Relationship between the Hounsfield Unit value of the greater trochanter and the risk of greater trochanteric fractures in anterolateral muscle-sparing minimally invasive total hip arthroplasty

Abstract

Background

No previous studies have investigated the association between the risk of greater trochanteric fractures and the Hounsfield Unit (HU) of the greater trochanter in muscle-sparing minimally invasive total hip arthroplasty (MIS-THA). This study aimed to investigate the risk factors for greater trochanteric fractures in anterolateral MIS-THA.

Hypothesis

Lower HU values of the greater trochanter are associated with a higher risk of intraoperative and early postoperative greater trochanteric fractures.

Patients and methods

This single-center retrospective observational study included 223 patients (257 hips) who underwent primary THA for osteoarthritis or osteonecrosis between January 2010 and August 2024 using a minimally invasive anterolateral approach in the lateral position. All surgeries were performed by four surgeons. Preoperative CT was used to reconstruct coronal sections including the femoral head center and proximal femoral axis, and cancellous HU values of the greater trochanter were measured. Postoperative CT (1 week) with metal artifact reduction was routinely performed; fractures were defined as cortical fracture lines on 3D-reconstructed CT and assessed by two independent orthopedic surgeons. Patients were divided into two groups according to the presence or absence of fractures.

Results

The incidence of greater trochanteric fractures was 6.6% (17/257 hips). Twelve of these fractures (70.6%) were recognized intraoperatively or immediately postoperatively. Full hydroxyapatite (HA)-coated stems were associated with an increased fracture risk compared with other designs (relative risk [RR], 2.68; 95% CI, 1.07–6.68). Age, sex, BMI, ASA physical status, and diagnosis were not significantly associated with fractures. Multivariate analysis identified lower HU values (odds ratio [OR], 0.973; p < 0.0001) and full HA-coated stems (OR, 13.3; p = 0.04) as independent predictors. Receiver operating characteristic (ROC) analysis determined an optimal cut-off of 72.0 HU (sensitivity, 0.941; specificity, 0.742), with a value ≤72.0 HU demonstrating high predictive power (RR, 36.7; p < 0.0001).

Conclusion

Preoperative measurement of HU values in the greater trochanter is a useful screening tool for identifying patients at increased risk of fractures in anterolateral MIS-THA. While an HU value of ≤ 72.0 necessitates careful intraoperative management and increased vigilance, it should be interpreted as an indicator of risk rather than a definitive predictor of fracture due to its moderate specificity.

Level of evidence

IV; retrospective study.