The technique of subcutaneous rod insertion without exposure of the curve has been proposed as a method of controlling the progression of scoliosis while allowing the spine to grow. We review the literature and present three patients whose spines spontaneously fused unexpectedly while undergoing this form of treatment. The fusion occurred posteriorly, and continued anterior growth led to increased deformity from the crankshaft phenomenon. Based on this experience, the authors recommend careful follow-up and early anterior fusion when the crankshaft phenomenon is observed.