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1. General Principles & Basic Science MCQs

Practice Set 761 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 15201

Topic: Biology, Genetics & Bone Healing

A 78-year-old patient with longstanding polyostotic Paget's disease notes rapid enlargement and extreme pain over his right humerus. Radiographs show a destructive lytic lesion with cortical breakthrough

. What is the generally accepted prognosis for this complication?

. Excellent with high-dose bisphosphonate therapy alone
. Curative with intralesional curettage and bone grafting
. Generally poor with high mortality despite aggressive surgical and systemic treatment
. Very high response rate to isolated definitive radiotherapy
. Complete resolution achievable with long-term calcium and vitamin D supplementation

Correct Answer & Explanation

. Generally poor with high mortality despite aggressive surgical and systemic treatment

Explanation

Secondary osteosarcoma occurs in approximately 1% of patients with Paget's disease. It represents a highly aggressive malignancy with a dismal prognosis, typically having a 5-year survival rate of less than 20% despite aggressive intervention.

Question 15202

Topic: 1. General Principles & Basic Science
Which of the following serum laboratory profiles is most characteristic of primary hyperparathyroidism?
. Low calcium, low phosphorus, high PTH
. High calcium, low phosphorus, high PTH
. Normal calcium, high phosphorus, low PTH
. Low calcium, high phosphorus, high PTH
. High calcium, high phosphorus, low PTH

Correct Answer & Explanation

. High calcium, low phosphorus, high PTH

Explanation

Primary hyperparathyroidism is typically caused by an autonomously functioning parathyroid adenoma. This results in an elevated PTH, which drives hypercalcemia (via bone resorption and renal retention) and hypophosphatemia (via renal phosphate wasting).

Question 15203

Topic: Infection, Pharmacology & VTE

A 2-week-old premature infant in the neonatal intensive care unit develops an acutely swollen left thigh and holds the hip in a flexed and externally rotated position. In addition to Staphylococcus aureus, which organism is a leading cause of septic coxitis in this age group and requires empirical coverage?

. Neisseria gonorrhoeae
. Haemophilus influenzae type B
. Group B Streptococcus
. Salmonella enteritidis
. Borrelia burgdorferi

Correct Answer & Explanation

. Group B Streptococcus

Explanation

In neonates (infants less than 4 weeks old), the most common causative organisms for septic arthritis are Staphylococcus aureus, Group B Streptococcus, and Gram-negative bacilli. Empiric antibiotic therapy must broadly cover these pathogens.

Question 15204

Topic: 1. General Principles & Basic Science

If an osteotomy and the hinge are both placed exactly at the Center of Rotation of Angulation (CORA), what is the geometric result of the deformity correction?

. Angulation without translation
. Translation without angulation
. Angulation with translation
. Lengthening only
. Shortening only

Correct Answer & Explanation

. Angulation without translation

Explanation

According to Paley's Rule 1 of osteotomy, if the osteotomy and hinge are both at the CORA, the deformity corrects by angulation without translation. This perfectly realigns the mechanical axis.

Question 15205

Topic: Physiology & Rehabilitation

During a normal gait cycle, maximal electromyographic activity of the ankle dorsiflexors (e.g., anterior tibialis) occurs during which phase?

. Initial contact to loading response
. Mid-stance
. Terminal stance
. Pre-swing
. Initial swing

Correct Answer & Explanation

. Initial contact to loading response

Explanation

The anterior tibialis contracts eccentrically from initial contact to the loading response to smoothly lower the foot to the ground and prevent 'foot slap'. This represents its maximal activity during the gait cycle.

Question 15206

Topic: Physiology & Rehabilitation

A 7-year-old child with spastic diplegic cerebral palsy presents with a crouch gait. Which of the following kinematic findings is most characteristic of this pattern?

. Excessive knee extension in stance
. Hip hyperextension in stance
. Increased ankle plantarflexion in stance
. Increased knee flexion in stance phase
. Premature heel rise

Correct Answer & Explanation

. Increased knee flexion in stance phase

Explanation

Crouch gait is characterized by excessive hip and knee flexion and excessive ankle dorsiflexion during the stance phase. This is often due to hamstring/psoas tightness and calf weakness.

Question 15207

Topic: 1. General Principles & Basic Science

When evaluating a standing long-leg AP radiograph, the mechanical axis line falls 25 mm medial to the center of the knee joint. What is the primary deformity?

. Varus deformity
. Valgus deformity
. Recurvatum deformity
. Procurvatum deformity
. Normal alignment

Correct Answer & Explanation

. Varus deformity

Explanation

A mechanical axis passing medial to the center of the knee joint indicates a varus deformity. This shifts the weight-bearing axis medially, increasing compressive forces on the medial compartment.

