Medial Metaphyseal Beak Angle as a Predictor for Langenskiöld Stage II of Blount's Disease.

OBJECTIVE: To determine the medial metaphyseal beak (MMB) cut-off angle predicting Langenskiöld stage II of Blount's disease and to study the intra-observer and inter-observer reliabilities of angle measurements and the influence of the experience level of observers. METHODS: A retrospective study was conducted on children aged 2-4 years from January 2000 to December 2017. Children were identified through a computer-based search. Children with Langenskiöld stage II of Blount's disease who had been initially evaluated at our institution were categorized into Blount group and children who were diagnosed with physiologic bowing were categorized into control group. Data on the patients' ages, genders, and affected sides were collected. The MMB angles were measured on standing anteroposterior radiographs of the knees. The angle was formed between one line drawn parallel to the medial cortex of the proximal tibia, and a second line running from the intersection of the first line with the proximal tibial metaphysis through to the most distal point of the MMB. Measurements were independently performed by six observers. All observers repeated the measurements 2 weeks after they were first done. RESULTS: There were 148 legs from 79 children (48 males and 31 females) with an average age of 28.6 months. The average MMB angle of the Blount group was 128.52° ± 5.38° (P-value <0.001) and of the control group was 114.45° ± 4.89°. The average femorotibial angle of the Blount group was 15.48° ± 6.81° (P-value <0.001) and of the control group was 7.71° ± 7.94°. The receiver operating characteristic curve showed that an MMB angle >122° (sensitivity 92.7%; specificity 97.0%) was associated with Langenskiöld stage II. The intraclass correlation coefficient of the intra-observer reliability ranged from 0.93-0.97, and the inter-observer reliability was 0.93. CONCLUSIONS: By using anteroposterior (AP) radiographs of the knee, the MMB angle is a potential radiographic parameter to distinguish between Langenskiöld stage II of Blount's disease and physiologic bowed legs, with an MMB angle >122° predicting Langenskiöld stage II.

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.