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1. General Principles & Basic Science MCQs

Practice Set 783 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 15641

Topic: 1. General Principles & Basic Science



When evaluating a long bone uniapical deformity, the intersection of the proximal and distal anatomical axes defines the CORA. If a closing wedge osteotomy is executed with the hinge placed on the convex cortex exactly at the CORA, what is the effect on the mechanical axis and overall bone length?

. Axis is restored and bone length is increased
. Axis is translated and bone length is unchanged
. Axis is restored and bone length is unchanged
. Axis is restored and bone length is decreased
. Axis is translated and bone length is decreased

Correct Answer & Explanation

. Axis is restored and bone length is decreased

Explanation

A closing wedge osteotomy hinged on the convex cortex at the CORA perfectly corrects the angular deformity, restoring collinearity to the mechanical axis. However, because a wedge of bone is removed without opening the opposite cortex, it inherently shortens the overall bone length.

Question 15642

Topic: 1. General Principles & Basic Science

The patellofemoral joint reaction force is highly dependent on knee flexion angle and quadriceps muscle force. During which of the following activities does this force reach its highest magnitude?

. Level walking
. Ascending stairs
. Descending stairs
. Deep squatting (past 90 degrees of knee flexion)
. Stationary cycling at low resistance

Correct Answer & Explanation

. Deep squatting (past 90 degrees of knee flexion)

Explanation

Patellofemoral joint reaction forces increase significantly with increasing degrees of knee flexion due to the required quadriceps force and the altered vector angle. It can reach up to 7 to 8 times body weight during a deep squat.

Question 15643

Topic: 1. General Principles & Basic Science

According to Paley's Rule 2 of deformity correction, if an osteotomy is performed at a level distinct from the CORA, but the hinge axis is placed exactly on the CORA, what structural outcome will result upon angular correction?

. Collinear realignment is achieved, but with expected translation at the osteotomy site
. Complete failure of angular correction due to hinge misplacement
. Angular correction is achieved alongside an iatrogenic mechanical axis deviation
. Perfect angular correction with no translation between the bone ends
. Translation of the bone ends without any angular correction

Correct Answer & Explanation

. Collinear realignment is achieved, but with expected translation at the osteotomy site

Explanation

Paley's Rule 2 states that if the osteotomy is separate from the CORA but the hinge remains exactly on the CORA, the mechanical axis will be successfully realigned. However, the bone ends will translate relative to each other at the osteotomy site.

Question 15644

Topic: 1. General Principles & Basic Science

During which of the following activities does the patellofemoral joint experience the highest joint reaction forces relative to body weight?

. Level walking
. Descending stairs
. Ascending stairs
. Deep squatting
. Rising from a chair

Correct Answer & Explanation

. Deep squatting

Explanation

The patellofemoral joint reaction force is highly dependent on the degree of knee flexion. Deep squatting generates the highest forces, reaching up to 7 to 8 times body weight. By comparison, descending stairs generates roughly 3 to 4 times body weight.

Question 15645

Topic: 1. General Principles & Basic Science

According to Paley's principles of deformity correction, if an osteotomy is performed at a level separate from the center of rotation of angulation (CORA), and the hinge axis is also placed at the osteotomy site rather than the CORA, what is the resulting alignment?

. Pure angular correction with collinear mechanical axes
. Complete restoration of the mechanical axis with no translation
. Overcorrection of the angular deformity
. Parallel but translated (non-collinear) mechanical axes
. Pure translational correction without angular change

Correct Answer & Explanation

. Parallel but translated (non-collinear) mechanical axes

Explanation

Under Paley's Rule 3, if both the osteotomy and the hinge are located at a level distinct from the CORA, the mechanical axes will not align collinearly. Instead, the proximal and distal axes become parallel, inadvertently creating a secondary translational deformity.

Question 15646

Topic: Physiology & Rehabilitation

A patient presents with a "foot slap" gait during the initial contact phase of walking. Weakness in which of the following muscles and what type of contraction is responsible for this abnormality?

. Tibialis anterior; concentric contraction
. Tibialis anterior; eccentric contraction
. Gastrocnemius; concentric contraction
. Gastrocnemius; eccentric contraction
. Tibialis posterior; concentric contraction

Correct Answer & Explanation

. Tibialis anterior; eccentric contraction

Explanation

Foot slap occurs during the loading response phase due to an inability to control ankle plantarflexion. The tibialis anterior normally contracts eccentrically to lower the foot smoothly to the ground. Weakness in this eccentric contraction results in a rapid drop of the forefoot.

Question 15647

Topic: Physiology & Rehabilitation

During normal human gait, maximum knee flexion is required to allow for adequate foot clearance. At which phase of the gait cycle does maximum knee flexion occur, and what is the approximate degree of flexion?

