Background: To assess the treatment of Lenke Type 1 Curves with anterior USS Instrumentation.

Methods: A retrospective radiographic review of 29 cases. Twenty nine patients with Lenke type 1 curves were treated with anterior USS instrumentation. The average age was 14.8 years (range 12–25 years) with an average of 17.4 month follow up (range 6–61 months). 27 were right sided curves, with 2 left sided. Standard AP and Lateral Standing X-rays were taken preoperatively (together with bending films), post-operatively and at follow-up. Measurements recorded at each assessment were the mean Cobb angle, sagittal and coronal balance, kyphosis and lordisis. Complications we associated with the instrumentation were also recorded.

Results: 12 patients had double minithoracotomies, the rest (17), single thoracotomies, the average blood loss at operation was 1055mls, with no significant difference between the two groups. The mean number ofleve1s instrumented was 6 (range 4–8). The mean pre-operative Cobb angle of the major thoracic curve was 53° (range 37–74). This value corrected to 24° on fulcrum bending films. The compensatory lumbar curve averaged 36° bending down to 6.°. The mean correction of these two curves post-operatively and then at most recent follow-up was 21 and 26 degrees for the thoracic curve, and 21 and 20 degrees for the lumbar curve. The mean pre-operative kyphosis was 25 increasing to 34 post-operatively and 39 at follow-up. The mean lumbar lordosis readings were 46, 46 and 45 respectively. Sagittal balance, gradually improved from a mean of 12mm to 11 then 10 at follow -up. Coronal balance did not show the same trend and was 3mm pre-operatively then 7 and 7 at final follow up. Instrumentation complications in total occurred in 9 cases, which included 4 cases of vertebral body fracture requiring circlage wiring and 5 cases of partial screw pulling out of the vertebral body. Fractures requiring wiring occurred at T5, T7, one case of three levels T6,7,8 and one case of two levels T6,7, this complication always occurred at the highest level instrumented. Partial screw pull-out always occurred at T5, with two cases occurring at two levels i.e T5,6.

Conclusion: Good correction was obtained with an mean of 6 instrumented levels. There was however a significant instrumentation complication (31 %). Despite this the intra-operative fractures caused no significant complications and good correction was still achieved in these cases. There are some concerns over mild deterioration in the curves over long term follow up but this deterioration is not clinically significant.