Expert's comment concerning Grand Rounds case entitled "Limited access surgery for 360 degrees in situ fusion in a dysraphic patient with high grade spondylolisthesis" (by M. A. König and B. M. Boszczyk).

The case of a 26 year-old woman with high grade spondylolisthesis, history of diastematomyelia and tethered cord, with acute onset of back pain and bilateral sciatica after a fall. This comment will focus on three issues: indication for surgery, indication for reduction and levels to be included in fusion. Surgery is indicated in this case for intermittent urinary incontinence and saddle anesthesia, and failure of conservative treatment to control pain. Other important determinant of surgical indication is risk of progression, depending rather on the degree of dysplasia as classified by Marchetti-Bartolozzi than on the degree of slip as classified by Meyerding. High dysplastic olisthesis is identified by excessive pelvic retroversion. Reduction is indicated in patients with high torque through L5-S1. L5 severity index (SI) correlates with the magnitud of torque through L5-S1. Similarly, the decision to include L4 in fusion can be made based on the value of SI for L4.