LowerLimb - Functional Anatomy of the Lower Limb Bill...

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Functional Anatomy of the Lower Limb Bill Sellers Email: wis@mac.com This lecture can be found at: http://mac-huwis.lut.ac.uk/~wis/lectures/ Following on from my lecture on the upper limb I would now like to treat the lower limb in a similar fashion: moving distally from the pelvic girdle to the foot. The pelvic girdle has two joints: the sacroiliac joint dorsally and the pubic symphysis anteriorly (figure 1). The pubic symphysis is a secondary cartilaginous joint (bone, cartilage, fibre, cartilage, bone) and is basically immobile although during pregnancy it does stretch to allow the pelvic outlet to enlarge during childbirth. The sacroiliac joint is an atypical synovial joint which does allow a small but significant movement. The main movement it allows is called nutation or nodding. This is a forward motion of the top of the sacrum that occurs as the weight of the trunk slides forward at the sacroiliac joint or due to the contraction of muscles like the hamstrings that can cause large rotational forces on the pelvis. It produces an inward motion of the iliac crests and an outward movement of the ischial tuberosities and so also leads to an increase in the diameter of the birth canal.
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The hip joint is a classic ball-and-socket joint allowing flexion, extension, adduction, abduction, and medial and lateral rotation. The hip joint is a much more stable joint than the shoulder since it has a much more substantial bony cup ( acetabulum ) for the head of the femur and has a more restricted range of movement. Even so the short lateral rotators ( obturator internus , the superior and inferior gemelli , piriformis , quadratus femoris ) do have an important stabilisation rôle. The prime movers can be grouped into four compartments: anterior, posterior, medial (adductor) and buttock, and their actions assigned accordingly as flexors, extensors, adductors and abductors. There is of course some overlap with several muscles having multiple actions: for example gluteus maximus acts as a hip extensor when the hip is flexed; and adductor magnus is also a hip extensor as well as an adductor. In addition muscles in the hamstring group ( biceps femoris, semitendinosus and semimembranosus ) are also knee flexors and the quadriceps muscles ( rectus femoris, vastus medialis, intermedius, lateralis ) are knee extensors. Such muscles cross more than one joint and this seems to be important in the lower limb for energy transfer between segments and to keep the muscles operating and their optimal length. Figure 3. Ligaments of the hip joint The hip joint itself is also stabilised by the actions of the iliofemoral , ischiofemoral and pubofemoral ligaments (figure 3). These wind around the neck of the femur in such a way that they tighten in extension. This drives the head of the femur firmly into the acetabulum preventing dislocation and also limits hip extension. The pubofemoral ligament, because of
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This note was uploaded on 01/16/2012 for the course BI 200 taught by Professor Potter during the Fall '11 term at Montgomery College.

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LowerLimb - Functional Anatomy of the Lower Limb Bill...

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