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1. General Principles & Basic Science MCQs

Practice Set 486 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 9701

Topic: Physiology & Rehabilitation

A patient has a fixed equinus contracture of the ankle due to spasticity. Over time, what is the most common compensatory deformity observed at the knee during the stance phase of gait?

. Genu recurvatum
. Genu varum
. Genu valgum
. Fixed flexion contracture
. Patella alta

Correct Answer & Explanation

. Genu recurvatum

Explanation

A fixed equinus contracture forces the tibia backward during the stance phase as the foot attempts to achieve plantigrade contact. This chronic posterior thrust stretches the posterior knee capsule, leading to compensatory genu recurvatum.

Question 9702

Topic: 1. General Principles & Basic Science

When defining the CORA using Paley's principles, the line that bisects the angle formed by the intersection of the proximal and distal anatomical axes is referred to as the:

. Mechanical axis line
. Joint orientation line
. Sagittal vertical axis
. Transverse bisector line
. Plumb line

Correct Answer & Explanation

. Transverse bisector line

Explanation

The transverse bisector line evenly divides the angle formed by the intersecting proximal and distal anatomical (or mechanical) axes. When an osteotomy is performed along this line, the cortical edges meet perfectly without step-off after angular correction.

Question 9703

Topic: 1. General Principles & Basic Science

A surgeon uses the Taylor Spatial Frame (TSF) "chronic mounting" parameters to correct a tibial deformity. Which of the following statements best describes the principle of the chronic mounting mode?

. The frame is mounted purely orthogonally to the anatomical axis of the distal fragment, ignoring the proximal segment.
. The frame is applied exactly matching the deformity, and the software corrects the hardware to a neutral position.
. The reference ring is mounted orthogonally to the reference bone segment, and deformity parameters are calculated from standard radiographs relative to this ring.
. The rings must be perfectly parallel to the joint lines before any osteotomy is made.
. It requires a single-stage acute correction in the operating room before struts are locked.

Correct Answer & Explanation

. The reference ring is mounted orthogonally to the reference bone segment, and deformity parameters are calculated from standard radiographs relative to this ring.

Explanation

In the TSF "chronic mounting" (or "rings first") technique, the reference ring is mounted orthogonally to the reference segment. The software then uses the measured mounting parameters on AP and lateral radiographs to virtually align the fragments.

Question 9704

Topic: 1. General Principles & Basic Science

You are treating a 16-year-old with a multi-apical tibial deformity using a single-level osteotomy at a compromised level between two CORAs. Based on Paley's principles, if a single osteotomy is used to correct a multi-apical deformity, what geometric compromise is inevitable?

. The mechanical axes will be collinear but bone length will decrease by 2 cm.
. A large translation will be required at the osteotomy site to achieve collinearity of the proximal and distal joints.
. The transverse bisector line will invariably become vertical.
. The joint line will be forced into 15 degrees of valgus.
. A secondary uniapical deformity will spontaneously correct.

Correct Answer & Explanation

. A large translation will be required at the osteotomy site to achieve collinearity of the proximal and distal joints.

Explanation

When a single osteotomy is used to correct a multi-apical deformity (or when correcting away from the CORA), significant translation of the bone ends must occur at the osteotomy site to restore collinearity of the mechanical axis.

Question 9705

Topic: Physiology & Rehabilitation

A young adult with a painful, chronically dislocated hip due to childhood sepsis undergoes an Ilizarov pelvic support osteotomy. This procedure involves a double level femoral osteotomy. What is the primary purpose of the distal femoral osteotomy in this specific reconstruction?

. To realign the mechanical axis and equalize limb length
. To provide a stable fulcrum against the ischium
. To prevent secondary hip flexion contractures
. To lateralize the greater trochanter and improve abductor pull
. To correct an underlying compensatory femoral retroversion

Correct Answer & Explanation

. To realign the mechanical axis and equalize limb length

Explanation

The proximal valgus osteotomy provides pelvic support (eliminating Trendelenburg gait) but introduces a massive mechanical axis deviation. The distal varus osteotomy (often with lengthening) is strictly required to realign the mechanical axis parallel to the plumb line and restore equal leg length.

Question 9706

Topic: Physiology & Rehabilitation



An Ilizarov pelvic support osteotomy is planned for a patient with a chronically dislocated, painful hip. To successfully eliminate Trendelenburg gait and restore mechanical alignment, which combination of femoral osteotomies is required?

