MCQs-Basic 4
ankle anterior to knee anterior to hip (ant. to everything)
– Loading response posterior to ankle posterior to knee anterior to hip
– Midstance anterior to ankle anterior to knee posterior to hip
– Terminal stance anterior to ankle anterior to knee posterior to hip
– Preswing anterior to ankle posterior to knee posterior to hip

– hamstrings are most active at swing phase

– the hamstring functions to decelerate the thigh in late swing

– during walking, the center of gravity has an up/down motion of about an inch (2.5 cm) – may increase with walking faster.

– at heel strike the subtalar joint EVERTS – this unlocks the midfoot so that it can roll easily during midstance. The tib post tendon then activates to INVERT the subtalar joint during mid-terminal stance and this locks the midfoot so that push off is against a rigid lever.

– the axis of the calcaneocuboid and talonavicular joints are aligned when the subtalar joint is everted – this allows midfoot motion and the foot to accommodate the loading. As the subtalar joint is inverted by tib post, the axis of the calcaneocuboid and talonavicular joints are divergent, and thus the midfoot is locked

– a flexion moment of the hip exists during heelstrike (the joint reaction force passes anterior to the hip); there is a flexion moment only at the beginning of the stance phase – the joint reaction force then moves BEHIND the hip at midstance. There is a flexion moment to the hip during all of the swing phase.

– center of gravity is highest at midstance; probably lowest during loading response (all joints are flexed)

– at heelstrike, tib ant, EDL (not EHL), hamstrings, and quadriceps are all active. The hip flexors are not.

– increased energy consumption for 3 point crutch walking is about 50% (1.5 x normal)

– bone: 70% mineral/inorganic material – vast majority of this is hydroxyapatite
25-22% organic matrix (osteoid) – vast majority of this osteoid is collagen and other proteins (98%) The remaining 2% are cells.
5-8% water

– Approximately 90% of the organic matrix of bone is type I collagen – the remainder consists of noncollagenous matrix proteins. (some say 95%)

– bone is anisotropic

– matrix vesicles in bone contain phosphatases such as alkaline phosphatase and pyrophosphatase, which remove calcification inhibitors and provide the phosphate ions that allow mineral precipitation to take place. Pyrophosphatases therefore enhance mineralization.

– mineralization occurs in the gaps and pores within collagen fibers

– the function of alk phosphatase is not entirely clear – it may be required to provide PO4 and render the matrix calcifiable. It has some sort of role in mineralization.

– while osteoblasts/cytes have alk phosphatase to aid in mineralization, osteoclasts have acid phosphatase. The osteoclasts interact with bone at the CLEAR ZONE and RUFFLED BORDER. The clear zone is where the osteoclast attaches – it surrounds and seals off the area where the bone is to be resorbed. Intracellular carbonic anhydrase produces acid which is used to degrade bone underneat this area.

– osteons are 250 microns in diameter;

– volkmann canals connect the haversion canals which run up the center of the osteon.

– for blood flow in diaphyseal bone – inner 2/3 from intraosseous (centrifugal); outer 1/3 from periosteum (centripetal). All the vessels, including the cortical capillaries drain to intramedullary venous sinusoids inside the bone (centripetal)
– in experimental conditions, the average angle of a spiral fracture is approximately 30 degrees

– in the hypertrophic cartilage zone, the glycogen is consumed till depleted, and the condrocytes synthesize alk phosphatase – so you’d expect increase alk phosphatase, decreased glycogen.

– proteoglycan typically consists of a core protein and glycosaminoglycans such as chondroitan sulfate and keratin sulfate and dermatin sulfate. Hyaluronic acid is a glycosaminoglycan, but it is not part of the proteoglycan per se. Many of

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