118. Prospective animal study of 5 FDA-approved cervical artificial discs

BACKGROUND CONTEXT Cervical arthroplasty is an increasingly popular alternative surgical option to anterior cervical discectomy and fusion for patients with cervical spondylotic radiculopathy refractory to conservative management. A number of FDA-approved cervical artificial discs are on the market with varying designs. The artificial discs may be categorized in several ways, eg, constrained, semi-constrained, and unconstrained, in terms of the mobility of the axis of rotation. Alternatively, they may be classified based on the number of mobile components (typically one, two, or three components). Another way to classify them is to look at their articulation point: metal-on-metal, polymer-on-metal, or fluid-filled capsule. Despite the varying designs, most existing studies in the literature are focused on comparing one particular device to cervical arthrodesis. Studies providing direct in vivo comparison of these various designs are limited. PURPOSE The purpose of this study is to provide direct in vivo comparison of five mechanically and materialistically different FDA-approved cervical artificial discs by using a previously validated caprine model. STUDY DESIGN/SETTING We performed a prospective study of adult female Alpine goats. These goats underwent C3-4 cervical arthroplasty with an FDA-approved cervical artificial disc under general anesthesia. The animals were monitored in a veterinary unit for six months. X-ray imaging was performed at the time of surgery and at regular intervals up to six months. PATIENT SAMPLE A total of 21 goats underwent C3-4 cervical arthroplasty. Group A (n=5) received Bryan (Medtronic) (unconstrained one-piece enclosed design). Group B (n=5) received ProDisc-C (Centinel Spine) (semi-constrained two-piece open metal-on-polymer design). Group C (n=4) received Mobi-C (Biomet Zimmer) (unconstrained three-piece open metal-polymer-metal design). Group D (n=3) received Prestige LP (Medtronic) (semi-constrained two-piece open metal-on-metal design). Group E (n=4) received Secure C (Globus Medical) (semi-constrained three-piece open metal-polymer-metal design). OUTCOME MEASURES During the observation period, the goats were observed for signs of pain and alterations in behavior. Radiographs were used to assess for hardware-related complications. METHODS As outlined above. RESULTS No goat in Group A had adverse effects. One out of five goats in Group B had anterior extrusion at three months. All four goats in Group C experienced anterior extrusion (three at one week and one at one month). Three out of three goats in Group D demonstrated anterior migration (one extruded at two months; one extruded at three months; one migrated anteriorly but did not extrude by the end of three months). One out of four in Group E anteriorly migrated at one week but did not extrude. CONCLUSIONS This caprine model simulates a highly active and flexible human cervical spine. Open multipiece semi-constrained or unconstrained designs with permissible translation of axis of rotation may be susceptible to anterior migration and possibly complete extrusion out of the disc space followed by disintegration. This should be considered when evaluating a patient for possible cervical arthroplasty and choosing a specific cervical disc prosthesis. FDA DEVICE/DRUG STATUS Medtronic Bryan (Approved for this indication), Medtronic Prestige LP (Approved for this indication), Centinel Spine ProDisc-C (Approved for this indication), Biomet Zimmer LDR Mobi-C (Approved for this indication), Globus Secure C (Approved for this indication).