Posterior Lumbar Interbody Fusion and Decompression (PLIF)

A posterior lumbar interbody infusion (PLIF) is a surgical procedure designed to stabilise the lumbar spine. As part of the procedure the intervertebral disc is removed, the nerve roots are decompressed and the spine is realigned if required. The main reasons for performing this procedure are spondylolisthesis and discogenic mechanical back pain. However there are other circumstances such as degenerative scoliosis where the procedure may also be useful.

Anatomy of the Lumbar Spine

The lumbar spine consists mainly of the vertebrae (bone of the spine) with a disc in between each bone. There are five lumbar vertebrae (referred to as L1-5). The main part of the vertebra is called the body and is located at the front. The disc is located between the vertebral bodies. Each disc is referred to by the bones between which it sits. For example the L4/5 disc is located between the L4 and L5 vertebral bodies. The surface of the bone over which the disc lies is referred to as the end-plate of the vertebral body.

Behind the vertebral bodies there is a ring of bone that contains the bottom of the spinal cord which ends at L1/2 and the nerve roots which occupy the space below. The back of this ring is made of the lamina and spinous processes to which several muscles are attached. The sides of the ring are made of the pedicles. On each side the lamina becomes thicker and joins two area of bone together and is termed the ‘pars’. The bone at the upper end and the bone at the lower end of the pars articulate (form a joint) with the corresponding piece of bone from the vertebra above and below. These joints are the facet joints.

For most of the lumbar spine, there is a group of nerve roots which trail down from the bottom of the spinal cord. The nerve roots, which are surrounded by spinal fluid and which are enclosed in a sac called the dura, are referred to as the cauda equina which translates to ‘horse’s tail’. At each level a nerve root exits the spine through a hole between each bone called the intervertebral foramen. The nerve root will supply feeling (sensation) to a particular area and will also supply particular muscles that perform different movements.

The disc is made of two main elements. The first is the annulus fibrosis. This is a strong outer layer made of criss-crossing fibres. The inside of the disc, or nucleus pulposis, is the soft gel-like centre which normally provides the cushioning functions of the disc. When a disc becomes unhealthy the nucleus can become shrunken and loses its normal water content. As a result the annulus tends to bulge and in some cases can rupture leading to protrusion of the unhealthy nucleus into the spinal canal.

Indications for Surgery

A PLIF may be performed for variety of reasons. The most common indications are those of spondylolisthesis and mechanical back pain. There also a variety of other reasons for performing a PLIF at one or more levels in the lumbar spine.

Spondylolisthesis

Spondylolisthesis is a condition where one vertebral body moves forward in relation to the next. This forward ‘slip’ can occur for a variety of reasons. These most common varieties of spondylolisthesis are:

Degenerative spondylolisthesis: occurs mainly in females and occurs most commonly at the L4/5 level. Usually the facet joints at the posterior aspect of the spinal are degenerative. The loss of integrity in these joints allows the superior vertebra to move forward. This may result in a number of problems:

Radiculopathy: It is a clinical condition usually due to compression of a nerve root. The nerve root is the start of a nerve as it exits from the spinal cord and spinal canal. It usually will join with other nerve roots outside of the spinal canal to form various peripheral nerves. Nerve roots normally supply sensation to a particular area of the body as well as supply various muscles to make them move. Radiculopathy is most commonly painful and the area in which the patient experiences pain will often indicate the particular nerve involved. In addition there is often numbness and paraesthesia. Paraesthesia is commonly referred to as pins and needles. Again these may indicate the nerve root that is affected. Finally there may be weakness of a particular muscle or of a particular movement.

Nerve root compression causing radiculopathy is most commonly due to a disc protrusion or bony spurs (osteophytes). In the case of a spondylolisthesis, the exit foramen, that is the space between the bones where the nerve exits the spine, becomes too narrow. In addition the space for the nerves within the spinal canal also becomes smaller and the nerve root may be compressed there as well.

