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1. General Principles & Basic Science MCQs

Practice Set 762 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 15221

Topic: Physiology & Rehabilitation

During normal human gait, six distinct determinants function to minimize the vertical and horizontal displacement of the body's center of gravity, thereby reducing energy expenditure. Which of the following is NOT one of the classic determinants of gait described by Saunders et al.?

. Pelvic rotation in the transverse plane.
. Pelvic tilt in the coronal plane.
. Knee flexion in the stance phase.
. Foot drop in the swing phase.
. Lateral displacement of the pelvis.

Correct Answer & Explanation

. Foot drop in the swing phase.

Explanation

The six classic determinants of gait are: pelvic rotation, pelvic tilt, knee flexion in stance, foot mechanisms (ankle and foot interactions), and lateral displacement of the pelvis. 'Foot drop in the swing phase' is a pathologic finding, not a normal determinant that conserves energy.

Question 15222

Topic: Biomechanics & Biomaterials

When analyzing gait kinematics, what is the normal relationship between walking speed, cadence, and step length in a healthy adult?

. As walking speed increases, cadence decreases and step length increases.
. As walking speed increases, both cadence and step length increase.
. Cadence remains constant regardless of walking speed.
. Step length remains constant while cadence increases proportionally with speed.
. As walking speed increases, cadence increases and step length decreases.

Correct Answer & Explanation

. As walking speed increases, both cadence and step length increase.

Explanation

Walking speed is the product of cadence (steps per minute) and step length. In a healthy adult, increasing walking speed is accomplished by increasing both the cadence and the step length simultaneously.

Question 15223

Topic: 1. General Principles & Basic Science

A surgeon is planning a deformity correction. The center of rotation of angulation (CORA) is determined to be at the level of the tibial tubercle. The surgeon performs the osteotomy at the distal tibial metaphysis, while keeping the axis of correction of angulation (ACA) at the distal metaphysis as well (Osteotomy Rule 3). What will be the alignment outcome of the mechanical axis?

. The mechanical axis will be completely restored with pure angulation.
. The mechanical axis will be completely restored with angulation and translation.
. The mechanical axes of the proximal and distal segments will become parallel but displaced (translation effect).
. The bone will shorten significantly without altering the mechanical axis.
. A secondary rotational deformity will be induced without changing the coronal alignment.

Correct Answer & Explanation

. The mechanical axes of the proximal and distal segments will become parallel but displaced (translation effect).

Explanation

According to Osteotomy Rule 3, if the osteotomy and the ACA are both placed at a level different from the CORA, the angulation will be corrected, but the mechanical axes of the proximal and distal segments will end up parallel to each other with a translation displacement (axis deviation).

Question 15224

Topic: 1. General Principles & Basic Science

A 14-year-old patient presents with a severe mid-diaphyseal tibial deformity. Preoperative planning determines the center of rotation of angulation (CORA). According to Paley's osteotomy rules, if the osteotomy is performed proximal to the CORA, but the hinge is placed directly on the CORA, what is the resulting biomechanical effect on the mechanical axis?

. Pure angulation with no translation, completely realigning the axis.
. Pure translation with no angular correction.
. Angulation combined with translation, resulting in collinear realigned mechanical axes.
. A secondary iatrogenic translation deformity leaving the axes parallel but not collinear.
. Compression of the osteotomy site without axis realignment.

Correct Answer & Explanation

. Angulation combined with translation, resulting in collinear realigned mechanical axes.

Explanation

According to Osteotomy Rule 2, when the hinge is placed on the CORA but the osteotomy is at a different level, the result is angulation and translation at the osteotomy site. This translation is necessary to achieve collinear realignment of the mechanical axes.

Question 15225

Topic: Physiology & Rehabilitation

During the normal human gait cycle, the primary muscle active at the ankle during the loading response (initial contact to opposite toe-off) is the tibialis anterior. What is the primary biomechanical function of the tibialis anterior during this specific phase?

