Anterior spondylodesis for spondylolisthesis: isthmic and degenerative types

We studied the influence of instability of the spondylolisthetic segment upon anterior interbody fusion (AIF) rates. A one-level AIF of the lumbar spine by the modified extraperitoneal Bailey-Badgley fusion construct was performed in 26 patients with chronic or recurring acute low-back pain and/or other symptoms due to grades I and II spondylolisthesis. Sixteen were degenerative type, and 10 were isthmic type. Seventeen were female and 9, male. The average age was 41.2 years. The number of cases of spondylolisthesis at the level of L4-5 and L5-S1 as 18 and 8, respectively. In the 16 cases of degenerative type, 13 were grade I slip, and 3 were grade II slip, while in the 10 cases of isthmic type, 8 were grade I slip, and 2 were grade II slip. The average postoperative follow-up was 6 years (range 2-10 years). Solid fusion was obtained in 15 (93.8%) of the cases of degenerative spondylolisthesis and in 6 of the cases of isthmic type. Thus, the overall fusion rate was 80.7% (21 cases). However, some graft crumbling and redisplacement developed in 1 of the cases of degenerative type and 6 of the cases of isthmic type. Non-union developed in 4 (57.1%) of those 7 cases of graft crumbling (3 isthmic and 1 degenerative type). Fusion took 7 months on average (range 5-9 months). It is hypothesised that the isthmic-type spondylolisthesis had more instability than the degenerative one. Therefore, AIF in the case of degenerative spondylolisthesis is a useful procedure, while in the isthmic type it is not advisable as a routine procedure.