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1. General Principles & Basic Science MCQs

Practice Set 119 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 2361

Topic: 1. General Principles & Basic Science

During preoperative planning for a proximal tibial deformity, an orthopedic surgeon measures a mechanical posterior proximal tibial angle (mPPTA) of 68 degrees (normal 77-84 degrees). Which of the following clinical findings best corresponds to this measurement?

. Knee hyperextension (recurvatum)
. Knee flexion contracture with a posterior bony apex
. Proximal tibial procurvatum (apex anterior) with increased posterior slope
. Genu valgum
. Genu varum

Correct Answer & Explanation

. Proximal tibial procurvatum (apex anterior) with increased posterior slope

Explanation

A decreased mPPTA (68 degrees) means the posterior angle is smaller than normal, indicating the joint line is tilted posteriorly relative to the shaft. This equates to an apex anterior deformity (procurvatum) and an increased posterior tibial slope.

Question 2362

Topic: 1. General Principles & Basic Science

A surgeon applies Paley's Osteotomy Rule 2 to correct a distal femoral sagittal deformity. The CORA is at the knee joint line, but the osteotomy is performed 5 cm proximal in the metaphysis. If the hinge is maintained at the CORA, what is the radiographic result?

. Pure angular correction with no translation
. Angular correction combined with collinear translation to realign the axis
. Angular correction with the creation of a parallel shifted translation deformity
. Pure translation with no angular correction
. Lengthening of the limb by precisely the distance from the CORA

Correct Answer & Explanation

. Angular correction combined with collinear translation to realign the axis

Explanation

Paley's Rule 2 states that if the osteotomy is away from the CORA but the hinge is at the CORA, the correction will result in both angulation and translation. This combination restores collinearity to the mechanical axis.

Question 2363

Topic: 1. General Principles & Basic Science

Which of the following interventions is most appropriate for a 28-year-old patient with an isolated, symptomatic 15-degree bony recurvatum of the proximal tibia (mPPTA = 96 degrees) with a CORA located 4 cm distal to the joint line?

. Distal femoral anterior opening wedge osteotomy
. Distal femoral posterior opening wedge osteotomy
. Proximal tibial anterior opening wedge osteotomy
. Proximal tibial anterior closing wedge osteotomy
. Soft tissue posterior capsulorraphy

Correct Answer & Explanation

. Proximal tibial anterior opening wedge osteotomy

Explanation

The deformity is in the proximal tibia (recurvatum/apex posterior). To correct this (decrease the mPPTA and restore slope), an anterior opening wedge osteotomy or a posterior closing wedge osteotomy of the proximal tibia is required.

Question 2364

Topic: 1. General Principles & Basic Science

A 50-year-old patient requires a distal femoral osteotomy for a combined 10-degree valgus and 15-degree recurvatum deformity. The surgeon plans a single-cut oblique osteotomy. In which plane does the true deformity exist?

. Strictly in the coronal plane
. Strictly in the sagittal plane
. In an oblique plane determined by the vector sum of both deformities
. In the axial plane only
. Parallel to the joint line in all planes

Correct Answer & Explanation

. In an oblique plane determined by the vector sum of both deformities

Explanation

A multi-planar deformity (coronal and sagittal) is geometrically a single angular deformity occurring in an oblique plane. A single-cut osteotomy perpendicular to this oblique plane can correct both deformities simultaneously.

Question 2365

Topic: 1. General Principles & Basic Science
During evaluation of a sagittal knee deformity, you utilize radiographic imaging. According to Paley's principles, what is the defining radiographic landmark for the proximal mechanical axis of the femur in the sagittal plane?
. The anterior cortex of the proximal femur
. The posterior aspect of the greater trochanter
. The center of the femoral head
. The center of the lesser trochanter
. The intramedullary canal of the femoral diaphysis

Correct Answer & Explanation

. The center of the femoral head

Explanation

The mechanical axis of the femur in any plane (coronal or sagittal) is defined by a line connecting the center of the femoral head to the center of the knee joint.

Question 2366

Topic: 1. General Principles & Basic Science

A surgeon analyzes a femur with severe bowing. Drawing the proximal and distal anatomic axes does not intersect at the maximum point of clinical deformity. Instead, the bowing spans the entire diaphysis. How should this multi-apical sagittal deformity be analyzed using Paley's method?