. Concentric contraction to initiate swing phase clearance.
. Isometric contraction to stabilize the ankle mortise.
. Eccentric contraction to decelerate passive plantarflexion and prevent foot slap.
. Eccentric contraction to control forward progression of the tibia over the foot.
. Concentric contraction to propel the limb forward.

Correct Answer & Explanation

. Eccentric contraction to decelerate passive plantarflexion and prevent foot slap.

Explanation

During the loading response, the ground reaction force creates a rapid plantarflexion moment. The tibialis anterior fires eccentrically to decelerate the foot and prevent a "slap" onto the ground.

Question 15226

Topic: 1. General Principles & Basic Science

When planning a Taylor Spatial Frame (TSF) or similar hexapod circular fixator application, the "reference fragment" must be carefully defined. What does the reference fragment represent in the software planning of the hexapod system?

. The fragment that is moving dynamically during the correction process.
. The fragment that is anatomically aligned with the reference ring, from which the deformity parameters are measured.
. The fragment that contains the primary osteotomy site.
. The intercalary segment during a bone transport procedure.
. The fragment with the most severe metaphyseal deformity.

Correct Answer & Explanation

. The fragment that is anatomically aligned with the reference ring, from which the deformity parameters are measured.

Explanation

In hexapod systems, the reference fragment is the bone segment considered stationary, and it is anatomically aligned with the reference ring (usually the proximal or larger segment). The software calculates the strut adjustments to move the "corresponding fragment" into alignment with this reference.

Question 15227

Topic: Physiology & Rehabilitation

A patient with severe right hip osteoarthritis exhibits a classic uncompensated Trendelenburg gait. However, after physical therapy, the patient develops a "compensated" Trendelenburg gait. What kinematic change defines this compensation during the stance phase on the affected right leg?

. The contralateral (left) pelvis drops excessively.
. The trunk leans laterally towards the affected (right) side to shift the center of mass.
. The trunk leans laterally away from the affected (right) side.
. The patient utilizes excessive lumbar lordosis to substitute for weak hip extensors.
. The ipsilateral knee is kept locked in extension to reduce the abductor moment.

Correct Answer & Explanation

. The trunk leans laterally towards the affected (right) side to shift the center of mass.

Explanation

In a compensated Trendelenburg gait (abductor lurch), the patient laterally flexes the trunk over the stance (affected) leg. This shifts the center of mass closer to the hip joint center, reducing the moment arm and the work required by the weak hip abductors.

Question 15228

Topic: 1. General Principles & Basic Science

A 26-year-old undergoes a medial opening-wedge high tibial osteotomy (HTO) for isolated medial compartment gonarthrosis with varus alignment. Postoperatively, what unintended sagittal plane alteration and patellofemoral change are most commonly associated with this specific procedure?

. Decreased posterior tibial slope and patella alta.
. Increased posterior tibial slope and patella baja.
. Increased posterior tibial slope and patella alta.
. Decreased posterior tibial slope and patella baja.
. No change in tibial slope but significant patella alta.

Correct Answer & Explanation

. Increased posterior tibial slope and patella baja.

Explanation

Medial opening-wedge HTO predictably increases the posterior tibial slope because the anterior medial cortex is narrower than the posterior medial cortex. It also relatively shortens the patellar tendon distance to the joint line, resulting in patella baja.

Question 15229

Topic: 1. General Principles & Basic Science

During a femoral lengthening procedure utilizing an external fixator, a 13-year-old patient develops significant resistance to knee flexion. By week 6, the patient has a rigid 30-degree knee extension contracture. Which soft tissue structure is primarily responsible for this specific contracture during femoral lengthening?

. Hamstrings
. Gastrocnemius
. Rectus femoris and Iliotibial band
. Adductor longus
. Sartorius

Correct Answer & Explanation

. Rectus femoris and Iliotibial band

Explanation

During femoral lengthening, the quadriceps mechanism (specifically the rectus femoris) and the iliotibial band are highly susceptible to tethering and contracture. This typically presents as loss of knee flexion (an extension contracture).

Question 15230

Topic: 1. General Principles & Basic Science

In deformity planning, Rule 3 of Paley's osteotomy rules states that if the osteotomy and the hinge are both placed away from the CORA (Center of Rotation of Angulation), what is the expected geometric outcome?

