Introduction Literature indicates that following microdiscectomy significant loss of disc height with corresponding recurrent back and/or leg pain may occur. Loss of disc material due to herniations and/or surgery can accelerate degeneration of the disc. NuCore™ Injectable Nucleus is an in-situ curing protein polymer hydrogel which mimics the properties of the natural nucleus. It is intended as an adjunct to microdiscectomy, replacing the natural nucleus lost to herniation and discectomy. The hydrogel is injected as a fluid through the annular defect, and adheres to the surrounding discal tissue as it cures. The material is designed to immediately fill the nuclear void and seal the anulotomy; and, in the long term, prevent recurrent herniation and further degeneration of the disc.

Methods Pre-clinical studies showed the device restores biomechanics, and the material is biocompatible, resistant to expulsion forces, and highly durable under simulated in vivo loading. A multi-center pilot clinical study is underway to evaluate NuCore™ Injectable Nucleus as an adjunct to microdiscectomy. At the time of this writing, the material has been implanted into thirteen patients aged between 23 and 52 years (6 females, 7 males) following a standard microdiscectomy procedure for monosegmental radicular pain non-responsive to conservative treatment. L5/S1 was treated in ten cases and L4/5 in three cases.

Results All surgeries were successfully completed using between 0.3 and 2.6cc of hydrogel, with an average injection volume of 1.2cc. Six patients currently are at twelve months follow-up and four others have reached six months. In all cases, pain subsided as normally expected following standard microdiscectomy. Neurologic evaluation, Oswestry index, SF36 and VAS scores were taken pre- and post-operatively, and at six, twelve, twenty-six, and fifty-two weeks post-op. All measures showed significant improvement. Average ODI scores dropped from 44 preoperatively to less than 10 at 12-month follow-up. Leg pain dropped from an average preoperative score of 6.8 to less than 1.0 at 12-month follow-up. All categories of the SF36 showed substantial improvement over preoperative scores. No patient had any device related complication. MRI assessments confirmed stable positioning of the implants at all time-points, and no recurrent herniations. Analysis of standing plain films indicated improved disc height maintenance relative to published literature, with an average loss of disc height at completed follow-ups of 4.4%.

Discussion To our knowledge, this is the first injectable nucleus replacement to have been implanted as an adjunct to microdiscectomy. Early clinical results indicate that NuCore™ Injectable Nucleus can be reliably used as a nuclear defect-filler. All patients are doing well clinically, and disc height and function appear to be maintained over the course of follow-up. Though early results indicate potential functional benefits, longer term follow-up will be necessary to fully determine the functional benefits of this treatment. Additional clinical studies have been approved to investigate the use of this hydrogel as an early intervention in degenerative disc disease.