Intraoperative Neurophysiologic Monitoring for Sacroiliac Fusion Hallie Loy bs CNIM

Anatomy of the Pelvis

Typical SI Fusion Patient… Symptoms: Low back pain Buttock and hip pain Ipsilateral LE weakness LE numbness and tingling Trouble sleeping Leg instability Problems sitting

SI joint as a cause of pain: 25% of all low back pain is caused by Sacroiliac joint disease. The incidence of SI joint degeneration in post-lumbar fusion surgery is 75% at 5 years post-op. SI joint is a pain generator in low back pain of 43% post- lumbar and lumbar-sacral fusion patients.

Diagnosis… Clinical tests Imaging studies (x-ray. CT scan, MRI) SI joint injections of a local anesthetic

Other treatment options Physical therapy Chiropractic manipulations Pain medication Injection therapy

SI Fusion Surgery

                                                                                     

SI Fusion Video

Why do we monitor SI fusions?

Iatrogenic nerve injury rates have been reported to be as low as 1% and as high as 18%.

Lower Limb Dermatomes Lower Limbs Myotomes Movement Nerve Root Segments Hip flexion L2/3 Hip extension L4/5 Hip adduction Hip abduction Knee extension L3/4 Knee flexion L5/S1 Ankle Dorsiflexion Great toe extension L5 Ankle plantarflexion S1/2

How do we monitor si fusions? SSEP EMG SE-EMG

Typical latencies (ms) ssep Stimulation: Uppers: Ulnar Nerve Lowers: Posterior Tibila Nerve   Low Freq Filter (Hz) High Freq Amp (μV) Typical latencies (ms) Stim. Intensity (mA) Stim Duration (ms) Rate (Hz) SEP median nerve cortical 30 250-1000 0.5-5 17-23 20-35 0.2-0.5 1.3-4.7 nerve subcortical 500-1000 0.5-3 11-16 SEP tibial 35-45 25-50 0.2-1 0-3 27-35

ssep Alarm Criteria: Amplitude decrease of 50% Latency increase of 10%

Examples of changes

Patient had LUE amplitude decrease of greater than 50% due to a positional issue.

Needle electrodes used in the following muscles: L5- Tibialis Anterior S1- Gastrocnemius S2- Anal Sphincter emg

Alarm Criteria: Any burst/firing from nerves on the side the surgeon is working. Free run EMG

SE-emg Stimulation probe used to stimulate either the guide wire/pin or the drill bit to insure a safe distance between the drill bit and the neural structures.

Se-emg Alarm Criteria: Response <8 mA with an absolute minimum of 6 mA

In the case of nerve injury LE numbness LE weakness Incontinence Foot drop

Questions?

References "Minimally Invasive Sacroiliac Joint Surgery." MIS Sacroiliac Joint Fusion Surgery. SI-BONE, n.d. Web. 08 Apr. 2013. Moed, B.R. (2008). Monitoring neural function during pelvic surgery. In M.R. Nuwer (Ed.), Intraoperative Monitoring of Neural Function Handbook of Clinical Neurophysiology (vol. 8, pp. 752-763). Elsevier B. V. Moore MD, M.R. (2012, January ). The Sacroiliac Joint: A Forgotten Pain Generator. The SI-BONE Sentinel, 1-2.