This study has three purposes A) to determine if Legg-Calvé-Perthes disease (LCP) is a risk factor for developing secondary hip osteoarthritis (OA), B) to determine the inter-relationship between Stulberg class and radiographic OA and C) to investigate the risk for insertion of total hip replacement (THR) compared with a sex- and age-matched control group.

From 1941 to 1962, 167 patients (191 hips) with LCP presented to The Community of Disabled in Kolding, Denmark. All hips were treated conservatively by a Thomas splint.

At follow-up weight-bearing AP pelvis radiographs were obtained. Radiographs of sex- and age-matched control persons were obtained from The Copenhagen City Heart Study.

In study A and B the following exclusion criteria were applied: Missing or destroyed radiographs, patients who refused to participate, emigrated persons, persons lost to follow-up, diseased persons and patients with previous operation at pelvis/lower limbs. Fifty-two patients (55 hips) were enrolled in the study. The follow-up period was 47 years.

In study C emigrated persons, persons lost to follow-up and patients with previous operation at pelvis/lower limb were excluded. 135 patients (156 hips) were enrolled in this study.

Data from the Danish Hip Arthroplasty Register and the Registries of the National Board of Health were collected. Radiographic definition of hip OA was a minimal joint space width (MJSW) of <2.0 mm.

LCP patients had a significant higher risk of having OA p=0.04 [OR=8.5 (CI=0.8-428.8)] and of having a THR than the control group, p<0.0001 [OR= 49.0 (CI 8.2-infinite)].

Patients in Stulberg class III/IV/V had a significantly increases risk of OA compared to patients in Stulberg class I/II, p=0.03 [OR=13.7 (CI 1.9-97.1)].

Only few long-time follow-up studies on patients with LCP disease have been performed and to our knowledge no case-control studies exist. The strengths of our study were that all the patients had the same conservative treatment regime. The reviewed Stulberg classification was used which is known to have good inter- and intraobserver agreement.

Our study has some weaknesses: Extreme pelvic inclination is a possible source of error in MJSW measurements. It was not possible to determine the inclination. 115 patients were excluded, however we do not have any reason to believe they were excluded systematically. Patients with THR might have been missed due to insufficient or wrong reports in the Registers. Information about emigrated patients was not available.

In conclusion, LCP patients have a significantly higher risk of OA than a sex- and age-matched control group as well as they had a significantly higher risk for THR.

Exact logistic regression analysis and odds ratio exact test were performed. A significance level of p<0.05 was chosen.