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Total Hip Arthroplasty (THA) MCQs

Practice Set 5 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 81

Topic: Total Hip Arthroplasty (THA)

A surgeon is performing a complex femoral deformity correction. Due to an error in preoperative planning and intraoperative execution, both the osteotomy and the corrective hinge of the external fixator are inadvertently placed away from the identified CORA. According to Paley's Osteotomy Rules, what is the most likely geometric outcome of this surgical error?

. Pure angulation will occur without any translation, resulting in a perfectly straight bone.
. The mechanical axes will become collinear, but significant translation will occur at the osteotomy site.
. A secondary iatrogenic deformity will be created, where the mechanical axes are parallel but not collinear, resulting in persistent translational deformity.
. The bone will be over-lengthened, leading to a significant leg length discrepancy.
. The osteotomy will fail to unite due to biomechanical instability.

Correct Answer & Explanation

. A secondary iatrogenic deformity will be created, where the mechanical axes are parallel but not collinear, resulting in persistent translational deformity.

Explanation

Correct Answer: CThis scenario directly describes Paley's Osteotomy Rule Three: 'When both the osteotomy and the corrective hinge are located away from the CORA, a secondary iatrogenic deformity is created. The mechanical axes will become parallel but willnotbe collinear. This results in a persistent, unsightly translational deformity.'Option A is incorrectbecause pure angulation without translation occurs only when both osteotomy and hinge are at the CORA (Rule One).Option B is incorrectbecause collinear axes with translation occur when the hinge is at the CORA but the osteotomy is away (Rule Two).Option D is incorrectbecause Rule Three describes an angular and translational deformity, not primarily a lengthening error, although length can be affected.Option E is incorrectbecause Rule Three describes the geometric outcome of the correction, not necessarily a failure of union, although malalignment can contribute to nonunion.

Question 82

Topic: Total Hip Arthroplasty (THA)

A 50-year-old patient presents with a long-standing knee flexion deformity. During gait analysis, it is noted that the patient exhibits a significant functional leg length discrepancy, with the pelvis dropping on the affected side during stance. This finding is most consistent with which of the following?

. A mild knee flexion deformity (5-15 degrees) with effective ankle dorsiflexion.
. A primary ankle equinus deformity without knee involvement.
. A severe knee flexion deformity (>20 degrees) overwhelming distal compensation.
. A fixed hip flexion contracture as the primary pathology.
. A posterior shift of the Ground Reaction Vector (GRV) anterior to the knee.

Correct Answer & Explanation

. A severe knee flexion deformity (>20 degrees) overwhelming distal compensation.

Explanation

Correct Answer: CThe case states that when the FFD exceeds 20-25°, the body's ability to compensate distally is overwhelmed. This leads to a rapid cascade of more severe gait abnormalities, including afunctional leg length discrepancy. The flexed posture functionally shortens the limb's vertical height, causing the pelvis to drop on the affected side during stance, leading to a shortened step length on the contralateral side and a noticeable limp. This is a hallmark of severe, uncompensated FFD.Option A is incorrect. Mild FFDs are typically compensated by ankle dorsiflexion and hip flexion/trunk lean, and while they cause some gait changes, a significant functional leg length discrepancy with pelvic drop is characteristic of more severe deformities.Option B is incorrect. While an ankle equinus deformity can contribute to gait issues, the question specifically points to a knee flexion deformity causing the functional leg length discrepancy and pelvic drop.Option D is incorrect. While a fixed hip flexion contracture can cause a functional leg length discrepancy, the question specifies akneeflexion deformity as the primary issue leading to this gait pattern.Option E is incorrect. In FFD, the GRV shiftsposteriorto the knee, creating a flexion moment, not anterior.

Question 83

Topic: Total Hip Arthroplasty (THA)

A surgeon corrects a proximal tibial procurvatum deformity. Both the osteotomy and the hinge are inadvertently placed 3 cm distal to the true CORA. According to Paley's Rule 3, what is the mechanical consequence of this execution?

. Pure angulation with collinear mechanical axes
. Overcorrection of the joint line orientation
. The proximal and distal mechanical axes will be parallel but translated
. An apex posterior secondary deformity will be induced
. The osteotomy will result in a leg length discrepancy but perfect alignment

Correct Answer & Explanation

. The proximal and distal mechanical axes will be parallel but translated

Explanation

Paley's Rule 3 dictates that if both the osteotomy and the hinge are located away from the CORA, the resulting mechanical axes will be parallel to each other but translated, creating a secondary translation deformity.

