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1. General Principles & Basic Science MCQs

Practice Set 782 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 15621

Topic: 1. General Principles & Basic Science

In a patient with a complex triplanar proximal tibial deformity (varus, procurvatum, and internal rotation), a single-cut focal dome osteotomy is planned. According to the principles of multiplanar deformity correction, how must the axis of rotation for the osteotomy be oriented?

. Perpendicular to the plane of maximal deformity.
. Parallel to the plane of maximal deformity.
. In the true coronal plane of the tibia.
. In the true sagittal plane of the tibia.
. Perpendicular to the anatomic axis of the femur.

Correct Answer & Explanation

. Perpendicular to the plane of maximal deformity.

Explanation

To correct a multiplanar deformity with a single osteotomy, the deformity must be calculated as a single oblique plane deformity. The axis of correction (hinge) must be placed perpendicular to this plane of maximal deformity.

Question 15622

Topic: 1. General Principles & Basic Science

A patient with patella alta complains of anterior knee pain and weakness during stair climbing. How does patella alta biomechanically alter the extensor mechanism during early knee flexion?

. It increases the moment arm of the quadriceps, reducing overall patellofemoral contact pressure.
. It decreases the moment arm of the quadriceps, requiring greater quadriceps force to generate the same extension torque.
. It increases the mechanical advantage of the patellar tendon by anteriorizing the force vector.
. It eliminates the lateral subluxation vector (J-sign) during terminal extension.
. It shifts the primary contact area of the patella to the distal pole during deep flexion.

Correct Answer & Explanation

. It decreases the moment arm of the quadriceps, requiring greater quadriceps force to generate the same extension torque.

Explanation

Patella alta delays engagement of the patella into the trochlear groove during early flexion. This effectively decreases the moment arm of the extensor mechanism, requiring higher quadriceps force to maintain torque, which can lead to anterior knee pain.

Question 15623

Topic: Physiology & Rehabilitation

During the loading response phase of a normal gait cycle, where does the ground reaction force (GRF) vector pass relative to the knee joint, and which muscle group is primarily active to control this motion?

. Posterior to the knee; Quadriceps (eccentric contraction)
. Anterior to the knee; Quadriceps (concentric contraction)
. Posterior to the knee; Hamstrings (eccentric contraction)
. Anterior to the knee; Hamstrings (concentric contraction)
. Directly through the knee axis; Gastrocnemius (isometric contraction)

Correct Answer & Explanation

. Posterior to the knee; Quadriceps (eccentric contraction)

Explanation

In the loading response, the GRF vector passes posterior to the knee, creating a flexion moment. The quadriceps fire eccentrically to absorb shock and control this early knee flexion.

Question 15624

Topic: 1. General Principles & Basic Science

According to Paley's rules of deformity correction (Rule 3), if an osteotomy is performed at a level separate from the Center of Rotation of Angulation (CORA) and the hinge axis is placed exactly at the osteotomy site, what is the resulting geometric change to the mechanical axis?

. Complete angular correction with the mechanical axes becoming perfectly collinear.
. Angular correction is achieved, but a secondary translation deformity is created.
. Translation is corrected, but an angular deformity remains.
. Pure lengthening occurs with no change to the mechanical axis.
. The mechanical axes remain parallel but fail to intersect.

Correct Answer & Explanation

. Angular correction is achieved, but a secondary translation deformity is created.

Explanation

Paley's Rule 3 states that if the osteotomy and hinge are both placed away from the CORA, angular correction will be accompanied by an iatrogenic translational deformity. To avoid this, the hinge must be kept on the CORA.

Question 15625

Topic: Physiology & Rehabilitation

In an uncompensated Trendelenburg gait due to right gluteus medius weakness, which kinematic abnormality is observed during the stance phase of the right lower extremity?

. The pelvis drops on the right side.
. The pelvis drops on the left side.
. The trunk leans excessively to the left side.
. The right knee goes into recurvatum.
. The left hip excessively externally rotates.

Correct Answer & Explanation

. The pelvis drops on the left side.

Explanation

In an uncompensated Trendelenburg gait, weak abductors on the stance leg (right) fail to maintain a level pelvis, causing the pelvis to drop on the contralateral (left) swing side.

Question 15626

Topic: Physiology & Rehabilitation

During the terminal stance phase of normal human walking, what is the primary role of the triceps surae (gastroc-soleus complex)?

. Concentric contraction to initiate early swing.
. Eccentric contraction to control tibial advancement over the planted foot.
. Concentric contraction to provide maximum push-off power.
. Eccentric contraction to decelerate knee extension.
. Isometric contraction to stabilize the subtalar joint.

Correct Answer & Explanation

. Eccentric contraction to control tibial advancement over the planted foot.

Explanation

During terminal stance, the gastroc-soleus complex primarily fires eccentrically to control the forward advancement of the tibia over the foot (controlling dorsiflexion). Peak concentric push-off power occurs slightly later in pre-swing.

