The effect of a radiographic solid fusion on clinical outcomes after minimally invasive transforaminal lumbar interbody fusion

Background context: The correlation between radiographic solid fusion and favorable clinical outcome has not been fully established. Many surgeons believe that patients who achieve a radiographic solid fusion will exhibit a more positive clinical outcome than those getting an unsuccessful fusion. To our knowledge, there is no study that has evaluated whether a solid fusion influences clinical outcome after minimally invasive lumbar fusion.

Purpose: This study was designed to evaluate the effect of radiographic solid fusion on clinical outcome after minimally invasive transforaminal lumbar interbody fusion (TLIF).

Study design: We conducted a retrospective study by comparing the prospectively collecting data.

Patient sample: The sample comprises 66 patients who had achieved a solid fusion or nonunion at least 2 years after minimally invasive TLIF for the treatment of low-grade spondylolisthesis or degenerative segmental instability.

Outcome measures: The outcome measures were visual analog scale (VAS) for back pain and radiating leg pain, Oswestry Disability Index (ODI), functional scale (defined as a modified method of Whitecloud et al.), and radiographic fusion status.

Methods: Two independent spine surgeons reviewed the completed medical records and radiographic data of 66 patients who had undergone minimally invasive TLIF by one surgeon at an institution. Clinical outcome was evaluated using VAS, ODI, and functional scale. The radiographic fusion status was assessed using flexion-extension lateral radiographs and computed tomography scans. Comparison and correlation analyses were performed to examine the relationship between fusion status and clinical outcome.

Results: There were 51 (77%) patients in the solid fusion (control) group and 15 patients in the nonunion group. The improvement from baseline with regard to VAS scores for back and leg pain as well as ODI scores was significant in both groups (all, p<.0001), with patients in the control group reporting significantly better improvement of back pain scores than those in nonunion group (p=.04). Conversely, the improvement of VAS scores for leg pain and ODI scores was comparable between two groups. Forty-one patients (80%) in the control group and 13 (87%) in the nonunion group demonstrated an excellent or good result in the final functional scale as well. The presence of radiographic solid fusion positively, but not strongly, correlated with the improvement of VAS scores for back pain (r=0.255, p=.039).

Conclusions: At least 2 years after minimally invasive TLIF, better reduction of back pain was noted in patients who achieved a radiographic solid fusion as opposed to those with nonunion. However, there was no clear evidence that radiographic solid fusion was associated with better clinical outcome scores or improvement in leg pain than nonunion.