20-Bio-A4 Anatomy and Physiology · May 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams, May 2017 — 04-Bio-A4, Biomechanics. 3-hour open-book exam; FOUR (4) questions of equal value constitute a complete paper, so all four are answered in full below.
Reference texts: Winter, Biomechanics and Motor Control of Human Movement; Zatsiorsky, Kinematics of Human Motion; Nordin & Frankel, Basic Biomechanics of the Musculoskeletal System.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
(a) Photo A shows the thigh swinging anteriorly at the hip — this is hip flexion, a sagittal-plane motion. Every sagittal-plane rotation occurs about the single axis perpendicular to the sagittal plane, which is the medio-lateral (transverse) axis passing through the centre of the femoral head.
(b) Photo B shows the same joint with the thigh swinging posteriorly — hip extension. It is the same sagittal-plane motion as (a), so it occurs about the same medio-lateral axis through the hip joint centre, simply in the opposite rotational sense.
(c) Photo C shows the foot moving up and down at the ankle (talocrural joint) — upward motion is dorsiflexion, downward is plantarflexion. This is again a sagittal-plane motion, occurring about the medio-lateral axis through the malleoli (the ankle mortise), not the hip's own axis — the axis is joint-local, only the plane classification repeats.
(d) The athlete is falling with the arm extended and the hand planted to arrest the fall — a classic FOOSH (fall onto an outstretched hand) mechanism. The ground reaction force is transmitted axially up the forearm into an elbow that is at or near full extension, forcing the joint into hyperextension with a superimposed valgus (medially-opening) moment as the body's momentum carries the trunk past the planted hand. The structures most likely injured are: the radial head/neck, which is compressed against the capitulum under the axial load (the single most common FOOSH elbow fracture); the anterior joint capsule and brachialis, stretched or torn by the forced hyperextension; the ulnar (medial) collateral ligament, strained by the valgus component; and, if the energy is high enough, a posterior elbow dislocation with a possible coronoid-process fracture as the trochlea is driven posteriorly out of the trochlear notch.
