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Total Hip Arthroplasty (THA) MCQs

Practice Set 6 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 101

Topic: Total Hip Arthroplasty (THA)

A 28-year-old male is undergoing treatment for a 5 cm post-traumatic tibial leg length discrepancy using the Lengthening Over a Nail (LON) technique. What is the primary advantage of LON compared to classic distraction osteogenesis using solely a circular external fixator?

. It increases the bone healing index required for consolidation.
. It eliminates the risk of deep infection entirely.
. It significantly decreases the external fixation index (time spent in the frame).
. It allows for earlier weight-bearing without crutches.
. It negates the need for a corticotomy.

Correct Answer & Explanation

. It significantly decreases the external fixation index (time spent in the frame).

Explanation

The LON technique allows the external fixator to be removed immediately after the distraction phase is complete, once the nail is locked. This drastically reduces the time the patient must wear the external frame.

Question 102

Topic: Total Hip Arthroplasty (THA)

A 12-year-old girl has a leg length discrepancy. Using the Paley Multiplier Method to predict her leg length discrepancy at maturity, the surgeon multiplies her current discrepancy by an age-specific multiplier. What physiological event marks the stabilization of the multiplier at 1.0 (indicating skeletal maturity) for females in this system?

. Closure of the distal fibular physis
. Onset of menarche
. Chronological age of 16 years
. Chronological age of 18 years
. Risser stage 5

Correct Answer & Explanation

. Onset of menarche

Explanation

In the multiplier method for females, skeletal growth significantly tapers and the multiplier approaches 1.0 around skeletal maturity, which closely correlates with bone age following the onset of menarche.

Question 103

Topic: Total Hip Arthroplasty (THA)

If a surgeon attempts to correct a multi-apical diaphyseal deformity of the tibia by performing a single osteotomy at the intersection point of the proximal and distal mechanical axes (the apparent single CORA), what is the inevitable geometric result?

. Perfect restoration of the anatomic axis without any translation.
. Restoration of the overall mechanical axis, but creation of severe translation of the middle bone segment.
. Failure to restore the overall mechanical axis.
. Creation of an apex posterior recurvatum deformity.
. Leg length discrepancy exceeding 5 cm.

Correct Answer & Explanation

. Restoration of the overall mechanical axis, but creation of severe translation of the middle bone segment.

Explanation

When a multi-apical deformity is corrected with a single osteotomy at the overall mechanical axis intersection, the mechanical axis is restored, but the intervening segment undergoes severe, un-anatomic translation.

Question 104

Topic: Total Hip Arthroplasty (THA)

A surgeon plans to correct a mid-diaphyseal tibial angular deformity. According to Paley's Rule 1 of osteotomy, if the osteotomy and the hinge axis are both placed exactly at the Center of Rotation of Angulation (CORA), what is the resulting geometric correction?

. Pure angular correction without any translation at the osteotomy site
. Angular correction with deliberate translation at the osteotomy site
. Pure translation of the distal segment without angular correction
. Angular correction with an unintended secondary translation deformity
. Correction of angulation but creation of a leg length discrepancy

Correct Answer & Explanation

. Pure angular correction without any translation at the osteotomy site

Explanation

According to Paley's Rule 1, placing both the osteotomy and the correction hinge at the CORA results in pure angular correction. The anatomic axes will become collinear without any translation at the osteotomy site.

Question 105

Topic: Total Hip Arthroplasty (THA)

According to Paley's Rule 2 of deformity correction, if the osteotomy is performed at a level different from the CORA, but the Angulation Correction Axis (ACA) remains at the CORA, what is the expected anatomical outcome?

. An uncompensated leg length discrepancy will invariably result.
. The proximal and distal axes will remain parallel but not collinear.
. Iatrogenic translation of the mechanical axis will occur.
. The mechanical axes will realign, but collinear translation will occur at the osteotomy site.
. The mechanical axes will realign perfectly without any local translation at the osteotomy site.

Correct Answer & Explanation

. The mechanical axes will realign, but collinear translation will occur at the osteotomy site.

Explanation

Paley's Rule 2 states that if the ACA is at the CORA but the osteotomy is not, the mechanical axes will fully realign. However, there will be an obligatory translation of the bone ends at the osteotomy site.

Question 106

Topic: Total Hip Arthroplasty (THA)

A 16-year-old patient with a severe varus deformity of the tibia is undergoing correction with an Ilizarov external fixator. According to Paley's Rule 1 of deformity correction, if the osteotomy and the hinge of the external fixator are both placed exactly at the Center of Rotation of Angulation (CORA), which of the following best describes the resulting alignment?

. The mechanical axes will realign with translation occurring at the osteotomy site.
. The mechanical axes will remain parallel but translated, creating a zig-zag deformity.
. The mechanical axes will realign completely without any translation at the osteotomy site.
. The deformity will be overcorrected into valgus due to the hinge placement.
. The osteotomy site will distract unequally, leading to a leg length discrepancy.