. Pure angulation restoring collinearity.
. Collinear realignment of the mechanical axes with no translation.
. An opening wedge pure angular correction.
. Angulation combined with an iatrogenic translation deformity.
. Failure of the osteotomy to heal due to excessive shear forces.

Correct Answer & Explanation

. Angulation combined with an iatrogenic translation deformity.

Explanation

Osteotomy Rule 3 states that if the hinge and the osteotomy are both placed at a level other than the CORA, the mechanical axes will remain parallel but will not be collinear. This introduces a secondary translation deformity.

Question 15231

Topic: Physiology & Rehabilitation

A patient with a common peroneal nerve palsy exhibits a "steppage" gait. Kinematic analysis of this patient's gait cycle will demonstrate which primary abnormality during the swing phase that necessitates this compensatory mechanism?

. Excessive ankle plantarflexion.
. Inadequate knee flexion.
. Excessive hip adduction.
. Premature heel strike.
. Excessive subtalar inversion.

Correct Answer & Explanation

. Excessive ankle plantarflexion.

Explanation

A common peroneal nerve palsy results in weakness of the tibialis anterior, causing a drop foot (excessive passive ankle plantarflexion during swing). To prevent the toes from dragging on the ground, the patient compensates by exaggerating hip and knee flexion (steppage gait).

Question 15232

Topic: Physiology & Rehabilitation

A 5-year-old with cerebral palsy undergoes instrumented gait analysis. Dynamic electromyography (EMG) reveals prolonged, continuous activity of the rectus femoris during the swing phase. Clinically, what gait deviation is most directly caused by this specific muscle overactivity?

. Crouch gait
. Trendelenburg gait
. Stiff-knee gait
. Equinus gait
. Calcaneus gait

Correct Answer & Explanation

. Stiff-knee gait

Explanation

Overactivity or spasticity of the rectus femoris during the swing phase prevents the knee from flexing adequately to clear the foot. This manifests clinically as a stiff-knee gait, characterized by reduced peak knee flexion during swing.

Question 15233

Topic: 1. General Principles & Basic Science

When planning a lower limb deformity correction, what is the expected mechanical consequence if an osteotomy and angulation are performed at a level separate from the Center of Rotation of Angulation (CORA) without adding any compensatory translation?

. Perfect realignment of the mechanical axis without secondary deformity
. Translation of the mechanical axis causing a step-off deformity
. Inadvertent lengthening of the bone segment
. Inadvertent shortening of the bone segment
. Premature consolidation of the regenerate bone

Correct Answer & Explanation

. Translation of the mechanical axis causing a step-off deformity

Explanation

According to the osteotomy rules, if the osteotomy is performed away from the CORA and only angulation is corrected, a secondary translation deformity will be created. To prevent this, simultaneous translation must be performed, or the hinge must be placed directly on the CORA.

Question 15234

Topic: 1. General Principles & Basic Science

During a gait analysis, a patient exhibits a 'steppage' gait with a pronounced foot drop during the swing phase. Which nerve and corresponding muscle group are most likely deficient?

. Tibial nerve; gastrocnemius-soleus complex
. Superficial peroneal nerve; peroneus longus and brevis
. Femoral nerve; quadriceps femoris
. Deep peroneal nerve; tibialis anterior
. Superior gluteal nerve; gluteus medius

Correct Answer & Explanation

. Deep peroneal nerve; tibialis anterior

Explanation

Foot drop and a steppage gait occur due to the inability to dorsiflex the ankle during the swing phase. This is caused by dysfunction of the deep peroneal nerve, which innervates the tibialis anterior and other ankle dorsiflexors.

Question 15235

Topic: Physiology & Rehabilitation

During gait observation, a patient demonstrates a backward lurch of the trunk immediately following heel strike. This specific compensatory mechanism is indicative of weakness in which muscle, and occurs during which phase of the gait cycle?

