Effects of knee joint angle and tilt table incline on force distribution at the fee and support straps

OBJECTIVE: To investigate the effects of tilt table incline and knee flexion angle on the degree of weight bearing and forces exerted across the supporting straps. DESIGN: A quantitative and exploratory study to investigate the effects of a mechanical procedure. SETTING: Physiotherapy gymnasium. SUBJECTS: Twelve healthy subjects (9 female, 3 male) aged 22-45 years. INTERVENTIONS: Subjects stood on a tilt table, on two occasions, with simulated contractures of 10 degrees and 40 degrees knee flexion. Nine tilt angles, between 10 degrees and 90 degrees, were maintained for 1 minute each in random order. MAIN OUTCOME MEASURES: Force was recorded from single-point load cells placed under the feet, and at knee and chest straps. RESULTS: The degree of simulated knee contracture (10 degrees or 40 degrees) influenced the distribution of forces at different recording sites. Weight bearing increased with table incline and was significantly less with the 40 degrees than the 10 degrees knee angle (p < 0.001). Conversely, forces across the knee straps were systemically higher with the 40 degrees knee angle (p < 0.0001). The effects were accentuated by greater body weight. Forces across the chest strap also increased with tilt and were significantly larger with the 40 degrees knee angle (p < 0.05). CONCLUSIONS: The relationships between table incline, angle of knee flexion and distribution of forces generated during tilt table standing have been quantified and described. Standing with flexed knees involved less weight bearing under the feet and greater force exerted across the supporting straps. These effects were more pronounced at the higher knee angle and with greater body weight, and could be modified by reducing table inclin