20-Bio-A4 Anatomy and Physiology · Undated paper
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams May 2019 — 04-Bio-A4, Biomechanics. 3 hours, open book (any non-communicating calculator permitted). FOUR (4) questions constitute a complete exam paper; each 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) The figure is a sagittal cross-section through the knee, femur superior and tibia inferior, with the patella anterior. A) = patella (the small anterior sesamoid bone embedded in the quadriceps tendon, arrowed at the front of the joint); B) = tibia (the larger inferior long bone forming the tibial plateau); C) = femur (the superior long bone, arrowed at its distal condyle, the main bony mass forming the upper half of the joint). Within the femoral condyle, bone tissue grades from a thin dense outer rim to a porous interior: D), arrowed at the condyle's outer margin nearest the joint surface, is cortical (compact) bone, and E), arrowed higher up at the metaphyseal/shaft region, is trabecular (cancellous, spongy) bone — the reverse of the diaphysis further up the shaft, where cortical bone thickens and the trabecular core all but disappears.
[Figure not reproduced: Figure 1 (redrawn schematic) — sagittal cross-section of the knee joint with the eight labelled structures. See the official exam paper.]
(b) F) = meniscus — the crescent-shaped fibrocartilage pad seated in the joint space between the femoral condyle and the tibial plateau. G) = articular (hyaline) cartilage — the smooth layer covering both the femoral condyle and tibial plateau surfaces. H) = quadriceps femoris — the large muscle mass immediately superior to the patella, continuing distally as the patellar tendon to its insertion on the tibial tuberosity.
(c) Contraction of the quadriceps femoris pulls the patella (and, via the patellar tendon, the tibial tuberosity) proximally and anteriorly, producing knee extension — straightening the joint by increasing the angle between the femur and tibia. The quadriceps is the knee's principal (and only major single-joint) extensor group.
(d) The meniscus (F) improves several aspects of knee mechanics: it increases the congruency between the convex femoral condyle and the comparatively flat tibial plateau, spreading contact load over a much larger area and lowering peak cartilage contact stress; it acts as a shock absorber during impact loading (gait, landing); it contributes to joint lubrication and nutrient distribution to the avascular articular cartilage by aiding synovial fluid circulation; and it adds a secondary stabilising role, particularly resisting anteroposterior and rotational translation of the femur on the tibia.
