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1. General Principles & Basic Science MCQs

Practice Set 784 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 15661

Topic: Physiology & Rehabilitation

A patient demonstrates an uncompensated Trendelenburg gait (pelvic drop) on the left side during the right swing phase. This is primarily caused by dysfunction of which muscle group and nerve?

. Right hip abductors; Right superior gluteal nerve
. Left hip abductors; Left superior gluteal nerve
. Right hip adductors; Right obturator nerve
. Left hip abductors; Left inferior gluteal nerve
. Right hip abductors; Right inferior gluteal nerve

Correct Answer & Explanation

. Left hip abductors; Left superior gluteal nerve

Explanation

A contralateral pelvic drop (left side drops down) during the swing phase of the unaffected (left) leg indicates weakness of the stance-leg (right leg) abductors. Wait, the question states 'pelvic drop on the left side during the right swing phase' - this means the right leg is in swing, so the left leg is in stance. Therefore, the weak abductors are on the LEFT leg, supplied by the left superior gluteal nerve.

Question 15662

Topic: Physiology & Rehabilitation
A patient with a stiff-knee gait (unable to flex the knee during swing phase) typically compensates to allow for foot clearance. Which compensatory mechanism occurs on the contralateral limb during the affected limb's swing phase?
. Circumduction
. Hip hiking
. Vaulting
. Steppage gait
. Crouching

Correct Answer & Explanation

. Vaulting

Explanation

Vaulting is a stance-phase deviation that occurs on the unaffected, contralateral limb. The patient plantarflexes the normal ankle (goes up on their toes) to raise the pelvis and allow the functionally longer, stiff affected limb to clear the ground during its swing phase.

Question 15663

Topic: 1. General Principles & Basic Science

When planning a corrective osteotomy for a diaphyseal angular deformity, what is the geometric consequence of placing the osteotomy hinge at a level that is physically separated from the Center of Rotation of Angulation (CORA), while fully correcting the angular deformity?

. A secondary angular deformity is created in the opposite direction.
. The mechanical axis will remain perfectly colinear with no secondary effects.
. A rotational deformity is unavoidably induced.
. An iatrogenic translation deformity is created at the osteotomy site.
. The mechanical axis will permanently deviate laterally.

Correct Answer & Explanation

. An iatrogenic translation deformity is created at the osteotomy site.

Explanation

According to the rules of deformity correction by Paley, if an osteotomy is performed away from the CORA and the angular deformity is corrected, an obligatory translation of the bone ends occurs. This translation is required to realign the proximal and distal mechanical axes.

Question 15664

Topic: Physiology & Rehabilitation

A patient with profound weakness of the right gluteus medius exhibits a classic Trendelenburg gait. During the stance phase on the right lower extremity, which of the following compensatory movements is expected to minimize the required abductor force?

. The trunk leans laterally towards the left side.
. The trunk leans laterally towards the right side.
. The pelvis elevates on the left side.
. The trunk extends posteriorly.
. The right knee flexes excessively to lower the center of gravity.

Correct Answer & Explanation

. The trunk leans laterally towards the right side.

Explanation

In an uncompensated Trendelenburg sign, the contralateral pelvis drops. In a compensated Trendelenburg gait, the patient leans their trunk laterally over the affected (ipsilateral) side during stance to move the center of gravity closer to the hip joint center, reducing the demand on the weak abductors.

Question 15665

Topic: 1. General Principles & Basic Science

A 45-year-old active male with medial compartment knee osteoarthritis undergoes a medial opening wedge high tibial osteotomy (HTO). Postoperatively, he is noted to have a new-onset genu recurvatum during gait. Which of the following technical errors during the HTO most likely caused this complication?

. The anterior gap was opened more than the posterior gap.
. The posterior gap was opened more than the anterior gap.
. The osteotomy hinge was left completely intact laterally.
. The osteotomy was positioned too distal to the tibial tubercle.
. A lateral closing wedge was inadvertently performed instead.

Correct Answer & Explanation

. The anterior gap was opened more than the posterior gap.

Explanation

The proximal tibia has a normal posterior slope. If a medial opening wedge HTO is opened more anteriorly than posteriorly, it decreases the posterior tibial slope (or introduces anterior slope), leading to knee hyperextension (recurvatum) during weight-bearing.

Question 15666

Topic: Physiology & Rehabilitation

In a patient with cerebral palsy presenting with a stiff-knee gait, electromyography (EMG) is most likely to show abnormal, continuous firing of which muscle during the swing phase of gait?

. Vastus medialis
. Biceps femoris
. Rectus femoris
. Tibialis anterior
. Gastrocnemius

Correct Answer & Explanation

. Rectus femoris

Explanation

Stiff-knee gait in cerebral palsy is characterized by diminished peak knee flexion during the swing phase. This is most commonly caused by abnormal, prolonged overactivity of the rectus femoris muscle during swing, which is often treated with a rectus femoris transfer.

