A biomechanical comparison of the thrust plate prosthesis and a stemmed prosthesis.

The thrust plate prosthesis (TPP) is a neck preserving femoral component in total hip arthroplasty (THA) which may facilitate more precise biomechanical reconstruction of the hip. The purpose of this study was to compare the biomechanical results of the TPP with a conventional THA. We compared anteroposterior radiographs from 60 patients who had undergone cementless THA, with 44 who had undergone a TPP. We measured the hip centre of rotation, femoral offset, limb length, and neck-shaft angle. The horizontal hip centre of rotation, vertical femoral offset, limb length and neck-shaft angle measurements showed a significant difference (p<0.05) in both groups when compared with preoperative values. However, the vertical hip centre of rotation and horizontal femoral offset measurements were different only in TPP patients when compared with preoperative values (p<0.05). When both groups (TPP and THA) were compared only the horizontal hip centre of rotation displayed a significant difference (p=0.003) in favor of the THA. Therefore, we found no difference in restoring the biomechanics of the hip using the two methods, and only the horizontal hip centre of rotation restoration favoured the THA. Our findings indicate that the TPP does not produce more accurate restoration of leg length or offset. Reproduction of hip mechanics after TPP may not be as good as has been suggested.