Solid fusion vs. non-union in long-term follow-up of in situ fusion without internal fixation in symptomatic spondylolisthesis in young patients.

A clinical and radiological long-term follow-up study is presented of 175 patients under the age of 20 years operated on for symptomatic isthmic spondylolisthesis of L5. The mean observation time was 15 years (range 5-30 years). There were 89 female and 86 male patients; mean age at operation was 14.8 years. Posterior fusion was carried out in 112 cases, posterolateral fusion in 60 and anterior fusion in 3; a concomitant laminectomy was performed in 34 cases. One segment (L5-S1) was fused in 54 patients, two segments (L4-S1) in 104, and three segments (L3-S1) in 17. Autogenous cortico-spongeous bone was used in 119 cases and free periosteal grafts in 56. At follow-up, solid bony fusion was found in 145 patients; 30 patients (17.1%) had non-union. The data for these two groups were compared statistically. The frequency of nonunion was significantly higher after posterior than after posterolateral fusion (P< 0.05), in two-level fusions than in one-level fusions (P = 0.003), and in cases where periosteal rather than cortico-spongeous bone grafts had been used (P<0.01). The posterior fusion technique using periosteal grafts gave the highest rate of non-unions, whereas the posterolateral technique with cortico-spongeous grafts gave the highest rate of successful fusions (P < 0.001). Non-union occurred significantly more often in cases of grade I slip (36%) than in cases of grade II (7%), III (8%) or IV slip (0%). The higher frequency of nonunions in grade I slips was associated with more frequent use of the posterior fusion technique in cases of minor or moderate grades of slip. The duration of postoperative bed rest or duration of immobilization in a corset had no statistically significant influence on fusion rate. The rate of non-union had no statistically significant association with the long-term clinical result. Postoperative pain symptoms, however, lasted longer in non-union patients (mean 14.2 months) than in successfully fused patients (mean 4.5 months; P<0.01). The results show the benign nature of the condition, which seems to be a self-limiting process leading to stabilization of the affected segment. The posterolateral fusion technique using autogenous cortico-spongeous bone grafts is recommended as the method of choice for most cases.