Instrumented Posterolateral Fusion

An instrumented posterolateral fusion is an operation undertaken on the lumbar / thoracic spine usually in conjunction with some other form of surgery. The most common associated surgery is spinal decompression (laminectomy) to relieve pressure on the nerves or spinal cord. Other indications are to stabilise the spine following resection of vertebral bodies of tumor or infection. Instrumented Posterolateral fusions are often used in conjunction with various other operations from the front of the spine to treat spinal deformity.

THE PROCEDURE

An Instrumented Posterolateral fusion occurs under a general anaesthetic. Once you are asleep a catheter is placed into the bladder and electrodes placed into muscle groups to monitor nerve function during the surgery. You are then placed on your stomach on a special operating table. An incision is made in the middle of the back. The size and length of the incision depends on whereabouts in the spine the surgery is required and over how many levels it is being undertaken. The muscles are then released from the bones at the back of the spine. Depending on the place and extent of the surgery, a marker may be placed on part of the spine or a separate stab incision made over the pelvis and a marker placed here. This allows special x-ray to be taken in the operation (equivalent to an intra operative CT scan) which allows infrared navigation of instruments and more accurate screw placement into the spine. Once screws are placed in the appropriate levels, removal of bone from the back of the spine (laminectomy) is usually undertaken. With deformity correction, this removal of bone usually passes through the side of the spine between the screws across the facet joint. This facilitates bony release of the spine and allows correction of the spinal deformity. Once the release has been completed and any other procedures have been undertaken, the rods are cut and bent into appropriate shape and placed into the screw heads. They are then fixed in place with appropriate locking nuts. During this stage, various manipulations are done to correct any spinal deformity. Subsequent x-ray check is undertaken confirming the screws are satisfactorily placed, the alignment of the spine is appropriate and the bony decompression has been satisfactorily performed. A burr is used to roughen the bones along the side of the spine and bone graft material is placed here to achieve fusion.

The wound is then closed and you are returned to your bed. The anaesthetic is reversed. When you wake up you will have a drip on your arm, hooked to a pump which you will control to give yourself pain relief. There will be a drain coming out from near the surgical site. You will have a catheter to the bladder. Depending on the extent of surgery you may spend a day or two in intensive care and if this is the case you may have some other drips or tubes for treatment and monitoring. One or two days after the surgery, the drips, catheter and drains will be removed. The physiotherapist will start some physiotherapy and the nurses will start getting you out of bed and mobilising. In most cases we will use injections of an anti inflammatory drug to help with the surgical pain as well as tablets for pain relief.

WHAT YOU CAN EXPECT AFTER YOUR SURGERY

The majority of cases are able to go home at day four or day five. The hospital stay may be longer for more extensive reconstructive procedures. In some cases some formal rehabilitation may be required.

Stitches are usually placed beneath the skin. The dressing on the wounds can be removed after five or six days. You can get your wound wet, but take care to dry it. I recommend you walk as much as you can for exercise as well as undertake the stretches the physiotherapist would have shown you in hospital. We usually organise for you to have a review appointment around six weeks after your surgery with an x-ray.

POTENTIAL RISKS/COMPLICATIONS

As with any surgical procedure there are potential risks and complications. The risks associated with posterior instrumented fusion include:

INFECTION

Infection rates from such surgery these days are pleasingly uncommon (in the region of half of one percent). If you get an infection, treatment ranges from requiring simple antibiotics through to needing further surgery to clean the infection out. Things to suggest an infection are post operative fever, chills or shakes, wound redness or discharge from the wound. If these occur please contact the rooms so we can review you.

BLEEDING

There can be significant bleeding from spinal fusion particularly in association with decompressions. A machine called a cell saver will be used intra operatively to recycle any lost blood and give it back to you. We also use medications with the anaesthetic to try and diminish bleeding. On some occasions however (particularly with more extensive surgery) blood transfusions and other blood products may be required.

CAUDA EQUINA SYNDROME

The cauda equina is the name given to the nerves coming off the end of the spinal cord running through the spinal canal. Cauda equina is latin for “horses tail”. The nerves here go to the legs but also the bladder and bowel. Cauda equina syndrome is where a lump develops which squashes these nerves and causes compression of them causing loss of function of bladder and bowel. Following surgery this could be due to a blood clot or an abscess. The symptoms of cauda equina syndrome are numbness in the groin around the genitals and anus, inability to pass urine with dribbling and incontinence of faeces. If this occurs, it is an emergency that the pressure is relieved with further surgery otherwise the pressure can cause permanent loss of bladder or bowel function. The incidence of developing such a problem after surgery and it being permanent despite surgical drainage is in the region of one in eight or nine thousand.

IMPLANT MALPOSITION OF FAILURE

When screws are placed into the spine, they are placed into bones with small margins for error or around nerves and other important structures. If the screws are placed too far toward the middle or bottom of the bone they can irritate or damage the spinal cord of nerves. If the screw is placed through the front of the spine the body’s major blood vessels (aorta and vena cava) can be damaged. It has been reported rarely that screws can damage these vessels with potentially life threatening bleeding. It is possible that the screws can loosen in the bone or break requiring replacement.

ADJACENT SEGMENT KYPHOSIS

Once a section of the spine has been fused with screws and rods, it becomes stiffer than the spine either side of it. At times, there can be fracture of the vertebra above or below the instrumentation. In most cases the fracture will heal without consequence. On some occasions the fracture can result in worsening deformity, pain or even spinal instability and further surgery may be required to extend the fusion.

MEDICAL COMPLICATIONS

There are a variety of medical complications which can occur with major surgical procedures. The likelihood that these will occur to some extent is determined by your health before surgery and past medical history. Fortunately with modern anaesthesia and perioperative care, medical risks involved in elective surgery are comparatively low. Common surgical complications such as deep venous thrombosis, pulmonary embolism, pneumonia, urinary tract infection and skin pressure areas are best avoided with early mobilisation.

If you have any further questions regarding your procedure, please don’t hesitate to ask.

Rob Kuru, Spinal Surgeon