New methods for assessing hip biomechanics.

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A complete and accurate understanding of the biomechanics of the human hip is essential for understanding its function and for designing treatments for disorders that affect this vital joint. A primary obstacle to studying hip mechanics is that there is a fluid layer within the joint, and the joint is sealed by a structure known as the acetabular labrum. Consequently, it is not possible to measure joint contact force, strain distribution or pressure by introducing a sensor into the joint because this would violate the seal and change the contact mechanics. This makes an imaging-based approach to studying hip mechanics essential. The long-term objectives of this program of research are to develop methods to assess hip mechanics under physiological conditions and to apply these methods to determine comprehensively how the most prevalent hip deformities and injuries change hip mechanics, and which treatment approaches most effectively restore hip mechanics to normal. Within this program, two short-term objectives are: In Aim 1, we will develop imaging-based methods for measuring cartilage strain in the hip joint in cadaver specimens loaded to simulate in vivo physiological loads. To make measurements that are more accurate than any that have been made previously, we will use the Canada Light Source synchrotron to perform three dimensional, computed tomography images of hips. To implement synchrotron imaging for measuring cartilage strain in physiologically loaded cadaver hips we will develop: a) a system for loading cadaver hip joints at physiological levels of load and at physiological positions within the imaging area of the synchrotron; b) a protocol for achieving full diffusion of contrast agent into the cartilage; c) image processing for determining cartilage deformation and strain; d) experiments quantifying the reproducibility of the method in five cadaver hip specimens In Aim 2 we will determine the effect of a prevalent type of hip deformity, femoroacetabular impingement (FAI), and acetabular labral damage on cartilage strain in hip specimens at physiological loads and hip positions. We will obtain ten cadaver hip specimens with documented cam deformities and, for the control group, ten specimens confirmed, by radiographs and CT scans, to have no deformities or other pathology. We will load each specimen in physiological positions, including those expected to lead to impingement, and assess strain in the acetabular and femoral cartilage using synchrotron imaging as described in Aim 1. This will be repeated after resection of the acetabular labrum. We will compare maximum strain, mean strain and the location of maximum strain between normal and FAI hips, and between the intact labrum and resected labrum states to assess the effects of FAI deformity and the labrum on compressive cartilage strain. Once this new method is developed, it will form the basis for further studies of the hip, including the mechanical behaviour of other tissues such as the acetabular labrum, and assessments of the effects of other hip disorders and treatments on hip mechanics.