Question 15667

Topic: Physiology & Rehabilitation

A 25-year-old patient presents with a 'steppage' gait secondary to a common peroneal nerve palsy. In a normal gait cycle, the primary muscle affected by this palsy functions in which of the following combinations of contractions?

. Concentric during loading response; eccentric during swing phase
. Eccentric during loading response; concentric during swing phase
. Isometric during loading response; concentric during mid-stance
. Eccentric during pre-swing; concentric during loading response
. Concentric during terminal stance; eccentric during swing phase

Correct Answer & Explanation

. Eccentric during loading response; concentric during swing phase

Explanation

The tibialis anterior (innervated by the deep peroneal nerve) normally functions eccentrically during loading response (heel strike to foot flat) to prevent foot slap, and concentrically during swing phase to dorsiflex the foot and clear the toes.

Question 15668

Topic: Physiology & Rehabilitation

A patient with a significant equinus contracture of the ankle presents with a characteristic secondary gait deviation during the stance phase. Which of the following is the most likely observed compensatory knee kinematic?

. Excessive knee flexion throughout stance (crouch gait)
. Genu recurvatum (knee hyperextension) during midstance
. Varus thrust during loading response
. Stiff knee with absent flexion during pre-swing
. Premature patellar tracking laterally

Correct Answer & Explanation

. Genu recurvatum (knee hyperextension) during midstance

Explanation

A fixed plantarflexion (equinus) contracture forces the tibia backward when the foot is planted flat on the ground during stance. This creates a plantarflexion-knee extension couple, driving the knee into hyperextension (recurvatum).

Question 15669

Topic: Biology, Genetics & Bone Healing

In distraction osteogenesis using an Ilizarov circular frame, which of the following histologic processes is primarily responsible for the formation of new bone in the distraction gap under ideal conditions of stability and rate?

. Endochondral ossification
. Creeping substitution
. Intramembranous ossification
. Appositional chondrogenesis
. Fibrocartilage metaplasia

Correct Answer & Explanation

. Intramembranous ossification

Explanation

Under appropriate conditions of stability, rhythm, and rate (typically 1 mm per day in 4 increments), the regenerate bone in distraction osteogenesis forms primarily via intramembranous ossification, occurring parallel to the tension vectors without a cartilage intermediate.

Question 15670

Topic: Physiology & Rehabilitation

A patient demonstrates a classic 'gluteus maximus lurch' during gait. Which kinematic alteration during the stance phase characterizes this gait pattern?

. The trunk leans forcefully forward to passively extend the hip.
. The trunk extends posteriorly to place the center of gravity behind the hip joint.
. The pelvis drops on the contralateral side to increase the effective limb length.
. The knee hyperextends to lock the limb in the absence of hip extension.
. The patient excessively dorsiflexes the ankle to compensate for weak hip extension.

Correct Answer & Explanation

. The trunk extends posteriorly to place the center of gravity behind the hip joint.

Explanation

In the presence of a weak gluteus maximus, the patient thrusts their trunk posteriorly at initial contact and early stance. This places the center of gravity posterior to the hip joint axis, generating an external extension moment that substitutes for the weak hip extensors.

Question 15671

Topic: 1. General Principles & Basic Science

A 60-year-old female undergoes a distal femoral osteotomy for a severe valgus knee deformity and isolated lateral compartment osteoarthritis. A medial closing wedge osteotomy is performed. What is the expected change to the mechanical axis of the lower extremity?

. Shifts the mechanical axis laterally to unload the medial compartment
. Shifts the mechanical axis medially to unload the lateral compartment
. Maintains the mechanical axis centrally while only correcting joint line obliquity
. Translates the mechanical axis posteriorly to improve knee flexion
. Translates the mechanical axis anteriorly to improve the extensor mechanism

Correct Answer & Explanation

. Shifts the mechanical axis medially to unload the lateral compartment

Explanation

A varus-producing distal femoral osteotomy (such as a medial closing wedge) is used for a valgus knee with lateral compartment osteoarthritis. It shifts the weight-bearing mechanical axis medially, offloading the diseased lateral compartment.

Question 15672

Topic: 1. General Principles & Basic Science

When planning an osteotomy for a uniplanar deformity, following Paley's Osteotomy Rule 1 dictates that the osteotomy and the axis of rotation both pass directly through the Center of Rotation of Angulation (CORA). What is the expected biomechanical outcome of this correction?

. Pure angulation without translation
. Angulation combined with translation
. Pure translation without angulation
. Correction of length discrepancy with lateral translation

Correct Answer & Explanation

. Pure angulation without translation

Explanation

Osteotomy Rule 1 states that if the osteotomy line and the hinge (axis of rotation) both pass through the CORA, the deformity corrects with pure angulation, restoring the mechanical axis without any translation at the osteotomy site.

Question 15673

Topic: Physiology & Rehabilitation

A patient exhibits a compensated Trendelenburg gait, leaning their trunk laterally over the stance limb. What is the primary biomechanical advantage of this compensatory mechanism?

