Influence of ulnar bow sign on surgical treatment of missed Bado type I Monteggia fracture in children

The present study aimed to explore the influence of ulnar bow on the surgical treatment of Bado type I missed Monteggia fracture in children. A retrospective review of 28 patients was conducted between November 2010 and June 2020. All patients were treated with open reduction of the radial head and ulnar opening wedge osteotomy without annular ligament reconstruction. Four months (range 1–12 months) was the mean interval between injury onset and surgery. The average age of patients at the time of surgery was 6.1 years old (range 2–10 years old). The maximum ulnar bow (MUB) and MUB position (P-MUB) via radiography were evaluated. The patients were divided into two groups according to P-MUB, as follows: middle group (A) included 17 cases, and the MUB was located at 40–60% of the distal ulna; and distal group (B) included 11 cases, and the MUB was located at 20–40% from the distal end of the ulna. The mean follow-up period was 33 months (range 6–102 months). At the last follow-up, all the children showed stable reduction of the radial head, and the flexion function of elbow joint improved after the operation (P < 0.05). Group A presented a larger ratio of maximum ulnar bow (R-MUB) and angle of ulnar osteotomy (OA) than group B (P < 0.05). The osteotomy angle was positively correlated with the R-MUB (R(2) = 0.394, P = 0.038). The osteotomy angle was positively correlated with the P-MUB (R(2) = 0.683, P = 0.000). The R-MUB was proportional to the P-MUB (R(2) = 0.459, P < 0.0001). The regression equation of P-MUB and osteotomy angle was as follows: OA = 32.64* P-MUB + 7.206. If the ulnar bow was positioned at the middle ulna, then a stable reduction of radial head needed to be achieved through a large angle in the ulnar osteotomy. If the position of maximum ulnar bow (P-MUB) was closer to the middle of the ulna, or the ratio of maximum ulnar bow (R-MUB) was larger, then the osteotomy angle was larger.