Comparison of morphological changes of gluteus medius and abductor strength for total hip arthroplasty via posterior and modified direct lateral approaches

Abstract

Background: It is a general belief among orthopedists that the muscle damage of the hip abductors after total hip arthroplasty (THA) is theoretically minimal via posterior approach. However, there is little data scientifically supporting the purported advantage. The purpose of this study was to quantifiably assess the injury to the gluteus medius (GMED) after THA via the minimally invasive (MIS) posterior and the modified direct lateral (mDL) approaches.

Methods: Sixty-four consecutive patients enrolled prospectively were randomly assigned to the MIS posterior and the mDL approach groups. Three-dimensional MRI reconstruction of bilateral GMED, abductor strength measurement as well as post-operative pain assessment were included in the analysis. Data were collected pre-operatively, six, 12, and 52 weeks post-operatively.

Results: Interestingly, in terms of the morphological changes of GMED, the MIS posterior approach showed a more significant degeneration caused by the surgical trauma compared with the mDL approach in both muscle volume atrophy and fatty infiltration from six to 52 weeks post-operatively. However, the improvement of abductor muscle strength on surgical side and VAS pain score were comparable between the two groups during the entire follow-up.

Conclusion: The injury of hip abductors after THA via posterior approach cannot be neglected. And, the planned detachment of partial GMED tendon combined with the reconstruction in situ could also achieve the satisfactory muscle recovery. Moreover, the post-operative rehabilitation of abductor strength was the aggregated results of a battery of factors, especially the pain, not just determined by the muscular morphological changes.

Keywords: Hip abductors; Muscle injury; Muscular morphology; Three-dimensional MRI reconstruction; Total hip arthroplasty.