. It increases the abductor moment arm.
. It moves the center of gravity closer to the hip joint, decreasing the body weight moment arm.
. It shifts the center of rotation superiorly.
. It increases the overall hip joint reaction force to stabilize the capsule.

Correct Answer & Explanation

. It moves the center of gravity closer to the hip joint, decreasing the body weight moment arm.

Explanation

By leaning the trunk laterally over the weak stance hip, the center of gravity is brought closer to the center of the hip joint. This dramatically decreases the body weight moment arm, reducing the moment that the weak abductors must counteract.

Question 15674

Topic: Physiology & Rehabilitation

During the normal human gait cycle, the gluteus maximus demonstrates its peak electromyographic (EMG) activity during which specific phase?

. Mid-stance to terminal stance
. Initial contact to loading response
. Pre-swing
. Initial swing to mid-swing

Correct Answer & Explanation

. Initial contact to loading response

Explanation

The gluteus maximus fires maximally from initial contact to the loading response phase. Its eccentric contraction decelerates the forward momentum of the trunk and prevents uncontrolled hip flexion.

Question 15675

Topic: Physiology & Rehabilitation

According to Saunders' determinants of gait, which of the following kinematic mechanisms is most responsible for minimizing the vertical displacement of the center of gravity during the peak of the stance phase?

. Pelvic rotation
. Knee flexion in stance
. Ankle plantarflexion at toe-off
. Lateral pelvic displacement

Correct Answer & Explanation

. Knee flexion in stance

Explanation

Normal knee flexion (~15 degrees) during the stance phase allows the pelvis and center of gravity to drop slightly at what would otherwise be the highest point of the arc, thereby flattening the trajectory and conserving energy.

Question 15676

Topic: Physiology & Rehabilitation

In the analysis of a normal adult gait cycle at a standard walking speed, the cycle is classically divided into the stance phase and the swing phase. What percentage of the total gait cycle is typically occupied by each phase?

. 50% stance, 50% swing
. 60% stance, 40% swing
. 40% stance, 60% swing
. 70% stance, 30% swing

Correct Answer & Explanation

. 60% stance, 40% swing

Explanation

A normal gait cycle is composed of approximately 60% stance phase (when the foot is in contact with the ground) and 40% swing phase (when the limb is advancing through the air).

Question 15677

Topic: Physiology & Rehabilitation

During the normal gait cycle, weakness of which muscle group and during which specific phase results in a classic 'foot slap'?

. Tibialis anterior; eccentric contraction during the loading response
. Tibialis anterior; concentric contraction during the swing phase
. Gastrocnemius; eccentric contraction during terminal stance
. Posterior tibialis; concentric contraction during pre-swing
. Extensor hallucis longus; eccentric contraction during mid-stance

Correct Answer & Explanation

. Tibialis anterior; eccentric contraction during the loading response

Explanation

A 'foot slap' occurs when the pretibial muscles (primarily the tibialis anterior) fail to eccentrically control plantarflexion from initial contact to the foot-flat phase (loading response).

Question 15678

Topic: 1. General Principles & Basic Science

In planning a corrective osteotomy for a diaphyseal tibial deformity, the surgical cut is planned proximal to the Center of Rotation of Angulation (CORA). To restore the mechanical axis perfectly without creating a secondary deformity, the osteotomy must include which of the following?

. Angulation only
. Translation only
. Angulation and translation
. Distraction and angulation
. Rotation only

Correct Answer & Explanation

. Angulation and translation

Explanation

When an osteotomy is performed at a level other than the CORA, correcting the angulation alone will result in a translation deformity (loss of mechanical axis alignment). Both angulation and translation must be performed to restore the axis.

Question 15679

Topic: 1. General Principles & Basic Science

A patient exhibits a posterior trunk lean immediately after heel strike during the stance phase of gait. This compensatory mechanism (gluteus maximus lurch) is most likely due to weakness of a muscle innervated by which nerve?

. Superior gluteal nerve
. Inferior gluteal nerve
. Femoral nerve
. Obturator nerve
. Sciatic nerve

Correct Answer & Explanation

. Inferior gluteal nerve

Explanation

A posterior trunk lean at initial contact shifts the center of gravity behind the hip joint, artificially locking it in extension. This compensates for weakness of the gluteus maximus, which is innervated by the inferior gluteal nerve.

Question 15680

Topic: Physiology & Rehabilitation

During the single-leg stance phase of normal walking gait, the hip joint reaction force is approximately what multiple of total body weight?

. 1 times body weight
. 1.5 times body weight
. 2.5 to 3 times body weight
. 4.5 to 5 times body weight
. 6 to 7 times body weight

Correct Answer & Explanation

. 2.5 to 3 times body weight

Explanation

During single-leg stance, the hip abductors must exert a force roughly 1.5 to 2 times body weight to maintain a level pelvis. Combined with body weight, the resultant joint reaction force across the hip is approximately 2.5 to 3 times body weight.

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