CO Anatomy, Biomechanics & Pathophysiology of the Musculoskeletal System 3 — Questions and Answers
Question 1: In the context of orthotic prescription, 'genu recurvatum' refers to:
- Excessive lateral bowing of the knee in the frontal plane
- Hyperextension of the knee beyond neutral in the sagittal plane (Correct answer)
- Inward collapse of the knee during stance
- Rotational deformity of the tibia relative to the femur
Correct answer: Hyperextension of the knee beyond neutral in the sagittal plane
Genu recurvatum is abnormal hyperextension of the knee joint past 0° in the sagittal plane, often seen in patients with quadriceps weakness or ligamentous laxity.
Question 2: Which anatomical structure is the primary static stabilizer of the medial ankle against eversion stress?
- Anterior talofibular ligament
- Calcaneofibular ligament
- Deltoid ligament complex (Correct answer)
- Spring (plantar calcaneonavicular) ligament
Correct answer: Deltoid ligament complex
The deltoid ligament is a strong, fan-shaped medial complex that is the primary restraint against eversion and lateral talar shift.
Question 3: Post-polio syndrome differs from acute poliomyelitis in that it presents as:
- New inflammatory destruction of anterior horn cells decades after initial infection
- Progressive new weakness and fatigue in muscles previously affected or unaffected, without new viral activity (Correct answer)
- Autoimmune demyelinating peripheral neuropathy triggered by poliovirus antigens
- Ascending flaccid paralysis with respiratory failure
Correct answer: Progressive new weakness and fatigue in muscles previously affected or unaffected, without new viral activity
Post-polio syndrome is a non-inflammatory condition of new progressive weakness occurring 15–40 years after acute polio, thought to involve overuse of remaining motor units.
Question 4: The center of mass (COM) of the human body in anatomical position is located approximately:
- At the level of the umbilicus anteriorly
- Just anterior to S2 vertebra in the pelvis (Correct answer)
- At the geometric center of the thoracic spine
- At the level of the iliac crest posteriorly
Correct answer: Just anterior to S2 vertebra in the pelvis
The COM in the average adult is located just anterior to the second sacral vertebra, roughly 55% of standing height from the ground.
Question 5: In a patient with L4 nerve root compression, which clinical finding is most characteristic?
- Weakness of ankle plantarflexion and loss of Achilles reflex
- Weakness of ankle dorsiflexion with diminished patellar reflex (Correct answer)
- Weakness of hip abduction and lateral thigh sensory loss
- Weakness of great toe extension with normal reflexes
Correct answer: Weakness of ankle dorsiflexion with diminished patellar reflex
L4 nerve root compression classically causes ankle dorsiflexor weakness (and occasionally inversion weakness), reduced patellar reflex, and medial leg/ankle sensory deficit.
Question 6: The moment arm of a muscle force is defined as the:
- Length of the muscle from origin to insertion
- Perpendicular distance from the joint axis to the line of action of the muscle force (Correct answer)
- Ratio of muscle force to the external load being lifted
- Cross-sectional area of the muscle belly
Correct answer: Perpendicular distance from the joint axis to the line of action of the muscle force
The moment arm is the perpendicular distance from the joint center (axis of rotation) to the line along which the muscle force acts, determining its torque-generating capacity.
Question 7: Tibial torsion is measured clinically as the angle between which two axes?
- The transcondylar axis of the knee and the transmalleolar axis of the ankle (Correct answer)
- The hip axis and the knee transcondylar axis
- The subtalar axis and the transmetatarsal axis
- The femoral neck axis and the tibial shaft axis
Correct answer: The transcondylar axis of the knee and the transmalleolar axis of the ankle
Tibial torsion is the axial rotation of the tibia measured between the proximal tibial (transcondylar) axis and the distal tibial (transmalleolar) axis, normally 20–30° external.
CO Anatomy, Biomechanics & Pathophysiology of the Musculoskeletal System 3
In the context of orthotic prescription, 'genu recurvatum' refers to: