Dynamically evoked, discrete-threshold electromyography in the extreme lateral interbody fusion approach Clinical article

Object Because the psoas muscle which contains nerves of the lumbar plexus, is traversed during the extreme lateral interbody fusion (XLIF) approach, appropriate nerve monitoring is needed to avoid nerve injury during surgery and prevent approach-related neural deficit This study was performed to assess the effectiveness of dynamically evoked electromyography (EMG) to detect and prevent neural injury during the XLIF approach Methods One hundred two patients undergoing XLIF at L3-4 and/or L4-5 were enrolled in a prospective multicenter nonrandomized clinical study The EMG threshold values for each of the 3 successive dilators were recorded at the surface of the psoas muscle, mid psoas and on the spine At each location, the dilators were rotated 360 degrees, taking recordings immediately posterior, superior anterior and inferior For each dilator the authors noted the rotational position (the angle in degrees) at which the lowest threshold was found Findings of pre- and postoperative neurological examinations were also recorded Results Nerves were identified within proximity of the dilators (alert-level EMG feedback) in 55 7% of all cases during the XLIF approach Although nerves were more commonly identified in the posterior margin (63%), there was significant variability in the location of nerves identified Despite the fact that the posterior half of the disc space was targeted in 90% of cases, no significant long-lasting neural deficits were identified in any case, 27 5% experienced new iliopsoas/hip flexion weakness and 17 6% experienced new postoperative upper medial thigh sensory loss Transient motor deficits were identified in 3 patients (2 9%) and all had resolved by the 6-month follow up visit Conclusions The ability to identify and report a discrete real time EMG threshold during the transpsoas approach helps to avoid nerve injury and is required for the safe performance of the XLIF procedure Additionally nerve location is variable thus reinforcing the need for real-time directional and proximity information (DOI 10 3171/2010 9 SPINE09871)