. By drawing a single line connecting the hip and knee centers
. By drawing mid-diaphyseal lines to create multiple CORAs
. By relying solely on the mPDFA and ignoring the diaphysis
. By calculating the patellofemoral congruence angle
. By assuming the CORA is always at the metadiaphyseal junction

Correct Answer & Explanation

. By drawing mid-diaphyseal lines to create multiple CORAs

Explanation

For multi-apical or sweeping deformities (like a bowed femur), the bone is divided into proximal, middle, and distal segments. Intersecting the axes of these individual segments defines multiple CORAs required to plan a multi-level correction.

Question 2367

Topic: 1. General Principles & Basic Science

A 40-year-old patient presents with 25 degrees of knee recurvatum. Full-length standing lateral radiographs reveal a Mechanical Posterior Distal Femoral Angle (mPDFA) of 83° and a Mechanical Posterior Proximal Tibial Angle (mPPTA) of 68°. Which of the following is the primary source of the deformity?

. Distal femoral recurvatum
. Proximal tibial recurvatum
. Distal femoral procurvatum
. Proximal tibial procurvatum
. Posterior capsular laxity

Correct Answer & Explanation

. Proximal tibial recurvatum

Explanation

The normal mPPTA is 77°-84°. A decreased mPPTA (e.g., 68°) indicates that the posterior joint angle is diminished, resulting in an abnormal posterior slope and proximal tibial recurvatum.

Question 2368

Topic: 1. General Principles & Basic Science

A 35-year-old male presents with a chronic, painful left hip dislocation following a childhood septic arthritis, resulting in a severe Trendelenburg gait. He is being evaluated for a Pelvic Support Osteotomy (PSO). Which of the following statements best describes the primary biomechanical mechanism by which the PSO corrects the Trendelenburg gait?

. It creates a new anatomical acetabulum for the femoral head.
. It directly strengthens the gluteus medius and minimus muscles through tendon transfers.
. It establishes a stable, medialized bony fulcrum against the ischium, preventing hip adduction and tensioning the abductors.
. It lengthens the limb to reduce the lever arm of body weight on the hip.
. It fuses the hip joint in a functional position, eliminating motion.

Correct Answer & Explanation

. It establishes a stable, medialized bony fulcrum against the ischium, preventing hip adduction and tensioning the abductors.

Explanation

Correct Answer: CThe core rationale of the pelvic support osteotomy is to create a mechanical block that prevents hip adduction, thereby preventing the pelvis from dropping. This is achieved by surgically creating an extreme valgus deformity at the proximal femur, causing it to rest securely against the ischium. This provides a new, stable, and medialized fulcrum. Furthermore, this extreme valgus correction drives the greater trochanter distally and laterally, effectively tensioning the slack abductor muscles and restoring their resting length and mechanical advantage. Options A and E are incorrect as the PSO does not create a new anatomical acetabulum or fuse the hip. Option B is incorrect as it's a bony procedure, not a muscle transfer. Option D is incorrect; while limb lengthening can occur, the primary mechanism for Trendelenburg correction is the valgus osteotomy and abductor tensioning, not just length.

Question 2369

Topic: 1. General Principles & Basic Science

A 40-year-old patient is undergoing preoperative planning for a double-level Pelvic Support Osteotomy for a chronically dislocated hip. Clinical examination reveals a maximum passive hip adduction of 50 degrees. During a single-leg stance test, the patient exhibits a pelvic drop of 40 degrees.

Based on the provided image (specifically diagram 'd') and the case material, what is the calculated total valgus correction required at the proximal osteotomy site?

. 40 degrees
. 50 degrees
. 55 degrees
. 65 degrees
. 70 degrees

Correct Answer & Explanation

. 55 degrees

Explanation

Correct Answer: CThe case explicitly provides the formula for calculating the magnitude of valgus correction at the proximal osteotomy: 'Total Valgus Correction = (Single Leg Stance Pelvic Drop Angle) + 15° of Overcorrection.' Given a single-leg stance pelvic drop of 40 degrees, the calculation is 40° + 15° = 55°. This 15° of overcorrection is a crucial safety factor to ensure the hip remains mechanically locked. Diagram 'd' in the provided image visually demonstrates this exact calculation.

Question 2370

Topic: 1. General Principles & Basic Science

During the planning of the proximal osteotomy for a Pelvic Support Osteotomy, a surgeon identifies a fixed hip flexion deformity (FFD) of 10 degrees and notes the characteristic external rotation of the femur when maximally adducted. To achieve optimal biomechanical function and prevent compensatory issues, what multiplanar corrections are required at the proximal osteotomy site?

