THE VARIABLE SCREW PLACEMENT SPINAL FIXATION SYSTEM - REPORT OF A PROSPECTIVE-STUDY OF 250 PATIENTS ENROLLED IN FOOD-AND-DRUG-ADMINISTRATION CLINICAL-TRIALS

The variable screw placement (VSP) system uses transpedicular screws a nd slotted plates to achieve constrained segmental fixation of the spi ne. A prospective multicenter study of 250 patients was performed unde r a Food and Drug Administration approved protocol to test the safety and effectiveness of this system. Complete 2-year follow-up data are r eported for 169 of 223 (73%) patients who had fixation of three spinal levels or fewer. ''Clinical success'' was defined as an excellent or good result or improvement of two grades in a 10-point combined pain a nd function scale. ''Fusion success'' was defined by presence of conti nuous trabecular bone bridging the fusion area. For 86 patients with p ostsurgical failed back syndrome, clinical success was achieved in 69 (80.2%) and fusion success in 76 of 83 (91.6%) patients. These success rates were statistically higher than previous literature reports (P = 0.01 for clinical success and P= 0.02 for fusion success). For spondy lolisthesis, clinical success was achieved in 44 of 57 patients (86.3% ) and fusion success in 43 of 47 (91.5%) patients. For spinal stenosis , clinical success was achieved in 25 of 32 patients (78.1%) and fusio n success in 30 of 31 (96.8%) patients. Overall fusion success was ach ieved in 186 of 200 (93%) patients with no statistical difference when comparing the numbers of levels fused. There were 21 device-related c omplications (8.4%) and 16 non-device-related complications (6.4%).