Neuroforaminal Bone Growth Leads to Slower Improvement Following Minimally Invasive Transforaminal Lumbar Interbody Fusion

Introduction: Although neuroforaminal bone growth (NFBG) can occur after minimally invasive transforaminal lumbar interbody fusion (MI-TLIF), its impact on postoperative course is unknown.

Methods: This retrospective cohort study included patients undergoing primary 1-/2-level MI-TLIF for degenerative lumbar pathology with 1-year minimum follow-up. Iliac crest bone graft, local autograft, or allograft was used in all cases. Cases with bone morphogenetic protein (BMP) use (n=10) were excluded. A radiologist assessed NFBG on a post-op 1-year CT. Patients were stratified into 2 groups (NFBG – yes/no). NFBG area was measured on sagittal and axial sections. Percentage occupancy of the neuroforamen by bone growth was measured on sagittal views. Patient-reported outcome measures (PROMs) and minimal clinically important difference (MCID) achievement were recorded. A subgroup analysis compared outcomes between patients who had >25% & < 25% foraminal occupancy of bone growth.

Results: From 114 patients, 30 (26%) had NFBG. Average bone growth area was 38.1 mm2 & 41.1 mm2 on sagittal & axial sections, respectively. Average neuroforamen occupancy percentage was 26.3% (range: 11 - 55%) ( < 25%: 16 patients, >25%: 14; >50%: 2). NFBG was more frequent in 2-level fusion compared to 1-level (50% vs. 23%, p=0.03). Patients with NFBG had significantly higher ODI than those without NFBG at < 3 months (28.6 vs. 20.9, p=0.03). Patients with NFBG didn’t show significant improvement in ODI (28.6 vs. 37 pre-op, p=0.06) and SF-12PCS (38.7 vs. 34.7 preoperative, p=0.06) at < 3 months. No difference was found in VAS-back/leg between the groups at < 3 months. At >6 months, the significant differences in ODI and SF-12PCS were not retained and the groups had significant improvement in all PROMs. PROMs MCID achievement rates showed no difference between the 2 groups at < 3 & >6 months. Subgroup analysis showed the < 25% & >25% foramen occupancy groups didn't show significant ODI and SF-12PCS improvement at < 3 months. No patient had a reoperation for symptoms related to NFBG.

Conclusion : 26% showed NFBG, on average a small area of 0.4 cm2 and >50% of foramen occupancy was seen only in 2 patients. Patients with NFBG had a slower but eventually similar improvement in outcomes.