Correct Answer & Explanation

. The mechanical axes will realign completely without any translation at the osteotomy site.

Explanation

Paley's Rule 1 states that when the osteotomy and the hinge (axis of correction) are both located at the CORA, the mechanical axes will realign perfectly. This results in pure angulation without translation at the osteotomy site.

Question 107

Topic: Total Hip Arthroplasty (THA)

A 22-year-old patient is undergoing distraction osteogenesis for a post-traumatic tibial leg length discrepancy. After the corticotomy, the surgeon waits 7 days before initiating distraction. What is the primary biological rationale for this latency period?

. To prevent early pin tract infections.
. To allow the hematoma to organize and initial angiogenesis to occur.
. To permit complete endochondral ossification of the fracture gap.
. To decrease the risk of deep vein thrombosis.
. To allow the patient's pain to subside before applying mechanical stress.

Correct Answer & Explanation

. To allow the hematoma to organize and initial angiogenesis to occur.

Explanation

The latency period (typically 5-10 days) allows the fracture hematoma to organize and mesenchymal stem cells to begin the early phases of angiogenesis and soft callus formation. Premature distraction disrupts this delicate vascular network, leading to poor regenerate bone.

Question 108

Topic: Total Hip Arthroplasty (THA)

The Paley multiplier method is frequently used to predict leg length discrepancy (LLD) at skeletal maturity. Which of the following data points is the most critical to accurately calculate the predicted LLD at skeletal maturity using this method?

. The patient's current LLD and skeletal age
. The patient's chronological age and current LLD only
. The patient's current LLD and parental heights
. The patient's bone age and exact femoral length only
. The patient's chronological age and body weight

Correct Answer & Explanation

. The patient's current LLD and skeletal age

Explanation

The Paley multiplier method predicts discrepancy at skeletal maturity by multiplying the current LLD by an age- and gender-specific multiplier. It is most accurate when the patient's current LLD and true skeletal age (rather than chronological age) are used.

Question 109

Topic: Total Hip Arthroplasty (THA)

A 12-year-old boy presents with a leg length discrepancy (LLD) secondary to prior physeal arrest. The surgeon decides to use the Paley Multiplier Method for preoperative planning. What is the primary purpose of this method?

. To calculate the safe daily rate of distraction osteogenesis
. To predict the final lower limb length discrepancy at skeletal maturity
. To determine the precise location of the anatomical CORA
. To select the correct ring size for a circular external fixator
. To estimate the duration of the consolidation phase

Correct Answer & Explanation

. To predict the final lower limb length discrepancy at skeletal maturity

Explanation

The Paley Multiplier Method utilizes age- and gender-specific coefficients to predict the limb length at skeletal maturity. It is highly accurate for calculating final leg length discrepancy and timing epiphysiodesis or lengthening procedures.

Question 110

Topic: Total Hip Arthroplasty (THA)

You are reviewing the alignment parameters of a 50-year-old patient.

The patient's mechanical axis deviation (MAD) is perfectly normal (0 mm). However, the knee joint line obliquity is significantly altered relative to the floor. Which of the following best explains this phenomenon?

. A pure intra-articular cartilage defect of the medial compartment
. A compensatory deformity with equal and opposite deformities in the femur and tibia
. A solitary diaphyseal deformity of the tibia
. A leg length discrepancy exceeding 2 cm
. Isolated lateral collateral ligament insufficiency

Correct Answer & Explanation

. A compensatory deformity with equal and opposite deformities in the femur and tibia

Explanation

Compensatory deformities (e.g., a valgus distal femur paired with a varus proximal tibia of equal magnitude) keep the mechanical axis passing through the center of the knee, resulting in a normal MAD, but cause the joint line to be oblique to the ground.

Question 111

Topic: Total Hip Arthroplasty (THA)

During the evaluation of a patient with a post-traumatic knee deformity, a weight-bearing radiograph reveals an abnormal Joint Line Convergence Angle (JLCA) of 6 degrees, opening laterally. What does an abnormal JLCA primarily indicate in the context of deformity planning?

. Intra-articular fracture step-off.
. A primary diaphyseal bowing deformity.
. Ligamentous laxity or unilateral cartilage loss.
. A pure translational deformity of the metaphysis.
. An underlying leg length discrepancy.

Correct Answer & Explanation

. Ligamentous laxity or unilateral cartilage loss.

Explanation

The JLCA measures the parallelism of the distal femoral and proximal tibial articular surfaces (normally 0-2 degrees). An increased JLCA typically indicates asymmetric cartilage loss or collateral ligament laxity, which must be accounted for to prevent undercorrection or overcorrection.

