neurosurg

Degenerative disease

What is degenerative disease?

Degenerative disease is, in fact not a real disease. It is a process of wear and tear that occurs with ageing in virtually all individuals. It is also referred to as osteoarthritis, arthrosis and spinal arthritis. The joint surface may become eroded and the gristle or cartilage that lines the joint is no longer smooth but pitted. This results in pain and inflammation occurring with movement. In addition to this there is a process of thickening in the ligaments around the joints as well, a gradual deformity of the joint itself rather like the end of a stick that has been hit with a mallet. The result is a splaying out of the joint surface and this edge of bone (osteophytes) causes a characteristic appearance with apparent swelling and enlargement of the joint itself. In addition to these changes, the joint may become inflamed with redness heat and swelling with accompanying pain. Typically the inflammation comes on overnight once the joint is rested and gradually wears off as the joint gets moving.

It is axiomatic that the inflammatory changes lead to a cycle of a few good months and a few bad months and that the attacks eventually become more frequent and finally confluent so that the patient has symptoms all the time. Typically the symptoms are worse first thing in the morning, the days activities being expressed in the worn joint by inflammatory changes occurring during the night when the joint is subject to less movement.

These changes occurring in the spine do not only produce pain in the joints but because of the deformity can cause pressure on nerves or the adjacent spinal cord. The result of the compression is a syndrome (collection of symptoms and signs) of pain in the distribution of the nerve, numbness and weakness all superimposed upon the background discomfort of moving worn joints.

The intervertebral disc is a structure that lies between the bodies of the vertabrae. It is held in place by strong ligaments or sinews which both encircle the bones and run up and down the spine. The disc material itself is soft jelly like material when normal and has the ability to absorb water readily. As the day wears on the water content of the disc material reduces because of pressure distributed throughout the spine, engendered by living in an atmosphere with pressure. The result is the disc height is minimally reduced when you go to bed. On arising the disc has re-absorbed some water and you are actually half a centimeter taller!

Disc degeneration reduces the discs ability to retain water and the texture changes gradually to that of a consistency similar to cooked prawns. It loosens from the margins of the disc space and may bulge backwards and eventually gets pushed through the retaining circular ligament (annulus fibrosus) and pokes out of the back of the disc space and catches the nerves or spinal cord producing a neurological clinical picture.

Trauma and the degenerative spine

The majority of experts accept that the effect of trauma is to accelerate the appearance of symptoms from degenerative disease rather than causing them to arise “de novo”. This means that a patient who already has degenerative changes in the neck or back and suffers an injury gets initial acute symptoms but if they fail to resolve within a reasonable timescale the most likely explanation for the continuation of symptoms is the background wear and tear degenerative change. It is important to note that the actual degenerative change is not accelerated but the symptoms have appeared ahead of the time when they might have, had the injury not occurred.

The thrust of this argument is that some people will in any case develop symptoms from degenerative disease and it is this group of patients who do not become completely better after injury. For legal purposes, this means that when a claimant has symptoms which do not settle it is because they belong to the group of patients who would have developed symptoms spontaneously in any case. The burning question in most cases seems to be : by how long has the patient experienced an acceleration of the appearance of symptomatic degenerative disease engendered by the trauma? A spread of opinion gives varying rates of acceleration. It is likely that if the patient remains symptomatic longer than two years despite all relevant treatment that they are unlikely to become completely asymptomatic for the indefinite future. Once you have permanent symptoms from degenerative disease it is likely that they will stay.

The symptoms themselves can take various forms however and this mirrors the natural history. When symptoms arise spontaneously they usually begin with a variably short attack of discomfort which may last for days weeks or months. In some patients the next attack never arises but usually there are further attacks of pain with or without neurological symptoms (numbness,, weakness, tingling, arm / leg pain). The attacks become more frequent and eventually coalesce leading to constant symptoms which become more severe and disabling. The timescale for this is extremely variable and is influenced by many factors. Such factors include:

Genetics: if you inherit a spine that is prone to wear and tear you will get it sooner and suffer more in the way of symptoms

Age: Someone who gets symptoms early in life has considerably more time in which to get a recurrence of symptoms

Heavy work: A heavy mechanical fitter for example, is more likely to have increasingly frequent attacks of symptoms that some one doing light industrial assembly simply because he is using the worn joints more and stressing them more.

