Artificial Disc Versus Fusion: A Prospective, Randomized Study With 2-Year Follow-up on 99 Patients

Rick C. Sasso, MD; Joseph D. Smucker, MD; Robert J. Hacker, MD; John G. Heller, MD

Disclosures

Spine. 2007;32(26):2933-2940. 

In This Article

Results

A total of 115 patients were randomized in a 1:1 ratio to either a Bryan cervical disc (N = 56) or an anterior cervical fusion with allograft and a plate (N = 59). There were 30 males and 26 females in the Bryan group and 32 males and 27 females in the fusion group. The average age was 43 years (Bryan) and 46 years (control). No statistically significant differences were noted in the demographics of the investigational and control populations. No differences in demographics, such as age, percent of males, height, weight, smoking history and percent worker's compensation, were present between groups (P > 0.05) ( Table 1 ).

The average operative time for the control group was 1.1 hours and the Bryan Group 1.7 hours. Average blood loss was similar (49 mL control, 64 mL Bryan). Average hospital stay was 0.6 days (control) and 0.9 days (Bryan).

For all of the following functional outcomes measures, both groups demonstrated statistically significant improvement compared with preoperative values. The P values relate to differences between groups at follow-up. Preoperative scores between groups were all statistically similar.

NDI before surgery was 47 (Bryan) and 49 (control). Twelve-month follow-up data were available for 110 patients (55 Bryan and 55 control) with NDI 10 (Bryan) and 18 (control) (P = 0.013). At 2-year follow-up, 99 patients were available (49 Bryan and 50 control). NDI for the Bryan group was 11 and the control Group 20 (P = 0.005). In addition to the group-to-group differences noted, both groups demonstrated a significant improvement in comparison to their preoperative scores (P < 0.001) (Figure 1).

NDI scores.

Neck pain VAS before surgery was 72 (Bryan) and 73 (control). Twelve-month follow-up data were available for 110 patients (55 Bryan and 55 control) with VAS 17 (Bryan) and 28 (control) (P = 0.05). At 2-year follow-up, 99 patients were available (49 Bryan and 50 control). VAS for the Bryan group was 16 and the control Group 32 (P = 0.005) (Figure 2). In addition to the group-to-group differences noted, both groups demonstrated a significant improvement in comparison to their preoperative scores (P < 0.001).

Neck pain VAS scores.

Arm pain VAS before surgery was 70 (Bryan) and 71 (control). Twelve-month follow-up data were available for 110 patients (55 Bryan and 55 controls) with Bryan arm pain VAS 12 and control 23 (P = 0.031). At 2-year follow-up, 99 patients were available with the arm pain VAS for the Bryan Group 14 and control 28 (P = 0.014). In addition to the group-to-group differences, both groups demonstrated a significant improvement in comparison to their preoperative scores (P < 0.001) (Figure 3).

Arm pain VAS scores.

SF-36 scores (Physical Component) were also notable: preoperative Bryan 34 and control 32. Twelve-month follow-up Physical Component Score data were available for 110 patients (55 Bryan and 55 control) with Physical Component Score 51 (Bryan) and 47 (control) (P = 0.031). At 24 months after surgery, the physical component of the SF-36 had changed to: Bryan 51 and control 46 (P = 0.009) (Figure 4). SF-36 Mental Component Scores were before surgery: Bryan 46 and control 49. By 24-months they were: Bryan 54 and control 52 (Figure 5). The group-to-group Mental Component Scores difference was not significant at 24-months (P > 0.05).

SF-36 Physical component scores.

SF-36 Mental component scores.

Cervical vertebral bodies were tracked on the digital radiographs using quantitative motion analysis software (QMA, Medical Metrics) to calculate the functional spinal unit motion parameters. The mean preoperative angular motion of the Bryan and fusion group was 6.43° ± 3.42° and 8.39° ± 4.54°, respectively. The difference was not statistically significant. As expected, significantly more motion (3, 6, 12, and 24 months) was retained in the disc replacement group than the plated group at the index level. The disc replacement group retained an average of 7.3° at 12 months and 7.9° at 24 months. In the 24-month Bryan group, this did not represent a statistically significant change from the preoperative measured angulation at the target level (P > 0.05). (Figure 6) In contrast, the average range of motion in the fusion group was 1.3° at the 3-month follow-up and gradually decreased to 0.6° at 24 months, a significant change from the preoperative measurements (P < 0.0001).

Mean flexion-extension angulation of the Bryan disc.

Over the 24-month follow-up period, a total of 6 subsequent surgical interventions were performed in the study population (4 control, 2 investigational). All subsequent surgical interventions were performed by the initial treating surgeon at the discretion of that surgeon. One patient in the control group required a posterior cervical fusion for symptomatic nonunion. Another patient in the control group required revision ACDF for nonunion, which was performed with rhBMP-2 and revision anterior cervical plating. Two patients in the control group required ACDF for adjacent level disease during the 24-month period.

Two patients in the investigational group required ACDF for adjacent level disease during the 24-month follow-up period. There were no incidents of radiographic or clinical implant complications noted at the target surgical levels (Bryan disc replacement) in the investigational group. There were no intraoperative complications, no vascular or neurologic complications, no spontaneous fusions, and no device failures or explantations in the Bryan cohort.

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