Question 15627

Topic: 1. General Principles & Basic Science

When analyzing the mechanical axis of the lower extremity for a complex femoral deformity

, the mechanical axis of the femur is normally oriented at what angle relative to the anatomic axis of the femur?

. 0 degrees
. 3 degrees of varus
. 5 to 7 degrees of valgus
. 9 to 11 degrees of varus
. 12 to 14 degrees of valgus

Correct Answer & Explanation

. 5 to 7 degrees of valgus

Explanation

The normal anatomic axis of the femur is typically in 5 to 7 degrees of valgus relative to its mechanical axis (which connects the center of the femoral head to the center of the knee).

Question 15628

Topic: 1. General Principles & Basic Science

Patellofemoral joint reaction forces (PFJRF) vary significantly depending on the activity. Among the following activities of daily living, which generates the highest peak PFJRF?

. Level walking
. Ascending stairs
. Descending stairs
. Cycling at moderate resistance
. Rising from a seated position

Correct Answer & Explanation

. Descending stairs

Explanation

Descending stairs generates the highest patellofemoral joint reaction forces, often reaching up to 7 to 8 times body weight due to the high eccentric quadriceps demand required to lower the body's center of gravity.

Question 15629

Topic: 1. General Principles & Basic Science

The 'screw-home' mechanism of the knee is essential for locking the joint in terminal extension. During the final 20 degrees of open-chain knee extension, what specific kinematic motion occurs?

. The tibia internally rotates relative to the femur.
. The tibia externally rotates relative to the femur.
. The femur externally rotates relative to the tibia.
. The patella translates inferiorly.
. The tibia translates posteriorly relative to the femur.

Correct Answer & Explanation

. The tibia externally rotates relative to the femur.

Explanation

In open-chain knee extension, the tibia externally rotates relative to the femur during the final degrees of extension to 'lock' the knee. In closed-chain extension, the femur internally rotates on the fixed tibia.

Question 15630

Topic: Physiology & Rehabilitation

Human gait utilizes several determinants to minimize the displacement of the center of gravity (COG), thereby reducing energy expenditure. Which of the following mechanisms is most responsible for limiting the highest vertical excursion of the COG during midstance?

. Pelvic rotation in the transverse plane
. Knee flexion during the stance phase
. Ankle plantarflexion at push-off
. Lateral displacement of the pelvis
. Arm swing during contralateral step

Correct Answer & Explanation

. Knee flexion during the stance phase

Explanation

Knee flexion during the stance phase (approximately 15 degrees) shortens the lower extremity during midstance, effectively limiting the peak vertical excursion of the center of gravity.

Question 15631

Topic: 1. General Principles & Basic Science

To accurately locate the center of rotation of angulation (CORA) in a uniapical diaphyseal deformity, a surgeon must plot two specific lines. Which of the following defines the CORA?

. The intersection of the proximal anatomical axis and the distal joint orientation line.
. The intersection of the proximal and distal anatomical or mechanical axes.
. The midpoint between the mechanical axis deviation and the joint line.
. The bisection of the angle formed by the metaphyseal-diaphyseal junction.
. The exact apex of the soft tissue deformity on the convex side.

Correct Answer & Explanation

. The intersection of the proximal and distal anatomical or mechanical axes.

Explanation

The CORA is defined geometrically as the point where the proximal mechanical (or anatomical) axis intersects the distal mechanical (or anatomical) axis of the deformed bone segment.

Question 15632

Topic: 1. General Principles & Basic Science

A patient is evaluated for a varus knee deformity. Radiographs reveal a Joint Line Convergence Angle (JLCA) of 6 degrees (normal is 0-2 degrees). This finding most strongly indicates the presence of which of the following?

. A purely diaphyseal bowing deformity
. An intra-articular deformity or ligamentous laxity
. A primary compensatory valgus deformity of the distal tibia
. A fixed rotational deformity of the femur
. A pure extra-articular metaphyseal deformity

Correct Answer & Explanation

. An intra-articular deformity or ligamentous laxity

Explanation

An abnormally widened Joint Line Convergence Angle (JLCA) indicates that the joint lines of the femur and tibia are not parallel. This points to an intra-articular deformity, such as asymmetric cartilage loss or collateral ligament laxity.

Question 15633

Topic: Biomechanics & Biomaterials

In biomechanical planning for fracture fixation, a surgeon contemplates replacing a stainless steel compression plate with a titanium plate of identical geometric dimensions. How will the bending stiffness of the construct change, and which material property is responsible?

. Stiffness will increase due to titanium's higher yield strength.
. Stiffness will decrease due to titanium's lower elastic (Young's) modulus.
. Stiffness will remain unchanged because the area moment of inertia is identical.
. Stiffness will increase due to titanium's higher area moment of inertia.
. Stiffness will decrease due to titanium's lower ultimate tensile strength.

Correct Answer & Explanation

. Stiffness will decrease due to titanium's lower elastic (Young's) modulus.