. Gluteus medius; mid-stance
. Gluteus maximus; loading response
. Quadriceps femoris; pre-swing
. Iliopsoas; initial swing
. Triceps surae; terminal stance

Correct Answer & Explanation

. Gluteus maximus; loading response

Explanation

A backward trunk lean (gluteus maximus lurch) occurs during the loading response phase to move the center of gravity posterior to the hip joint. This mechanically maintains hip extension, compensating for a weak gluteus maximus.

Question 15236

Topic: 1. General Principles & Basic Science

In a normal lower extremity, the Mechanical Axis Deviation (MAD) is typically defined as the mechanical axis line passing through which location at the level of the knee?

. Directly through the center of the knee joint
. 1 to 8 mm medial to the center of the knee joint
. 10 to 15 mm lateral to the center of the knee joint
. Directly through the medial collateral ligament
. Directly through the lateral collateral ligament

Correct Answer & Explanation

. 1 to 8 mm medial to the center of the knee joint

Explanation

In a normal limb, the mechanical axis passes slightly medial to the center of the knee joint. The normal Mechanical Axis Deviation (MAD) is generally accepted to be roughly 1 to 8 mm medial to the exact center of the joint.

Question 15237

Topic: Biology, Genetics & Bone Healing

Following hardware removal after successful deformity correction via tension-band plating (guided growth), rebound deformity is a known complication. This phenomenon is most frequently observed in which patient population?

. Adolescents approaching skeletal maturity
. Patients with idiopathic genu varum
. Patients with underlying skeletal dysplasia or metabolic bone disease
. Patients treated with rigid staples rather than plates
. Patients who achieve correction in less than 6 months

Correct Answer & Explanation

. Patients with underlying skeletal dysplasia or metabolic bone disease

Explanation

Rebound deformity after hardware removal is significantly more common in younger patients and those with pathologic causes of deformity, such as skeletal dysplasias, hypophosphatemic rickets, or metabolic bone diseases.

Question 15238

Topic: 1. General Principles & Basic Science

When planning a corrective osteotomy, you desire to perfectly correct an angular deformity without intentionally lengthening or shortening the limb segment. Where must the axis of rotation (hinge) be positioned?

. At the concave cortex of the deformity
. At the central longitudinal axis of the bone
. At the convex cortex of the deformity
. Outside the bone on the concave side
. Outside the bone on the convex side

Correct Answer & Explanation

. At the central longitudinal axis of the bone

Explanation

To achieve angular correction without length change (a neutral wedge), the hinge must be placed at the central longitudinal axis of the bone. Hinging at the concave cortex lengthens (opening wedge), while hinging at the convex cortex shortens (closing wedge).

Question 15239

Topic: Physiology & Rehabilitation

A patient with profound triceps surae weakness undergoes computerized gait analysis. Which of the following kinematic abnormalities is most likely to be identified during the stance phase?

. Excessive knee flexion during initial contact
. Pelvic drop on the contralateral side during mid-stance
. Delayed or absent heel-off during terminal stance
. Excessive ankle plantarflexion during loading response
. Increased trunk lateral bending to the ipsilateral side

Correct Answer & Explanation

. Delayed or absent heel-off during terminal stance

Explanation

The triceps surae (calf muscles) are responsible for ankle plantarflexion, which elevates the heel during terminal stance. Weakness results in prolonged heel contact, excessive dorsiflexion, and a 'calcaneal' or delayed heel-off gait.

Question 15240

Topic: Biology, Genetics & Bone Healing

During distraction osteogenesis, what is the primary biological purpose of the 5- to 7-day 'latency period' strictly observed prior to initiating distraction?

. To allow for complete resolution of postoperative edema
. To give the patient time to learn how to turn the struts
. To allow for organization of the fracture hematoma and early angiogenesis
. To allow early woven bone to fully mature into lamellar bone
. To prevent pin tract infections from migrating into the corticotomy site

Correct Answer & Explanation

. To allow for organization of the fracture hematoma and early angiogenesis

Explanation

The latency period allows the fracture hematoma to organize, mesenchymal stem cells to migrate and proliferate, and a delicate capillary network to form. Distracting too early disrupts this initial critical phase of bone healing.

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