title: Regression models to predict hip joint centers in pathological hip population.
abstract: The purpose was to investigate the validity of Harrington's and Davis's hip joint center (HJC) regression equations on a population affected by a hip deformity, (i.e., femoroacetabular impingement). Sixty-seven participants (21 healthy controls, 46 with a cam-type deformity) underwent pelvic CT imaging. Relevant bony landmarks and geometric HJCs were digitized from the images, and skin thickness was measured for the anterior and posterior superior iliac spines. Non-parametric statistical and Bland-Altman tests analyzed differences between the predicted HJC (from regression equations) and the actual HJC (from CT images). The error from Davis's model (25.0 ± 6.7 mm) was larger than Harrington's (12.3 ± 5.9 mm, p<0.001). There were no differences between groups, thus, studies on femoroacetabular impingement can implement conventional regression models. Measured skin thickness was 9.7 ± 7.0mm and 19.6 ± 10.9 mm for the anterior and posterior bony landmarks, respectively, and correlated with body mass index. Skin thickness estimates can be considered to reduce the systematic error introduced by surface markers. New adult-specific regression equations were developed from the CT dataset, with the hypothesis that they could provide better estimates when tuned to a larger adult-specific dataset. The linear models were validated on external datasets and using leave-one-out cross-validation techniques; Prediction errors were comparable to those of Harrington's model, despite the adult-specific population and the larger sample size, thus, prediction accuracy obtained from these parameters could not be improved.
authors.affiliation: School of Human Kinetics, University of Ottawa, Canada.
authors.forename: Giulia
authors.initials: G
authors.lastname: Mantovani
authors.affiliation: Department of Mechanical Engineering, University of Ottawa, Canada.
authors.forename: K C Geoffrey
authors.initials: KC
authors.lastname: Ng
authors.affiliation: School of Human Kinetics, University of Ottawa, Canada; Department of Mechanical Engineering, University of Ottawa, Canada. Electronic address: mlamon@uottawa.ca.
authors.forename: Mario
authors.initials: M
authors.lastname: Lamontagne
mesh_terms: D000328:Adult; D015992:Body Mass Index; D016022:Case-Control Studies; D005260:Female; D057925:Femoracetabular Impingement / Q000000981:diagnostic imaging*; D006621:Hip Joint / Q000000981:diagnostic imaging*; D006801:Humans; D016014:Linear Models; D008297:Male; D012885:Skinfold Thickness; D014057:Tomography, X-Ray Computed
keywords: Accuracy; Computed tomography; Femoroacetabular impingement; Hip joint center; Regression equations; Skin thickness