Neurogenic claudication: This term refers to pain, numbness and/or paraesthesia (pins and needles) that occurs during walking. Typically, the symptoms begin when the patient walks long distances only and is relieved by a few minutes of rest after which they can walk again for a similar distances. Over time, as the condition progresses, the distance for which the patient is able to walk, or time that they can stand for, is reduced. Eventually the symptoms become so severe that they occur at rest and may significantly limit mobility. The most common reason for this condition is a spinal canal stenosis. This means that the space inside the spinal canal has become too small for the nerves. Essentially they become crowded together and compressed.

Mechanical back pain: The low back pain that people experience in this condition can take several forms. Typically patients find that small degrees of flexion (bending forward) can cause significant pain. An example of this is experiencing pain while leaning over a sink to brush their teeth. However they often also report that the pain is relived by supporting their upper body on their elbows. For example, they find that leaning forward on the handle of the shopping trolley is the more comfortable than when they walk straight upright.

Isthmic spondylolisthesis: is a condition that is more common in males and occurs mostly at the L5/S1 level. It occurs when there are pars defects. The pars (or pars interarticularlis) are small areas of bone one each side at the posterior aspect of the spine. It joins one facet joint to another. When the pars is fractured or has a defect, the main part of the superior vertebra is allowed to ‘slip’ forward. In most cases this is a small slip but it can be quite severe and rarely the superior bone can have completely ‘slipped’ off the one below. This is called spondyloptosis and is fortunately very rare.
Isthmic spondylolisthesis is common but rarely requires surgery. The problems and their symptoms that occur due to isthmic spondylolisthesis are very similar to those described for degenerative spondylolisthesis. That is, it can result in neurogenic claudication, radicular pain and lower back pain. Surgery for this condition is performed only in patients who have significant symptoms that have not responded to more conservative treatment. Therefore only a minority of people with this condition will require surgery during their lifetime.

Other forms of spondylolisthesis: These include trauma, congenital spinal dysplasia, tumour and infection.

Discogenic / Mechanical back pain

Lumbar spinal fusion is commonly performed for mechanical back pain. Before recommending this procedure patients must be aware of three facts:

1. Surgery for back pain (as opposed to leg pain) in the absence of pathology such as spondylolisthesis is not as successful as other surgeries (see below)
2. Surgery is not a stand-alone treatment and needs considerable physical therapy after surgery to gain the most benefit
3. Surgery is not designed to necessarily cure back pain but to reduce the pain to a level that will allow them to function more normally

In order to be a suitable candidate for surgery, patients need to have been through other conservative treatments and have failed these treatments. In most instances they will also be referred to a pain management specialist in order to ensure that all other reasonable alternative strategies have been exhausted.

Other indications

Spinal stenosis with deformity: Spinal canal stenosis is a condition where the diameter of the spinal canal becomes too small. The nerves passing through this region become compressed. This normally causes symptoms of neurogenic claudication. Neurogenic claudication is simply leg pain associated with walking which is relieved by rest. It is often accompanied by back pain. In many cases this can be treated by a simple laminectomy to create more room for the nerves. However, where there is pre-existing spinal deformity such as a curve (scoliosis) or slip (spondylolisthesis), there is a risk of further spinal deformity after laminectomy and therefore this may be supplemented by a fusion procedure.

Before Surgery

Prior to surgery, patients may be asked to attend a preadmission clinic. This will involve routine blood tests and for some patients an ECG and chest X-ray. Patients that have significant co-morbidities or illness may require extra assessment. Patients at Westmead Private Hospital will have a pre-operative Doppler of the lower limbs which will be repeated after surgery. This is to assess patients for the presence of deep vein thrombosis (DVT).

Patients who are on aspirin or clopidogrel should cease those medications 7 days before surgery. For patients who are on warfarin, management will depend on the original reason for their warfarin. Some patients will require early admission and be started on heparin, for example, patients with mechanical heart valves. Others will just need to stop taking warfarin 2 days before surgery. The INR will be checked before surgery.

