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1. General Principles & Basic Science MCQs

Practice Set 787 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 15721

Topic: Physiology & Rehabilitation

A 65-year-old patient with severe hip abductor weakness demonstrates a compensated Trendelenburg gait. Which of the following biomechanical adaptations is characteristic during the stance phase of the affected limb?

. Shift of the center of mass away from the affected hip
. Shift of the center of mass toward the affected hip
. Increased varus moment at the knee
. Premature heel off
. Prolonged swing phase

Correct Answer & Explanation

. Shift of the center of mass toward the affected hip

Explanation

In a compensated Trendelenburg gait, the patient leans their trunk laterally over the affected hip during stance. This shifts the center of mass toward the joint, significantly reducing the moment arm and the force required by the weak hip abductors to maintain a level pelvis.

Question 15722

Topic: 1. General Principles & Basic Science

When planning a lower extremity deformity correction using an osteotomy, the osteotomy is placed proximal to the Center of Rotation of Angulation (CORA), but the angulation correction axis (ACA) passes directly through the CORA. Which of the following describes the resulting geometric outcome?

. Pure angulation without translation of the bone ends
. Angulation with translation of the bone ends at the osteotomy site
. Pure translation without angular correction
. Creation of an unintended joint line obliquity
. Unintended limb lengthening of exactly 1 centimeter

Correct Answer & Explanation

. Angulation with translation of the bone ends at the osteotomy site

Explanation

According to the principles of deformity correction (Rule 2), if the ACA passes through the CORA but the osteotomy is made at a different level, the mechanical axis will be restored. However, this results in angulation combined with translation of the bone ends at the osteotomy site.

Question 15723

Topic: Physiology & Rehabilitation

During the normal human gait cycle, which muscle acts eccentrically to control the transition from initial contact to foot flat (the first rocker)?

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

Correct Answer & Explanation

. Tibialis anterior

Explanation

The first rocker (heel rocker) occurs from initial contact to foot flat. The tibialis anterior acts eccentrically during this phase to control plantarflexion and prevent the foot from slapping against the ground.

Question 15724

Topic: Infection, Pharmacology & VTE

In a primary total knee arthroplasty for a patient with a rigid 15-degree varus deformity, what is the generally accepted initial sequence of medial soft tissue release after removal of all osteophytes?

. Superficial MCL, deep MCL, pes anserinus
. Deep MCL, posteromedial capsule, superficial MCL
. Pes anserinus, superficial MCL, deep MCL
. Posterior cruciate ligament, superficial MCL, deep MCL
. Semimembranosus, deep MCL, posteromedial capsule

Correct Answer & Explanation

. Deep MCL, posteromedial capsule, superficial MCL

Explanation

For a fixed varus deformity, osteophytes are first removed. The initial sequential release typically involves the deep MCL, followed by the posteromedial capsule, and then the superficial MCL or pes anserinus if further correction is needed.

Question 15725

Topic: 1. General Principles & Basic Science

A patient requires a high tibial osteotomy for a varus deformity but also exhibits significant genu recurvatum. To simultaneously correct the varus malalignment and the recurvatum, how should the tibial slope be managed during the osteotomy?

. Increase the posterior slope by performing an anterior opening wedge osteotomy
. Decrease the posterior slope by performing an anterior opening wedge osteotomy
. Perform a neutral opening wedge osteotomy without slope modification
. Increase the posterior slope by performing an anterior closing wedge osteotomy
. Decrease the posterior slope by performing a posterior closing wedge osteotomy

Correct Answer & Explanation

. Increase the posterior slope by performing an anterior opening wedge osteotomy

Explanation

Genu recurvatum is associated with a decreased posterior tibial slope. To correct recurvatum during a high tibial osteotomy, the surgeon should increase the posterior tibial slope, which can be achieved through an anterior opening wedge technique.

Question 15726

Topic: 1. General Principles & Basic Science

A patient with generalized lower extremity weakness is prescribed a solid ankle-foot orthosis (AFO) locked in 5 degrees of plantarflexion. How will this orthotic intervention primarily alter knee biomechanics during the stance phase of gait?

. Increase the knee flexion moment
. Increase the knee extension moment
. Eliminate the varus moment at the knee
. Shift the center of pressure laterally
. Increase knee anterior shear force

Correct Answer & Explanation

. Increase the knee extension moment

Explanation

An AFO set in plantarflexion limits forward progression of the tibia over the foot during the stance phase. This maintains the ground reaction force vector anterior to the knee, creating a knee extension moment which helps prevent knee buckling in patients with weak quadriceps.

Question 15727

Topic: 1. General Principles & Basic Science

A patient with an anterior cruciate ligament (ACL) deficient knee exhibits a specific gait adaptation to reduce anterior tibial translation during walking. Which of the following best describes the kinematics of this "quadriceps avoidance" gait?

