In Vivo Determination and Comparison of Total Hip Arthroplasty Kinematics for Normal, Preoperative Degenerative, and Postoperative Implanted Hips.

BACKGROUND: The study objective is to analyze subjects having a normal hip and compare in vivo kinematics to subjects before and after receiving a total hip arthroplasty. METHODS: Twenty subjects, 10 with a normal hip and 10 with a preoperative, degenerative hip were analyzed performing normal walking on level ground while under fluoroscopic surveillance. Seven preoperative subjects returned after receiving a total hip arthroplasty using the anterior surgical approach by a single surgeon. Using 3-dimensional to 2-dimensional registration techniques, joint models were overlayed on fluoroscopic images to obtain transformation matrices in the image space. From these images, displacements of the femoral head and acetabulum centers were computed, as well as changes in contact patches between the 2 surfaces throughout the gait cycle. RESULTS: Implanted hips experienced the least amount of separation, compression, and overall sliding throughout the entire gait cycle, but they did show signs of edge loading contact patterns. Conversely, the degenerative hips experienced the most compression, sliding, and separation, with the maximum amount of sliding being 6.9 mm. The normal group ranged in the middle, with the maximum amount of sliding being 1.75 mm. CONCLUSION: Current analysis revealed trends that degenerative hips experience more abnormal hip kinematics that leads to higher articulating surface forces and stresses within the acetabulum. None of the implanted hips experienced hip separation.