Posterior lumbar interbody fusion versus circumferential fusion using the B-Twin expandable spinal system

We reviewed the medical files of 32 patients with degenerative disc disease, spinal stenosis, and spondylolisthesis who underwent posterior lumbar interbody fusion using the B-Twin system. In 12 of these patients, posterior lumbar interbody fusion has been supplemented with posterior lumbar-instrumented fusion (circumferential fusion) because of spinal instability. Clinical and functional outcomes were assessed. The quality of fusion and disc height were recorded. The mean follow-up was 36 months (range, 18 to 42 months). At the latest examination, clinical improvement and fusion were statistically significant in both groups; the mean Oswestry disability index improved from 55% to 24%, and to 22% in the patients with more than 20 months follow-up; the mean Rolland-Morris disability questionnaire improved from 52% to 29% (p < 0.001); 95.6% (22/23) of the levels managed with the B-Twin system alone and 92.9% (13/14) of the levels managed with circumferential fusion showed solid fusion; and the intervertebral disc height increased from 8.1 +/- 0.74 mm to 11.4 +/- 0.93 mm in the B-Twin group and from 7.7 +/- 0.75 mm to 10.6 +/- 0.91 mm in the circumferential fusion group. However, in comparing the two groups there was no statistical significant difference. The B-Twin system is safe and effective for the management of degenerative disc disease as a stand-alone device. The combination with posterior lumbar-instrumented fusion systems for circumferential fusion yields statistically significant differences in fusion rate and functional outcome.