[Surgery for degenerative lumbar disc disease. Should the black disc be grafted?].

Purpose Of The Study: To determine predictive factors allowing to improve the results of fusion in low back pain treatment.

Material And Method: Fifty six patients were retrospectively reviewed. Average age at surgery was 42. In 29 cases, discectomy or nucleolysis had been previously performed. All patients were treated by anterior lumbar interbody fusion. Functional results were assessed by the Beaujon index, with determination of a relative improvement rate. Results were analyzed according to clinical symptoms, fused level, previous surgery, association to posterior osteosynthesis and MRI changes. MRI changes were classified according to Modic types.

Results: The average relative improvement rate was 66 per cent. Pain topography, previous surgery, fused level, association with posterior osteosynthesis had not statistical effect on the functional result. Inversely, a close relation was observed between pre-operative MRI changes and the result of surgery: best results were observed in Modic I changes on adjacent vertebral end plates, with decreased signal of T1 and increased signal on T2 weighted images, suggesting inflammatory changes; poor results were observed in isolated disc degeneration without vertebral end-plates changes; poor results were observed in Modic II changes with increased signal on both T1 and T2 weighted images, suggesting degenerative changes; but among 5 non unions, 3 were observed in Modic II changes.

Discussion: The authors identify a lumbar disc dysfunction syndrome characterized by mechanical pain, with disc narrowing and anterior condensation of the vertebral plates on MRI (Modic I changes). This syndrome should be differentiated from common degenerative disc disease, without vertebral plates abnormalities (the "black disc" on MRI).

Conclusion: Anterior fusion is effective for the treatment of low-back pain due to degenerative disc disease, when associated to vertebral plate changes; as the pathology is mainly anterior. We prefer an anterior mini-invasive approach; furthermore, posterior elements are intact and canal exploration is unnecessary. However, an additional posterior osteosynthesis is preferable in Modic type II, as non union rate is increased by fatty degenerative involution.