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1. General Principles & Basic Science MCQs

Practice Set 120 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 2381

Topic: 1. General Principles & Basic Science

When planning deformity correction using the Paley CORA method, what happens if an osteotomy is performed at a level different from the CORA but correction of angulation is achieved around a hinge placed exactly at the CORA?

. The bone ends will perfectly appose with no translation
. The axis will remain permanently under-corrected
. The bone ends will undergo obligatory translation relative to each other
. The correction will necessitate an opening wedge technique only
. The mechanical axis will be shifted parallel to its original pathological path

Correct Answer & Explanation

. The bone ends will undergo obligatory translation relative to each other

Explanation

According to Paley's Osteotomy Rule 2, if the osteotomy is made away from the CORA but the hinge remains at the CORA, obligatory translation of the bone ends occurs during angular correction. This principle is often utilized to simultaneously correct translational deformities.

Question 2382

Topic: 1. General Principles & Basic Science

During a Paley double-level pelvic support osteotomy, the proximal osteotomy frequently incorporates both a valgus and an extension component. What is the primary purpose of adding the extension component?

. To compensate for an established fixed hip flexion contracture
. To prevent anterior subluxation of the distal femur
. To improve knee extension strength during swing phase
. To tension the anterior joint capsule and iliofemoral ligament
. To facilitate placement of the half-pins for the external fixator

Correct Answer & Explanation

. To compensate for an established fixed hip flexion contracture

Explanation

Chronically dislocated hips almost universally develop fixed flexion contractures. Adding an extension component to the proximal osteotomy simultaneously corrects this deformity and restores upright sagittal balance.

Question 2383

Topic: Biology, Genetics & Bone Healing

In distraction osteogenesis utilized during the distal osteotomy of a Paley PSO, what is the ideal latency period before initiating distraction in a healthy adult patient?

. 0-1 days
. 2-3 days
. 7-10 days
. 14-21 days
. 28 days

Correct Answer & Explanation

. 7-10 days

Explanation

A latency period of 7-10 days is optimal in adults. This duration allows the critical early phases of fracture healing (hematoma organization and initial soft callus formation) to establish a biologic environment robust enough to sustain distraction osteogenesis.

Question 2384

Topic: 1. General Principles & Basic Science

In planning lower extremity deformity correction, a surgeon maps two separate CORAs in the same plane on a malunited femur. If a single osteotomy is selected to correct both deformities simultaneously, what will be the inevitable geometric consequence?

. Creation of an iatrogenic limb length discrepancy
. Obligatory translation at the osteotomy site
. Rotational malalignment of the distal segment
. Joint line obliquity at the knee
. Premature consolidation of the osteotomy

Correct Answer & Explanation

. Obligatory translation at the osteotomy site

Explanation

When a bone has a multi-apical deformity (multiple CORAs) but is corrected with only a single osteotomy, obligatory translation must occur at the osteotomy site to successfully realign the proximal and distal mechanical axes.

Question 2385

Topic: 1. General Principles & Basic Science

When calculating the precise osteotomy angles for the distal component of a Paley double-level PSO, the joint orientation line of the knee must remain horizontal to the ground. What normal mechanical lateral distal femoral angle (mLDFA) is targeted to achieve this?

. 75 degrees
. 81 degrees
. 88 degrees
. 95 degrees
. 100 degrees

Correct Answer & Explanation

. 88 degrees

Explanation

The normal mLDFA is approximately 87-88 degrees. In a double-level PSO, restoring this angle at the distal varus osteotomy ensures that the knee joint orientation line remains appropriately horizontal relative to the newly established mechanical axis.

Question 2386

Topic: 1. General Principles & Basic Science

You are assessing a patient for a potential double-level PSO. The patient has a Girdlestone hip secondary to chronic, multidrug-resistant MRSA osteomyelitis of the native proximal femur. How does this history influence the surgical approach?

