Follow-up of patients with delayed union after posterior fusion with pedicle screw fixation.

STUDY DESIGN: A retrospective study. OBJECTIVE: To investigate the long-term course of patients with delayed union after posterior fusion with pedicle screw fixation (PS) for degenerative lumbar disease. SUMMARY OF BACKGROUND DATA: There have been few studies on the long-term course of patients with delayed union after posterior fusion with PS. METHODS: The subjects were 48 patients (54 discs) with delayed union 2 years after PS, who showed no or only mild symptoms, and could be observed for 3 years or longer thereafter. All had received an autograft using iliac bones, and the method was posterior lumbar interbody fusion in 12 disc levels and posterolateral lumbar fusion in 42 disc levels. Delayed union occurred in 28 disc levels with neurologically responsible lesions (Group A) and in 26 disc levels at the ends of multilevels fusions (Group B). Serial changes in radiographic and clinical findings were evaluated. RESULTS: In Group A, bone union was observed more than 2 years after surgery in 10 disc levels of 9 patients (34.6%). In Group B, bone union was observed in 4 disc levels of 4 patients (18.2%). In the bone union group of both groups, the mean maximum postoperative intervertebral range of motion was significantly smaller than that in the persistent delayed union group (P < 0.05). The disc height generally decreased with time, but the decrease was significantly larger in the bone union group (P < 0.05). In both groups, clinical results were excellent or good in 100% of patients. No significant difference was noted between the bone union and persistent delayed union groups. CONCLUSION: Bone union occurred more than 2 years after posterior fusion with PS in about 30% of patients with delayed union. Its occurrence was related to the intervertebral range of motion and disc height. Firm bone union was not necessarily essential for good clinical results.