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Boyer diss 2009 1046..

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Figure 4.25. Surface reconstruction of innominate (In) and femur (Fm) of Plesiadapis<br />

cookei (UM 87990) based on CT data [CT image resolution = 0.18(x) x 0.18(y) x 0.20(z)<br />

mm]. A, shows major increments of change in femoral orientation and articulation with<br />

innominate during gait cycle. 5 – closest packed posture suggesting that the usual or<br />

average posture of the femur is one in which it is flexed, abducted and slightly laterally<br />

rotated. Steps 1-5 show how abduction-adduction, mediolateral rotation, and flexionextension<br />

movements combined during the gait cycle to bring the thigh through a large<br />

positional and angular excursion, while keeping the joint surfaces of the acetabulum and<br />

femur in maximal overlap. Going from the closest-packed position of the hip to pushing<br />

off the substrate (5 1) would have simply entailed extension the abducted femur.<br />

During the swing phase (1 2) the thigh was adducted and flexed without any axial<br />

rotation. At touch down (2 3) the femur was probably medially rotated, especially if<br />

the tibia and foot were incorporated into increasing the length of the stride (see below).<br />

The beginning of the propulsive phase (3 4) likely entailed abduction until the<br />

posterolateral extension of the femoral head articular surface abutted the acetabulum.<br />

From here, lateral rotation would have brought the femur back to its closest packed<br />

position while also causing the body to swing forward (anteriorly) and ventrally on the<br />

tibae (4 5). From the closest packed position the femur could have extended, thus<br />

pushing the body further anteriorly. B, summary of movements in different planes<br />

through the gait cycle.<br />

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