Question 15208

Topic: Physiology & Rehabilitation

A patient exhibits a compensated Trendelenburg gait. Which kinematic adaptation is most typically observed during the stance phase on the affected side?

. Lateral trunk lean toward the affected side
. Lateral trunk lean away from the affected side
. Increased hip flexion
. Knee hyperextension
. Contralateral pelvic drop

Correct Answer & Explanation

. Lateral trunk lean toward the affected side

Explanation

In a compensated Trendelenburg gait, the patient leans their trunk laterally over the affected hip during stance. This shifts the center of gravity closer to the hip joint center, reducing the moment arm and the demand on the weak abductor muscles.

Question 15209

Topic: Biology, Genetics & Bone Healing

During distraction osteogenesis of the femur at a rate of 1 mm/day, radiographs at 3 weeks reveal premature consolidation of the regenerate bone. What is the most appropriate next step?

. Increase the distraction rate to 2 mm/day temporarily
. Decrease distraction to 0.5 mm/day
. Stop distraction and remove the fixator
. Return to OR for re-osteotomy
. Administer systemic bisphosphonates

Correct Answer & Explanation

. Return to OR for re-osteotomy

Explanation

Premature consolidation means the bone has healed completely before the desired length was achieved. The treatment requires returning to the operating room to recut the bone (re-osteotomy) before distraction can resume.

Question 15210

Topic: 1. General Principles & Basic Science

According to Paley's rules of deformity correction (Rule 2), if the osteotomy is made at a level separate from the CORA, but the hinge is placed on the transverse bisector line passing through the CORA, what is the geometric outcome?

. Angulation without translation
. Translation without angulation
. Angulation with translation
. Complete loss of bone contact
. Shortening of the mechanical axis

Correct Answer & Explanation

. Angulation with translation

Explanation

Paley's Rule 2 states that if the hinge is at the CORA but the osteotomy is at a different level, the correction will result in angulation along with translation. This successfully realigns the mechanical axis but displaces the bone ends.

Question 15211

Topic: Physiology & Rehabilitation

A patient with cerebral palsy presents with a stiff-knee gait, visibly dragging the toe during the swing phase. Which of the following is the most common underlying cause?

. Overactivity of the rectus femoris
. Weakness of the triceps surae
. Overactivity of the hamstrings
. Gluteus medius weakness
. Spasticity of the anterior tibialis

Correct Answer & Explanation

. Overactivity of the rectus femoris

Explanation

Stiff-knee gait in CP is primarily caused by overactivity or spasticity of the rectus femoris during the swing phase. This prevents the necessary knee flexion required for foot clearance.

Question 15212

Topic: Physiology & Rehabilitation

During normal human walking, the vertical ground reaction force (GRF) exhibits a characteristic pattern. Which of the following best describes this pattern during the stance phase?

. A single distinct peak at mid-stance
. A bimodal 'm-shaped' curve with peaks at loading response and terminal stance
. A linear increase from heel strike to toe-off
. A bimodal curve with peaks at mid-stance and initial swing
. A constant plateau throughout the entire stance phase

Correct Answer & Explanation

. A bimodal 'm-shaped' curve with peaks at loading response and terminal stance

Explanation

The normal vertical ground reaction force is bimodal ('m-shaped'). The first peak corresponds to weight acceptance (loading response), and the second peak corresponds to push-off (terminal stance).

Question 15213

Topic: 1. General Principles & Basic Science

What is the generally accepted maximum percentage of lengthening of a single bone segment before the risk of severe complications (e.g., joint subluxation, nerve injury) increases exponentially?

. 5-10%
. 15-20%
. 30-35%
. 50-60%
. 75-80%

Correct Answer & Explanation

. 15-20%

Explanation

Lengthening a bone by more than 15-20% of its original length significantly increases complication rates. These include adjacent joint subluxation, severe soft tissue contractures, and neurovascular compromise.

Question 15214

Topic: Physiology & Rehabilitation

During computerized gait analysis of a patient with cerebral palsy, the kinematic data reveals severely diminished peak knee flexion during the swing phase. Electromyography (EMG) demonstrates continuous firing of the rectus femoris. What is the most appropriate surgical intervention to address this specific abnormality?

. Rectus femoris transfer to the sartorius or semitendinosus.
. Fractional lengthening of the vastus medialis.
. Distal femoral extension osteotomy.
. Patellar tendon advancement.
. Medial hamstring lengthening.

Correct Answer & Explanation

. Rectus femoris transfer to the sartorius or semitendinosus.

Explanation

Continuous firing of the rectus femoris during the swing phase causes a 'stiff-knee gait' by preventing normal knee flexion. Transferring the rectus femoris distally converts it from a knee extensor to a knee flexor, improving swing-phase clearance.

