OTSR - 2026-07-11 - Journal Article
Lower Preoperative Hip Abductor Muscle Attenuation on CT Is Associated With Early Total Hip Arthroplasty Dislocation: A Matched Case Control Study.
Coulomb R, Jamaleddine Y, Laborde A, Haignere V, Rekik MA, Fairag R, Kouyoumdjian P
Topics
Key Takeaway
Preoperative gluteus medius/minimus attenuation below 41.6 HU on CT is associated with early THA dislocation (AUC 0.794, 75% sensitivity, 89% specificity) despite cups within the Lewinnek safe zone.
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Summary
This retrospective matched case-control study asked whether preoperative CT-derived abductor muscle quality predicts early dislocation after primary THA in patients with acceptable cup positioning. Gluteus medius and minimus attenuation was measured at the ASIS level; cases were matched 1:1 to controls by age, sex, BMI, and diabetes status. Post-segmentation MMA was significantly lower in dislocators (33.2 ± 15.1 HU vs. 45.9 ± 6.7 HU, p<0.001), with a threshold of 41.6 HU yielding an AUC of 0.794 and PPV of 87.1%.
Key Limitation
The 41.6 HU threshold was derived and tested in the same small cohort without external validation, making its clinical applicability uncertain.
Original Abstract
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.