Question 84

Topic: Total Hip Arthroplasty (THA)

When planning an anterior closing wedge osteotomy of the distal femur to correct a symptomatic procurvatum deformity, the surgeon must counsel the patient on which inherent consequence of this specific osteotomy technique?

. Limb lengthening
. Limb shortening
. Increased patellofemoral tracking instability
. Obligatory posterior translation of the mechanical axis
. Iatrogenic patella alta

Correct Answer & Explanation

. Limb shortening

Explanation

A closing wedge osteotomy removes a segment of bone, inherently resulting in some degree of limb shortening. This must be factored into preoperative planning, especially if a leg length discrepancy already exists.

Question 85

Topic: Total Hip Arthroplasty (THA)

The right panel of the provided image shows the final radiograph of the patient after fixator removal and bony consolidation following a proximal femoral osteotomy for a severe adduction deformity. What key biomechanical outcome is demonstrated in this final radiograph, indicating successful correction according to Paley's principles?

. Persistent pelvic obliquity and an apparent leg length discrepancy.
. Creation of an iatrogenic translational deformity (MAD).
. A perfectly level pelvis and a straight, collinear mechanical axis.
. Increased varus malalignment of the proximal femur.
. A significant increase in true leg length discrepancy.

Correct Answer & Explanation

. A perfectly level pelvis and a straight, collinear mechanical axis.

Explanation

Correct Answer: CThe caption for the image explicitly states that the 'Right Panel: The final radiograph after fixator removal and bony consolidation shows a perfectly level pelvis and a straight, collinear mechanical axis, demonstrating the successful restoration of overall limb alignment and functional leg length.' This directly reflects the ultimate goal of Paley's deformity correction system, where the PMA and DMA become perfectly collinear and perpendicular to a level pelvic horizontal line. Options A, B, D, and E describe outcomes of failed or incomplete correction, which are clearly contradicted by the image and its description.

Question 86

Topic: Total Hip Arthroplasty (THA)

A 40-year-old patient presents with a proximal femoral deformity where the CORA is located deep within the femoral neck, an anatomically challenging and potentially avascular region. The surgeon decides to perform the osteotomy at a more practical and healthy level in the intertrochanteric region, while ensuring the axis of correction (hinge) still passes through the original CORA. Which of Paley's osteotomy rules is being applied, and what is its primary implication?

. Rule 1; it will result in pure angular correction with zero translation.
. Rule 3; it will create an unintentional secondary translation deformity.
. Rule 2; it will result in a calculated, necessary translation simultaneously with the angular correction.
. Rule 1; it is a planning error and should be avoided.
. Rule 2; it will only correct the leg length discrepancy, not the angulation.

Correct Answer & Explanation

. Rule 2; it will result in a calculated, necessary translation simultaneously with the angular correction.

Explanation

Correct Answer: CThis scenario perfectly describes Paley's Osteotomy Rule 2: 'The osteotomy is at a different level than the CORA, but the axis of correction (hinge) still passes through the CORA.' The text states this is 'a highly powerful and frequently used technique in the hip' when the CORA is in an inaccessible or undesirable location. The primary implication is that 'the bone ends will undergo a calculated, necessary translation simultaneously with the angular correction. This translation is vital to perfectly realign the mechanical axis.'Option A is incorrectbecause Rule 1 applies when both the osteotomy and the hinge pass through the CORA, resulting in pure angular correction without translation.Option B is incorrectbecause Rule 3 describes a planning error where both the osteotomy and the hinge are away from the CORA, leading to unintentional translation.Option D is incorrectbecause Rule 1 is the ideal scenario for pure angular correction, not a planning error. The scenario described is Rule 2.Option E is incorrectbecause Rule 2 is designed for both angular and calculated translational correction to realign the mechanical axis, not solely for leg length discrepancy.

Question 87

Topic: Total Hip Arthroplasty (THA)

According to the Paley multiplier method for predicting leg length discrepancy at skeletal maturity, which combination of variables is utilized to derive the correct multiplier?

. Current chronological age and height
. Bone age determined by Greulich and Pyle atlas and gender
. Chronological age and gender
. Current length of the normal limb and gender
. The exact etiology of the limb length discrepancy and age

Correct Answer & Explanation

. Chronological age and gender

Explanation

The Paley multiplier method relies on multiplying the current measurement by a coefficient that is specific to the patient's chronological age and gender. It rarely requires bone age calculations unless the child has an overtly abnormal skeletal growth syndrome.

Question 88

Topic: Total Hip Arthroplasty (THA)

A 24-year-old male is undergoing an Ilizarov hip reconstruction (double-level pelvic support osteotomy). What is the primary biomechanical purpose of the distal osteotomy in this procedure?

