A fast method for finding maximum range of motion in the hip joint

Introduction: For diagnosing some of the hip diseases, it is important to obtain the hip's range of motion. For example loss of internal rotation in the hip is one of the first signs of internal hip pathology and can be related to diagnoses, such as arthritis. Also, increase in femoral or acetablular anteversion usually demonstrates an increase in the internal rotation. Clinical hip examinations are usually based on rotating the hip in the special orientations. For instance, the flexion ad-duction internal rotation test is used to aid in the diagnosis of femoroacetabular impingement in the anterior location. Such practical methods are usually based on the patient's feedback during the examinations and therefore the diagnosis may not be easy and accurate [MAR05]. On the other hand, after diagnosing the hip disease, the treatment may be based on surgery. For example options for treatment of femoroacetabular impinge-ment include trimming of the anterior aspect of the acetabular rim, and surgical resection of part of the anterolateral aspect of the neck. Since the operation can be highly invasive, it is essential that surgeon has knowledge of maximum range of motion before operation to know exactly about the surgery strategy and reduce the risk of miss-operation [MGC05]. Having a computer aided method for finding the hip's range of motion can help us to have a more accurate diagnosis and/or surgery strategy. The computer aided methods for hip simulations usually exploit the reconstructed 3D model of the hip tissues obtained from MRI. The traditional methods for finding range of motion are based on repetitive collision detection for numerous rotation steps until a collision happen, [KSMM03]. This can be highly time-consuming. We propose a novel method for finding maximum range of motion for hip joint based on cylindrical segmentation. The method is faster than traditional ones, and needs to be performed only once per axis orientation. This method is illustrated on the case of finding maximum range of motion in the human hip joint, which is not only useful for further hip simulation but also provides information Total hip replacement 498 about hip disease for surgeon. Methods: The method works by segmenting the object spatial occupancy with cylindrical coordinates. At the first step we trim out non colliding parts by calculating distance between the rotating axis and different parts of the objects. In the next step the objects are cylindrically segmented. The corresponding ring-shaped sampling cells (see …