. Proximal femoral varus osteotomy and distal femoral valgus osteotomy
. Proximal femoral valgus-extension osteotomy and distal femoral varus osteotomy
. Proximal femoral flexion osteotomy and distal femoral extension osteotomy
. Isolated proximal femoral valgus osteotomy
. Proximal femoral valgus osteotomy and distal femoral internal rotation osteotomy

Correct Answer & Explanation

. Proximal femoral valgus-extension osteotomy and distal femoral varus osteotomy

Explanation

The pelvic support osteotomy requires a proximal valgus-extension osteotomy to eliminate the Trendelenburg gait and support the pelvis. A secondary distal femoral varus osteotomy is required to realign the mechanical axis of the lower extremity parallel to the contralateral limb.

Question 9707

Topic: 1. General Principles & Basic Science

According to Paley's rules of osteotomy, what occurs geometrically when both the osteotomy and the Axis of Correction of Angulation (ACA) are placed away from the Center of Rotation of Angulation (CORA)?

. Pure angulation with colinear realignment of the mechanical axes
. Pure translation with colinear realignment of the mechanical axes
. Angulation and translation with colinear realignment of the mechanical axes
. Angulation with a parallel translation of the mechanical axes (zigzag deformity)
. Complete correction of the deformity without translation

Correct Answer & Explanation

. Angulation with a parallel translation of the mechanical axes (zigzag deformity)

Explanation

Paley's Rule 3 states that if the ACA and the osteotomy are independent of the CORA, the deformity correction will result in a parallel shift (translation) of the proximal and distal mechanical axes. This creates a secondary translation or "zigzag" deformity.

Question 9708

Topic: Physiology & Rehabilitation

In a pelvic support osteotomy (Ilizarov hip reconstruction) for a chronically dislocated hip, what is the primary biomechanical purpose of the distal femoral osteotomy?

. To correct leg length discrepancy by pure lengthening.
. To realign the mechanical axis parallel to the anatomic axis.
. To correct the secondary mechanical axis deviation created by the proximal valgus osteotomy.
. To induce spontaneous hip reduction via soft tissue tensioning.
. To increase femoral anteversion for better abductor mechanics.

Correct Answer & Explanation

. To correct the secondary mechanical axis deviation created by the proximal valgus osteotomy.

Explanation

The proximal osteotomy in a pelvic support procedure is performed in valgus and extension to eliminate Trendelenburg gait and support the pelvis. This creates a secondary mechanical axis deviation that must be corrected by a distal femoral osteotomy to re-center the mechanical axis over the knee.

Question 9709

Topic: 1. General Principles & Basic Science

When applying a circular external fixator to correct a severe fixed equinus contracture without performing an osteotomy, where should the theoretical center of rotation (hinge) be placed to stretch the posterior structures while avoiding anterior joint compression?

. Anterior to the center of the talar dome
. Posterior and distal to the anatomical center of the talar dome
. At the exact tip of the lateral malleolus
. At the medial clear space
. Directly through the calcaneal tuberosity

Correct Answer & Explanation

. Posterior and distal to the anatomical center of the talar dome

Explanation

Placing the hinge slightly posterior and distal to the axis of rotation causes distraction of the joint space as it rotates out of equinus. Placing it anteriorly would cause severe anterior joint compression (crushing) during dorsiflexion.

Question 9710

Topic: 1. General Principles & Basic Science

During deformity planning, drawing the proximal and distal anatomical axes of a deformed tibia reveals that the two lines are completely parallel but do not collinearize (they never intersect). What type of deformity does this represent?

. A single juxta-articular CORA
. A combined rotational and angular deformity
. A pure translational deformity
. An intra-articular joint line deviation
. A normal diaphyseal bow

Correct Answer & Explanation

. A pure translational deformity

Explanation

When the proximal and distal axes are completely parallel but not collinear, the CORA is effectively at infinity. This indicates a pure translational deformity without an angular component.

Question 9711

Topic: 1. General Principles & Basic Science

A patient with a complex distal tibial deformity is undergoing correction. According to Paley's Rule 3, if both the osteotomy and the hinge are positioned outside the CORA (Center of Rotation of Angulation) and outside the transverse bisector line, what is the geometric result of the correction?

