Alterations of the Lumbar Curve Related to Posture and Seating

Industrial seating and spinal loading

“…Keegan (1953) pointed to the "normal" shape of the spine with a lordosis in the lumbar and cervical regions. His definition of "normal" shape was minimal wedging of the intervertebral discs, especially the fourth and fifth lumbar discs, and minimal strain in the annular ligaments.…”

“…As a result of that, the pelvis is tilted backwards and thus creates a lumbar kyphosis. The opposite occurs at large angles between the trunk and thighs (Keegan 1953). In that posture, the psoas and quadriceps muscles and the ilio-femoral ligaments (Schoberth 1962) cause a forward tilt of the pelvis, and thereby an exaggerated lumbar lordosis is created (Keegan 1953).…”

“…In that posture, the psoas and quadriceps muscles and the ilio-femoral ligaments (Schoberth 1962) cause a forward tilt of the pelvis, and thereby an exaggerated lumbar lordosis is created (Keegan 1953). Keegan (1953).…”

“…Straight knees tilt the pelvis further backwards and thereby act towards lumbar kyphosis, but the influence of the knee angle is of less importance than the angle between the trunk and thighs (Keegan 1953). In unsupported sitting, also the position of the centre of gravity in relation to the ischial tuberosities affects the pelvic tilt.…”

“…In standing, the pelvis is slightly forward tilted (Keegan 1953). He also claimed that the "normal" posture of the lumbar spine and the pelvis occurred-when the angle between trunk and thighs was 135' and the knee angle also was 135*.…”