Other medications should be continued including those usually taken on the morning of surgery. These medications should be taken with a sip of water even though the patients may be nil by mouth otherwise

All patients undergoing a general anaesthetic will need to fast. That is, they should have nothing to eat or drink for around 8 hours prior to surgery. Failure to comply with this may necessitate cancellation of the procedure as it may expose the patient to significant risk. As most patients are admitted on the day of the surgery, the hospital will contact them to inform them of the time for admission, likely time of surgery and the required fasting times on the day before the surgery.

Smoking

It is well documented that the largest risk for failure of the bones to unite or fuse is smoking. Therefore patients must cease smoking prior to the surgery and must not restart smoking after the surgery. Failure to comply with this advice places the patient at risk of failure of fusion with pain and other problems as a consequence. Patients should seek help from their general practitioner in order to stop smoking prior to spinal fusion surgery.

Hospital Admission

Most patients are admitted to hospital on the day of the surgery. Patients need to ensure that their latest X-rays, CT scans and MRI scans are with them when they come to hospital. These scans are the surgeon’s road map and without them the operation cannot proceed. If you do not have your pictures with you when you are admitted the operation may need to be cancelled. Except in rare circumstances, patients are responsible for these films, and are normally given back to them at the time of consultation. Patients at Westmead Public Hospital who have images taken at that hospital will usually have their films at the hospital.

Operation

The operation is performed under a general anaesthetic with patient laying face down on a specialised operating table. The incision is marked and the patient prepared. The incision is made in the middle of the back for a standard open PLIF and the length will depend on the patients and the number of levels that require surgery.

The muscles are dissected from the posterior aspect of the vertebrae. The spinous process and lamina of the level in question are moved. This also normally includes part of the fact joint on each side at that level. This exposes the main dural sac containing the fluid and nerve roots. The nerve roots as they pass through their foramen and the nerve roots going down to exist at the next level are also exposed. The disc is then removed from each side and the surface of the vertebral bodies above and below the disc, that is the end-plates, is prepared. Interbody cages, packed with the bone that has been removed from the spine at the start of the operation, are inserted into the disc space on each side. Bone graft is also packed between the cages.

Bone screws are then inserted on each side above and below the level that is to be fused. These bone screws, called pedicle screws, are joined on each side by a rod and smaller set screws. The vertebrae are usually gently compressed and the set screws tightened. X-rays are taken throughout the procedure to ensure that the level is correct and that the instrumentation is placed satisfactorily.
In some cases further bone graft is placed down each side of the spine. This is referred to as a posterolateral bone graft. The bone graft used in the procedure is obtained from the bone that is removed at the start of the operation that is the lamina, spinous process and facet joints. Bone is generally not taken from the patient’s pelvis unless there is a specific reason.

At the end of the operation a drain is in the wound and an epidural catheter is also inserted. The wound is then closed using dissolving sutures. A dressing is applied and the patient is returned to the supine position before they are awoken from the anaesthetic. Once awake the patient goes either to the recovery room or straight to the HDU/ICU.

Minimally invasive PLIF

In some instances a minimally invasive procedure can be performed. This involves several small incisions in the back on each side. The aim of performing the surgery using this technique is to reduce the operative trauma to the spinal muscles, thereby reducing blood loss and post-operative pain and speeding recovery. However, the use of this technique is limited to selected cases and depends on the indication for the surgery and the problem that needs to be fixed.

Hospital stay

The hospital stay is normally around 4-7 days in total but varies depending on the patient and their underlying condition. During the hospital stay the patient receives daily physiotherapy. Patients will receive prophylactic subcutaneous heparin injections and are required to wear stockings to prevent DVTs. At Westmead Private Hospital DVT scans are routinely performed before and after surgery.
After surgery there is normally some discomfort and analgesia is provided. For the first night after surgery an epidural is used to deliver pain relief. The epidural catheter is placed at the time of the surgery and is normally removed the next day. It is not uncommon for patients to experience numbness in their legs due to the epidural which resolves shortly after it is stopped. Once the epidural is removed another form of analgesia is normally used which may be through a drip and/or tablet. Constipation is a common complaint after surgery and is usually due to analgesics. You should inform staff if this becomes an issue.

