Influence of facet and posterior muscle degeneration on clinical results of lumbar total disc replacement: two-year follow-up.

OBJECTIVE: There has been little analysis assessing the correlation between the clinical functional result of total disc replacement and the arthrosis of the posterior facets or the fatty degeneration of the spinal muscles. However, such knowledge is essential for understanding the long-term outcome of devices in functional terms. This prospective study reports the outcome of 64 Maverick (Medtronic) devices implanted between January 2002 and November 2003.
RESULTS: Oswestry score preoperatively and at 2-year follow-up was 43.8 and 23.1, respectively (P < 0.05). Low back pain improved from a mean Visual Analog Scale (VAS) score of 7.6 +/- 1.7 preoperatively to 3.2 +/- 1.8 at 2 years. Mean VAS leg pain score decreased from 3.9 to 2.1 at 2 years (P < 0.05). Facet osteoarthritis grade 1 or 2 did not influence outcome (P = 0.82). On the other hand, muscle degeneration of grades 1 and 2 led to a better outcome than grades 3 and 4 (P = 0.006).
CONCLUSIONS: This is the first study showing that a semiconstrained implant with a fixed posterior center of rotation can be implanted with grade 1 and 2 facet arthrosis with a good clinical outcome. This seems to confirm previous work showing that a posterior center of rotation lightens the load on the facets. This is also the first study to show a relationship between muscle fatty degeneration and clinical results since the greater the amount of fat, the less satisfactory the result. These promising midterm results must be confirmed by further studies.