1. Intraoperative Neurophysiologic Monitoring for Sacroiliac Fusion
Hallie Loy bs CNIM

2. Anatomy of the Pelvis

3. 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

4. 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.

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

6. Other treatment options
Physical therapy
Chiropractic manipulations
Pain medication
Injection therapy

7. SI Fusion Surgery

9. SI Fusion Video

10. Why do we monitor SI fusions?

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

12. 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

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

14. 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
0.5-5
17-23
20-35
nerve subcortical
0.5-3
11-16
SEP tibial
35-45
25-50
0.2-1
0-3
27-35

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

16. Examples of changes

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

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

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

20. 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.

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

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

23. Questions?

24. References
"Minimally Invasive Sacroiliac Joint Surgery." MIS Sacroiliac Joint Fusion Surgery. SI-BONE, n.d. Web. 08 Apr
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 ). Elsevier B. V.
Moore MD, M.R. (2012, January ). The Sacroiliac Joint: A Forgotten Pain Generator. The SI-BONE Sentinel, 1-2.