THE POSTERIOR LAYER OF THE THORACOLUMBAR FASCIA - ITS FUNCTION IN LOAD-TRANSFER FROM SPINE TO LEGS

Study Design. The superficial and deep lamina of the posterior layer o f the thoracolumbar fascia have been studied anatomically and biomecha nically. In embalmed human specimens, the posterior layer has been bee n loaded by stimulating the action of various muscles. The effect has been studied using raster photography. Objectives. To study the role o f the posterior layer of the thoracolumbar fascia in load transfer bet ween To understand and treat low back pain, models are spine, pelvis, legs, and arms. Summary of Background Data. It has been determined whe ther muscles such as the gluteus maximus, latissimus dorsi, erector mu scle, and biceps femoris are functionally coupled via the thoracolumba r fascia. The caudal relations of the posterior layer of the thoracolu mbar fascia have not been previously studied. Methods. Dissection was directed to the bilaminar posterior layer of the thoracolumbar fascia of 10 human specimens. The superficial and deep lamina were studied us ing visual inspection and raster photography. Tension to the posterior layer of the fascia was simulated by traction to various muscles and measured by studying the displacement in the posterior layer. Results. Traction to a variety of muscles caused displacement of the posterior layer. This implies that in vivo, the superficial lamina will be tens ed by contraction of various muscles, such as the latissimus dorsi, gl uteus maximus and erector muscle, and the deep lamina by contraction o f the biceps femoris. Caudal to the level of L4 (in some specimens, L2 -L3), tension in the posterior layer was transmitted to the contralate ral side. Conclusions. Anatomic structures normally described as hip, pelvic, and leg muscles interact with so-called arm and spinal muscles via the thoracolumbar fascia. This allows for effective load transfer between spine, pelvis, legs, and arms-an integrated system. Specific electromyographic studies should reveal whether the gluteus maximus mu scle and contralateral latissimus dorsi muscle are functionally couple d, especially during rotation of the trunk. In that case, the combined action of these muscles assists in rotating the trunk, while simultan eously stabilizing the lower lumbar spine and sacroiliac joints.