Question 112

Topic: Total Hip Arthroplasty (THA)

During the all-arthroscopic extensive anterior and posterior synovectomy for this patient's diffuse TGCT of the knee, a critical technical challenge is ensuring thorough clearance of the posterior compartments. Which of the following best describes the arthroscopic approach to address the posterior compartments while minimizing neurovascular risk?

. Rely solely on trans-notch visualization from anterior portals for posterior clearance.
. Perform an open posterior approach as the primary method for all posterior disease.
. Establish posteromedial and posterolateral portals under direct intra-articular visualization, carefully avoiding neurovascular structures.
. Utilize a posterior midline portal to access both posteromedial and posterolateral compartments simultaneously.
. Perform a complete posterior capsulectomy through a single large posterior incision.

Correct Answer & Explanation

. Establish posteromedial and posterolateral portals under direct intra-articular visualization, carefully avoiding neurovascular structures.

Explanation

Correct Answer: C - Establish posteromedial and posterolateral portals under direct intra-articular visualization, carefully avoiding neurovascular structures.The case emphasizes: "Thorough clearance of the posterior compartments is the most critical step in preventing recurrence in diffuse TGCT. Trans-notch visualization is insufficient for a complete posterior synovectomy." It then describes the technique: "An 18-gauge spinal needle was used to localize a posteromedial portal under direct intra-articular visualization, ensuring it was superior to the joint line and posterior to the medial collateral ligament to avoid the saphenous nerve and vein. ... Similarly, a posterolateral portal was established under direct visualization, taking extreme care to stay anterior to the biceps femoris tendon and fibular head to protect the common peroneal nerve." This highlights the importance of direct visualization and careful portal placement.A. Rely solely on trans-notch visualization from anterior portals for posterior clearance:The case explicitly states this is "insufficient for a complete posterior synovectomy," leading to higher recurrence rates.B. Perform an open posterior approach as the primary method for all posterior disease:While an open posterior approach is an option, the case states that an all-arthroscopic approach was chosen because "there was no extra-articular extension... that would mandate an open posterior approach." Modern arthroscopic techniques allow for thorough posterior clearance without the morbidity of an open approach in many cases.D. Utilize a posterior midline portal to access both posteromedial and posterolateral compartments simultaneously:A posterior midline portal is not a standard or safe approach for comprehensive posterior knee arthroscopy due to the risk to the popliteal neurovascular bundle. Separate posteromedial and posterolateral portals are used.E. Perform a complete posterior capsulectomy through a single large posterior incision:This describes an open posterior approach, which was not the chosen method for this patient and is associated with higher morbidity and arthrofibrosis compared to arthroscopy.

Question 113

Topic: Total Hip Arthroplasty (THA)

When evaluating a patient for lower extremity deformity, the mechanical axis deviation (MAD) is measured.

If the MAD falls medial to the center of the knee joint, what is the next step in the standard Malalignment Test to accurately identify the source of the deformity?

. Measure the joint line convergence angle (JLCA)
. Measure the mechanical lateral distal femoral angle (mLDFA)
. Measure the mechanical medial proximal tibial angle (mMPTA)
. Measure the anatomic axis of the femur
. Compare the leg length discrepancy using scanograms

Correct Answer & Explanation

. Measure the mechanical lateral distal femoral angle (mLDFA)

Explanation

Once a medial MAD (varus) is identified, the standard Malalignment Test dictates evaluating the joint orientation angles starting proximally. The mechanical lateral distal femoral angle (mLDFA) is measured first to determine if the femur is the source of the deformity.

Question 114

Topic: Total Hip Arthroplasty (THA)

A 16-year-old male presents with a leg length discrepancy (LLD) and requires lengthening of the right tibia using an Ilizarov frame. During the distraction phase, the patient develops a rigid plantarflexion deformity. Which of the following is the primary pathoanatomical cause of this specific complication?

. Overactivity of the tibialis anterior muscle.
. Relative shortening and contracture of the gastrosoleus complex.
. Premature consolidation of the fibular osteotomy.
. Inadvertent tethering of the deep peroneal nerve.
. Subluxation of the distal tibiofibular joint.

Correct Answer & Explanation

. Relative shortening and contracture of the gastrosoleus complex.

Explanation

Equinus contracture is the most common complication during tibial lengthening. It occurs because the gastrosoleus complex spans two joints and becomes relatively shorter and tighter as the tibia is distracted.

Question 115

Topic: Total Hip Arthroplasty (THA)

A 30-year-old patient has a complex tibial deformity characterized by varus, procurvatum, and internal rotation. The surgeon elects to use a Taylor Spatial Frame (TSF). What engineering concept allows the TSF to correct all six degrees of freedom simultaneously?