. Extend the femur by 10 degrees and externally rotate by 15 degrees.
. Extend the femur by 5 degrees and internally rotate to compensate for adduction-induced external torsion.
. Extend the femur by 15 degrees and internally rotate to compensate for adduction-induced external torsion.
. Flex the femur by 10 degrees and internally rotate by 15 degrees.
. No sagittal or axial plane corrections are typically needed at the proximal osteotomy.

Correct Answer & Explanation

. Extend the femur by 15 degrees and internally rotate to compensate for adduction-induced external torsion.

Explanation

Correct Answer: CThe case details the multiplanar corrections for the proximal osteotomy. For sagittal plane correction, it states: 'At the proximal osteotomy, the femur should be extended by the amount of the flexion deformity of the hipplus an additional 5° of extension.' Therefore, for a 10° FFD, the required extension is 10° + 5° = 15°. For axial plane correction, it notes: 'the surgeon needs to internally rotate the proximal osteotomy to compensate for this automatic external torsion' that occurs when the femur is maximally adducted. Option C correctly combines these two specific requirements.

Question 2371

Topic: 1. General Principles & Basic Science

A surgeon is meticulously planning a Pelvic Support Osteotomy. To accurately determine the ideal level for the proximal osteotomy, which specific radiograph is considered mandatory and provides the most crucial information?

. Full-length standing AP radiograph of both lower extremities.
. Single-leg standing radiograph of the affected limb.
. Supine AP pelvis in maximum adduction (cross-legged view).
. Lateral radiograph of the hip to assess fixed flexion deformity.
. CT scan with 3D reconstruction of the pelvis and proximal femur.

Correct Answer & Explanation

. Supine AP pelvis in maximum adduction (cross-legged view).

Explanation

Correct Answer: CThe case explicitly states under 'The Mandatory Radiographic Protocol': 'Supine AP Pelvis in Maximum Adduction (Cross-Legged View):This is the key radiograph for planning the proximal osteotomy. It demonstrates the precise relationship between the proximal femur and the ischial tuberosity at the absolute limit of adduction.' It further explains that a horizontal line connecting the inferior margins of both ischial tuberosities, where the medial cortex of the adducted femur crosses it, defines the ideal level for the proximal osteotomy. While other radiographs are important for overall planning, the cross-legged view is critical for determining the proximal osteotomy level.

Question 2372

Topic: 1. General Principles & Basic Science

During planning for the distal osteotomy of a double-level Pelvic Support Osteotomy, the calculated Center of Rotation of Angulation (CORA) is found to be in the proximal diaphysis, which is deemed suboptimal for external fixator application and regenerate formation. The surgeon decides to perform the distal osteotomy more distally, in the mid-diaphysis. According to Paley Osteotomy Rule 2, what additional maneuver is required to maintain mechanical axis alignment?

. No additional maneuver is needed, as angular correction alone will suffice.
. The proximal segment must be translated laterally by one half-shaft thickness.
. The distal segment must be translated medially by approximately one half-shaft thickness.
. An additional osteotomy must be performed at the CORA.
. The varus angulation must be increased by 15 degrees.

Correct Answer & Explanation

. The distal segment must be translated medially by approximately one half-shaft thickness.

Explanation

Correct Answer: CThe case describes Paley Osteotomy Rule 2: 'If an osteotomy is performedaway fromthe CORA, pure angular correction will cause a parallel shift (translation) of the mechanical axis. To prevent this, a corrective translation must be built into the osteotomy plan.' It then specifies for the distal osteotomy: 'In this scenario, the distal segment should be displaced approximately one half-shaft thickness medially, together with the required varus angulation, to ensure the mechanical axis remains perfectly aligned.' Therefore, translating the distal segment medially is the correct maneuver.

Question 2373

Topic: Physiology & Rehabilitation

Following a successful double-level Pelvic Support Osteotomy, a patient is undergoing rehabilitation. Which of the following kinematic changes would be an expected and desirable outcome of the procedure?

. Increased hip adduction range of motion.
. Persistent lumbar hyperlordosis.
. Decreased functional hip abduction range of motion.
. Elimination of the Trendelenburg gait and correction of lumbar hyperlordosis.
. Increased hip flexion range of motion.

Correct Answer & Explanation

. Elimination of the Trendelenburg gait and correction of lumbar hyperlordosis.

Explanation

Correct Answer: DThe case outlines the 'Expected Kinematic Changes Post-Reconstruction.' It states that a correctly executed double-level PSO 'Eliminates the Trendelenburg gait entirely' and 'Corrects lumbar hyperlordosis by eliminating the fixed flexion deformity of the hip.' Regarding range of motion, it notes that 'functional hip abduction range is significantly increased, while the adduction range is decreased' and 'hip flexion is slightly decreased, while hip extension is functionally increased.' Therefore, options A, B, C, and E describe outcomes that are either incorrect or undesirable.

