Determination of the in vivo posterior loading environment of the Coflex interlaminar-interspinous implant.

BACKGROUND CONTEXT: The in vivo loading environment of load-bearing implants is generally largely unknown. Loads are typically approximated from cadaver tests or biomechanical calculations for the preclinical assessment of a device's safety and efficacy. PURPOSE: To determine the actual in vivo loading environment of an elastic interlaminar-interspinous implant (Coflex). STUDY DESIGN: A retrospective radiographic study to noninvasively measure the in vivo implant loads of 176 patients. METHODS: For this study, neutral, flexion, and extension radiographs were quantitatively analyzed using validated image analysis technology. The angle between the Coflex arms was measured for each radiograph and statistically evaluated. Separately, the Coflex implant was characterized using mechanical test data and finite element analysis, which resulted in a load-deformation formula that describes the implant load as a function of its size and elastic deformation. Using the formula and the elastic implant deformation data obtained from the radiographic analysis, the exact implant load was calculated for each patient and each posture. For statistical analysis, the patients were grouped by indication and procedure, which resulted in 12 different groups. The determined loads were compared with the strength of the posterior lumbar spinal elements obtained from the literature and with the static and dynamic mechanical limits of the Coflex interlaminar-interspinous implant. RESULTS: The force data were independent of implant size, diagnosis (with one exception), number of levels of the decompression procedure, number of levels of implantations (one or two), and follow-up time. The median compressive force acting on the Coflex implant was found to be 45.8 N. The maximum load change between flexion and extension was 140 N; the maximum overall load exceeded 239 N in extension. CONCLUSIONS: The average loads exerted by the Coflex implant on the spinous process and lamina are 11.3% and 7.0% of their respective static failure load. The implant fatigue strength is significantly higher than the measured median force, which explains the extremely rare observation of a Coflex fatigue failure.

Survivorship of coflex Interlaminar-Interspinous Implant.

BACKGROUND: The purpose of this study was to determine the indications for implantation of the coflex device (Paradigm Spine, LLC, New York, New York), assess long-term complications, and evaluate the long-term clinical outcomes of patients. METHODS: A total of 127 patients underwent placement of a coflex implant for various indications by one orthopaedic spine surgeon. The mean follow-up was 6.3 years. The original indications for implantation were determined based upon the data provided in the case report forms. Preoperatively and postoperatively, patients were asked to grade their low-back and leg pain using the visual analog scale (VAS) and the pain severity scale: no pain (0), mild pain (1), moderate pain (2), or severe pain (3). Patients were queried about their satisfaction with the surgical procedure. Follow-up radiographs were taken to determine any device-related issues. RESULTS: The most prevalent diagnoses for implantation were spinal stenosis (19.7%) and spinal stenosis with lumbar disc herniation (35.4%). The mean severity of low-back pain was decreased by 33% (from moderate to mild) at the 2-year follow-up (P < .001) and at the 5-year follow-up (from moderate to mild, P < .001). The mean severity of leg pain was decreased by 66% (from severe to mild) at the 2-year follow-up (P < .001) and at the 5-year follow-up (from severe to mild, P < .001). At the mean follow-up period of 6.3 years, a patient satisfaction query demonstrated that 7% were unsatisfied, 46% were satisfied, and 46% were very satisfied with their clinical outcome. Based on the follow-up radiographs, 92 of patients had no devicerelated issues and 8% had device-related issues. CONCLUSION: The data provided have demonstrated that the coflex implant provides pain relief for patients with low-back pain and leg pain. The most common indications for implantation were spinal stenosis and spinal stenosis with lumbar disc herniation. There were very few device-related complications. CLINICAL SIGNIFICANCE: Using coflex is a safe and viable option in the selection of instrumentation for spinal stabilization.