MIS spine surgery is based on the principle of minimal soft tissue disruption. It is not minimal access surgery and so the overall incision length or time of surgery may not defer from traditional open access surgery. However, by minimising the injury to soft tissues, there is a theoretical advantage by reducing blood loss and more rapid recovery.
MIS surgery relies on special instruments which include tubular retractors and screws that can pass over guide wires. MIS surgery requires additional x-rays to position any implants.
In select cases, motion preserving technology (disc replacement) may be used. Despite its theoretical advantages, long term results demonstrate that they are at least as good as ACDF procedures. However, patient selection is essential. The main indication is young patients with no neck deformity, instability or myelopathy.
The approach and procedure are essentially the same as an ACDF, however more x-rays are required as positioning is essential.
Cervical Laminectomy is performed to decompress the spinal cord in cases of myelopathy. The patient is usually placed prone (face down) with the head supported by a clamp. In incision is made on the back of the neck and the muscles moved to either side to expose the bony elements.
The lamina and spinous process are then removed of the affected level, thereby decompressing the spinal cord.
In some cases where there is pre-existing instability, this may be supplemented by fixation with screws and rods at the same time.
Deformity correction surgery covers a vast array of spinal deformities. These include idiopathic scoliosis and kyphosis in younger patients to adult degenerative deformities in the older age group. The exact procedure and technique is patient-specific but may include screw fixation at multiple levels, bony cuts to correct the spine (osteotomy) as well as releasing the spine completely and realigning. Occasionally the procedure involves going through the chest or abdomen as well as through the back.
Deformity correction is usually performed by two spine consultants to reduce the risks. Techniques such as intra-operative cell salvage and spinal cord monitoring may also be used.
Useful patient information is available on the SRS website.
PLIF is carried out in cases where there is instability, deformity, narrowing of the nerves where they come out (foramen), or where extensive decompression is required that will render the spine unstable. The procedure fuses a given level of spine with the aid of a cage in the disc space and screws with rods.
PLIF is performed by approaching the spine through the back. The soft tissues are dissected to expose the spine. Special screws called pedicle screws are inserted to the level above and below. A extensive microdecompression and discectomy is then performed. The disc space is then packed with bone graft and a cage.
Any deformity or slip may be corrected before finally connecting the screws with rods.
At this point a spinal microscope is bought into the operating area. This offers better visualisation of the neural elements. In a microdecompression, parts of the bone is cleared (laminotomy) and a portion of the facet joint may be removed (medial facetectomy) to create for the nerves (blue area on diagram). This is followed by removal of the yellow thickened ligament (ligament flavum) which is frequently a cause of the compression.
Micro decompression may then be repeated on the other side of the spine, thereby leaving intact the important ligaments in the middle of the spine. Alternatively, an over the top decompression may be performed (direction of green arrow on diagram). This is technically more challenging, but offers the advantage of leaving the muscles, soft tissues and joints on the other side of the spine intact. This reduces risks of late instability as well as quicker recovery.
Microdiscectomy uses the same approach and technique. However, the nerves are moved to one side to expose the disc. Any loose fragments of disc are removed (sequestrectomy). The disc space may be exposed (annulotomy) and any free fragments are removed.
LLIF relies on the same principle as PLIF. However, this approaches the spine through the side. The advantages are that it allows a bigger cage to be inserted, thereby increasing stability and fusion. It allows allows indirect decompression of the spine as well as correction of deformity.
Disadvantages of LLIF include still requiring screws into the back of the spine. Other risks include the risk of exposing the spine through the side (the abdominal content such as bowel and kidney as well as nerves that sit within the muscle that covers the side of the spine). Furthermore, it is not possible at all levels.
The patient is positioned on their side and a left sided approach is used. The approach is minimally invasive. It relies on x-ray to confirm the position and nerve monitoring to ensure that the nerves are safe.
Anterior Cervical Decompression & Fusion (ACDF) is a procedure that involves approaching the neck through the front of the spine. The aim of the operation may be to decompress the spinal cord (causing myelopathy) or a nerve root (causing arm pain). It may also be performed to correct a deformity of the neck or in cases of neck instability.
The cervical spine is approached through the front, with the incision usually being in one of the skin creases. In most cases, this is through the right hand side (for a right-handed surgeon). A plane is developed between the main blood vessels passing through the neck and the windpipe (trachea) and gullet (oesophagus).
Using a microscope, the disc is removed and the spinal cord as well as the roots are decompressed.
The space left is replaced by a cage (usually made of a special plastic called PEEK) and secured with a plate. In some cases an implant integrating both principles may be used.
Microdiscectomy & Microdecompression of the Lumbar spine are one of the commonest spine procedures performed. These defer from a lumbar laminectomy (which removes all of the bone from the back of the spine - as in cervical laminectomy) as the aim is to minimise any disruption to the stability of the spine.
The procedure is performed with the patient in the prone position (face down) on a special operating table. After x-rays are performed to mark the level, a midline skin incision is made and the muscles on the side of surgery are cleared to expose the spine. Before proceeding, another x-ray is taken to check the correct level.
MIS surgery is not suitable for all cases or patients and therefore patient selection is important. Mr Yasin will discuss MIS surgery if it is felt to be appropriate for you.