Question 2374

Topic: 1. General Principles & Basic Science

A surgeon performs a proximal femoral osteotomy for a hip deformity. Postoperatively, a full-length standing radiograph reveals that the Proximal Mechanical Axis (PMA) and the Distal Mechanical Axis (DMA) are parallel to each other but are not collinear, resulting in a persistent Mechanical Axis Deviation (MAD). Which of Paley's Osteotomy Rules was most likely violated to produce this outcome?

. Rule One: The Ideal Correction (Collinear Restoration)
. Rule Two: Correction with Intentional Translation
. Rule Three: The Common Pitfall (Iatrogenic Deformity)
. The Malalignment Test (MAT) principle
. The Reverse Planning Method

Correct Answer & Explanation

. Rule Three: The Common Pitfall (Iatrogenic Deformity)

Explanation

Correct Answer: CThe case describes 'Rule Three: The Common Pitfall (Iatrogenic Deformity)' as occurring when 'The osteotomy and the hinge of correction (ACA) areboth placed at a location different from the CORA.' The result is that 'The angular deformity mayappearvisually corrected on the operating table, but anunplanned, iatrogenic translationis created. The PMA and DMA become parallel but arenotcollinear. This leaves the patient with a persistent Mechanical Axis Deviation (MAD).' This perfectly matches the scenario described in the question. Rule One describes ideal correction with no translation, and Rule Two describes intentional translation to achieve collinearity when the osteotomy is not at the CORA but the hinge is. The MAT and Reverse Planning Method are diagnostic and planning tools, not osteotomy rules.

Question 2375

Topic: 1. General Principles & Basic Science

A 12-year-old patient with a history of rickets presents with a complex multiapical deformity involving a proximal femoral varus, a distal femoral valgus, and a proximal tibial varus in the same limb. The surgeon is meticulously planning the correction using Paley's principles. What is the recommended sequence for planning the correction of these multiple deformities?

. Address the most proximal deformity (proximal femoral varus) first, then move distally.
. Address the largest magnitude deformity first, regardless of its location.
. Utilize a 'Reverse Planning Method,' starting from the distal normal anatomy (ankle) and working proximally to the hip.
. Correct all deformities simultaneously using a multi-level osteotomy with a single external fixator.
. Prioritize correction of the deformity causing the most pain or functional limitation.

Correct Answer & Explanation

. Utilize a 'Reverse Planning Method,' starting from the distal normal anatomy (ankle) and working proximally to the hip.

Explanation

Correct Answer: CThe case explicitly states that for multiapical deformities, 'Surgeons often use a"Reverse Planning Method"—starting from the distal normal anatomy (e.g., the ankle), working proximally, and ensuring each individual bone segment is corrected to restore its normal joint orientation angle before moving to the next segment, culminating at the hip.' This systematic approach ensures that each segment is corrected relative to the segment distal to it, ultimately restoring the overall mechanical axis from the ground up. Options A, B, D, and E do not align with the systematic, mathematical approach advocated by Paley for multiapical deformities.

Question 2376

Topic: 1. General Principles & Basic Science

A surgeon is preparing to plan a complex hip deformity correction for a 25-year-old patient. According to Paley's step-by-step guide for preoperative planning, what is the absolute non-negotiable first step in the radiographic planning process, after obtaining standardized radiographs?

. Draw the Proximal Mechanical Axis (PMA).
. Locate the Center of Rotation of Angulation (CORA).
. Establish the Pelvic Horizontal Line.
. Measure the Lateral Proximal Femoral Angle (LPFA).
. Evaluate for multiapical deformities by measuring mLDFA and MPTA.

Correct Answer & Explanation

. Establish the Pelvic Horizontal Line.

Explanation

Correct Answer: CThe case explicitly states under 'A Step-by-Step Guide to Preoperative Planning' that after obtaining standardized radiographs, the next step is to 'Establish the Pelvic Horizontal Line: Draw the reference line on your digital AP radiograph using the inferior SI joints or sacral foramina. This is your unshakeable foundation.' The section 'The Non-Negotiable First Step: Establishing the Pelvic Reference Line' further emphasizes its foundational importance, stating 'Before any femoral axis can be drawn, before any deformity can be accurately measured, and certainly before any bone is cut, a true horizontal reference must be established.' All other options are subsequent steps that rely on this initial foundation.