The wound is normally cleaned and the dressing changed each day. There is normally a drain left in the wound which is removed after 24-48 hours. After discharge no dressing is required. You may shower and then pat the wound dry with a clean towel afterwards. While the wound may get wet, do not soak it in the bath or in a pool for at least 2 weeks after the surgery. Do not rub the wound. If there are any concerns such as excessive redness, pain or ooze then you should have your GP review the wound as the first step.

Most patients are able to be discharged directly home as they are independently mobile and self-caring. However, some patients, particularly those who are older or who live alone may benefit from a short stay in a rehabilitation facility such as Westmead Private Rehabilitation, Mt Wilga or Lady Davidson Hospitals.

At home

After discharge, it is advisable to rest for 2 weeks which should consist of normal daily activities. One should maintain a good posture as advised by the physiotherapists, For example, you should not slouch in a chair. You should not spend too long in any one position. Once you feel more confident then activities such as driving can resume. Normally one can drive after 2 weeks from the date of surgery. A return to work depends on the work environment. Those with sedentary jobs can usually begin to go back to work after 4-6 weeks. Those with more manual jobs should wait at least 6-8 weeks but it should be discussed with A/Prof Owler prior to surgery and again at the follow-up appointment.

Post-operative follow-up

You should make an appointment to see A/Prof Owler 6 weeks from the date of surgery or thereabouts. At that visit any concerns can be discussed and the wound will be checked. If there are any significant problems then you should contact his office earlier. At that time a follow-up x-ray is arranged. This is normally performed around 3 months after the surgery. A/Prof Owler will review those x-rays when they are delivered to the office and inform the patient of the result. In most cases no further follow-up is required unless there are any significant on-going issues.

Risks of the surgery

All surgical procedures have risk. There are risks common to all surgeries such as infection, bleeding, deep vein thrombosis (DVT), pulmonary embolism and those associated with a general anaesthetic.
In relation to PLIF surgery, most infections that occur are superficial and easily treated with antibiotics. However, very occasionally, a deep seated infection can occur and this may require removal of the pedicle screws and may result in further surgery and chronic pain. Pre-existing diabetes increases the risk of this complication.

Bleeding can be significant with PLIF surgery. In most patients the operation is at one level only and the risk of requiring a blood transfusion is low (<5%). However when two or more levels are involved the risk of requiring a blood transfusion will increase.

The spinal cord is normally well clear of the site of the surgery. In the lower lumbar spine the spinal cord has changed into a group of nerve roots called the cauda equina. While patients commonly worry about complications such as paraplegia and incontinence, such problems are very rare. More common is the chance of injuring one nerve root at the site of the surgery and the risk of this is approximately 1% and may result in numbness or weakness of the leg which may be permanent.

Persistent or recurrent pain in the leg can occur for several reasons. It may be that there is a disc recurrence as mentioned above. However some patients will experience leg pain because of changes that occur in the nerve itself after it has been compressed severely or for an extended period, i.e., neuropathic pain. Some patients will develop scar tissue around the nerve. Some scarring is normal as it is the body's natural response to healing. However excessive scar tissue is thought to be a reason for recurrence of pain as well.

In relation to the fusion itself, there is a risk of the bones not healing together as one, i.e., non-union / failure of fusion. The risk of this is small and most patients will not have symptoms but it may result in back pain and revision surgery. There is a risk of adjacent segment disease. As the spine is fused at the level(s) of the pathology, more stress is placed across the levels above and below the level of the fusion. This may accelerate changes at those levels and cause similar problems, sometimes requiring surgery.

