20-Bio-A4 Anatomy and Physiology · May 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams May 2015 — 04-Bio-A4 Biomechanics, 3 hours, open book (any non-communicating calculator permitted). Four questions constitute a complete exam paper; each question is of equal value (15 marks).
Reference texts: Winter, Biomechanics and Motor Control of Human Movement (4th ed.); Zatsiorsky, Kinematics of Human Motion; Nordin & Frankel, Basic Biomechanics of the Musculoskeletal System (5th ed.).
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) Tendon stress-strain curve. Tendon is a collagenous, viscoelastic tissue whose loading curve has a characteristic non-linear then near-linear then failing shape:
The toe region is the initial, low-stiffness, concave-up portion where the tendon's crimped collagen fibrils straighten under small loads; the elastic region follows as a much stiffer, near-linear segment as the now-straightened fibrils are stretched and fully recover if unloaded; the yield stress marks the onset of microscopic collagen fibril sliding/failure, beyond which the plastic region shows permanent (non-recoverable) deformation at a reduced, falling slope; the curve terminates at the failure stress, where gross rupture occurs.
b) Motion at the left knee. The tackle in Figure 3 drives the standing player's lower leg laterally out from under the trunk while the foot stays planted — a combined valgus (abduction) load with tibial external rotation forced onto a knee that is at or near full extension.
c) Structures at risk. This valgus + external-rotation mechanism is the classic “unhappy triad” pattern: the medial collateral ligament (MCL) is stretched and sprained/torn by the valgus opening on the medial side; the anterior cruciate ligament (ACL) is commonly torn by the coupled external rotation/anterior tibial translation; and the medial meniscus, tethered to the MCL and compressed as the femoral condyle rotates over it, is frequently torn at the same time.
d) Surgical treatment. The dominant surgical procedure is arthroscopic ACL reconstruction (typically using an autograft — bone–patellar tendon–bone or hamstring tendon), often combined with arthroscopic partial meniscectomy or meniscal repair for the associated tear; a low-grade MCL sprain is usually managed non-operatively (bracing) and allowed to heal alongside the ACL reconstruction rather than repaired surgically itself.
