How hip joint shape variation is associated with osteoarthritis

Statistical shape modelling (SSM) is a new technique, which allows quantitative measurements of the hip shape from 2-dimensional images (radiographs). The objective of this study  was to identify hip joint anatomical abnormalities that could be associated with osteoarthritis development based on radiographic measurements and SSM. 123 hospitalized unilateral hip osteoarthritis patients in Hospital of Traumatology and Orthopaedics for hip arthroplasty surgery (Arthritic group) and 100 patients with no hip pain and no/mild radiographic signs of osteoarthritis (Tonnis grade 0, I) (Control group) from year 2018 to 2020 were included in the study. Predefined radiographic parameters (lateral center edge angle, neck shaft angle, alpha angle, acetabular depth, acetabular index, Singh index, cortical thickness index, pistol grip deformity, crossover sign) were measured and assessed using the Impax-Orthopaedic-Tools 3.0.2.3 program. A statistical shape model was built using the BoneFinder 1.3.4 program which detects and sets 75 landmark points on the proximal femur and hemipelvis in AP radiographs to analyse the shape variations between the two groups. The obtained data were statistically analysed by the IBM SPSS 23 program. The mean age in the Control group was 75.40± 10.75 and Arthritis group 67.50± 8.75 years. Comparing predefined radiographic parameters between the Arthritic and Control group, increased alpha angle (>50o) (p<0.001), Pistol grip deformity (p<0.001) (characteristic for Cam deformity) and center-edge-angle less than 25o (p<0.001) (characteristic for acetabular dysplasia) was significantly more prevalent in the Arthritic group. Patients with hip osteoarthritis had significantly higher scores of shape modes 1, 2 and 4 (p=0.002; p=0.01; p=0.02). By applying predefined radiographic measurements and SSM- defined hip joint characteristics, Cam deformity, acetabular dysplasia, flattened head–neck junction, non-spherical femoral head and prominent acetabular posterior wall can be associated with osteoarthritis. Anatomical shape of the hip joint may play an important role in the development of osteoarthritis.