Background: Post-operative tensor fascia lata (TFL) muscle atrophy due to superior gluteal nerve (SGN) injury during total hip arthroplasty (THA) can affect patients' post-operative hip function. This study aimed to determine the incidence of TFL muscle atrophy in THA performed via the modified Watson-Jones anterolateral approach and the risk factors for TFL atrophy.
Methods: We reviewed pre- and post-operative magnetic resonance imaging (MRI) data of 164 patients who underwent cementless THA via the modified Watson-Jones approach at one institution. TFL atrophy was defined as worsening of ≥ 2 grades in the Goutallier classification or > 40% decrease in the cross-sectional area (CSA) of the TFL on post-operative MRI compared to that on preoperative MRI. Patients' backgrounds were compared between those with or without TFL atrophy to determine the risk factors of TFL atrophy. Fatty atrophy grade and CSA of the gluteus minimus and medius were also evaluated.
Results: Thirteen (8.0%) cases of TFL atrophy were detected. The mean body mass index (BMI) in the cases with TFL atrophy was significantly higher than in those without TFL atrophy (p = 0.012). The fatty atrophy grade was worse post-operatively than preoperatively; moreover, the CSA of the gluteus minimus decreased.
Conclusions: We found a low incidence of TFL atrophy due to SGN injury after THA using the modified Watson-Jones approach. High BMI can be a risk factor for nerve injury. The gluteus minimus can be injured directly during surgery. We suggest that overexposure of the surgical site should be avoided, especially in patients with high BMI.
Keywords: Atrophy; Magnetic resonance imaging; Tensor fascia lata; Total hip arthroplasty.