Lack of exercise: strong muscles supporting joints or the spine are the best protection as they increase stability and protect the worn structures

Obesity: overweight people put considerably more strain on joints and the spine than people of slim build.

Severity of degenerative change on X-ray or MRI or CT scan: the worse the demonstrated general state of the spine the more likely you are to get more frequent attacks

The thesis therefore is that when trauma occurs ligaments are overstretched, strain is put on muscles leading tearing of muscle fibres and joint surfaces are traumatised. This leads on to local build up of inflammation and pain in the acute phase. This acute response to injury gradually resolves and the pain begins to die down in the absence of degenerative change. The symptoms become intermittent and less severe and gradually decline into insignificance unless there is significant degenerative disease.

A soft tissue injury therefore has an acute phase of severe continuous discomfort and a longer phase when the symptoms gradually decline. The symptoms from soft tissue injury generally do not persist for longer than two years (at the outside!). It would be very difficult to describe any pathological mechanism for the occurrence of pain from a purely soft tissue injury as scar tissue in itself is insensitive and there is rarely any long tem change seen on MRI scanning or other investigation. The only mechanism in my opinion that will produce pain in the long term with movement is when a ligament is torn and heals by scar tissue and this limits the movement in the joint but logically the result would not necessarily cause pain but rather limitation of movement which can theoretically cause mild chronic strain upon adjacent joints or disc spaces which have to compensate by increasing their rang of movement.

In the presence of degenerative disease the effect of trauma is to cause a combination of acute soft-tissue injury and symptoms from the degenerate joint / spine. The soft tissue element will resolve within two years. Residual symptoms in the vast majority of cases are due to the degenerative disease which has become symptomatic and prevented resolution. The acceleration period will depend upon the above factors which determine the occurrence of symptoms from degenerative disease and these include Age, work pattern, previous history, severity of degenerative change on investigation, severity of the trauma and to some extent genetics and bodily habitus.

How long an acceleration period one decides upon as a medical expert seems to vary considerably and leads to a large spread of opinion. One has to accept that because there is a large spread of opinion particular experts are picked by particular defendants or claimants. This of course is understood by the courts who frequently make judgements base upon their own assessment. The recent reforms in English law however may well help to encourage experts to never give partisan opinions or to exaggerate acceleration periods in the hope of them being averaged out by the courts and one hopes that opinions are always given within the exact extent of the expert’s opinion.

Disc prolapse

Disc prolapse is the end stage of the degenerative process. The changes in the disc are such that it appears dehydrated on an MRI scan, ( MRI picks up differences in water content in different tissues) as it can no longer hold water like a normal disc. The ligament that holds it in place may have a bulge which gets thinner. This process is painful and leads to neck or back pain (depending on which disc is affected). Eventually the ligament gives way and the loosened disc material is squeezed backward and catches the nerve or spinal cord where it runs behind the disc space. Neurological symptoms then occur with pain in the limb and numbness and/or weakness in the distribution characteristic to that particular nerve. The back or neck pain tends to reduce and the limb pain comes to the fore.

A healthy disc does not prolapse immediately with injury. Indeed some experts feel that trauma has no effect at all in the evolution of disc prolapse. The reasoning behind this is based upon biomechanical models and the fact that in a healthy spine a force sufficient to break the bones may not cause disc prolapse. In these particular models, using cadaver (dead) spines prolapse of the disc only occurred with a combination of flexion and twisting but required tremendous force.

This is too rigid a stance however, as it is contrary to everyone’s experience. It is much more likely that patients who already have a degree of disc degeneration and are subjected to a bending and twisting strain, tear the thin part of the annulus (retaining ligament) which is already bulging and the disc material is squeezed out leading to a disc syndrome. This process can in fact take a while so that the effect of the injury where there is a degenerate disc may well be that there is initial back or neck pain followed by limb pain when the nerve is impinged upon. The process takes a variable time to occur and the length if time that it takes may well be a measure of either the severity of the trauma to the degenerate disc or the severity of the degenerative change.

The key to whether trauma has caused the symptoms of disc prolapse is probably whether or not the patient has had continuous symptoms in the neck or back or limb since the injury took place. Once the nerve pressure has started, although there may be a variation in severity there is not likely to be a complete remission of symptoms.

The occurrence of disc prolapse in an injury therefore is probably easiest to explain as an acceleration process on the basis that there already was some disc degeneration present at the time when the accident occurred.