. It represents an absolute contraindication to a PSO
. The PSO should be performed strictly using custom intramedullary nails
. An external fixator-assisted PSO is highly advantageous as fixation can completely bypass the infected zone
. The osteotomy must be deliberately performed through the zone of osteomyelitis to debride it
. The procedure cannot proceed without a massive structural allograft

Correct Answer & Explanation

. An external fixator-assisted PSO is highly advantageous as fixation can completely bypass the infected zone

Explanation

A profound advantage of Ilizarov/Paley external fixator techniques for PSO is the ability to achieve rigid fixation and complex deformity correction entirely outside of a chronically infected bone segment, avoiding hardware contamination.

Question 2387

Topic: 1. General Principles & Basic Science

In the principles of deformity correction, Paley's Osteotomy Rule 1 states that if the osteotomy and the mechanical hinge are both placed exactly at the CORA, what type of correction will be achieved?

. Angulation combined with obligatory translation
. Pure angulation without any translation
. Pure translation without angular correction
. Creation of an intentional rotational deformity
. Lengthening without any correction of angulation

Correct Answer & Explanation

. Pure angulation without any translation

Explanation

Paley's Osteotomy Rule 1 dictates that an osteotomy and a hinge perfectly co-located at the CORA will result in pure angular correction without any translation of the bone ends.

Question 2388

Topic: Biology, Genetics & Bone Healing

A 25-year-old is undergoing the distraction phase of the distal osteotomy in a double-level PSO. What is the most reliable radiographic indicator that the daily rate of distraction is occurring too rapidly?

. Rapid consolidation of the regenerate bone into thick trabeculae
. Development of a wide radiolucent or cystic gap in the regenerate without bridging callus
. Erythema and serous drainage at the distal pin sites
. Decreased range of motion in the ipsilateral knee
. Symmetric widening of the medial and lateral joint spaces of the knee

Correct Answer & Explanation

. Development of a wide radiolucent or cystic gap in the regenerate without bridging callus

Explanation

A wide, radiolucent gap or cystic changes within the distraction gap on plain radiographs indicate that bone formation is failing to keep pace with the distraction. This requires immediately slowing or temporarily halting the distraction rate.

Question 2389

Topic: 1. General Principles & Basic Science

Following completion of a Paley double-level pelvic support osteotomy and successful frame removal, a patient exhibits a significant residual internal rotation gait. What step in the preoperative planning or surgical execution was most likely omitted?

. Intentional overcorrection of the proximal valgus osteotomy
. Calculation and correction of excessive femoral antetorsion at the distal osteotomy
. Use of a multi-planar hexapod external fixator instead of a monolithic frame
. Incorrect application of the Paley multiplier method for leg length
. Failure to release the iliopsoas tendon

Correct Answer & Explanation

. Calculation and correction of excessive femoral antetorsion at the distal osteotomy

Explanation

Chronically dislocated hips frequently feature complex multi-planar deformities, including severe excessive femoral anteversion. If this rotational deformity is not explicitly calculated and corrected (typically at the distal osteotomy), the patient will be left with a rotational gait abnormality.

Question 2390

Topic: Physiology & Rehabilitation

A 28-year-old patient with a chronically dislocated hip from childhood sepsis undergoes a Paley double-level pelvic support osteotomy. The proximal osteotomy is designed to provide pelvic support. What is the primary biomechanical purpose of the distal osteotomy?

. To improve hip flexion and extension
. To restore the mechanical axis and allow for simultaneous limb lengthening
. To provide a broad surface for ischial impingement
. To lateralize the femoral shaft
. To correct excessive femoral version

Correct Answer & Explanation

. To restore the mechanical axis and allow for simultaneous limb lengthening

Explanation

The proximal osteotomy in a PSO creates significant valgus to support the pelvis and eliminate the Trendelenburg gait. The distal osteotomy corrects the resulting valgus mechanical axis deviation, restores parallel knee joint orientation, and serves as the site for limb lengthening.

