LETTERS Relation

between ectopic ossification after total hip arthroplasty and activity of general inflammation in patients with ankylosing spondylitis Ectopic ossification (EO) is a well known complication after total hip arthroplasty (THA). Some previous studies have consid-ered ankylosing spondylitis (AS) a risk factor of EO, however other studies have refuted this association.1 The reported incidence of EO varies widely in diVerent series.2 We retrospectively studied a total of 20 pri-mary THAs in 16 Japanese patients with definite AS. The age of the patients at surgery ranged from 30 to 64 years (mean 45). All THAs apart from three cases were performed using bone cement. Surgical exposure was achieved by the posterolateral approach. The length of follow up averaged 93 months (range 29 to 148). Compared with the incidence of EO in AS patients, we investi-gated 126 primary THAs (92 osteoarthritis (OA), 26 rheumatoid arthritis (RA) and eight aseptic necrosis of the femoral head (ANF)) in 107 patients (15 male/92 female, mean age 61 years; range 32 to 85, mean follow up period 63 months; range 28 to 128). Bone cement was used in 118 of these 126 cases of THA. We evaluated supine anteroposterior roentgenographic findings of the hips. EO was graded according to Brooker’s classification.3 Six of 20 THA cases showed evident radiographic EO after THA in AS patient