The Effect of Somatic Dysfunction of the Pelvis, Sacrum and Lower Lumbar Spine on Weight Bearing

Most sources claim that in individuals with leg length discrepancies, they tend to place more weight through the shorter lower extremity.1,2 Few cases state that the opposite is true.3 Many health care practitioners diagnose leg length discrepancies. Osteopathic physicians who practice with Osteopathic Manipulative Medicine (OMM) will also diagnose leg length discrepancies. They use testing to evaluate whether a leg length discrepancy is structural or functional. A structural leg length discrepancy is associated with shortening of bony structures.4 The structures affected can be due to congenital defects, which result in possible structural shortening of the tibia or femur, slipped capital femoral epiphyses (SCFE), or congenital dislocation. Other causes of structural leg length discrepancies include post total hip replacement, infections, tumors, paralysis, and trauma, including fractures where the gross length of a limb is altered.4 A structural leg length discrepancy can be most accurately assessed by physically measuring the distance between the anterior superior iliac spine (ASIS) and medial malleolus.4 The most reliable method of diagnosing a structural short leg is through full body radiographs. 6 A functional leg length discrepancy is a result of altered mechanics of the lower extremities. It is thought that a functional short leg occurs secondarily to a rotated pelvis caused by joint contractures and/or axial misalignments, including scoliosis.4 In osteopathic literature; functional leg length discrepancies are also thought to be the result of altered positions of the pelvis and sacrum. It is also thought in osteopathic philosophy that the position of the fifth lumbar vertebra affects the position of the sacrum. Therefore dysfunction of L5 will change the position of the sacrum such that a functional short leg is created.2(p.780-782) A common cause of functional leg length discrepancies diagnosed by osteopathic physicians is that of sacral base unleveling.5 The way in which a leg length discrepancy causes unleveling of the sacrum is through the femoral head of the longer leg driving the pelvis into a posterior rotation via forces placed through acetabular contact. Then the pelvis will typically rotate forward in attempts to lengthen the shorter leg, causing the sacral base to become unlevel.5 In addition, the sacral base tilts toward the side of the short leg.6 Standing postural x-rays, which outline sacral declination, are often used by chiropractors and osteopathic physicians to diagnose functional leg length discrepancies.6 Another way that functional leg length discrepancies are confirmed is through the supine to long sitting test, which tests for the presence of innominate rotations that may affect leg length as the cause.

There is no research known to support the presence of somatic dysfunctions, leg length discrepancies and altered weight bearing through lower extremities secondary to this.

It is common practice among osteopathic physicians who utilize OMM to diagnose musculoskeletal somatic dysfunctions of the pelvis, sacrum and lumbar spine. All these findings can contribute to low back pain. Therefore, it is the common practice of these physicians to diagnose leg length discrepancies, as it may ultimately result in low back pain.

Somatic dysfunction in osteopathic nomenclature is defined as 'impaired or altered function of related components of the somatic (body framework) system: Skeletal, arthrodial and Myofascial structures, and related vascular, lymphatic and neural elements'.2

There are specific somatic dysfunctions that lead to leg length differences. These effects include the sacral base tilting toward the side of the short leg, a low iliac crest on the short leg side, a forward rotation of the innominate on the shorter side and/or a posterior rotation of the innominate on the side of the longer leg as a compensatory measure. The lumbar spine will develop a convexity toward the side of the short leg.6 Their definitions are as follows: