Postoperative muscle atrophy and fatty degeneration with respect to surgical approaches in total hip arthroplasty.

Background
Total hip arthroplasty is the gold standard for treatment of hip osteoarthritis. The different surgical approaches utilize different intervals to access the hip joint. There is concern that some surgical approaches cause soft tissue trauma resulting in post-operative muscle weakness of patients undergoing THA. We therefore asked whether the implantation of a total hip prosthesis by each of four common surgical approaches (anterior, anterolateral, direct lateral and posterior) leads to (i) muscle atrophy (defined as decreased muscle cross-sectional area [CSA]) and (ii) muscle degeneration (defined as fatty infiltration) of 12 specific periarticular hip muscles. Further, if significant change is found, can we establish an associated pattern with a particular surgical approach?
Method
We retrospectively evaluated 493 patients undergoing computed tomography of the pelvis in HFR hospital Fribourg, Switzerland, between 2014 and 2020. All patients had undergone a primary THA at some point prior to their CT scan. Trauma, metastasis, bone tumor, neurologic disorder, infection, and revision cases were excluded. Twelve periarticular hip muscles were measured for CSA and degree of fatty infiltration according to the Goutallier scale on axial and sagittal views of both the operative and nonoperative hips.
Results
CSA of the operative hip muscles differed significantly depending on approach. Similarly, there was a statistically significant difference in muscle degeneration in the operative hips according to the Goutallier classification. We observed a specific level and pattern of muscle atrophy for each approach.
Conclusion
In all approaches, there is a trade-off between the muscles they affect, their role, and whether there is a possibility of partial compensation by other muscles. The anterior approach was the least harmful to the gluteus medius muscle.