Similarities and differences between unilateral and bilateral Perthes' disease.

Background. The aim of our research was to compare unilateral and bilateral Perthes disease. Material and methods. The study population consisted of 261 patients with unilateral Perthes disease and 50 with bilateral. The hip joints were followed up from onset to the end of the growth period. The mean age at onset in unilateral disease was 7 years 1 month (range: 2.5-13 years), and in bilateral, 5 years and 10 months (range: 2.5-10.4 years). The mean follow up was 13.4 years (range: 4-50 years). Necrosis was estimated using the Herring and Catterall classifications. Outcome was evaluated using the Stulberg and Mose classification. Results. There was no correlation between gender and unilateral or bilateral Perthes disease. Onset in patients with unilateral femoral head necrosis averaged 15 months later than in the bilateral group. The greatest incidence of Perthes' disease was between age 6 and 9 in the unilateral group and under 6 in the bilateral group. There was no difference between unilateral and bilateral Perthes disease according to Stulberg classification. Age at onset correlated with Stulberg classification. Better results were achieved significantly more often in younger patients. There was no correlation between age at onset and Herring's classification in either group. Statistical analysis revealed that patients with unilateral disease in Catterall group 4 were the youngest. Conclusion. The age at onset of bilateral Perthes disease averaged 15 months earlier than with unilateral disease. There was no significant difference between unilateral and bilateral femoral head necrosis according to the Stulberg classification.