. To provide a fulcrum against the obturator foramen.
. To induce valgus to compensate for leg length discrepancy.
. To correct the lateral mechanical axis deviation and allow for limb lengthening.
. To correct persistent hip flexion contractures.
. To distalize the greater trochanter to restore abductor tension.

Correct Answer & Explanation

. To correct the lateral mechanical axis deviation and allow for limb lengthening.

Explanation

The proximal valgus osteotomy shifts the mechanical axis laterally, creating a significant lateral mechanical axis deviation (MAD). The distal varus osteotomy realigns the mechanical axis and serves as the site for lengthening to correct the limb length discrepancy.

Question 89

Topic: Total Hip Arthroplasty (THA)

Following a successful proximal valgus-extension osteotomy in an Ilizarov hip reconstruction, the surgeon must now plan the distal osteotomy. What are the two vital functions of this distal varus-lengthening osteotomy?

. A. To provide the critical buttress against the ischium and tension the slackened abductor musculature.
. B. To acutely correct the hip flexion contracture and eliminate compensatory lumbar lordosis.
. C. To act as the 're-centering' osteotomy to correct lateral Mechanical Axis Deviation (MAD) and serve as the site for gradual distraction osteogenesis to correct leg length discrepancy.
. D. To fuse the hip joint, providing definitive stability and pain relief.
. E. To prevent patellar instability and restore the Joint Line Congruency Angle (JLCA) to 0 degrees without affecting limb length.

Correct Answer & Explanation

. C. To act as the 're-centering' osteotomy to correct lateral Mechanical Axis Deviation (MAD) and serve as the site for gradual distraction osteogenesis to correct leg length discrepancy.

Explanation

Correct Answer: CThe case clearly outlines the functions of the distal osteotomy: 'A Distal Varus-Lengthening Osteotomy: This serves two vital functions. First, it acts as the 're-centering' osteotomy, correcting the lateral MAD created by the proximal cut and restoring a normal mLDFA. Second, it serves as the site for gradual distraction osteogenesis to correct the leg length discrepancy.'Option A is incorrectas these are the functions of theproximalvalgus-extension osteotomy.Option B is incorrectas these are also functions of theproximalextension osteotomy.Option D is incorrectas the modern standard of care aims to preserve a functional, mobile hip joint, not to fuse it.Option E is incorrectbecause while it helps prevent knee pathology, its primary functions are MAD correction and LLD correction, and it does affect limb length.

Question 90

Topic: Total Hip Arthroplasty (THA)

A newborn is noted to have a significant posteromedial bowing of the left tibia and a calcaneovalgus positioning of the left foot. What is the most expected natural history of this condition?

. Progressive angular deformity leading to pseudoarthrosis
. Spontaneous resolution of the angular deformity with progressive leg length discrepancy
. Development of anterolateral bowing by age 2
. Spontaneous resolution of both the bowing and leg length discrepancy
. High risk of associated neurofibromatosis type 1

Correct Answer & Explanation

. Spontaneous resolution of the angular deformity with progressive leg length discrepancy

Explanation

Posteromedial bowing of the tibia typically undergoes spontaneous remodeling and improvement of the angular deformity, but it invariably leaves the patient with a residual leg length discrepancy that requires monitoring.

Question 91

Topic: Total Hip Arthroplasty (THA)

A 6-year-old girl has a leg length discrepancy (LLD) secondary to a malunited femur fracture. Using the Paley multiplier method, how is the predicted LLD at skeletal maturity most accurately calculated?

. Current LLD divided by the chronologic age multiplier
. Current LLD multiplied by the skeletal age multiplier
. Current length of the normal limb multiplied by the chronologic age multiplier
. Predicted mature length of the normal limb minus the current LLD
. Current LLD multiplied by a gender-specific constant

Correct Answer & Explanation

. Current LLD multiplied by the skeletal age multiplier

Explanation

The Paley multiplier method predicts LLD at maturity by multiplying the current LLD by an age- and gender-specific multiplier. Skeletal age should be used if it deviates significantly from chronologic age.

Question 92

Topic: Total Hip Arthroplasty (THA)

A 6-year-old girl has a congenital short femur with a current leg length discrepancy (LLD) of 3 cm. Using the Paley multiplier method, how is the predicted LLD at skeletal maturity most accurately calculated?

. By multiplying the current LLD by the age- and gender-specific multiplier.
. By adding 1 cm for each year of remaining skeletal growth.
. By multiplying the normal femur length by the multiplier and subtracting the short femur length.
. By comparing her current percentile on the Green-Anderson charts and extrapolating to age 16.
. By dividing the current LLD by the mother's height multiplier.

