Intraoperative monitoring of the inferior alveolar nerve during mandibular sagittal-split osteotomy.

In order to evaluate the risk of nerve injury and to prevent iatrogenic damage at different stages of bilateral sagittal-split osteotomy (BSSO) of the mandible, we monitored the function of the inferior alveolar nerve (IAN) continuously on both sides in 13 orthognathic patients undergoing BSSO. The IAN was stimulated at the mental foramen with two monopolar needle electrodes fixed to the dental splint, and the orthodromic sensory nerve action potentials (SNAP) of the IAN were recorded with a silver-wire electrode inserted near the oval foramen on each side. The latencies, amplitudes, and sensory nerve conduction velocities at baseline, after medial opening, sawing, splitting, eventual manipulation, and fixation of the mandible were analyzed. The monitoring method functioned technically well in 25 of 26 nerves. Both the surgical technique and the duration of medial opening had conspicuous effects on the function of the IAN, which led us to modify the medial approach. When finer instruments were used for retraction and the duration of medial opening was shortened to less than 10 min, the SNAP of the IAN was always preserved at this stage. Monitoring of the IAN also prevented nerve injury during splitting and fixation. This technique for intraoperative monitoring of the IAN seems to be a feasible and promising tool for objective evaluation of intraoperative events and for prevention of nerve injury during BSSO.

Electrophysiologic evidence for extremely late sensory collateral reinnervation in humans.

We present a patient in whom unexpectedly late sensory recovery occurred over 5 years after removal of a 3-cm piece of the right inferior alveolar nerve (IAN) in tumor surgery of the mandible. For a year after surgery, the distribution of the mental nerve, the terminal branch of the IAN, was totally anesthetic. Thereafter, a gradual subjective sensory recovery occurred centripetally from the surrounding skin distributions. Five years after surgery, findings in electrophysiologic tests were consistent with a total lesion of the right IAN. Two years later, electrophysiologic tests gave, for the first time in humans, objective evidence for sensory collateral sprouting in trigeminal distribution.

The mental nerve blink reflex in the diagnosis of lesions of the inferior alveolar nerve following orthognathic surgery of the mandible.

The purpose of this study was to evaluate the diagnostic value of a new modification of the blink reflex test with stimulation of the distribution of the mental nerve in iatrogenic lesions of the inferior alveolar nerve. The test was performed on 23 patients undergoing orthognathic surgery of the mandible, most of them (20) with bilateral sagittal split osteotomies. The function of the inferior alveolar nerve was studied preoperatively, and 2 weeks, 2 months, 6 months and 1 year postoperatively with both mental nerve blink reflex test and clinical neurosensory testing. The objective electrophysiological test proved to be useful in the diagnosis and follow-up of sensory impairment of the inferior alveolar nerve. The results of the mental nerve blink reflex test and clinical neurosensory testing were closely related. The results of the two tests did not differ statistically significantly in the two first postoperative examinations. The positive predictive value of the mental nerve blink reflex test was better than that of clinical neurosensory testing: an initially abnormal reflex response predicted persistent subjective sensory symptoms after one year more reliably than did altered sensation at the first two examinations. Irrespective of the possible coexistent sensory symptoms and signs, a normal mental nerve blink reflex within 2 months after operation also predicted a reasonably good sensory recovery at 1 year.

Evaluating function of the inferior alveolar nerve with repeated nerve conduction tests during mandibular sagittal split osteotomy.

PURPOSE: This article evaluates a new intraoperative recording technique for measuring the sensory nerve conduction velocity (SNCV) of the human inferior alveolar nerve (IAN) during orthognathic surgery of the mandible to assess the effects of intraoperative strain on function of the IAN. MATERIALS AND METHODS: The new test was successfully applied in 10 patients during bilateral sagittal split osteotomy of the mandible (20 IANs). The recordings were made with active wire electrodes at foramen ovale and stimulation was done at the mental foramen with two monopolar needle electrodes. The sensory nerve action potentials (SNAP) were recorded intraoperatively at three stages: 1) before the split, 2) after splitting of the mandible and possible mobilization of the IAN from the proximal bone fragment, and 3) at the end of the operation after fixation of the proximal and distal fragments with screws. RESULTS: The SNCV values (mean 64.1 m/sec) were obtained in all 20 nerves at stage 1, with no significant differences between the sides in latency or amplitude of the SNAPs. The sNAPs remained stable in the IANs not exposed during the operation. In the remaining nerves, the most obvious and statistically significant changes indicating nerve injury occurred between stages and 1 and 2. Partial transsection and mobilization of the IAN were equally potent in bringing about abnormal results in objective neurophysiologic tests as well as subjective sensory disturbances. The results of the intraoperative SNCV recordings correlated well with the findings of the mental nerve blink reflex tests conducted 2 weeks after the operation, whereas comparison of the results of clinical neurosensory testing with the intraoperative events and SNCVs were more inconsistent. CONCLUSIONS: Recording of the SNCV offers a useful objective tool for the examination of the IAN both intraoperatively and in clinical diagnosis.

Clinical application of the blink reflex with stimulation of the mental nerve in lesions of the inferior alveolar nerve.

We evaluated the clinical usefulness of a new modification of the blink reflex (BR) test with electrical stimulation of the innervation area of the mental nerve (MN). We studied the MN BR in 28 patients with traumatic lesions of the inferior alveolar nerve and compared the results with the clinical sensory examination. Within 3 months of the trauma, the MN BR was abnormal in 18 of 20 nerves. In lesions older than 3 months, the test was often normal (in 9 of 11 nerves) despite subjective sensory symptoms and mild clinical signs. Anatomic obstacles to nerve regeneration also gave rise to abnormal MN BR in two patients examined 2 and 4 years after the trauma. The MN BR responses were often absent after violently traumatic lesions, whereas milder injuries commonly produced only latency prolongation of the reflex components. The MN BR is a useful objective method in the diagnosis of sensory loss in the distribution of the MN.