Selection of the Distal Fusion Level in Posterior-Only Surgery of Scheuermann Kyphosis: The Concept of the FLV-1

Background Data: Lumber spine mobility is very important clinically and functionally especially in younger patients. Fusion in Scheuermann kyphosis is a long fusion surgery that usually extends into the lumber spine leaving less mobile segments. Debate has focused on the selection of the LIV. Some recommend fusing into the SSV to decrease the incidence of DJK while others use the FLV which is just caudal to the first lordotic disc as the LIV to save more motion segments. Few studies recommend fusion into the vertebra just cephalic to the first lordotic disc (FLV-1).Study Design: A prospective clinical case study.Purpose: To evaluate the outcomes of fusing into the FLV-1 in surgical treatment of SK and whether it is associated with increased incidence of distal junctional failure and DJK or not.Patients and Methods: The study included 25 patients with SK treated by posterior-only surgery using all pedicular screw instrumentation with or without posterior release/Ponte osteotomies using the FLV-1 as the LIV. The study was done in the period between February 2011 and February 2015. Patients were evaluated radiologically by full length standing biplanar X-rays and hyperextension flexibility X-ray. Parameters assessed included KA, TK, LL, and SVA for assessments of sagittal balance together with three pelvic parameters including the PI, PT, and SS angles. Clinical outcome was measured by the ODI and SRS-30 scores. Any complication encountered was documented, especially DJK, PJK, or implant failure.Results: Mean follow-up period of the patients was 40±14.88 months. The average KA improved from 82.2±9.2◦ preoperatively to 38.2±5.47◦ yielding 53.54% correction rate with minimal change at final follow-up of 39.9±5.47◦ and 2% loss of correction. SVA improved from 6.35 mm (range, 60–40) to 12.25 mm (range, 25–10) at final follow-up. The difference between the FLV and FLV-1 was 1 segment whereas the difference between the SSV and FLV-1 was 1.7±0.47 segments (range, 1-2) and the difference between the SSV and the FLV was 0.7±0.47 segments (range, 0-1). PJK occurred in 2 patients without symptoms and another 2 patients suffered mild radiological DJK and all required no treatment. Only one patient had screw pull-out and required revision. Final SRS-30 score was 125.4±15.71 (range, 95–140) and the average ODI was 7.3±2.56 (range, 4–12) without any disability.