Correct Answer & Explanation

. By multiplying the current LLD by the age- and gender-specific multiplier.

Explanation

The Paley multiplier method simplifies the prediction of LLD at skeletal maturity by multiplying the patient's current LLD by an established, gender- and age-specific constant. This method has been shown to be highly accurate and does not require complex bone age calculations or growth chart plotting.

Question 93

Topic: Total Hip Arthroplasty (THA)

A 50-year-old female with severe lateral compartment knee osteoarthritis and a 12-degree valgus deformity requires a distal femoral osteotomy (DFO). She also has a 1.5 cm ipsilateral leg length discrepancy (the affected leg is shorter). Which osteotomy technique is most appropriate to correct both issues simultaneously?

. Medial closing wedge DFO
. Lateral opening wedge DFO
. Medial opening wedge DFO
. Lateral closing wedge DFO
. Dome DFO

Correct Answer & Explanation

. Medial opening wedge DFO

Explanation

A medial opening wedge DFO corrects valgus deformity and simultaneously lengthens the limb, addressing her leg length discrepancy. A lateral closing wedge DFO would correct the valgus but further shorten the already deficient limb.

Question 94

Topic: Total Hip Arthroplasty (THA)

A 50-year-old female presents with severe medial compartment knee osteoarthritis and a varus deformity. Standing radiographs reveal a mechanical axis deviation (MAD) of 45 mm medial to the knee center and a joint line convergence angle (JLCA) of 7 degrees opening laterally. What does this abnormal JLCA primarily indicate in this clinical context?

. An extra-articular tibial diaphyseal deformity
. An extra-articular femoral diaphyseal deformity
. An intra-articular deformity or collateral ligament laxity
. A combined rotational and sagittal malalignment
. A functional leg length discrepancy

Correct Answer & Explanation

. An intra-articular deformity or collateral ligament laxity

Explanation

The Joint Line Convergence Angle (JLCA) normally measures 0-2 degrees. An increased JLCA indicates intra-articular pathology, such as asymmetric cartilage loss (osteoarthritis) or collateral ligament laxity.

Question 95

Topic: Total Hip Arthroplasty (THA)

A 45-year-old patient requires a distal femoral osteotomy for a severe procurvatum deformity. According to Paley's osteotomy rules, if the osteotomy and the hinge are both placed exactly at the Center of Rotation of Angulation (CORA), what is the resultant biomechanical effect?

. Correction of angulation with secondary translation
. Correction of angulation without translation
. Pure translation without angular correction
. Paradoxical worsening of the mechanical axis deviation
. Correction of angulation with an iatrogenic leg length discrepancy

Correct Answer & Explanation

. Correction of angulation without translation

Explanation

According to Paley's Osteotomy Rule 1, when the osteotomy and the hinge are both located at the CORA, angular correction is achieved without any translation. This maintains the collinearity of the proximal and distal mechanical axes.

Question 96

Topic: Total Hip Arthroplasty (THA)

A 28-year-old patient with a large, multiplanar angular deformity of the tibia requires correction while preserving limb length and maximizing bony contact for rapid healing. The surgeon opts for a focal dome osteotomy, as depicted in the intraoperative fluoroscopy image below. What is the primary advantage of this specific osteotomy design in this clinical scenario?

. It allows for significant limb lengthening, addressing concomitant leg length discrepancy.
. It creates broad cortical-to-cortical contact, promoting rapid primary bone healing without graft.
. It simplifies the surgical technique, requiring minimal specialized instrumentation.
. It inherently shortens the limb, which is beneficial for overgrowth deformities.
. It eliminates the need for any internal or external fixation post-correction.

Correct Answer & Explanation

. It creates broad cortical-to-cortical contact, promoting rapid primary bone healing without graft.

Explanation

Correct Answer: BThe focal dome osteotomy is an advanced technique characterized by a cylindrical, semi-circular cut made along the arc of a circle centered at the CORA. As seen in the image, the cut surfaces are curved, allowing the bone fragments to slide and rotate against each other during correction while maintaining maximum, continuous cortical contact. This unique geometric property provides extraordinary intrinsic stability and promotes rapid osseous union, often without the need for bone graft. It is particularly advantageous for large angular corrections where preserving limb length and maximizing bony contact are critical.Option A is incorrect. The focal dome osteotomy is designed to correct angular deformitywithoutaltering limb length, unlike an opening wedge osteotomy which lengthens.Option C is incorrect. Focal dome osteotomies are technically demanding and often require specialized guides and drill bits, making them more complex than simple transverse cuts.Option D is incorrect. The focal dome osteotomy preserves limb length, it does not inherently shorten it. Closing wedge osteotomies shorten the limb.Option E is incorrect. While it provides intrinsic stability, fixation (internal or external) is still required to hold the correction and allow for healing.

