Selection of fusion levels in adolescent idiopathic scoliosis using fulcrum bending prediction - A prospective study

Study Design. A prospective study of 50 consecutive patients undergoing selective thoracic fusion for idiopathic scoliosis with minimum 2 year follow-up. Objective. We aim to establish the validity and safety of a new strategy using fulcrum bending (FB) radiographs and the inherent flexibility of the curve to select fusion levels for King type 2 and 3 curves (Lenke 1a, 1b, and 1c). The purpose of this new strategy is to preserve motion segments compared to the traditional method of selecting fusion levels. Summary of Background Data. The aim of fusion in idiopathic scoliosis is to achieve a balanced spine with the shortest fusion preserving motion segments particularly in the lumbar spine. Conventional strategies for choosing fusion levels have been based on the standing radiographs and have not taken into account the flexibility of the curve. Methods. We followed 50 consecutive patients who underwent selective thoracic fusion for King 2 and 3 curves (Lenke 1a, 1b, and 1c). The fusion levels were chosen based on our new strategy using the FB radiograph. Twenty-five patients were fused using a hook system and 25 with a hybrid system of hooks and screws. All patients were observed until skeletal maturity and a minimum of 2 years. The curve correction, trunk shift, radiographic shoulder height, list were recorded at the preoperative stage, postoperative stage, and final follow-up. Results. The patients had an average age of 15.4 years. The average preoperative Cobb angle was 55.4 degrees and final follow-up Cobb angle for the primary curve was 24.1 degrees, with no difference between the 2 groups. With the new strategy, we were able to save levels in 31 patients (62%), compared to the conventional method of selecting the lowest instrumented vertebra. There was a statistically significant difference in the correction of the fusion mass Cobb angle between the hook and hybrid groups. There was significant improvement in the trunk shift after surgery. Ninety-six percent of patients had balanced or minimally imbalanced shoulders at final follow-up. Three patients had tilting of the vertebra below the fusion mass into the primary curve that did not progress at skeletal maturity. Conclusion. The new objective strategy for determining fusion levels using FB radiographs is safe and effective. With considering the flexibility of the curve, we are able to save levels distally in over 60% of patients. This strategy takes into account the power of modern instrumentation.