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Lower preoperative hip abductor muscle attenuation on CT is associated with early total hip arthroplasty dislocation:
Remy Coulomb1, Youssef Jamaleddine2, Alexandre Laborde3
1CHU de Nîmes, Université de Montpellier, Department of Orthopaedic and Traumatology Surgery and Spine Surgery, Hôpital Universitaire Carémeau, 4 Place du Pr Robert-Debré, 30029 Nîmes Cedex 9, France; Université de Montpellier, 2 rue École de Médecine, CS 59001, 34060 Montpellier Cedex 2, France; LMGC, Université de Montpellier, CNRS, 860 Rue de Saint-Priest, 34090 Montpellier, France.
Background:
Dislocation after total hip arthroplasty (THA) may occur despite acceptable component positioning, suggesting that patient-specific soft-tissue factors contribute to instability. Evidence regarding the role of preoperative abductor muscle quality in early THA dislocation remains scarce. This study assessed whether computed tomography (CT)-derived gluteus medius and minimus muscle quality differed between patients with early THA dislocation and matched controls.
Hypothesis:
Lower preoperative abductor muscle quality, particularly lower Mean Muscle aAttenuation (MMA), would be associated with early dislocation after primary THA.
Patients And Methods:
This retrospective matched case-control study included patients who underwent primary THA between January 2009 and December 2020 and had an available preoperative CT-scan. Cases were patients who sustained dislocation within 2 years after primary THA. Patients with acetabular cups outside the Lewinnek target zone, revision arthroplasty, neurological or cognitive disorders, documented hip-spine syndrome, alcohol use disorder, non-primary THA dislocation causes, non-interpretable CT images, or femoral head size other than 32 mm were excluded. Thirty-six dislocation cases were matched 1:1 with 36 controls without dislocation according to age, sex, body mass index, and diabetes status. The gluteus medius and minimus were assessed on a standardized axial CT slice at the anterior superior iliac spine. Mean muscle attenuation, Cross-Sectional Area (CSA), and Intramuscular Fatty Fraction (IFF) were measured before and after attenuation-based segmentation using a -30 to 150 Hounsfield unit thresholds.
Results:
Post-segmentation MMA was significantly lower in the dislocation group than in controls: 33.2 ± 15.1 HU versus 45.9 ± 6.7 HU (p < 0.001). Pre-segmentation MMA was also lower in the dislocation group: 17.3 ± 20.6 HU versus 25.4 ± 13.2 HU (p = 0.048). No significant between-group differences were observed for CSA or IFF. Receiver operating characteristic analysis showed moderate discrimination for post-segmentation MMA, with an area under the curve of 0.794. A threshold below 41.6 HU yielded 75.0% sensitivity, 88.9% specificity, 87.1% positive predictive value, and 78.0% negative predictive value. Inter-observer reliability for post-segmentation MMA was good, with an intra-class correlation coefficient of 0.87.
Discussion:
In this selected cohort, lower preoperative CT-derived abductor muscle attenuation was associated with early THA dislocation despite acceptable acetabular cup position. The 41.6 HU threshold should be considered exploratory and hypothesis-generating because it was derived from a small retrospective cohort without external validation.
Level Of Evidence:
III; retrospective matched case-control study.