Question 97

Topic: Total Hip Arthroplasty (THA)

A 48-year-old patient presents with a significant genu varum deformity and a concomitant 1.5 cm leg length discrepancy (LLD) in the affected limb. The deformity is localized to the proximal tibia. The surgeon's primary goal is to correct the varus and simultaneously address the LLD. Which osteotomy design is most appropriate for this patient?

. A closing wedge osteotomy of the proximal tibia.
. A focal dome osteotomy of the proximal tibia.
. An opening wedge osteotomy of the proximal tibia.
. A transverse osteotomy with acute shortening.
. A bi-level osteotomy involving both femur and tibia.

Correct Answer & Explanation

. An opening wedge osteotomy of the proximal tibia.

Explanation

Correct Answer: CThe patient has a varus deformity and a concomitant leg length discrepancy (LLD) where the affected limb is shorter. An opening wedge osteotomy is performed by making a single transverse or oblique cut and opening a gap on the concave side of the deformity. A key advantage of this technique is that itlengthens the limb, which is highly beneficial for patients with a pre-existing LLD. While it requires bone graft and has a longer consolidation time, it directly addresses both the angular deformity and the length discrepancy.Option A is incorrect. A closing wedge osteotomy inherentlyshortensthe limb, which would exacerbate the existing LLD.Option B is incorrect. A focal dome osteotomy corrects angular deformitywithoutaltering limb length, so it would not address the LLD.Option D is incorrect. A transverse osteotomy with acute shortening would worsen the LLD.Option E is incorrect. While bi-level osteotomies exist, the deformity is localized to the proximal tibia, and the question asks for the most appropriateosteotomy designfor the given goals, not necessarily the number of osteotomies. An opening wedge at the tibia can address both issues.

Question 98

Topic: Total Hip Arthroplasty (THA)

A patient requires correction of a diaphyseal tibial deformity. Preoperative planning identifies the Center of Rotation of Angulation (CORA). The surgeon performs the osteotomy exactly at the CORA and places the hinge axis at the CORA. According to Paley's osteotomy rules, what is the expected biomechanical outcome?

. Collinear realignment of the mechanical axes with no translation at the osteotomy site.
. Collinear realignment of the mechanical axes with intentional translation at the osteotomy site.
. Parallel alignment of the mechanical axes resulting in a zig-zag deformity.
. Incomplete angular correction due to hinge constraint.
. Creation of an iatrogenic leg length discrepancy without angular correction.

Correct Answer & Explanation

. Collinear realignment of the mechanical axes with no translation at the osteotomy site.

Explanation

According to Paley's Osteotomy Rule 1, placing both the osteotomy and the hinge axis at the CORA results in collinear realignment of the proximal and distal mechanical axes without translation. This is the ideal scenario for perfect anatomic restoration.

Question 99

Topic: Total Hip Arthroplasty (THA)

A junior resident plans a proximal tibial osteotomy for a varus deformity. By mistake, both the osteotomy and the center of the hinge are placed 5 cm proximal to the true CORA. According to Paley's principles, what is the geometric consequence of this technical error?

. Anatomic collinear correction of the mechanical axes.
. Collinear mechanical axes with translation at the osteotomy site.
. Parallel mechanical axes with an induced translation (zig-zag deformity).
. Overcorrection into valgus with joint line obliquity.
. Pure leg length discrepancy without angular change.

Correct Answer & Explanation

. Parallel mechanical axes with an induced translation (zig-zag deformity).

Explanation

Paley's Osteotomy Rule 3 states that if the hinge and osteotomy are placed at a level other than the CORA, the mechanical axes will become parallel rather than collinear. This induces a translation and creates a zig-zag deformity.

Question 100

Topic: Total Hip Arthroplasty (THA)

A patient presents with a multi-apical tibial deformity demonstrating two distinct CORAs. If the surgeon decides to correct the entire deformity using a single osteotomy at the proximal CORA, what compensatory action must be incorporated to achieve a collinear mechanical axis?

. Pure angular correction at the proximal CORA.
. Translation at the single osteotomy site.
. Overcorrection of the valgus angulation by 15 degrees.
. Placement of the ACA at the distal CORA.
. Creation of an intentional leg length discrepancy.

Correct Answer & Explanation

. Translation at the single osteotomy site.

Explanation

When a multi-apical deformity is corrected with a single osteotomy located at one of the CORAs, angular correction alone will leave a translation deformity. Translation must be purposefully added at the osteotomy site to restore collinearity of the overall mechanical axis.

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