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1. General Principles & Basic Science MCQs

Practice Set 781 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 15601

Topic: 1. General Principles & Basic Science

A patient with severe bilateral coxa valga presents for biomechanical evaluation. How does coxa valga structurally alter hip joint biomechanics compared to normal anatomy?

. It increases the abductor moment arm and decreases joint reaction forces
. It decreases the abductor moment arm and increases joint reaction forces
. It increases the moment arm of body weight and decreases abductor muscle force
. It decreases both the abductor moment arm and joint reaction forces
. It has no significant effect on joint reaction forces but increases limb length

Correct Answer & Explanation

. It decreases the abductor moment arm and increases joint reaction forces

Explanation

Coxa valga is associated with a more vertical femoral neck, which decreases the lever arm of the hip abductors. This forces the abductors to contract more forcefully to maintain a level pelvis, significantly increasing the hip joint reaction force.

Question 15602

Topic: Physiology & Rehabilitation

During normal gait, "foot slap" immediately following initial contact is clinically prevented by which of the following muscular actions?

. Concentric contraction of the gastrocnemius
. Eccentric contraction of the tibialis anterior
. Isometric contraction of the tibialis posterior
. Concentric contraction of the extensor hallucis longus
. Eccentric contraction of the soleus

Correct Answer & Explanation

. Eccentric contraction of the tibialis anterior

Explanation

From initial contact to loading response, the ankle rapidly plantarflexes. The tibialis anterior and other ankle dorsiflexors contract eccentrically to control this descent, preventing an abrupt "foot slap."

Question 15603

Topic: 1. General Principles & Basic Science

When performing a medial opening wedge high tibial osteotomy (HTO) for a varus deformity, what is the most common unintended sagittal plane alteration if the osteotomy gap is opened symmetrically anteriorly and posteriorly?

. Increase in posterior tibial slope
. Decrease in posterior tibial slope
. Anterior translation of the tibial tubercle
. Proximal migration of the patella
. Posterior translation of the distal tibial segment

Correct Answer & Explanation

. Increase in posterior tibial slope

Explanation

Because the medial tibia is triangular (narrower anteriorly than posteriorly), a symmetric rectangular opening wedge will disproportionately prop open the anterior aspect. This commonly results in an unintended increase in the posterior tibial slope.

Question 15604

Topic: 1. General Principles & Basic Science

According to Paley's rules of deformity correction, if an osteotomy is performed at a level different from the Center of Rotation of Angulation (CORA), but the mechanical hinge is placed exactly on the CORA, what will be the resulting geometric alignment?

. Complete correction of angulation without any translation
. Partial correction of angulation with secondary translation
. Complete correction of angulation with an expected and planned translation
. Overcorrection of angulation with gap formation
. Pure translation without angular correction

Correct Answer & Explanation

. Complete correction of angulation with an expected and planned translation

Explanation

Osteotomy Rule 2 states that placing the axis of rotation at the CORA but making the osteotomy cut at a different level will completely correct the angular deformity. However, collinearity is restored at the cost of a planned, expected translation of the bone segments at the osteotomy site.

Question 15605

Topic: Physiology & Rehabilitation

During normal level walking, at what phase of the gait cycle does the compressive joint reaction force at the ankle reach its maximum, and what is its approximate magnitude relative to body weight (BW)?

. Mid-stance; 1 to 2 times BW
. Terminal stance; 4 to 5 times BW
. Initial contact; 2 to 3 times BW
. Loading response; 1 to 2 times BW
. Swing phase; less than 1 time BW

Correct Answer & Explanation

. Terminal stance; 4 to 5 times BW

Explanation

The ankle joint reaction force peaks during terminal stance (heel off) due to the massive contraction of the triceps surae required for push-off. This compressive force routinely reaches 4 to 5 times body weight (and sometimes higher).

Question 15606

Topic: Physiology & Rehabilitation

A patient exhibits a compensated Trendelenburg gait on the right side. During the stance phase of the right leg, which of the following kinematic adaptations is predominantly observed?

. The pelvis drops significantly on the right side
. The pelvis drops significantly on the left side
. The trunk leans laterally over the right hip
. The trunk leans laterally over the left hip
. Excessive external rotation of the right leg

Correct Answer & Explanation

. The trunk leans laterally over the right hip

Explanation

In a compensated Trendelenburg gait, the patient leans their trunk laterally over the weak stance hip (right side). This shifts the body's center of mass closer to the hip joint center, reducing the moment arm of body weight and decreasing the demand on the weak abductor muscles.

Question 15607

Topic: Biomechanics & Biomaterials

The Taylor Spatial Frame (TSF) utilizes Stewart-Gough platform biomechanics. How many independent parameters (degrees of freedom) must be established to fully define the spatial deformity of the moving fragment relative to the reference fragment?

. Four
. Five
. Six
. Eight
. Nine

Correct Answer & Explanation

. Six

Explanation

The Taylor Spatial Frame corrects deformities in all six degrees of freedom: anterior-posterior translation, lateral-medial translation, axial translation (length), anterior-posterior angulation (procurvatum/recurvatum), lateral-medial angulation (varus/valgus), and axial rotation.