. Initial contact; 15 degrees
. Mid-stance; 30 degrees
. Terminal stance; 0 degrees
. Initial swing; 60 degrees
. Terminal swing; 45 degrees

Correct Answer & Explanation

. Initial swing; 60 degrees

Explanation

Maximum knee flexion during normal gait is essential for proper toe clearance to prevent tripping. This peaks during the initial swing phase, where the knee flexes to approximately 60 degrees.

Question 15648

Topic: 1. General Principles & Basic Science

A patient presents with a procurvatum deformity of the tibial diaphysis. If an anterior closing wedge osteotomy is planned, where must the hinge axis be located relative to the apex of the deformity to avoid unintended shortening or lengthening of the mechanical axis?

. At the anterior cortex of the tibia
. At the posterior cortex of the tibia
. Within the central intramedullary canal
. At the medial cortex
. At the lateral cortex

Correct Answer & Explanation

. At the posterior cortex of the tibia

Explanation

A procurvatum deformity has an anterior apex. To perform a closing wedge osteotomy without altering limb length, the wedge is removed from the convex (anterior) side, and the hinge must be placed exactly on the intact concave side, which is the posterior cortex.

Question 15649

Topic: Physiology & Rehabilitation

During normal human walking, the gastrocnemius-soleus complex provides the primary propulsive force. At which phase of the gait cycle do these ankle plantarflexors exhibit their peak electromyographic (EMG) activity?

. Loading response
. Mid-stance
. Terminal stance
. Initial swing
. Terminal swing

Correct Answer & Explanation

. Terminal stance

Explanation

The gastrocnemius-soleus complex provides the power for push-off during normal gait. Peak EMG activity of the ankle plantarflexors occurs during terminal stance to stabilize the ankle and propel the body forward.

Question 15650

Topic: Physiology & Rehabilitation

An uncompensated Trendelenburg gait (abductor lurch) involves leaning the trunk laterally over the stance leg. What is the primary biomechanical consequence of this compensatory movement?

. Increases the hip abductor moment arm
. Moves the center of gravity closer to the hip's center of rotation
. Increases the total joint reaction force for joint stability
. Increases the passive tension in the iliotibial band
. Facilitates contralateral limb clearance during swing phase

Correct Answer & Explanation

. Moves the center of gravity closer to the hip's center of rotation

Explanation

Leaning the trunk laterally over the affected hip shifts the body's center of mass closer to the center of rotation of the hip joint. This dramatically decreases the body weight moment arm, reducing the workload required by the weak hip abductors.

Question 15651

Topic: Physiology & Rehabilitation

A patient presents with an audible "foot slap" immediately following initial contact during gait. Which phase of the gait cycle is affected, and what specific muscle contraction is failing?

. Initial contact to loading response; concentric contraction of tibialis anterior
. Initial contact to loading response; eccentric contraction of tibialis anterior
. Midstance; concentric contraction of gastrocnemius
. Terminal stance; eccentric contraction of soleus
. Swing phase; concentric contraction of extensor hallucis longus

Correct Answer & Explanation

. Initial contact to loading response; eccentric contraction of tibialis anterior

Explanation

Foot slap occurs due to the failure of the tibialis anterior to adequately decelerate plantarflexion after heel strike. This requires an eccentric contraction of the ankle dorsiflexors during the transition from initial contact to the loading response phase.

Question 15652

Topic: 1. General Principles & Basic Science

According to the principles of deformity correction (Osteotomy Rule 1), if an osteotomy and the axis of correction of angulation (ACA) are both positioned exactly at the Center of Rotation of Angulation (CORA), what is the resulting geometric effect?

. Pure angulation with complete translation
. Pure translation with no angulation
. Pure angulation without translation
. Angulation accompanied by paradoxical shortening
. Collinear alignment with varus translation

Correct Answer & Explanation

. Pure angulation without translation

Explanation

Osteotomy Rule 1 dictates that when both the osteotomy and the ACA are placed at the CORA, the bone segments undergo pure angulation. The mechanical axis is fully realigned without introducing any secondary translational deformity.

Question 15653

Topic: Physiology & Rehabilitation

A patient walking with a stiff right knee due to arthrofibrosis demonstrates a vaulting gait. Which of the following best describes the kinematic hallmark of this compensatory gait pattern?

. Excessive right hip hiking during the right swing phase
. Excessive plantarflexion of the left ankle during the left stance phase
. Excessive circumduction of the right leg during swing
. Excessive dorsiflexion of the right ankle during stance
. Lateral trunk lean towards the left side during stance

Correct Answer & Explanation

. Excessive plantarflexion of the left ankle during the left stance phase

Explanation

A vaulting gait is a compensatory mechanism used to clear a functionally long limb (such as a stiff knee) during its swing phase. It is characterized by excessive plantarflexion (rising on the toes) of the contralateral, normal stance limb.

