• Primary safety and effectiveness to determine patient success are: 1 .15% ODI improvement vs baseline at 24 mos; 20 mm leg and back pain VAS improvement vs baseline at 24 mos. [ Designated as safety issue: No ]
  
• 2. improvement of at least 20 mm in leg pain at 24 months compared to baseline using a VAS pain scale; [ Designated as safety issue: No ]
  
• 3. maintenance or improvement of neurological status; [ Designated as safety issue: No ]
  
• 4. no revisions, supplemental fixation, and removals; [ Designated as safety issue: Yes ]
  
• 5. absence of major device-related complications (device component degradation or breakage, device component separation or disassembly, device component loosening (including screw loosening)) requiring revisions, supplemental fixation, and removals; [ Designated as safety issue: Yes ]
  
• 6. absence of spontaneous fusion in the investigational group and lack of fusion in the control [ Designated as safety issue: Yes ]
  

• Secondary outcome measurements that will be assessed include: 1. Zurich Claudication Questionaire scores, SF-36 scores, and VAS back pain score [ Designated as safety issue: No ]
  
• 2. Adverse events [ Designated as safety issue: Yes ]
  
• 3. time to recovery, work status, OR time, blood loss, and pharmaceutical use [ Designated as safety issue: No ]
  
• 4. radiographic measurements (degree of stenosis & spondylolisthesis, disc height, disc angle, alignment, translational motions, Range of Motion (affected level and entire lumbar spine), disc health (affected & adjacent levels), fusion status. [ Designated as safety issue: Yes ]
  

This study is being conducted to evaluate a new surgical implant (TOPS™ System, Impliant). The TOPS™ System is an alternative to spinal fusion that is designed to stabilize but not fuse the affected vertebral level following decompression surgery to alleviate pain stemming from moderate/severe lumbar spinal stenosis while maintaining range of motion.

When non-surgical treatment is ineffective, decompression (including laminectomy and medial facetectomy) and fusion of the spinal segments with moderate/severe lumbar spinal stenosis has been used to stabilize the motion segment and to alleviate the patient's clinical symptoms. Spinal fusion surgery using metal instrumentation is designed to stop motion at a painful, unstable spinal segment by permanently fusing the segment. While fusion may decrease pain generated at the treated segment, the procedure also eliminate motion at the implanted level and transfers and thus increases loads on the adjacent segments.

The TOPS System is intended to provide stabilization following decompression in patients with disease at one level from L3 to L5. The ideal goal of stabilization is to preserve mobility but eliminate abnormal motion and prevent deformity. By using the TOPS System, it may be possible to preserve load-bearing dynamics and spinal biomechanics, and thereby maintaining motion at the treated segment.

The TOPS surgical technique, utilizing a standard top loading pedicle screw-based system, is the same as a standard posterior spinal fusion with the exception of the placement of the TOPS motion segment. Therefore, the surgeon will be executing the steps of surgical exposure, decompression, insertion of pedicle screws (with attention to proper placement/alignment) and closure in the same manner as he/she would in a standard posterior spinal fusion.

The objective of the clinical investigation is to compare the safety and effectiveness of the TOPS System to a control group of patients undergoing posterior spinal fusion with pedicle screws and local autograft bone in the treatment of back and leg pain that results from moderate/severe lumbar spinal stenosis at a single vertebral level between L3 to L5.

Prior to entering the study, patients will be evaluated by the investigator according to the inclusion/exclusion criteria. Patients recruited to the study will be randomized in a 1:1 ratio to undergo implantation of the TOPS System or the control spinal fusion procedure. Patient follow-up will be evaluated immediately post-operatively and at discharge, 6 weeks, 3 months, 6 months, 12 months, and 24 months.