During the procedure a small tear may occur in the covering of the nerves (dura). This dural tear will result in leakage of spinal fluid. Therefore when it occurs it is repaired with sutures. The tear happens because the spinal canal can be very tight and because adhesions may develop between the degenerative structures and the dura. If this occurs, it is repaired at the time. The patients is normally asked to stay flat in bed for 24 hours after surgery and the drain will be kept in for a longer period. In the majority of cases there are no other consequences and the recovery proceeds as normal. However in some patients the leak will continue and this may necessitate a return to the operating theatre to resuture or repair the leak.

This is not an exhaustive list of potential complications but this information provides an overview of the more common complications that patients may be exposed to.

There are numerous other very rare complications that may also occur including those associated with a general anaesthetic such as reactions to medication, visual loss, and operation at the incorrect level despite the use of x-rays.

Expectations of surgery

The outcome of surgery is dependent on the indication for surgery and often the severity and duration of symptoms prior to surgery. No guarantees can be given in relation to the surgery.

Pain is the most common symptom of radiculopathy and, in most cases, is the first symptom to improve; often immediately after the surgery. Pins and needles may take longer but tend to improve quickly. Numbness takes the longest period to recover, perhaps even over 12 months and some patients may not experience full recovery of numbness. Weakness has variable recovery depending on severity and duration before surgery. Some patients will experience recovery immediately while others may have persistent weakness despite the surgery. Normally physiotherapy is required to treat weakness. Overall about 80% of patients will experience significant improvement in pre-operative symptoms while a further 20% will not improve as much as is hoped and 1-2% percentage will be worse off in relation pain or some other problem. Neurogenic claudication normally responds well to surgery. Over 80% of patients are expected to improve significantly with surgery. With successful surgery they can normally begin to increase their fitness and increase the distances that they are able to walk and the time that they are able to stand for. Back pain associated with spondylolisthesis normally also improves. About 80% of patients will experience significant improvement in their pain allowing them to reduce their analgesic requirements and resume their normal activities.

When a PLIF is performed for mechanical back the expectations are different. We would expect that 70% of patients will experience a significant improvement in their pain such that they can reduce their analgesics and begin to return to their previous activities. However, this will vary depending on the nature of the underlying problem as well as the duration of symptoms prior to surgery. As mentioned earlier there are several points that are emphasised to patients undergoing spinal fusion surgery for back pain. These are that aim of surgery is to reduce the pain to level where the patient can function more effectively but that the surgery will not cure their pain, that the surgery is not a stand-alone treatment that it is expected that they patient will need extensive spinal physiotherapy and treatment in order to recondition the muscles and other regions of the spine, and that as previously mentioned, the rate of success is significantly lower with surgery for this indications than for others.

On-going care of the spine

The main reason for on-going care of the spine after fusion surgery is to avoid injuring the levels adjacent to the site of a fusion. However it also helps reduce the chance of long term lumbar spinal pain. A/Prof Owler’s philosophy is to attempt to return the patient to a normal active life rather than place onerous restrictions on the patient. However there are two aspects of spinal care that are important to patient’s that have undergone surgery.

The first, and somewhat obvious, advice is to avoid activities that may reinjure the spine. In the simplest form this includes not lifting heavy or awkward objects. As a general rule no-one should generally be lifting weights above 20Kg. In the short term the lifting restrictions are much less (see above). When lifting, good technique should be used such as keeping the knees bent and back straight while keeping the object being lifted close to the body. People should avoid simultaneous lifting and twisting. Those who are golf enthusiasts should wait 3 months after surgery before resuming golf.

The second aspect to long term care is maintaining spinal fitness. This includes weight loss, core strengthening and on-going exercise. The best exercises are those which are non impact such as swimming and cycling. All patients are normally taught core-strengthening exercises. These should be continued independently by the patient at home indefinitely.

Important Information

This information was provided to assist you. While it has been prepared to provide accurate information the practice and techniques of surgery will differ between surgeons. Likewise the information is a generalisation in relation to the surgery and will vary between patients depending on the individual and their pathology. This information cannot cover all aspects of the surgery especially in relation to surgical risks and should not be considered an exhaustive explanation. Please contact A/Prof Owler’s office if there are any further concerns or questions.