CSRS edition:37 location:Salt Lake City, UT, USA date:3-5 December 2009
INTRODUCTION: Intermediate-term follow-up studies with the Bryan Cervical Disc Prosthesis have shown preserved mobility in a majority of patients. It is hypothesized that this mobility protects against acceleration of adjacent level degeneration, as seen after anterior cervical discectomy with fusion (ACDF). However, data is lacking on how the mobility of the index level and adjacent levels and how degeneration of the adjacent levels evolves over time on the long run. Moreover, it remains unknown whether these radiographic results have an impact on the clinical outcome. Therefore the purpose of this longitudinal study is to assess the change in motion at the index and adjacent levels in addition to the evolution of adjacent level disc degeneration up to 8 years after surgery. Next, these results are correlated with clinical outcome.
METHODS: Patients with a preoperative diagnosis of single-level symptomatic disc degeneration with(out) spondylosis causing radiculopathy and/or myelopathy were consecutively and prospectively enrolled. Based on lateral radiographs, ROM is calculated using a custom motion tool (measurement error: 0.3°). Intervertebral disc degeneration is assessed using a validated scoring system ranging from 0 (no degeneration) to 9 (severe degeneration). Clinical outcome is evaluated using the Odom score.
RESULTS: In total, 90 single-level patients were included. Up to date, 82 patients had 4 years, 79 had 6 years, and 25 had 8 years radiographic and clinical follow-up.
On average, preoperative ROM was 9.7+/-5.2° at index level, and 11.7+/-4.6° and 10.0+/-5.0° at the cranial and caudal adjacent levels. At index level ROM stabilized slightly above the preoperative value at 4, 6 and 8 year follow-up (p>0.05). At the adjacent levels, a similar trend was observed (p>0.05).
The preoperative degeneration score was 2.4+/-2.0 at the index level, 1.1+/-1.5 at the cranial and 0.8+/-1.4 at the caudal adjacent level. There was a mild progression of degeneration score at the adjacent levels at 4, 6 and 8 year follow-up. There was a significant correlation between preoperative and postoperative degeneration for both adjacent levels (r>0.76).
At 4 years follow-up 89% of the patients had a good to excellent clinical outcome. At 6 and 8 years follow-up this increased to 90% and 92% respectively (figure 2). At 4 and 6 years follow-up, clinical outcome was significantly correlated with motion at the index level (p<0.05). At 8 years follow-up this relation was not significant. At 6 and 8 years follow-up, clinical outcome was significantly and negatively correlated with the change in degeneration score of the cranial or caudal adjacent level compared to the preoperative situation (p<0.05).
CONCLUSIONS: The mobility of the treated level is maintained up to 8 years after surgery. Moreover, the insertion of the prosthesis did not lead to an abnormal increase in mobility of the adjacent levels and seems to protect against acceleration of adjacent level degeneration, as seen after ACDF.
Over 90% of all patients had a good to excellent clinical outcome on the long run. A mobile prosthesis and little change in degeneration of the adjacent levels appear to promote better clinical outcome.