Question 2391

Topic: Physiology & Rehabilitation

When planning the proximal osteotomy in a Paley pelvic support osteotomy, the required angle of valgus correction is calculated based on preoperative radiographs. Which of the following formulas correctly determines the angle of the proximal osteotomy?

. Maximum hip abduction angle plus 15 degrees
. Maximum hip adduction angle plus 15 degrees
. Angle of mechanical axis deviation minus 10 degrees
. Maximum hip adduction angle minus 15 degrees
. Anatomic axis of the femur plus 10 degrees

Correct Answer & Explanation

. Maximum hip adduction angle plus 15 degrees

Explanation

The proximal osteotomy angle must equal the maximum adduction angle of the hip plus an additional 15 degrees of overcorrection. This overcorrection ensures the proximal femur adequately abuts the pelvis during weight-bearing, functionally eliminating the Trendelenburg gait.

Question 2392

Topic: 1. General Principles & Basic Science

To achieve optimal biomechanical stability in a pelvic support osteotomy, what is the ideal anatomic level for the proximal femoral osteotomy?

. At the level of the lesser trochanter
. 2 cm distal to the greater trochanter
. At the intersection of the mechanical axis and the femoral neck
. Just distal to the level of the ischial tuberosity with the hip in maximum adduction
. At the mid-diaphyseal level

Correct Answer & Explanation

. Just distal to the level of the ischial tuberosity with the hip in maximum adduction

Explanation

The proximal osteotomy should be performed just below the level of the ischial tuberosity when the hip is in maximal adduction. This precise level ensures that the proximal femoral segment will successfully abut the ischium to provide a stable pelvic fulcrum.

Question 2393

Topic: 1. General Principles & Basic Science

According to Paley's principles of deformity correction (Osteotomy Rule 1), if both the osteotomy and the axis of hinge correction are placed exactly at the Center of Rotation of Angulation (CORA), what is the resultant geometric effect on the bone segments?

. Angulation and translation occur simultaneously
. Only translation occurs
. Only angulation occurs without translation
. The mechanical axis is translated laterally
. A secondary CORA is inadvertently created

Correct Answer & Explanation

. Only angulation occurs without translation

Explanation

Paley's Osteotomy Rule 1 states that when both the osteotomy and the hinge (axis of correction) are located at the CORA, the deformity corrects by angulation alone. The bone ends remain fully apposed without any translation.

Question 2394

Topic: 1. General Principles & Basic Science

A surgeon plans to correct a diaphyseal femoral deformity. To prioritize bone healing, the osteotomy is made outside the CORA, but the axis of hinge correction remains at the CORA. What is the expected outcome according to Paley's Rule 2?

. Pure angulation without translation
. Pure translation without angulation
. Angulation with expected and necessary translation at the osteotomy site
. Mechanical axis deviation requiring a second osteotomy
. Iatrogenic joint line obliquity

Correct Answer & Explanation

. Angulation with expected and necessary translation at the osteotomy site

Explanation

Paley's Osteotomy Rule 2 describes placing the hinge at the CORA but making the osteotomy at a different level. This correctly realigns the bone axes but creates a deliberate and expected translation at the osteotomy site.

Question 2395

Topic: 1. General Principles & Basic Science

A 16-year-old female presents with genu valgum. Preoperative planning involves drawing the mechanical axis and joint orientation lines.

Based on standard deformity principles, what is the normal range for the mechanical lateral distal femoral angle (mLDFA)?

. 80-84 degrees
. 85-90 degrees
. 91-95 degrees
. 96-100 degrees
. 101-105 degrees

Correct Answer & Explanation

. 85-90 degrees

Explanation

The normal mechanical lateral distal femoral angle (mLDFA) ranges from 85 to 90 degrees, with an average of approximately 88 degrees. Values outside this range indicate a distal femoral deformity requiring correction.

