LLD at skeletal maturity assuming constant inhibition?

. 2.5 cm
. 3.75 cm
. 4.5 cm
. 5.0 cm

Correct Answer & Explanation

. 3.75 cm

Explanation

The multiplier method predicts the ultimate LLD at skeletal maturity by multiplying the current discrepancy by the age- and gender-specific multiplier. For this patient, 2.5 cm x 1.5 = 3.75 cm.

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