Abstract
Introduction
Patients with reduced lumbar spine mobility are at higher risk of dislocation after THA as their hips have to compensate for spinal stiffness. Therefore our study aimed to 1) Define the optimal protocol for identifying patients with mobile hips and stiff lumbar spines and 2) Determine clinical and standing radiographic parameters predicting high hip and reduced lumbar spine mobility.
Methods
This prospective diagnostic cohort study followed 113 consecutive patients with end-stage hip osteoarthritis (OA) awaiting THA. Radiographic measurements were performed for the lumbar lordosis angle, pelvic tilt and pelvic-femoral angle on lateral radiographs in the standing, ‘relaxed-seated’ and ‘deep-seated’ (i.e. torso maximally leaning forward) position. A “hip user index” was calculated in order to quantify the contribution of the hip joint to the overall sagittal movement performed by the femur, pelvis and lumbar spine.
Results
Radiographs in the relaxed-seated position had an accuracy of 56% (95%CI:46–65%) to detect patients with stiff lumbar spines, compared to a detected rate of 100% in the deep-seated position.
The mean ‘hip user index’ was 63±12% and ten patients (9%) were hip users, having an index of 80% or more. A standing pelvic tilt of ≥18.5° was the only predictor for being a hip user with a sensitivity of 90% and specificity of 71% (AUC 0.83). Patients with a standing pelvic tilt ≥18.5° and an unbalanced spine with a flatback deformity had a 30xfold relative risk (95%-CI:4–226; p<0.001) of being a hip user.
Conclusion
Patients awaiting THA and having high hip and reduced lumbar spine mobility can be screened for with lateral standing radiographs of the spinopelvic complex and a thorough clinical examination. If the initial screening is positive, radiographs in the deep-seated position allow for better identification of patients being ‘hip users’ compared to radiographs in the relaxed-seated position.