Explanation

Bending stiffness depends on both geometry (area moment of inertia) and the material's elastic modulus (Young's modulus). Titanium has a lower elastic modulus than stainless steel, making a plate of identical dimensions less stiff.

Question 15634

Topic: 1. General Principles & Basic Science

The Taylor Spatial Frame (TSF) utilizes the Stewart-Gough platform principle for complex deformity correction. Through its six adjustable struts, the TSF is mathematically capable of simultaneous correction in a maximum of how many degrees of freedom?

. 3
. 4
. 5
. 6
. 7

Correct Answer & Explanation

. 6

Explanation

The hexapod system controls spatial position via 6 degrees of freedom: translation in three planes (coronal, sagittal, axial) and rotation in three planes (angulation in coronal/sagittal planes and rotation in the axial plane).

Question 15635

Topic: 1. General Principles & Basic Science

According to Paley's Rule 1 of deformity correction, when the osteotomy is performed exactly at the CORA and the hinge axis is also placed exactly at the CORA, what is the kinematic outcome of the opening wedge correction?

. Angular correction with complete elimination of translation.
. Angular correction with intentional, controlled translation.
. Lengthening of the mechanical axis with secondary translation.
. Collinear realignment of the anatomical axis with an induced mechanical axis deviation.
. Translation of the distal segment without any angular change.

Correct Answer & Explanation

. Angular correction with complete elimination of translation.

Explanation

Paley's Rule 1 states that if both the osteotomy and the hinge of the corrective device are located at the CORA, the mechanical and anatomical axes will correct collinearly with pure angulation and no secondary translation.

Question 15636

Topic: Physiology & Rehabilitation

Peak knee flexion during the stance phase of normal human walking occurs at which specific event, and what is its primary function?

. Initial contact, to decelerate the forward momentum of the trunk
. Loading response, to facilitate shock absorption
. Midstance, to lower the center of gravity
. Terminal stance, to store energy for push-off
. Pre-swing, to clear the toes from the ground

Correct Answer & Explanation

. Loading response, to facilitate shock absorption

Explanation

Peak knee flexion during the stance phase (approximately 15 to 20 degrees) occurs at the end of the loading response (about 15% of the gait cycle). Its primary biomechanical function is to absorb the shock of initial ground contact.

Question 15637

Topic: 1. General Principles & Basic Science

In a static single-leg stance, the abductor muscle force required to maintain a level pelvis is primarily determined by the ratio of the body weight lever arm to the abductor lever arm. What is the approximate ratio of these lever arms (body weight : abductors) in a normal adult pelvis?

. 1:1
. 2:1
. 3:1
. 4:1
. 5:1

Correct Answer & Explanation

. 3:1

Explanation

The lever arm for body weight from the center of the femoral head is roughly three times longer than the lever arm for the abductor muscles. Consequently, the abductors must exert a force approximately three times body weight to maintain a level pelvis.

Question 15638

Topic: Physiology & Rehabilitation

During normal human walking, at which phase of the gait cycle does the ankle plantarflexor muscle group generate its maximum concentric power (often referred to as the A2 power burst)?

. Initial contact
. Loading response
. Midstance
. Terminal stance into pre-swing
. Initial swing

Correct Answer & Explanation

. Terminal stance into pre-swing

Explanation

The peak concentric power generation of the ankle plantarflexors occurs during terminal stance and transitions into pre-swing. This provides the primary propulsive force (push-off) for forward progression of the body.

Question 15639

Topic: 1. General Principles & Basic Science

When utilizing a hexapod external fixator (e.g., Taylor Spatial Frame) for multiplanar deformity correction, the user must input accurate "mounting parameters" into the software. What do these parameters specifically define?

. The length and sequence of the six adjustable struts
. The spatial relationship between the reference ring and the origin of the corresponding bone segment
. The magnitude and direction of the mechanical axis deviation
. The anticipated chronologic schedule of strut adjustments
. The center of rotation of angulation (CORA) in three dimensions

Correct Answer & Explanation

. The spatial relationship between the reference ring and the origin of the corresponding bone segment

Explanation

Mounting parameters define the exact spatial position (anteroposterior, lateral, and axial translation) of the reference ring relative to the bone it is fixed to. Inaccurate mounting parameters will result in an erroneous deformity correction trajectory.

Question 15640

Topic: Physiology & Rehabilitation

A patient exhibits a compensated Trendelenburg gait (abductor lurch) over the right lower extremity. How is the body's center of mass shifted during the stance phase to minimize the demands on the affected right hip abductors?

. Shifted anteriorly over the right hip joint
. Shifted laterally over the left lower extremity
. Shifted laterally over the right lower extremity
. Shifted posteriorly to lock the hip joint
. Maintained centrally by decreasing the stride length

Correct Answer & Explanation

. Shifted laterally over the right lower extremity

Explanation

In a compensated Trendelenburg gait, the patient leans the trunk laterally over the weak (right) hip. This shifts the center of gravity closer to the center of rotation of the hip joint, shortening the body weight lever arm and reducing the required abductor force.

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