Medial Metaphyseal Slope as a Predictor of Recurrence in Blount Disease.

Objective: This study was aimed to find the radiographic parameter predicting recurrence of stage 2 Blount's disease.

Method: We retrospectively reviewed radiographs of 82 legs from 49 patients diagnosed with stage 2 Blount's disease by Langenskiöld classification who had failed brace treatment and underwent valgus osteotomy between 1998 to 2016. Age ranged from 26 to 47 months. The metaphyseal-diaphyseal angle was measured preoperatively. The medial metaphyseal slope of the proximal tibia and femorotibial angle were measured preoperatively and 3, 6, 12, and 24 months postoperatively in both non-recurrence (group 1) and recurrence (group 2) group. The receiver operating characteristic curve calculated using MedCalc software was used to determine the medial metaphyseal slope predicting risk for recurrence. Statistical analysis was performed using SPSS software.

Results: The mean follow-up time was 4.83 ± 0.38 years. The mean age was 34.57 ± 5.76 in group 1 and 33.2 ± 1.48 in group 2 (P = 0.258). The mean preoperative metaphyseal slope was 62.39° ± 9.75° in group 1 and 73.22° ± 6.59° in group 2 (P = 0.02). The mean preoperative femorotibial angle (FTA) was -14.31° ± 8.25° in group 1 and -18.89° ± 7.74° in group 2 (P = 0.1). The mean preoperative metaphyseal diaphyseal angle (MDA) was 14.75° ± 4.21° in group 1 and 20.11° ±5.16° in group 2 (P = 0.001). Demographic data including age, gender, weight, height, and body mass index showed no statistically significant difference between both groups. Out of 82 legs, 9 (10.97%) had recurrence. Preoperatively, the metaphyseal-diaphyseal angle showed statistical significance between both groups. The medial metaphyseal slope showed statistically significant difference between group 1 and group 2 at 3, 6, 12, and 24 months postoperatively. The receiver operating characteristic curve showed that a medial metaphyseal slope more than 70° at 12 months (sensitivity 88.89% and specificity 69.86%) and more than 62° at 24 months postoperatively (sensitivity 100%, specificity 52.3%) was a predictor for recurrence of stage 2 Blount's disease.

Conclusion: Medial metaphyseal slope more than 62° over the 24-month follow-up was associated with recurrence of varus deformity.