Musculoskeletal Anatomy of the Lower Limb

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COMPARISON OF UPPER AND LOWER LIMBS

• Upper and lower limbs develop from same primordial tissue type • Bud grows to become limb • Difference is in rotation of limb

• Tetrapods have common pattern of limb bone structure • Stylo/propodial – single proximal element • Zygo/epipodials – two middle bone segments that articulate, some

species have lost one • Autopodium – two or three carpal or tarsal rows, pentadactyl

• Understanding homology helps understand shared limb structure and function • Not all homologies are linear due to ontogenic limb rotation • Some fundamental differences between limbs due to biomechanics and

functional differences – being bipedal has caused changes

PELVIS

• Pelvic girdle composed of three elements: • Two os coxae – left and right

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• Sacrum – unites os coxae, series of fused sacral vertebrae

• Os coxa begins as three units in utero that fuse to form one bone and

acetabulum: • Ilium – homologue for scapula, although no defined spine • Ischium – homologue for coracoid process, gradually fuses onto ilium • Pubis – no direct homologue • Acetabulum is socket for head of femur, point where all three bones

join

• When born, os coxa is cartilage

• Doesn’t begin to fuse until 8 or 9 years old • Entirely fused and ossified by 25

• Subdivisions of pelvis: • Pelvic inlet – inner ring of pelvis, defined by bony pelvic brim • False pelvis – superior to pelvic inlet, occupied by abdominal viscera • True pelvis – inferior to pelvic inlet, occupied by pelvic viscera

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• Pelvic outlet (inferior pelvic aperture) – bounded by pubic arch anteriorly, ischial tuberosities laterally, inferior margin of sacrotuberous ligament posterolaterally and tip of coccyx posteriorly

• Differences between male and female anatomy of pelvis:

• Biological continuum – gynecoid and android are extremes of each, but

can be anywhere along scale • Android pelvic inlet heart-shaped and narrow, gynecoid oval and

rounded, and wide