Crankshaft Phenomenon in Patients Operated for Adolescent Idiopathic Scoliosis

Introduction Crankshaft phenomenon is determined as a loss of three-dimensional correction of the scoliosis curve, which occurs after posterior fusion in children who have not completely finished skeletal growth. Dubousset named this phenomenon when he noticed that the entire spine and torso gradually turn and deform anterior spine, which continues to grow and rake around the axis of the fusion mass. This is mostly seen in infantile and juvenile idiopathic scoliosis, however this also occur in adolescents who are immature at the time of the last fusion. Aim To analyze this phenomenon in adolescents who have not finished skeletal growth and were operated for idiopathic scoliosis. Material and Methods This retrospective–prospective study analyzed 48 randomly selected adolescents operated for idiopathic scoliosis in Clinic for Orthopaedic and Traumatology in Tuzla between 1996 and 2011. Patients operated only with a posterior stabilization and fusion were divided into two groups. One group consisted of adolescents with intensive growth (12 years for girls and 14 years for boys) and another group consisted of adolescents at final stage of skeletal growth (14 years for girls and 16 years for boys). We measured Cobb angle at standard X-rays performed in an upright posture immediately after the surgery and at the latest X-rays done at the end of skeletal growth at the age of 18 years. Results Increasing Cobb angle was noted in 53% of studied patients. In group A higher values of Cobb angle noted in 69.56% examinees and in 36% in group B. When we analyzed both groups Cobb angle increased from preoperative 19.6 degrees to postoperative 22 degrees (2.4 degrees—12.2%) (r = 0.98), In group A preoperative Cobb angle increased from preoperative 20.6% degrees to postoperative 24 degrees (3.4 degrees—16.22%) (r = 0.97), while in group B from 18.60 to 20 degrees (1.4 degrees—7.52%) (r = 0.98). Conclusion Postoperative deformity progression of anterior column in adolescents operated for idiopathic scoliosis could be seen even if the stable fusion achieved. The risk for progression is higher in younger patients.