Abstract
Introduction
Untreated hip osteoarthritis is a debilitating condition leading to pain, bone deformation, and limited range of motion. Unfortunately, studies have not been conducted under in vivo conditions to determine progressive kinematics variations to a hip joint from normal to pre-operative and post-operative THA conditions. Therefore, the objective was this study was to quantify normal and degenerative hip kinematics, compared to post-operative hip kinematics.
Methods
Twenty unique subjects were analyzed; 10 healthy, normal subjects and 10 degenerative, subjects analyzed pre-operatively and then again post-operatively after receiving a THA. During each assessment, the subject performed a gait (stance and swing phase) activity under mobile, fluoroscopic surveillance. The normal and diseased subjects had CT scans in order to acquire bone geometry while implanted subjects had corresponding CAD models supplied. Femoral head and acetabular cup centers were approximated by spheres based on unique geometries while the component centers were pre-defined as the center of mass. These centers were used to compare femoral head sliding magnitudes on the acetabular cup during the activity for all subjects. Subjects were noted to have separation with changes in center magnitudes of more than 1 mm during gait. Utilizing 3D-to-2D registration techniques, the hip joint kinematics were derived and assessed. This allowed for visualization of normal subject positioning, pre-op bone deterioration, and implant placement within the bones.
Results
None of the normal, experienced femoral head sliding (FHS) within the acetabulum. Two of the normal subjects revealed tendencies more similar to a degenerative hip. However, 4/10 of the degenerative subjects saw significant FHS with an average maximum of 1.344 0.522 mm. It was interesting to note that none of the implanted subjects experienced FHS, demonstrating improved kinematic trends more normal-like and revealing better kinematic patterns post-operative compared to their pre-operative conditions.
Discussion
Overall, analysis has revealed trends of degenerative hips experiencing more abnormal hip kinematics due to lower surface area and greater magnitudes of femoral center head displacement. The implanted subjects saw decreased amounts of displacement which correlated to increases in contact area. These results more closely matched normal hip kinematics and showed an improvement over their diseased condition. It seems that the surgeon in this study better replicated the stem version angle to the pre-operative conditions, leaving less transverse stress of the femoral head on the acetabular cup, possibly leading to the femoral head remaining within the acetabular cup and the subjects not experiencing FHS.
Significance
Pre-operative, degenerative hip subjects displayed abnormal femoral hip displacement at greater magnitudes to normal hip subjects. After THA, these subjects saw reduced magnitudes of displacement more in line with normal hip kinematics.
For any figures or tables, please contact authors directly.
