Abstract
Background: Sacro-iliac (SI) joint is vertically oriented and subject to a large shear force on weight bearing. Gluteus maximus is strongly active when we experience an abrupt limb loading and need a stable SI joint. Suboptimal gluteus activity could disrupt weight transference and lead to low back pain as the body attempts compensation by recruiting biceps femoris, which could exert its influence through attachment to sacrotuberous ligament. A biomechanical model of SI joint dysfunction was proposed. The model was tested on a pilot study.
Methods: Two male volunteers participated in the study. One was a normal subject. The other had pain suggestive of SI origin. Electromyogram was recorded using pairs of disposable bipolar surface Ag/AgCl electrodes on the symptomatic side for the lumbar multifidus, gluteus maximus and biceps femoris muscles. Subjects were asked to walk in a straight line. Each test was taken three times for two full gait cycles. Two dimensional high speed video was used to capture data of walking motion. Raw electromyogram data was processed according to published protocols.
Results and discussion: Gluteus activation was poor in the symptomatic individual and failed to reach a peak in loading response. Biceps remained activated on terminal swing event with another peak activation in ipsilateral pre-swing event. Unlike normal volunteer, gluteus failed to show increased activity in terminal stance to pre swing events. The study showed a difference in gluteus maximus and biceps femoris activity in between the two volunteers. A larger study is planned to validate the model.
Correspondence should be addressed to Ms Alison McGregor, c/o BOA, SBPR at the Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PE.
