Risk factors for heterotopic ossification and spur formation after total knee arthroplasty

Introduction The present study investigated the incidence and risk factors of heterotopic ossification (HO) after implantation of knee prosthesis. Materials and methods We undertook a retrospective cohort study in 434 cases (363 patients) treated with a total knee replant using a Press-Fit-Condylar (P.F.C. ® Sigma ® ) prosthesis. The occurrence of HO in radiograph after a follow-up period of 11.2 ± 2.4 months was correlated in a regression model with a variety of influencing factors. Results 21 patients (4.8 %) developed heterotopic ossifications, all located in the area of the distal femur. The only risk factor found concerning the development of HO was osteoarthritis when compared to rheumatoid arthritis (OR = 4.07, 95 % CI 1.18–14.05; p = 0.0201) and postoperative wound healing problems (OR = 11.32, 95 % CI 3.26–39.33; p = 0.0001). Notching (OR = 2.22, 95 % CI 0.92–5.36; p = 0.0765) and osteophyte forming (hypertrophic) arthrosis (OR = 2.40, 95 % CI 0.97–5.95; p = 0.0596), however, were associated with the development of a bony spur in the contact area of the femoral component of the prosthesis. Conclusions Our study has revealed that patients with rheumatoid arthritis are at lower risk of HO than patients with osteoarthritis. An impairment of wound healing would appear to promote the development of a HO. Notching and hypertrophic arthrosis are highly likely to be associated with the development of a bony spur in the ventral contact area of the prosthesis.