. Pure angulation without any translation.
. Angulation combined with translation that perfectly realigns the proximal and distal mechanical axes.
. Angulation combined with translation that displaces the axes, creating a new translation deformity.
. Pure translation without any change in angular alignment.
. Pure lengthening along the mechanical axis without angulation.

Correct Answer & Explanation

. Angulation combined with translation that displaces the axes, creating a new translation deformity.

Explanation

Paley's Rule 3 states that if the hinge and osteotomy are both off the CORA and not on the transverse bisector line, the resulting correction will induce an unintended secondary translation deformity. The proximal and distal axes will not realign properly.

Question 9712

Topic: 1. General Principles & Basic Science

In a patient presenting with a pure translation deformity of the tibial diaphysis (a "bayonet" apposition), the proximal and distal anatomical axes are perfectly parallel but not collinear. Based on Paley's principles, where is the CORA located?

. At the mid-point of the translation overlap.
. At the closest adjacent joint line.
. At infinity.
. At the distal metaphysis.
. Translation deformities do not possess a mathematically definable CORA.

Correct Answer & Explanation

. At infinity.

Explanation

In a pure translation deformity, the proximal and distal anatomical axes are parallel and will theoretically never intersect. Therefore, the Center of Rotation of Angulation (CORA) is mathematically located at infinity.

Question 9713

Topic: 1. General Principles & Basic Science

A patient undergoes analysis for a lower extremity deformity.

According to standard deformity planning principles, what defining characteristic confirms that the patient has a uniapical deformity rather than a multiapical deformity?

. The mechanical and anatomical axes are perfectly parallel throughout the bone.
. The proximal and distal mid-diaphyseal lines intersect at a single point within the bone.
. Two distinct centers of rotation of angulation (CORAs) are identified.
. The joint orientation lines remain parallel to the diaphyseal axis.
. The magnitude of the angulation is measured at less than 15 degrees.

Correct Answer & Explanation

. The proximal and distal mid-diaphyseal lines intersect at a single point within the bone.

Explanation

A uniapical deformity is defined by the intersection of the proximal and distal anatomical (mid-diaphyseal) or mechanical axes at a single distinct point. This single intersection point represents a solitary CORA.

Question 9714

Topic: 1. General Principles & Basic Science

A patient presents with a multiplanar tibial deformity. The AP radiograph demonstrates 30 degrees of varus, while the lateral radiograph demonstrates 40 degrees of recurvatum. To accurately determine the true magnitude and precise axis of the maximum deformity for surgical planning, which mathematical method is employed?

. The golden ratio rule of thumb.
. Simple addition of the angles (70 degrees).
. Measurement of the joint orientation lines exclusively.
. Trigonometric calculation to identify the oblique plane of deformity.
. The Pythagorean theorem applied to the bone length only.

Correct Answer & Explanation

. Trigonometric calculation to identify the oblique plane of deformity.

Explanation

Most complex deformities exist in an oblique plane rather than purely coronal or sagittal planes. The true magnitude and axis of the deformity are determined using trigonometric calculations (or specialized graphic grids) that combine the projected AP and lateral angular values.

Question 9715

Topic: 1. General Principles & Basic Science

A surgeon plans a corrective osteotomy for a tibial diaphyseal deformity. During preoperative templating, it is determined that both the osteotomy and the correction hinge will be placed at a distance from the Center of Rotation of Angulation (CORA). According to Paley's principles of deformity correction, what is the expected geometric outcome of this procedure?

. Angulation with complete realignment of the mechanical axis and no translation
. Angulation with translation of bone ends resulting in complete mechanical axis realignment
. Angulation and translation resulting in a secondary CORA and failure to realign the mechanical axis
. Pure translation without angulation, fully restoring length
. Correction of the angular deformity with unavoidable excessive shortening of the limb

Correct Answer & Explanation

. Angulation and translation resulting in a secondary CORA and failure to realign the mechanical axis

Explanation

Paley's Rule 3 states that if both the osteotomy and the hinge are placed away from the CORA, the mechanical axis will not realign. This introduces a translation deformity, creating a new secondary CORA.

Question 9716

Topic: 1. General Principles & Basic Science

You are evaluating a patient with a tibial diaphyseal 'sweeping' bow, representing a multi-apical deformity. The surgeon opts to correct the entire deformity using a single osteotomy rather than multiple focal osteotomies. To fully restore the overall mechanical axis of the limb, which maneuver is mandatory at the osteotomy site?