Question 15608

Topic: Physiology & Rehabilitation

A patient with a 4 cm structural true limb length discrepancy (short right leg) presents for gait evaluation. Which of the following is the most common biomechanical compensation observed during the stance phase of the short (right) extremity?

. Increased right knee flexion
. Right ankle dorsiflexion
. Right ankle equinus (plantarflexion)
. Left pelvic drop
. Left trunk lean

Correct Answer & Explanation

. Right ankle equinus (plantarflexion)

Explanation

To functionally lengthen a short limb and reach the ground without dropping the pelvis excessively, patients typically adopt an equinus (plantarflexed) posture at the ankle on the shorter side during stance.

Question 15609

Topic: 1. General Principles & Basic Science

According to Paley's rules of deformity correction, if an osteotomy is performed at a level different from the Center of Rotation of Angulation (CORA), but the axis of correction (hinge) is placed exactly at the CORA, what is the resulting effect on the bone?

. Pure angular correction without translation
. Angulation with translation, restoring collinearity of the mechanical axes
. Pure translation without angular correction
. Angulation with translation, creating a secondary mechanical axis deviation
. Lengthening and rotation only

Correct Answer & Explanation

. Angulation with translation, restoring collinearity of the mechanical axes

Explanation

Paley's Rule 2 states that if the osteotomy is distinct from the CORA but the hinge (axis of correction) is at the CORA, angulation and translation occur simultaneously. This results in perfectly realigned (collinear) mechanical axes.

Question 15610

Topic: Physiology & Rehabilitation

During the normal human gait cycle, which of the following muscles acts eccentrically during the loading response (first rocker) to control the deceleration of the foot to the ground?

. Gastrocnemius
. Soleus
. Tibialis anterior
. Gluteus maximus
. Quadriceps

Correct Answer & Explanation

. Tibialis anterior

Explanation

The tibialis anterior acts eccentrically from initial contact to foot flat (loading response) to prevent foot slap. The gastrocnemius and soleus act eccentrically later in stance (second rocker) to control tibial advancement.

Question 15611

Topic: Physiology & Rehabilitation

A patient presents with a 'Trendelenburg gait' characterized by a lateral trunk lean towards the stance limb. Which of the following best describes the biomechanical rationale for this compensatory trunk shift?

. It increases the lever arm of the weak gluteus medius
. It shifts the center of gravity away from the affected hip joint
. It reduces the moment arm of the body weight relative to the hip joint center
. It creates an extensor moment at the knee to compensate for quadriceps weakness
. It maximizes the moment arm of the contralateral hip abductors

Correct Answer & Explanation

. It reduces the moment arm of the body weight relative to the hip joint center

Explanation

In a Trendelenburg gait, shifting the trunk laterally over the weak stance hip moves the body's center of gravity closer to the hip joint center. This reduces the moment arm of body weight, drastically decreasing the demand on the weak gluteus medius to maintain pelvic leveling.

Question 15612

Topic: 1. General Principles & Basic Science

When performing a medial opening wedge high tibial osteotomy (HTO), which of the following intraoperative technical errors is most likely to inadvertently increase the posterior tibial slope?

. Creating an opening gap that is equal anteriorly and posteriorly
. Releasing the superficial medial collateral ligament
. Creating an opening gap that is larger posteriorly than anteriorly
. Failing to osteotomize the fibula
. Using a locking plate with unicortical screws

Correct Answer & Explanation

. Creating an opening gap that is larger posteriorly than anteriorly

Explanation

The proximal tibia has a naturally triangular shape. Opening the anterior cortex equally to the posterior cortex in a medial opening wedge HTO will inadvertently increase the posterior tibial slope; typically, the anterior gap must be roughly half the posterior gap to maintain slope.

Question 15613

Topic: Physiology & Rehabilitation

In normal gait, what is the peak amount of knee flexion achieved during the swing phase to ensure adequate foot clearance?

. 20 degrees
. 40 degrees
. 60 degrees
. 80 degrees
. 100 degrees

Correct Answer & Explanation

. 60 degrees

Explanation

Normal human gait requires approximately 60 to 65 degrees of knee flexion during the initial and mid-swing phases to ensure adequate foot clearance. The knee then extends again in preparation for initial contact.

Question 15614

Topic: 1. General Principles & Basic Science

When applying a Taylor Spatial Frame for the correction of a multiplanar tibial deformity, what is the most critical function of the 'mounting parameters' entered into the software?

. They define the position of the reference ring relative to the bone and the true deformity
. They determine the rate of daily strut adjustments
. They specify the mechanical axis deviation of the contralateral limb
. They dictate the size of the osteotomy required
. They limit the maximum length of the struts used

Correct Answer & Explanation

. They define the position of the reference ring relative to the bone and the true deformity

Explanation

In the Taylor Spatial Frame system, mounting parameters strictly define the position and orientation of the reference ring to the underlying bone segment. Accuracy here is absolutely critical, as the software algorithm depends on this relationship to calculate the exact spatial deformity correction path.

