Abstract
Introduction
Hip osteoarthritis can be debilitating, often leading to pain, poor kinematics and limiting range of motion. While the in vivo kinematics of a total hip arthroplasty (THA) are well documented, there is limited information pertaining to the kinematics of native, non-arthritic (normal) hips and degenerative hips requiring a THA.
The objective of this study is to evaluate and compare the in vivo kinematics of the normal hip with pre-operative, degenerative hips and post-operative THA.
Methods
Twenty subjects, ten having a normal hip and ten having a pre-operative, degenerative hip that were analyzed before surgery and then post-operatively after receiving a THA. Each subject was asked to perform gait while under mobile fluoroscopic surveillance. Normal and pre-operative degenerative subjects underwent a CT scan so that 3D models of their femur and pelvis could be created. Using 3D-to-2D registration techniques, the hip joint kinematics were derived and assessed.
Femoral head and acetabular cup rotational centers were derived using spheres. The centers of these spheres were used to obtain the femoral head sliding distance on the acetabular cup during the activity. The patient-specific reference femoral head values were obtained from the subjects’ CT scans in a non-weight bearing situation.
Results
Overall, 0% of the normal subjects experienced femoral head sliding (FHS) within the acetabulum, and 33% of the degenerative subjects experienced FHS. The degenerative hips experienced an average maximum sliding of 0.902 ± 0.864 mm. Further evaluation seems to indicate that the femoral head ligament played a significant role in hip separation. If this ligament was not functioning, it appeared that the femoral head experienced more abnormal motion. Therefore, degenerative hip subjects having an intact femoral head ligament did not experience femoral head sliding of their femoral head within the acetabulum.
A further analysis was then conducted to assess the contact area between femoral head and acetabular cup (Figure 1). After THA implantation, subjects experienced greater abnormal hip motion leading to hip separation.
Discussion
Overall, our current analysis has revealed trends that degenerative hips experience more abnormal hip kinematics that lead to higher bearing surface forces and stresses. It was interesting to note that the intact femoral head ligament did stabilize the hip joint leading to no femoral head sliding. Therefore, further research needs to be conducted to determine the role of the femoral head ligament and degeneration of the hip joint. Also, it is worth noting that the maximum displacement usually occurs during swing phase of the gait, just before heel-strike for degenerative hips, similar to total hip arthroplasty, evaluated in previous fluoroscopic studies. Further investigation is being conducted to evaluate component placement for the THA subjects, comparing their motion pre and post-operatively.
