Clinical and radiological outcomes of modified techniques in Bryan cervical disc arthroplasty

Kyphosis may occur after arthroplasty as the result of the disc insertion angle and overmilling; however, few studies have described techniques to avoid these factors. We investigated whether modified techniques of Bryan cervical disc arthroplasty can prevent adverse outcomes. Twenty patients (control group) underwent surgery using techniques described in the Bryan disc product monograph (Medtronic Sofamor Danek, Minneapolis, MN, USA). Twenty-nine patients (investigation group) underwent surgery using a modified technique which included changes in disc insertion angle, reducing overmilling of the endplates, ensuring the anterior borders of the two halves of the prosthesis were at the same horizontal line, and accurately fitting the prosthesis. Disability and pain were assessed using self-administered questionnaires and the change in functional spinal unit (FSU) angle between the two groups was also compared. Both groups demonstrated statistically significant improvement compared with preoperative values for the following functional outcomes measures. The mean neck pain Visual Analog Scale (VAS) scores before surgery were 73.45 (control) and 74.53 (investigation); at the 2-year follow-up these scores were 22.1 and 14.79 (p=0.0013), respectively. After surgery, 14 of 20 patients in the control group developed a tendency toward kyphosis of the FSU in the neutral position (range=-9°-13°, mean=-1.1°±5.05). Conversely, none of the 29 patients in the investigation group developed kyphosis of the FSU in the neutral position (range=0-10°, mean=3.79°±2.90) (p=0.0007). There was no statistically significant difference between the groups regarding preoperative and postoperative scores with the exception of neck pain VAS and FSU angle changes. There were no intraoperative complications, vascular or neurologic complications, spontaneous fusions, or device failures or explantations.