Outcome analysis of surgical treatment of Blount disease in Nigeria.

OBJECTIVE: The objective was to evaluate the results of surgery of Blount diseases using the postoperative metaphyseal-diaphyseal angle (MDA) at 2-year follow-up.

BACKGROUND: The goal of surgery in Blount disease is to restore the normal configuration of the articular surface of the proximal end of the tibia in proper relationship to the mechanical axis of the limb. Our hypothesis is that patients will demonstrate significant clinical improvements following surgery and predictive models can be developed.

MATERIALS AND METHODS: All patients who had surgery for Blount disease from January 2002 till December 2007 at the National Orthopaedic Hospital Lagos Nigeria and follow-up for 2 years were included. Data extracted were gender, affected limb, Blount's type, age when deformity was noted, and age at presentation, preoperative femoral tibial angle (TFA), Langenskiold score, preoperative MDA, and postoperative MDA. Linear regression was used to assess the predictive effect of selected clinical and radiographic measures on post-MDA. The model was adjusted for confounders: age deformity noted, age at presentation, affected limb, Blount's type, and gender. Variables in the adjusted model achieving significance at P < 0.05 were included in a multiple regression analysis.

RESULTS: Eighty-six knees in 57 patients were included. The mean preoperative and postoperative MDA at 2 years was 34.6° ± 8.9° and 10.6° ± 4.3°, respectively. Seventy-three knees (84.9%) have correction of ≤10° with recurrence in 13 (15.1%) knees at 2 years (P < 0.001). The postoperative MDA was graded into good outcome if ≤10°. There was a significant improvement between preoperative MDA and postoperative MDA (P < 0.001). The multilinear analysis demonstrated that the preoperative MDA was a significant predictor of the postoperative MDA. The postoperative MDA was predicted with a standard error of 0.92 with the following formula: post-MDA = 1.027 + 0.404 pre-MDA.

CONCLUSION: The mean postoperative MDA of 84.9% of the knees operated at 2 years was 9.4° ± 3.1° with recurrence rate of 15.1%. Postoperative MDA is a good outcome measure for surgical treatment of Blount disease and surgical correction should aim at producing post MDA ≤10°.