The Prognosis of L5 Radiculopathy after Reduction and Instrumented Fusion of Adult Isthmic High-Grade Lumbosacral Spondylolisthesis and the Role of Multimodal Intraoperative Neuromonitoring

Objective: Iatrogenic L5 nerve root injury is a common complication of reduction of isthmic high-grade spondylolisthesis (HGS). However, the clinical presentation and prognosis as well as its impact on patient-rated outcome have never been analyzed systematically and the role of multimodal intraoperative neuromonitoring (MIOM) is largely unknown. Methods: Clinical and radiographic data from consecutive patients who underwent reduction and instrumented fusion of HGS between 2005 and 2013 in a single center were analyzed. The multidimensional Core Outcome Measures Index (COMI) was completed before and after surgery. MIOM with transcranial MEP and continuous EMG of index muscles were performed. Results: A total of 17 patients (13 females, 4 males) with a mean radiographic follow-up of 19 (range 3–48) months were included. Mean ( ± SD) age was 26.5 ( ±  9.2) years. The mean L5-S1 slip was 72% ( ±  21%), which was reduced to 19% ( ±  13%). After 1 year, COMI improved from 6.7 ± 1.7 to 3.7 ± 3.1, leg pain from 5.2 ± 3.1 to 2.3 ± 3, and back pain from 6.2 ± 1.9 to 3.4 ± 2.6. In five patients (29%), an incomplete L5 motor deficit occurred: two with ⅗ paresis or worse, and three with ⅘. Four of these patients fully recovered after 3 months, and one (5.9%) was lost to follow-up (FU). In 15 out of 17 procedures, 25 intraoperative MIOM alerts were recorded. Based on intraoperative recovery of the signals, MIOM predicted 1 new neurological deficit and 16 patients without deficits. The patient with the MIOM true positive deficit was the one lost to FU. Related to the long-term outcome of patients with FU, MIOM has a sensitivity and specificity of 100%. However, in predicting the early postoperative and mostly transient L5 motor deficits (occurring in 5/17 [29%]), the sensitivity was only 20%. Conclusions: Reduction and instrumented fusion of HGS showed a satisfactory outcome. The rate of transient L5 palsy was relatively high. However, the prognosis for this deficit is favorable and full recovery can be expected after 3 months in most cases. MIOM alerts occurred in 88% of the procedures and thereby possibly limited the prevalence of neurological deficits to 5.9%. Intraoperative recovery of deteriorating MIOM signals cannot predict transient neurological deficits.