Positive or negative x-axis rotation of the innominate as a cause of a functional leg length inequality

Abstract

The objective of this research was to determine whether there was any reasonable biomechanical evidence to support the chiropractic theory that a positive (anterior) or negative (posterior) x-axis rotation of the innominate bone, could result in a significant functional leg length inequality. This theory was advocated by winterstein J.F. 1991, Gatterman M.I. 1990 and Herbst R.W. (undated) ~ The object was achieved by clamping six fresh cadaveric pelves in a specially designed instrument which measured the positive (anterior) and negative (posterior) x-axis rotation of the innominate via the sacroiliac joint and the symphysis pubis, the forces involved, and the associated y-axis translation, zaxis translation and x-axis rotation of the roof of the acetabulum. The extra-capsular iliac tubercle was used as the axis of rotation due to easy palpation and identification of this point. Some authors placed the axis at this point, or at a point very close to this area, ( Bakland o. et al. 1984; Weisle H. 1955; Bernard T.N. et al. 1991; Bellamy N. et al. 1983) . The results were tabulated, and thereafter a Pearson's moment correlation coefficient was done to show the linearity of the results. Graphs were then drawn to depict this linearity graphically. Finally a mean of the differences for each set of results of each cadaver was done to show how the results of each cadaver compared. The results showed that a positive (anterior) and a negative (posterior) x-axis rotation of the innominate caused a functional lengthening and shortening of the lower limb respectively. These findings concur with those of winterstein J.F. 1991, Gatterman M.I. 1990 and Herbst R.W. (undated) The maximum amount of lower limb lengthening varied between 11.75 millimetres and 6.17 millimetres among different cadavers, when 9 degrees of anterior innominate rotation was induced. The maximum amount of lower limb shortening varied between 10.58 millimetres and 6.16 millimetres among different cadavers when 9 degrees of posterior innominate rotation was induced. This 9 degrees of rotation was via both sacroiliac joints, thus effectively allowing 4,5 degrees of rotation per sacroiliac joint.