. The Ilizarov rigid ring principle.
. The Charnley low-friction principle.
. The Stewart-Gough platform concept.
. The tension-band wiring mechanism.
. The Hooke's law of elasticity mechanism.

Correct Answer & Explanation

. The Stewart-Gough platform concept.

Explanation

The TSF is based on the Stewart-Gough platform, a hexapod mechanism that allows movement in all six degrees of freedom. A computer program calculates a "virtual hinge" to correct multi-planar deformities simultaneously.

Question 116

Topic: Total Hip Arthroplasty (THA)

During a multi-apical tibial deformity correction, a surgeon identifies two separate CORAs. If the surgeon decides to perform only a single osteotomy located exactly halfway between the two CORAs and corrects the angulation perfectly, what unintended deformity will inevitably result?

. Leg length discrepancy
. Rotational malalignment
. A translation deformity of the mechanical axis
. A reversed joint line convergence angle
. Intra-articular valgus

Correct Answer & Explanation

. A translation deformity of the mechanical axis

Explanation

Correcting a multi-apical deformity with a single osteotomy between the CORAs effectively follows Rule 3. While angulation can be corrected, the mechanical axes will remain parallel but offset, creating a translation deformity.

Question 117

Topic: Total Hip Arthroplasty (THA)

A 32-year-old female presents with a diaphyseal femoral deformity. The surgeon places the hinge at the CORA but performs the osteotomy at a different level due to poor soft tissue quality. According to Paley's principles, what is the expected outcome upon correction?

. Pure angulation at the osteotomy site with restoration of the mechanical axis.
. Angulation and translation at the osteotomy site with restoration of the mechanical axis.
. Angulation and translation at the osteotomy site without restoration of the mechanical axis.
. Pure translation at the osteotomy site without restoration of the mechanical axis.
. Translation that corrects the axis but introduces a leg length discrepancy.

Correct Answer & Explanation

. Angulation and translation at the osteotomy site with restoration of the mechanical axis.

Explanation

Paley's Osteotomy Rule 2 states that if the hinge is at the CORA and the osteotomy is at a different level, the correction will result in both angulation and translation at the osteotomy site, but the mechanical axis will be restored.

Question 118

Topic: Total Hip Arthroplasty (THA)

A patient has a congenital distal femoral valgus deformity (mLDFA = 75°). Over time, the proximal tibia develops a varus deformity (MPTA = 75°). The overall mechanical axis deviation (MAD) is currently 0 mm. What radiographic finding is most likely to be significantly abnormal in this patient?

. Mechanical Axis Deviation
. Joint Line Obliquity
. Leg Length Discrepancy
. Neck-Shaft Angle
. Lateral Distal Tibial Angle (LDTA)

Correct Answer & Explanation

. Joint Line Obliquity

Explanation

When adjacent bones have opposing deformities (femoral valgus and tibial varus) that cancel each other out, the overall MAD may be zero. However, this compensatory mechanism leads to an abnormal, non-horizontal knee joint line (joint line obliquity).

Question 119

Topic: Total Hip Arthroplasty (THA)

A 24-year-old male with a symptomatic tibial varus deformity is planned for correction using Paley's principles. Preoperative planning identifies a single Center of Rotation of Angulation (CORA) in the mid-diaphysis. If the surgeon decides to perform the osteotomy exactly at the CORA and places the axis of correction (hinge) exactly at the CORA, what is the anticipated radiographic and mechanical outcome based on Paley's Rule 1?

. The deformity corrects with an expected secondary translation of the bone ends.
. The angular deformity corrects purely without translation, resulting in collinear mechanical axes.
. The mechanical axes remain parallel but laterally translated.
. A significant leg length discrepancy will inevitably result.
. The mechanical axes will deviate by the exact angle of the original deformity.

Correct Answer & Explanation

. The angular deformity corrects purely without translation, resulting in collinear mechanical axes.

Explanation

According to Paley's Osteotomy Rule 1, placing both the osteotomy and the axis of correction (hinge) at the CORA results in pure angulation correction. This optimally realigns the proximal and distal mechanical axes without inducing unwanted translation.

Question 120

Topic: Total Hip Arthroplasty (THA)

A surgeon evaluating a varus knee notes an elevated Joint Line Convergence Angle (JLCA) of 6 degrees on standing AP radiographs. What does this finding primarily suggest?

. Bony diaphyseal deformity of the femur
. Ligamentous laxity or intra-articular cartilage loss
. Torsional malalignment of the tibia
. Normal anatomic variation
. Leg length discrepancy

Correct Answer & Explanation

. Ligamentous laxity or intra-articular cartilage loss

Explanation

The JLCA measures the convergence of the distal femoral and proximal tibial articular surfaces, which is normally 0-2 degrees. An increased JLCA indicates intra-articular deformity, asymmetrical cartilage loss, or collateral ligament laxity.

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