Question 15215

Topic: 1. General Principles & Basic Science

A surgeon is planning a tibial osteotomy

based on Osteotomy Rule 2. If the axis of correction of angulation (ACA) is at the center of rotation of angulation (CORA), but the osteotomy is performed at a different level, what is the expected geometric outcome?

. The mechanical axis will fail to realign, leaving a parallel axis deviation.
. The mechanical axis will be restored, but angulation and translation will occur at the osteotomy site.
. Pure translation will occur without any correction of angulation.
. Pure angulation will occur without any translation at the osteotomy site.
. The CORA will migrate distally, causing a secondary procurvatum deformity.

Correct Answer & Explanation

. The mechanical axis will be restored, but angulation and translation will occur at the osteotomy site.

Explanation

According to Osteotomy Rule 2, when the ACA is at the CORA but the osteotomy is made at a different level (e.g., to cut through better metaphyseal bone), the mechanical axis is successfully restored. However, this correction requires both angulation and translation to occur at the osteotomy site.

Question 15216

Topic: Physiology & Rehabilitation

During the normal gait cycle, the vertical ground reaction force (vGRF) curve demonstrates a characteristic 'M' shape or two-peak pattern. In which phases of the gait cycle do these two peak vertical forces occur?

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

Correct Answer & Explanation

. Loading response and terminal stance

Explanation

The two peaks of the vertical ground reaction force curve occur during loading response (weight acceptance) and terminal stance (push-off). During mid-stance, the vGRF dips as the body's center of mass reaches its highest point.

Question 15217

Topic: Physiology & Rehabilitation

During the initial phase of the gait cycle (first rocker), the foot transitions from heel strike to a foot-flat position. Which muscle performs the primary eccentric contraction to control this motion and prevent 'foot slap'?

. Gastrocnemius
. Posterior tibialis
. Anterior tibialis
. Peroneus longus
. Extensor hallucis longus

Correct Answer & Explanation

. Anterior tibialis

Explanation

The anterior tibialis fires eccentrically from heel strike (initial contact) to foot flat (loading response) to smoothly lower the forefoot to the ground. Failure of this mechanism leads to a 'foot slap' gait.

Question 15218

Topic: Physiology & Rehabilitation

A patient with severe unilateral hip osteoarthritis walks with a classic uncompensated Trendelenburg lurch, shifting their torso over the affected hip during the stance phase. What is the primary biomechanical advantage of this compensatory gait mechanism?

. It increases the lever arm of the weak gluteus medius muscle.
. It reduces the moment arm of the body weight relative to the center of the hip joint.
. It increases the joint reaction force to stabilize the femoral head.
. It anteriorly shifts the center of gravity to assist with hip flexion.
. It locks the knee in extension to provide a stable pillar for weight bearing.

Correct Answer & Explanation

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

Explanation

Shifting the trunk over the affected hip during stance (an abductor lurch) brings the center of gravity closer to the hip joint center. This significantly decreases the body weight moment arm, reducing the torque requirement on the weak or painful abductor muscles and thereby decreasing the total hip joint reaction force.

Question 15219

Topic: Biomechanics & Biomaterials

An orthopaedic surgeon uses a Taylor Spatial Frame (TSF)

to correct a complex multidirectional lower limb deformity. The software program requires the surgeon to define a 'reference fragment'. The mathematical algorithm utilized by the TSF to calculate strut adjustments is based on which of the following kinematic principles?

. Eulerian rigid body dynamics
. Stewart-Gough platform kinematics
. The Ilizarov principle of distraction histiogenesis
. Navier-Stokes equations
. Paley's Multiplier theorem

Correct Answer & Explanation

. Stewart-Gough platform kinematics

Explanation

The Taylor Spatial Frame is a hexapod external fixator based on the Stewart-Gough platform. It provides 6 degrees of freedom, allowing simultaneous correction of angulation, translation, rotation, and length via a web-based software algorithm.

Question 15220

Topic: Biology, Genetics & Bone Healing

During distraction osteogenesis, plain radiographs are monitored to evaluate the 'regenerate' bone. At approximately what time post-osteotomy does the regenerate bone typically first become visible on standard radiographs, and what is its characteristic appearance?

. 1 week; dense homogenous sclerosis
. 2 to 3 weeks; central radiolucent interzone flanked by sclerotic bone
. 6 weeks; bridging callus crossing the entire gap
. 3 months; complete cortical recanalization
. 48 hours; delicate woven bone spicules

Correct Answer & Explanation

. 2 to 3 weeks; central radiolucent interzone flanked by sclerotic bone

Explanation

Regenerate bone typically becomes visible on radiographs 2 to 3 weeks after the start of distraction. It characteristically appears as columns of new bone with a central radiolucent 'fibrous interzone' where active distraction and histiogenesis are occurring.

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