Stretch neuropraxia after L5-S1 anterior lumbar interbody fusion: effect of cage height and lordosis

Purpose To evaluate the impact of disc height (DH) and lordotic change after anterior lumbar interbody fusion (ALIF) on the development of postoperative neuropraxia. Methods Adults with degenerative spine pathology who underwent L5-S1 ALIF were identified. Anterior and posterior DHs were measured, and associations with segmental and global lumbar lordosis were evaluated using multivariate regression analyses. Postoperative neuropraxia, whether transient or persistent, was identified up to one-year postoperatively. Receiver operating characteristic (ROC) curve analyses were performed to establish thresholds for DHs that predicted postoperative neuropraxia. Results In total, 101 patients were included with mean age of 52.5 years, 55% were females, and mean CCI of 1.7. After ALIF, DHs increased by mean of 8.7 mm anteriorly and 3.0 mm posteriorly, L5-S1 segmental lordosis increased by mean of 7.0 degrees, and L1-S1 lumbar lordosis increased by mean of 3.6 degrees. A 1 mm improvement in anterior DH was associated with 0.3 degrees increase in L5-S1 segmental lordosis (p < 0.001) and 0.2 degrees increase in L1-S1 lordosis (p = 0.019). Among this cohort, 28% developed neuropraxia, of which 75% were transient that resolved by 3 months postoperatively. ROC analyses identified cutoffs of 18.9 mm and 8.6 mm for postoperative anterior and posterior DH, and 9.5 mm and 8.6 mm for change in preoperative to postoperative anterior and posterior DH, respectively. Patients above these thresholds had nearly 4-fold higher likelihood of developing postoperative neuropraxia (p < 0.01). Conclusion Large increases in anterior or posterior disc heights during ALIF achieved improvements in lumbar lordosis but were associated with increased odds of neuropraxia postoperatively. Patients with a postoperative anterior disc height of 19 mm and a posterior disc height of 9 mm had 4-fold higher odds of developing neuropraxia. While three-fourth of neuropraxias were transient and resolved spontaneously in the early postoperative period, the high incidence of neuropraxia following ALIF may inform preoperative planning and counselling.