Question 15654

Topic: 1. General Principles & Basic Science

During an opening wedge high tibial osteotomy (HTO) for medial compartment osteoarthritis, the anterior gap is opened more than the posterior gap. What is the expected sagittal plane consequence?

. Decreased posterior tibial slope
. Increased posterior tibial slope
. Anterior translation of the tibia relative to the femur
. Development of patella baja
. Development of patella alta

Correct Answer & Explanation

. Increased posterior tibial slope

Explanation

Due to the triangular cross-section of the proximal tibia, maintaining the native sagittal slope requires the posterior gap to be larger than the anterior gap (roughly 2:1). Opening the anterior gap more than the posterior gap tilts the proximal fragment posteriorly, increasing the posterior tibial slope.

Question 15655

Topic: Physiology & Rehabilitation

During the normal human gait cycle, the peak joint reaction force at the hip occurs during which phase?

. Initial contact
. Mid-stance
. Terminal stance
. Mid-swing
. Terminal swing

Correct Answer & Explanation

. Terminal stance

Explanation

The hip joint reaction force is biphasic with peaks at early stance and late stance. The highest peak (up to 3-4 times body weight) occurs during terminal stance (push-off) due to the combination of maximum active abductor and flexor muscle forces stabilizing the pelvis.

Question 15656

Topic: 1. General Principles & Basic Science

Based on the principles of deformity correction, if an osteotomy is performed at a level different from the Center of Rotation of Angulation (CORA), but the hinge (axis of correction) is placed exactly on the CORA, what is the resulting alignment of the bone?

. Purely angular correction without any translation.
. Angular correction combined with a predictable translation of the bone ends.
. Complete failure of angular correction, resulting only in translation.
. An iatrogenic secondary deformity where the mechanical axes remain parallel but not collinear.
. A rotational deformity strictly in the axial plane.

Correct Answer & Explanation

. Angular correction combined with a predictable translation of the bone ends.

Explanation

This is Paley's Rule 2 of deformity correction. When the osteotomy is remote from the CORA but the hinge axis is on the CORA, the mechanical axis is restored (collinear), but the bone ends will translate relative to each other at the osteotomy site.

Question 15657

Topic: Physiology & Rehabilitation

In patients with spastic diplegic cerebral palsy, crouch gait is a common ambulatory deviation. Overactivity and contracture of which muscle group is the primary driver of this specific gait pattern?

. Quadriceps
. Gluteus maximus
. Tibialis anterior
. Hamstrings
. Triceps surae

Correct Answer & Explanation

. Hamstrings

Explanation

Crouch gait is characterized by excessive hip and knee flexion during the stance phase. It is primarily driven by spasticity and contracture of the hamstrings and psoas, often exacerbated by a lengthened or weak Achilles tendon (triceps surae).

Question 15658

Topic: Physiology & Rehabilitation

During the first rocker (heel rocker) of the stance phase in normal gait, which muscle undergoes eccentric contraction to control the rate of plantarflexion and prevent 'foot slap'?

. Gastrocnemius
. Soleus
. Tibialis anterior
. Tibialis posterior
. Extensor hallucis longus

Correct Answer & Explanation

. Tibialis anterior

Explanation

The first rocker occurs from initial contact to loading response. The tibialis anterior contracts eccentrically to slow the plantarflexion of the foot, smoothing the transition to foot flat and preventing a 'slap'.

Question 15659

Topic: Physiology & Rehabilitation

A patient with severe unilateral quadriceps weakness will classically compensate during the stance phase of gait by demonstrating which of the following trunk movements?

. Lateral trunk lean toward the affected side.
. Lateral trunk lean away from the affected side.
. Forward trunk lean over the affected leg.
. Backward trunk lean over the affected leg.
. Excessive pelvic rotation in the transverse plane.

Correct Answer & Explanation

. Forward trunk lean over the affected leg.

Explanation

To compensate for quadriceps weakness, the patient uses a forward trunk lean during the early stance phase. This shifts the body's center of gravity anterior to the knee axis, creating an extensor moment that mechanically locks the knee and prevents buckling.

Question 15660

Topic: Physiology & Rehabilitation

A patient with a drop foot demonstrates a 'steppage gait'. This compensatory mechanism primarily involves exaggerated motion at which joints during which phase of gait?

. Exaggerated hip and knee flexion during the stance phase.
. Exaggerated hip and knee flexion during the swing phase.
. Exaggerated hip extension and knee flexion during the swing phase.
. Exaggerated pelvic hike and circumduction during the stance phase.
. Exaggerated ankle dorsiflexion of the contralateral limb during the stance phase.

Correct Answer & Explanation

. Exaggerated hip and knee flexion during the swing phase.

Explanation

Steppage gait is a swing-phase deviation used to clear a plantarflexed foot (drop foot). The patient compensates by increasing hip and knee flexion on the affected side to lift the foot higher during swing.

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