. Increased knee flexion during the swing phase
. Exaggerated hip extension during the terminal stance
. Decreased knee flexion during the loading response
. Avoidance of knee extension during the swing phase
. Increased ankle plantarflexion during initial contact

Correct Answer & Explanation

. Decreased knee flexion during the loading response

Explanation

In a "quadriceps avoidance" gait, patients with ACL deficiency decrease normal knee flexion during the loading response (early stance). This minimizes quadriceps contraction, which would otherwise pull the tibia anteriorly and provoke instability.

Question 15728

Topic: 1. General Principles & Basic Science

When performing a corrective osteotomy for a lower extremity angular deformity, placing the osteotomy and the mechanical hinge exactly at the Center of Rotation of Angulation (CORA) will result in which of the following?

. Correction of angulation with translation of the mechanical axis
. Correction of angulation without translation
. Creation of a secondary deformity in the orthogonal plane
. Pure lengthening of the limb segment
. Translation without angular correction

Correct Answer & Explanation

. Correction of angulation without translation

Explanation

The CORA principle dictates that when the osteotomy and the mechanical hinge are both placed precisely at the CORA, pure angular correction is achieved without any resultant translation of the bone segments.

Question 15729

Topic: Physiology & Rehabilitation

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

. Pelvic rotation
. Lateral displacement of the pelvis
. Knee flexion in stance
. Ankle pronation
. Hip adduction

Correct Answer & Explanation

. Knee flexion in stance

Explanation

Knee flexion during the stance phase (typically around 15 degrees) helps to lower the apex of the center of gravity's vertical excursion. This mechanism smoothes the pathway of the body's center of mass, thereby reducing overall energy expenditure.

Question 15730

Topic: 1. General Principles & Basic Science

A patient undergoes a medial opening-wedge high tibial osteotomy (HTO) for a symptomatic varus knee deformity. Compared to a lateral closing-wedge HTO, the opening-wedge technique is inherently more likely to cause which of the following?

. Decreased posterior tibial slope
. Increased posterior tibial slope
. Patella alta
. Limb shortening
. Direct injury to the common peroneal nerve

Correct Answer & Explanation

. Increased posterior tibial slope

Explanation

Due to the triangular shape of the proximal tibia (narrower anteriorly than posteriorly), a medial opening-wedge HTO inherently increases the posterior tibial slope unless the anterior gap is intentionally kept smaller than the posterior gap.

Question 15731

Topic: Physiology & Rehabilitation

During the stance phase of gait, a patient demonstrates a pronounced lateral trunk lean towards the side of the supporting limb (gluteus medius lurch). This specific kinematic adaptation most effectively achieves which of the following biomechanical goals?

. Increases the moment arm of the hip abductor muscles
. Decreases the joint reaction force across the supporting hip
. Increases the vertical ground reaction force
. Compensates for an excessively weak gluteus maximus
. Accelerates the swing phase of the contralateral limb

Correct Answer & Explanation

. Decreases the joint reaction force across the supporting hip

Explanation

A lateral trunk lean (Trendelenburg gait) shifts the body's center of gravity closer to the center of the stance-phase hip joint. This dramatically reduces the abductor muscle force required to maintain a level pelvis, thereby decreasing the overall hip joint reaction force.

Question 15732

Topic: Physiology & Rehabilitation

During normal human walking, the vertical ground reaction force (vGRF) curve typically exhibits a characteristic "double-hump" pattern. The two peaks of this curve correspond precisely to which events in the normal gait cycle?

. Initial contact and pre-swing
. Loading response and terminal stance
. Mid-stance and initial swing
. Heel strike and toe-off
. Mid-stance and terminal swing

Correct Answer & Explanation

. Loading response and terminal stance

Explanation

The "double-hump" vGRF pattern occurs due to weight acceptance during the loading response (first peak) and push-off during terminal stance (second peak). The trough between them represents mid-stance when the center of mass is at its highest point.

Question 15733

Topic: Physiology & Rehabilitation

A 65-year-old female with severe unilateral hip osteoarthritis exhibits a pronounced Trendelenburg gait. Biomechanically, how does the observed lateral trunk shift during the stance phase of the affected limb alter the forces acting on the hip joint?

. It shifts the center of mass away from the hip joint, increasing the abductor muscle moment arm.
. It shifts the center of mass toward the hip joint center, decreasing the demand on the weak abductor muscles.
. It lengthens the functional length of the affected limb, increasing ground reaction forces.
. It increases the external adductor moment, requiring a greater concentric force from the gluteus medius.
. It shifts the ground reaction force vector posterior to the hip joint, generating an extension moment.

Correct Answer & Explanation

. It shifts the center of mass toward the hip joint center, decreasing the demand on the weak abductor muscles.

Explanation

A Trendelenburg (abductor lurch) gait compensates for weak hip abductors by laterally shifting the trunk over the stance limb. This moves the body's center of mass closer to the hip joint center, significantly reducing the external adductor moment and decreasing the demand on the deficient abductor muscles.

