01 Feb The Battle of ALIF vs. PLIF
NMA University is excited to contribute to the new NMA blog posts! Our focus will be on the education and training of IONM. We plan to present interesting case data, difficult cases, advanced monitoring topics, IONM changes, and any new neuromonitoring topics presented in the field. Our first post focuses on the common physiologic changes seen during ALIF surgeries. Please take some time to review the case data and assess strategies for monitoring these cases.
Why perform ALIF over PLIF?
- Bigger cage
- Better column stability
- Less time
- Lower blood loss
- Spondylolisthesis correction
- Can be used with Posterior Fusion
- Common iliac artery/vein compression or injury
- Post-operative thrombus
- Retrograde ejaculation
- General/Vascular surgeon performs exposure of spine (they may arrive before Spine Surgeon)
- Exposure time can vary significantly
- Obesity can increase exposure time
- Major stage of surgery, and MUST be documented
- Retraction places major vessels (Iliacs) at risk for ischemia
- The higher the level, the more retraction (L4-5, L5-S1 common for ALIF)
- Iliac vessel ischemia leads to reduction of blood flow to lower extremites and is reflected by loss of LOWER EXTREMITY SSEP (PTN)
- Following exposure, spine surgeon will perform discectomy
- Spine surgeon will then place cage and possible screw or plate/screws
- SSEP main modality to watch during this time to watch for ischemia, with EMG secondary for nerve root insult (pretty far from nerve roots because anterior)
- 50 year old pt with Spinal stenosis and pseudoarthrosis L4-5
- Pt was 6’2” and 205 lbs
- This Pt was actually in 3 positions posterioràanterioràposterior
- Posterior removal of hardware L4-5
- anterior fusion L3-4, L4-5 & L5-S1
- posterior fusion of L3-4; L4-5 & L5-S1
- Changes would happen during the anterior portion
Study 2: TcMEP used on case
- 36 year old pt with Spinal stenosis and spondylolisthesis
- Pt was 5’11” and 185 lbs
- Case was a L5-S1 anterior/posterior fusion
- Changes would happen during instrumentation of the anterior portion
TcMEP Waterfall: Note RLE motors present, LLE Lost
- Several things were ruled out
- Not anesthesia
- Not stimulation
- Not the implant
- Not the positioning
- No pulse in the leg
- Must be the retractors
Important Points for Monitoring ALIFs
- Patient will be supine with arms out, so set up is quick.
- General/Vascular surgeon performs exposure, so you may not see Spine Surgeon at start of case.
- Obtain reliable lower extremity SSEP quickly as critical stage of retraction can happen quickly.
- There is a lot of variability in exposure time.
- DOCUMENT vascular retraction.
- Continuously monitor lower SSEP responses and watch for subtle amplitude and latency changes (start of major change).
- Take screenshots of any small changes in data.
- Traditionally, left leg ischemia is the main limb change seen, however, right leg or bilateral leg ischemia can occur.
- Communicate all suble or significant changes to online supervisor.
- RULE out technical and anesthetic changes prior to reporting ischemic changes to surgeon.
- Limbs can tolerate prolonged ischemia, so surgeons may not release retractors right away. However, continue to update them on response status and length of time since loss of responses.
- Continue to monitor through closure, even if responses return. This is a vascular change, so small bleeds or thrombus can contribute to etiology of issue.
- Takes LOTS of screenshots, monitor anesthetics closely, and document all communications with surgeon/anesthesia/online supervisor.