Background: Higher non-occupational contact stress in the hip joint has been implicated in idiopathic osteoarthritis development. The aim of our study was to explore, whether additional increase in contact hip stress during lifting of heavy objects might contribute to earlier hip arthroplasty.
Methods: Fifty female subjects with suitable standard pelvic radiographs made years prior to surgery were carefully selected from a list of consecutive recipients of hip endoprosthesis due to idiopathic osteoarthritis. Mass of the lifted loads (Mload) and body weight were obtained through an interview for each subject. Maximum loads lifted more than 5 times a day, more than 3 times a week and for more than 10 years were recorded. Peak contact hip stress in the one-legged stance (pmax) was calculated for sixty-five hips from body weight and parameters of the pelvic-hip contours with the HIPSTRESS method. Regression analysis was used to correlate non-occupational (pmax) and occupational (Mload) load on the hip joint with age at hip arthroplasty. In addition, a univariate model with natural logarithm of occupational contact hip stress (pocc), acting as an independent variable, was constructed.
Results: An increase in pmax by 1.00 MPa (non-occupational load) was associated with hip arthroplasty 7.3 years earlier (R2=0.137; P-value<0.001) and an increase in Mload by 10 kg (occupational load) with 1.3 years earlier hip arthroplasty (R2=0.107; P-value=0.014). A bivariate regression analysis incorporating pmax as well as Mload was also performed (adjusted R2=0.214, P-value< 0.001).With the univariate model, addressing pocc, we were able to explain 22.8 % of variability in age at hip arthroplasty (adjusted R2=0.228, P-value<0.001).
Conclusions: In our study, work-related lifting of heavy objects with increase in occupational contact hip stress has been associated with earlier hip arthroplasty.