Question 15615

Topic: Physiology & Rehabilitation

Which of the following descriptions best characterizes the 'second rocker' of the normal gait cycle?

. It occurs from initial contact to foot flat, pivoting around the heel
. It involves pivoting of the tibia over the plantigrade foot, relying on eccentric calf muscle control
. It occurs from heel off to toe off, transferring weight to the metatarsal heads
. It is the phase where the hip flexors initiate the swing phase
. It involves concentric contraction of the tibialis anterior to clear the toes

Correct Answer & Explanation

. It involves pivoting of the tibia over the plantigrade foot, relying on eccentric calf muscle control

Explanation

The second rocker (ankle rocker) occurs during mid-stance when the tibia rolls forward over the planted foot. This forward momentum is eccentrically controlled by the soleus and gastrocnemius muscles to prevent premature dorsiflexion collapse.

Question 15616

Topic: 1. General Principles & Basic Science

According to Paley's deformity correction principles, what occurs if both the osteotomy and the axis of correction (hinge) are located outside the Center of Rotation of Angulation (CORA)?

. Pure angular correction without translation
. Restoration of perfectly collinear mechanical axes
. Creation of a new translation deformity with parallel, non-collinear mechanical axes
. Pure length correction without angular change
. Rotational deformity only

Correct Answer & Explanation

. Creation of a new translation deformity with parallel, non-collinear mechanical axes

Explanation

Paley's Rule 3 dictates that if the osteotomy and hinge are placed away from the CORA, the mechanical axes of the proximal and distal segments will become parallel but not collinear. This effectively introduces a new translation deformity.

Question 15617

Topic: Physiology & Rehabilitation

A 16-year-old female presents with bilateral in-toeing. Clinical examination reveals 80 degrees of hip internal rotation and 10 degrees of hip external rotation bilaterally. Which of the following compensatory gait abnormalities is most likely to be observed simultaneously?

. Excessive external tibial torsion
. Varus thrust at the knee
. Trendelenburg gait
. Steppage gait
. Excessive pelvic rotation during swing phase

Correct Answer & Explanation

. Excessive external tibial torsion

Explanation

The clinical examination indicates excessive femoral anteversion. These patients often develop compensatory external tibial torsion to keep the feet relatively straight during gait, leading to a complex torsional profile known as Miserable Malalignment Syndrome.

Question 15618

Topic: 1. General Principles & Basic Science

Which of the following mechanical environments is MOST critical to optimize distraction osteogenesis during the lengthening phase using a circular external fixator?

. Rigid absolute stability to allow primary bone healing
. Axial micromotion with high torsional and shear stability
. High shear motion with minimal axial load
. Continuous compression across the osteotomy site
. Large gap formation prior to initiating the latency phase

Correct Answer & Explanation

. Axial micromotion with high torsional and shear stability

Explanation

Distraction osteogenesis thrives on controlled axial micromotion (dynamization), which stimulates bone formation and maturation. However, shear and torsional forces are highly detrimental to the regenerate and must be minimized by the tensioned wire circular frame construct.

Question 15619

Topic: 1. General Principles & Basic Science

An opening wedge osteotomy is planned for a distal femoral valgus deformity.

The osteotomy cut is made through the Center of Rotation of Angulation (CORA), and the hinge is placed on the convex cortex exactly at the CORA. Which osteotomy rule is being applied, and what is the expected outcome regarding translation?

. Osteotomy Rule 1; angular correction is achieved without translation.
. Osteotomy Rule 2; angular correction is achieved with expected translation.
. Osteotomy Rule 3; angular correction is achieved with unexpected translation.
. Osteotomy Rule 1; angular correction is achieved with expected translation.
. Osteotomy Rule 2; angular correction fails due to premature consolidation.

Correct Answer & Explanation

. Osteotomy Rule 1; angular correction is achieved without translation.

Explanation

Under Osteotomy Rule 1, both the osteotomy cut and the hinge are located at the CORA. This results in pure angulation and realignment of the mechanical axis without any translation of the bone fragments.

Question 15620

Topic: Physiology & Rehabilitation

During the stance phase of gait, a patient exhibits a contralateral pelvic drop accompanied by a compensatory lateral trunk lean toward the stance limb. Biomechanically, what is the primary purpose of this lateral trunk lean?

. To shift the center of gravity laterally, reducing the required hip abductor force.
. To increase the moment arm of the hip abductors, generating more torque.
. To counteract a deficient gluteus maximus and prevent anterior trunk flexion.
. To prevent knee buckling secondary to quadriceps weakness.
. To increase the mechanical advantage of the ipsilateral adductor longus.

Correct Answer & Explanation

. To shift the center of gravity laterally, reducing the required hip abductor force.

Explanation

A Trendelenburg gait with a lateral trunk lean shifts the body's center of gravity closer to the center of rotation of the hip joint. This reduces the lever arm of the body weight, thereby decreasing the torque that the weakened hip abductors must counteract.

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