Question 2396

Topic: 1. General Principles & Basic Science

Pelvic Support Osteotomy is a salvage procedure for a chronically dislocated, painful hip. Which of the following is considered an absolute contraindication to performing a PSO?

. Previous septic arthritis of the hip
. Absence of the femoral head and neck
. Severe Trendelenburg gait
. Ipsilateral knee ankylosis or severe instability
. Limb length discrepancy greater than 5 cm

Correct Answer & Explanation

. Ipsilateral knee ankylosis or severe instability

Explanation

PSO relies heavily on a functional, stable, and mobile ipsilateral knee to tolerate the mechanical adjustments and the circular frame required for lengthening. Severe knee instability or ankylosis prevents the patient from accommodating the new biomechanics and is an absolute contraindication.

Question 2397

Topic: Physiology & Rehabilitation

After a successful double-level Pelvic Support Osteotomy, the patient's Trendelenburg lurch is resolved. Which structure serves as the primary fulcrum stabilizing the pelvis during the single-leg stance phase on the operative side?

. The greater trochanter abutting the ilium
. The lesser trochanter or proximal femur abutting the ischium
. The tightened gluteus medius muscle
. The tightened iliotibial band
. The psoas tendon abutting the superior pubic ramus

Correct Answer & Explanation

. The lesser trochanter or proximal femur abutting the ischium

Explanation

In a PSO, the proximal osteotomy is placed at the level of the ischial tuberosity. During weight-bearing, the proximal segment abuts the ischium, creating a mechanical fulcrum that provides pelvic support and prevents pelvic drop.

Question 2398

Topic: 1. General Principles & Basic Science

Due to the extreme valgus angulation created at the proximal osteotomy site in a Paley pelvic support osteotomy, the biomechanical action of the iliopsoas muscle is functionally altered. Which new role does the iliopsoas primarily take on?

. Hip internal rotator
. Hip extensor
. Hip abductor
. Knee extensor
. Pelvic depressor

Correct Answer & Explanation

. Hip abductor

Explanation

Because of the high degree of abduction (valgus) created in the proximal segment, the line of pull of the iliopsoas is shifted laterally. This alters its primary function, allowing it to act dynamically as a hip abductor to assist in stabilizing the pelvis.

Question 2399

Topic: 1. General Principles & Basic Science

Preoperative evaluation for a Pelvic Support Osteotomy reveals a 30-degree hip flexion contracture. How should this contracture be technically addressed during the PSO procedure?

. Soft tissue release of the rectus femoris only
. Adding 30 degrees of flexion to the proximal osteotomy
. Adding 30 degrees of extension to the proximal osteotomy
. Correcting the contracture entirely at the distal osteotomy
. Postoperative serial casting

Correct Answer & Explanation

. Adding 30 degrees of extension to the proximal osteotomy

Explanation

Fixed flexion contractures of the hip must be accommodated during the proximal osteotomy to allow upright posture. The distal segment must be extended by an amount equal to the flexion contracture, effectively adding extension to the proximal osteotomy.

Question 2400

Topic: 1. General Principles & Basic Science

A patient undergoing a double-level pelvic support osteotomy has a normal sagittal profile preoperatively. To prevent iatrogenic recurvatum or procurvatum, the hinges of the circular external fixator at the distal osteotomy site must be mounted parallel to which axis?

. The mechanical axis of the femur
. The mechanical axis of the tibia
. The knee joint orientation line in the sagittal plane
. The knee joint orientation line in the coronal plane
. The anatomic axis of the proximal femur

Correct Answer & Explanation

. The knee joint orientation line in the sagittal plane

Explanation

To correct deformity without introducing a new sagittal plane deformity (like recurvatum or procurvatum), the fixator hinges must be aligned parallel to the true knee joint axis in the sagittal plane. Improper hinge placement leads to out-of-plane angular translation during lengthening.

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