. A simple medial opening wedge correction
. A simple lateral closing wedge correction
. An osteotomy combined with intentional translation of the bone segments
. An osteotomy with pure rotation along the mechanical axis
. Placement of the hinge precisely at the center of the medullary canal

Correct Answer & Explanation

. An osteotomy combined with intentional translation of the bone segments

Explanation

When a multi-apical (sweeping) deformity is corrected with a single osteotomy, the osteotomy is inherently outside the true apices of the curves. To realign the mechanical axis, intentional translation at the osteotomy site must be combined with the angular correction.

Question 9717

Topic: Biology, Genetics & Bone Healing

During a gradual deformity correction and lengthening of the tibia using a hexapod circular frame, the patient develops premature consolidation of the regenerate bone. Which of the following factors most likely predisposed the patient to this complication?

. A distraction rate of 1.0 mm per day
. A latency period of 2 days prior to starting distraction
. Performing the corticotomy with a Gigli saw rather than a drill
. A distraction rhythm of 0.25 mm every 6 hours
. A latency period of 14 days prior to starting distraction

Correct Answer & Explanation

. A latency period of 14 days prior to starting distraction

Explanation

A prolonged latency period (e.g., 14 days) allows for excessive callus formation before distraction forces are applied, significantly increasing the risk of premature consolidation. The standard latency period for diaphyseal lengthening is typically 5 to 7 days.

Question 9718

Topic: 1. General Principles & Basic Science



A surgeon plans to correct a severe distal tibial recurvatum (apex posterior) deformity. To avoid compromised soft tissue at the apex, the osteotomy is performed proximal to the CORA. However, the hinge is correctly placed on the transverse bisector line at the level of the CORA. According to Paley's Rule 2, what is the expected morphological result at the osteotomy site?

. Angulation with complete axis realignment and no translation of bone ends
. Angulation with axis realignment and anterior translation of the distal segment
. Angulation with axis realignment and posterior translation of the distal segment
. Pure translation with an uncorrected mechanical axis
. Angulation resulting in a secondary varus deformity

Correct Answer & Explanation

. Angulation with axis realignment and posterior translation of the distal segment

Explanation

Paley's Rule 2 states that if the osteotomy is outside the CORA but the hinge is on the CORA bisector line, the mechanical axis realigns but the bone ends translate. Correcting recurvatum (flexing the distal segment) with a proximal osteotomy causes the distal segment to translate posteriorly.

Question 9719

Topic: 1. General Principles & Basic Science

When analyzing a multi-apical deformity of the femur using Paley's principles,

what is the consequence of utilizing a single functional CORA and a single osteotomy rather than addressing each anatomical CORA individually?

. It restores the mechanical axis perfectly without any translation at the osteotomy site.
. It corrects the mechanical axis but inherently causes anatomical translation and deviation of the anatomical axis.
. It corrects the anatomical axis but leaves the mechanical axis deviated.
. It eliminates the need for calculating the transverse bisector line.
. It completely avoids altering the absolute length of the femur.

Correct Answer & Explanation

. It corrects the mechanical axis but inherently causes anatomical translation and deviation of the anatomical axis.

Explanation

Using a single functional CORA for a multi-apical deformity treats the entire bone as having one angulation. Correcting this with a single osteotomy realigns the overall mechanical axis but produces significant translation and anatomical axis deviation at the correction site.

Question 9720

Topic: Physiology & Rehabilitation

A patient with a chronically dislocated hip and severe Trendelenburg gait is scheduled for a pelvic support osteotomy (Ilizarov). This procedure involves two distinct osteotomies. What is the primary biomechanical goal of the proximal osteotomy in this specific technique?

. To equalize limb length by acute distraction
. To extend and highly abduct the proximal femur, locking it against the pelvis to eliminate the Trendelenburg lurch
. To strictly medialise the mechanical axis of the lower extremity
. To create a severe varus deformity that compensates for femoral shortening
. To articulate a new false joint at the level of the greater trochanter

Correct Answer & Explanation

. To extend and highly abduct the proximal femur, locking it against the pelvis to eliminate the Trendelenburg lurch

Explanation

The proximal osteotomy in a pelvic support osteotomy extends and abducts the femur. This functionally locks the proximal fragment against the ischium/pelvis during weight-bearing, restoring abductor tension and eliminating the Trendelenburg gait.

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