Heterotopic ossification after primary cemented and noncemented total hip arthroplasty in patients with osteoarthritis and rheumatoid arthritis.

OBJECTIVE: To compare the frequency and severity of heterotopic ossification (HO) in patients with osteoarthritis or rheumatoid arthritis who undergo cemented or noncemented total hip arthroplasty.

DESIGN: A prospective case study.

SETTING: A university referral centre.

PATIENTS: One hundred and sixty one patients underwent 184 total hip arthroplasties. The 184 hips were categorized as follows: cemented total hip arthroplasty--60 osteoarthritis hips, 26 hips affected by rheumatoid arthritis; noncemented total hip arthroplasty--67 osteoarthritic hips, 31 hips affected by rheumatoid arthritis.

INTERVENTIONS: Total hip arthroplasty. A standard approach was used to implant either a cemented or noncemented prosthesis. Radiographs were obtained of each hip preoperatively, immediately postoperatively and 6 weeks, 3 months, 6 months and 1 year postoperatively.

MAIN OUTCOME MEASURES: Radiographs were graded in blind fashion for HO, according to the criteria of Brooker. Modified Harris hip scores were calculated at 1 and 2 years postoperatively.

RESULTS: HO (incidence of Brooker grades 2, 3 and 4) was greater after cemented (22%) than noncemented (9%) total hip arthroplasty in osteoarthritic hips (p < 0.05), but there was no significant difference between the two types of prosthesis in hips affected by rheumatoid arthritis. When both types of prosthesis were considered together there was no significant difference in the incidence of HO between osteoarthritic hips (15%) and hips affected by rheumatoid arthritis (12%). With respect to Harris hip score, the presence of grade 4 HO was associated with a significantly (p < 0.05) lower score (50.6) than grade 3 (89.4) and grade 2 (91) HO.

CONCLUSIONS: Cemented total hip arthroplasty increases the frequency of HO only in osteoarthritic hips. Compared with Brooker's grades 2 and 3 HO, grade 4 HO significantly lowers the Harris hip score after total hip arthroplasty.