The Lumbar I/F Cage for posterior lumbar interbody fusion with the variable screw placement system: 10-year results of a Food and Drug Administration clinical trial

Abstract

Background context: The Lumbar I/F Cage is a carbon fiber reinforced polymer (CFRP) device designed to separate the mechanical and device functions of interbody fusion. A Investigational Device Exemption (IDE) clinical study of the CFRP cage was conducted during an enrollment period from 1991 to 1993. Based on the 2-year results of this study, the cage was approved by the US Food and Drug Administration (FDA) in February 1999. Since then, the Lumbar I/F Cage device has become widely used in the United States.

Purpose: This study was designed to determine the long-term results of patients who received this device during the 1991-1993 enrollments.

Study design/setting: Investigators from the original study were asked to evaluate their original patients according to FDA-reviewed case report forms. Although many of the centers were unable to provide significant follow-up, two centers that enrolled almost half of the original study group provided reports on a high percentage of their original patients. This paper reviews the results in those patients.

Patient sample: Inclusion criteria included patients with degenerative disc disease who had at least one failed lumbar discectomy or decompression procedure at one or more levels.

Outcome measures: Clinical success was defined by a modified Prolo score evaluating pain, function, medication usage and economic status. Fusion success, determined by evaluation of plain radiographs, was defined by continuous bone bridging the fusion area with no lucencies. Flexion-extension X-rays were done on patients who had previous removal of pedicle screw implants. Any motion on flexion-extension films indicated pseudarthrosis.

Methods: All patients were contacted at their last known address. Internet search services were used to locate additional patients. Thirty-three of 43 eligible patients (77%) were evaluated, including 31 patients who reported for examination and X-ray and 2 additional patients by telephone survey and written questionnaire.

Results: Clinical success was achieved in 32 of 37 patients (86.5%) at 24 months and in 29 of 33 patients (87.8%) at 10 years. This included 61% excellent, 27% good, and 12% fair results. Fusion success was reported in 37 of 37 patients (100%) at 24 months and in 29 of 30 patients (96.7%) at 10 years. Patient satisfaction was reported in 31 of 33 (93.9%). Further lumbar surgery was done in 23 patients: in 18 patients for elective removal of pedicle screws and in 5 patients to extend the fusion to adjacent levels. Adjacent segment degeneration occurred in 61% of patients but was clinically significant in only 20%. Smokers had equal clinical and fusion success with nonsmokers at 24 months and 10 years and had adjacent segment degeneration in 37%, a rate significantly lower than nonsmokers at 87%.

Conclusions: The high rate of clinical success, fusion success, and patient satisfaction at 24 months was maintained at 10-year follow-up. Adjacent segment degeneration was common but was usually not clinically significant.