Question 2377

Topic: 1. General Principles & Basic Science

A surgeon is planning a proximal femoral osteotomy for a patient with a hip deformity. Due to poor bone quality at the precise location of the CORA, the osteotomy is performed 2 cm distal to the CORA. However, the external fixator hinge (Axis of Correction of Angulation - ACA) is meticulously placed exactly at the CORA. According to Paley's Osteotomy Rules, what is the expected outcome of this planned correction?

. An iatrogenic translational deformity will be created, with the PMA and DMA becoming parallel but not collinear.
. The angular deformity will be perfectly corrected, and the PMA and DMA will become perfectly collinear without any translation of the bone fragments.
. The angular deformity will be perfectly corrected, and the PMA and DMA will become perfectly collinear, but this will require an intentional, mathematically planned translation of the bone fragments at the osteotomy site.
. The angular deformity will persist, and the mechanical axis will remain deviated.
. A 'dog-leg' deformity will inevitably result, requiring further corrective surgery.

Correct Answer & Explanation

. The angular deformity will be perfectly corrected, and the PMA and DMA will become perfectly collinear, but this will require an intentional, mathematically planned translation of the bone fragments at the osteotomy site.

Explanation

Correct Answer: CThis scenario perfectly describes 'Rule Two: Correction with Intentional Translation.' The case states its condition as: 'The osteotomy is performed at a leveldifferent from the CORA(often due to poor bone quality at the CORA, the presence of hardware, or soft tissue constraints), but the hinge for correction (ACA) is still placedexactly at the CORA.' The result is: 'The angular deformity is corrected, and the mechanical axis is successfully restored (PMA and DMA become collinear). However, achieving this requires anintentional, mathematically planned translation(displacement) of the bone fragments at the osteotomy site.' This technique is useful when the ideal osteotomy site is surgically inaccessible. Option A and E describe the outcome of Rule Three (iatrogenic deformity). Option B describes Rule One (ideal correction at CORA). Option D is incorrect as the angular deformity is corrected.

Question 2378

Topic: Physiology & Rehabilitation

In a Paley double-level pelvic support osteotomy (PSO), what is the primary biomechanical rationale for incorporating the second, more distal osteotomy?

. Correcting residual Trendelenburg gait by tensioning the abductors
. Compensating for the extreme valgus mechanical axis deviation at the knee
. Improving a residual hip flexion contracture
. Providing a proximal fulcrum against the ilium
. Restoring the true anatomic center of rotation of the native hip

Correct Answer & Explanation

. Compensating for the extreme valgus mechanical axis deviation at the knee

Explanation

The proximal valgus osteotomy creates pelvic support but severely shifts the mechanical axis laterally, causing valgus overload at the knee. The distal varus osteotomy realigns the mechanical axis and allows for simultaneous limb lengthening.

Question 2379

Topic: 1. General Principles & Basic Science

According to Paley's principles of pelvic support osteotomy, at what precise anatomic level should the proximal valgus-extension osteotomy be performed to optimize pelvic support?

. At the level of the lesser trochanter
. At the intersection of the mechanical axis and the anatomic axis of the femur
. At the level of the ischial tuberosity with the hip in maximum adduction
. 5 cm distal to the tip of the greater trochanter
. At the center of rotation of angulation (CORA) of the mechanical axis

Correct Answer & Explanation

. At the level of the ischial tuberosity with the hip in maximum adduction

Explanation

The proximal osteotomy is performed at the level of the ischial tuberosity while the femur is maximally adducted. This creates a functional bony fulcrum against the pelvis, substituting for an incompetent abductor mechanism.

Question 2380

Topic: Physiology & Rehabilitation

A 12-year-old with untreated developmental dysplasia of the hip presents with a high dislocation and severe limp. If a pelvic support osteotomy is planned, what specific preoperative radiographic measurement determines the exact magnitude of valgus correction required at the proximal osteotomy?

. Neck-shaft angle of the dislocated proximal femur
. Center-edge angle of Wiberg
. Maximum passive adduction angle of the femur on AP pelvis radiograph
. Mechanical lateral distal femoral angle (mLDFA)
. Acetabular index

Correct Answer & Explanation

. Maximum passive adduction angle of the femur on AP pelvis radiograph

Explanation

The required degree of valgus is calculated by taking the maximum adduction angle of the femur and adding an overcorrection (typically 15 degrees). This ensures the newly created proximal femoral angle maintains contact with the ischium during stance phase.

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