Question 15734

Topic: Physiology & Rehabilitation

A patient presents with a Trendelenburg gait due to severe hip abductor weakness. During the stance phase of the affected limb, what is the primary biomechanical purpose of the compensatory lateral trunk shift?

. To increase the moment arm of the hip abductors
. To shift the center of mass closer to the hip joint center
. To decrease the force required by the quadriceps
. To increase the ground reaction force vector magnitude
. To prevent internal rotation of the pelvis

Correct Answer & Explanation

. To shift the center of mass closer to the hip joint center

Explanation

By shifting the trunk laterally over the affected hip, the patient moves the center of mass closer to the center of the hip joint. This significantly decreases the lever arm of body weight, thereby reducing the torque that the weak abductors must counteract.

Question 15735

Topic: 1. General Principles & Basic Science

According to 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 of the correction device is placed exactly at the CORA, what is the geometric result?

. Pure angulation without translation
. Pure translation without angulation
. Collinear alignment with expected translation at the osteotomy site
. Loss of limb length with paradoxical varus
. Joint line obliquity

Correct Answer & Explanation

. Collinear alignment with expected translation at the osteotomy site

Explanation

Osteotomy Rule 2 states that if the hinge is at the CORA but the osteotomy is at a different level, the mechanical axis will realign collinearly. However, this inevitably results in translation of the bony fragments at the osteotomy site.

Question 15736

Topic: Infection, Pharmacology & VTE

During a primary TKA for a severe varus deformity, step-wise medial soft tissue release is necessary. After releasing the deep medial collateral ligament (MCL) and removing osteophytes, the knee remains tight in extension. Which structure should typically be released next to address this extension-predominant tightness?

. Superficial MCL
. Posteromedial capsule
. Pes anserinus tendons
. Popliteus tendon

Correct Answer & Explanation

. Posteromedial capsule

Explanation

The posteromedial capsule is a primary restraint to knee extension on the medial side. Releasing it selectively corrects a tight medial extension gap more than the flexion gap, preserving the superficial MCL for coronal stability if possible.

Question 15737

Topic: 1. General Principles & Basic Science

Anterior opening-wedge high tibial osteotomy (HTO) is planned to correct a severe genu recurvatum deformity. If the hinge is placed too far anteriorly, which of the following is the most likely consequence regarding the patellofemoral joint?

. Patella alta due to proximal translation of the tibial tubercle
. Patella baja due to distalization of the tibial tubercle
. Increased lateral patellar tilt
. Decreased Q-angle

Correct Answer & Explanation

. Patella baja due to distalization of the tibial tubercle

Explanation

An anterior opening-wedge osteotomy increases the posterior slope and lengthens the anterior cortex. This effectively distalizes the tibial tubercle relative to the joint line, increasing the risk of iatrogenic patella baja.

Question 15738

Topic: Physiology & Rehabilitation

During the loading response phase of a normal gait cycle, what is the primary role of the quadriceps muscle group?

. Concentric contraction to accelerate the limb into swing
. Isometric contraction to prevent any knee motion
. Eccentric contraction to absorb shock and control knee flexion
. They are entirely inactive during this phase

Correct Answer & Explanation

. Eccentric contraction to absorb shock and control knee flexion

Explanation

During the loading response (weight acceptance), the knee flexes approximately 15 degrees. The quadriceps contract eccentrically to control this flexion, which serves as a crucial shock-absorbing mechanism.

Question 15739

Topic: 1. General Principles & Basic Science

When utilizing a computer-assisted hexapod circular external fixator (e.g., Taylor Spatial Frame) for complex lower extremity deformity correction, which of the following parameters is an absolute prerequisite to generate an accurate software prescription?

. The osteotomy must be located exactly at the master ring level
. Accurate definition of the reference ring and its precise mounting parameters relative to the reference bone fragment
. A minimum of six orthogonal radiographic views
. Placement of the master ring parallel to the ground

Correct Answer & Explanation

. Accurate definition of the reference ring and its precise mounting parameters relative to the reference bone fragment

Explanation

The hexapod software calculates strut adjustments based on the exact spatial relationship between the reference ring and the bone. Inaccurate mounting parameters (AP, lateral, and axial offsets) will lead to an incorrect prescription and malalignment.

Question 15740

Topic: Physiology & Rehabilitation

According to the determinants of normal gait, which of the following kinematic mechanisms is most responsible for minimizing the superior vertical excursion of the body's center of mass during mid-stance?

. Pelvic rotation
. Pelvic drop (tilt) and stance phase knee flexion
. Ankle plantarflexion at toe-off
. Lateral trunk shift

Correct Answer & Explanation

. Pelvic drop (tilt) and stance phase knee flexion

Explanation

Pelvic drop (tilt on the swing side) and knee flexion during stance both serve to lower the peak vertical height of the center of mass during mid-stance. This conserves energy by reducing vertical displacement.

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