What Is Facet Joint Arthropathy

The term 'arthropathy' covers the wide range of this disorder, from fleeting joint sprain of the capsular ligaments, right through to frank arthritis of the joint.

Breakdown of the facets comes about in several ways: when the disc between two vertebrae flattens, causing the upper vertebra to settle down on the one below and jam the back compartment, just as letting air out of a car tyre makes it run along on its rim. It also develops when the facets have to overdo their preventative role, either restraining forward bending, or preventing twist of the lumbar segments.

The lumbo-sacral facets are particularly taxed when the sacrum is permanently tipped forward, to cause a deep hollow in the low back (a pronounced lumbar lordosis). Then the opposing surfaces, of the lumbo-sacral facets particularly, are forced to butt up against one another to stop the spine slipping forward off the sacrum. A leg length discrepancy can also affect several facets in the low back (and even into the thoracic spine and neck if the difference is great enough) as the lateral dip in the sacrum encourages the lumbar segments to slide sideways and twist.

However, attrition of the joints caused by these background factors may take years to bring facet pain on. Trouble usually comes to the fore when lurking inflammation is provoked by additional small-scale injury. The slightest ricking or twisting incident, such as slipping on a shiny floor when you are turning to talk, or turning over in bed, can put a match to smoldering trouble and set it blazingly alight.

Facet Joint Arthropathy
Figure 3.1 Facet arthropathy can begin as a fleeting capsular strain-similar to any joint sprain—and eventually becomes frank arthritis, with bony outgrowths (osteophytes) developing around the margins of the joint.

I believe capsular inflammation of the facets is very common and a potent source of back pain. Because the facet capsules play a substantial role in protecting the facets they are easily sprained. They act as tough elastic sleeves to absorb or dampen all jolts passing through the facets, thus sparing them bone-to-bone bruising.

The facets are the most likely part of the spine to pull apart and come undone; in effect their sliding-apart freedom at the back of the spine is also their Achilles heel. The lumbar spinal segments have great difficulty controlling the first imperceptible degrees of bend-and-twist because there are so few diagonally criss-crossing ligaments and muscles to control the action (see Chapter 4). We depend on the disc being primed to give us this stability but the facet capsule too has to do what it can to be all things to all movements. The controlling of the joints and sheltering them from impact mean the facet capsules are constantly in the line of fire.

In most respects the capsules are admirably equipped to cope. They are incredibly elastic and strong with a rich blood supply to keep up running repairs. However, their onerous protective role can cause inflammation and swelling which may irritate a nearby spinal nerve, creating severe leg pain.

Figure 3.2 Facet capsules are extremely strong and richly served with both blood and nerve supply.

The facet capsules have a prolific nerve supply to pick up any affront to the joint and relay it to the brain. However, the very sophistication of the nervous network may be part of the making of a back problem; the super-sensitivity of the facet capsule may make it slightly too ready to invoke a reaction from its muscles.

This enthusiasm to protect the joint after it has suffered a strain can make a major problem out of a minor one. Thus a tiny wrench to your back when wrestling with a suitcase can lock you up for weeks, when it should be gone in a day. On the other hand, supreme sensitivity from long-term joint pain may cause the muscles to reflexly under-act, thus causing another set of problems.

When the joint guarding is too attentive it jumps into action at the first sign of trouble. The nervous mechanism lights up and the muscles (local fibres of multifidus and the long erector spinae muscles if the reaction is extreme) clench to protect it more. The prolonged muscle contraction can cause more inflammation, by slowing the

Facet Joint Capsule

Figure 3.2 Facet capsules are extremely strong and richly served with both blood and nerve supply.

fine lacework of nerves and blood vessels compressec facet joint spasm of left multifidus fibres compressec facet joint spasm of left multifidus fibres

Figure 3.3 In the acute phase, multifidus develops a holding contraction (spasm) which can keep a facet joint engorged. In the chronic phase, multifidus reflexly inhibits, the 'under contraction' rendering the facet vulnerable to extraneous movement.

flow of blood through the capsule. As the joint becomes more engorged it sends off more messages of pain to the brain and the protective cycle intensifies.

This over-reaction explains why it is so important to work through any minor discomfort and not allow it to get the better of you. It may also explain why the muscles stop acting altogether in cases of chronic facet pain. We know that multifidus in particular is under-active when the back has been painful for a long time and this may be another type of defense mechanism—this time deliberate under-activity to spare the sensitive joint added compression. Although the back may be more comfortable in the short term, in the long term there is a risk of introducing instability to the segment.

Whereas mild capsular strain is relatively easy to acquire and fairly universal, true 'arthritic' change of the facets' bony surfaces is less common and may take years to evolve. Furthermore, I believe that even when arthritis is painful, its origins (certainly in the early stages) are 'capsular' rather than 'bone', at least until it gets to the point of actual bony destruction.

This may explain why treating advanced arthritic facets with the hands—in the way physiotherapists, osteopaths and chiropractors and some masseurs do—often relieves the pain. The accessing and handling of the tissues around a problem joint often interrupts the inflammatory cycle in a way which cannot be explained as doing things to the bone. Unlike the bone, capsular changes are more reversible and respond quite quickly to the comfort of treatment pressures.

Diagnosis by manual palpation

Just as with early stiffening of a spinal segment (Chapter 2), early capsular changes of the facets are only detectable via palpation with the hands, particularly the thumbs. Although the pain from an acutely inflamed joint may be crippling, routine imaging may be equivocal. In the same way, a twisted ankle is unlikely to show anything on a picture; the best way of telling if a facet is troublesome is by sensing whether it will move, by the way it feels, and by the way it responds to being handled.

Although not necessarily relevant in a self-help book such as this, it is interesting that human hands can tell such a lot about a facet problem. With early—otherwise undiagnosable—trouble with a facet the capsule feels like a dome of pulpy swelling under the skin when the thumbs probe in about 1.5 cm out to the side of the spine. If the problem is longstanding the capsule has a thickened leathery feel, caused by the chronic fibrosis, whereas a normal one will feel like nothing at all; health is conspicuous by its inconspicuousness. Experienced hands can also feel if there is over-activity of multifidus (it feels twangy, like an over-taut mini trampoline) or under-activity (when there is a leathery hollow where multifidus should be). Careful reading of MRIs can also reveal local atrophy of multifidus and a higher fat content, indicative of under-activity.

Once there are bony changes, palpation through the hands can tell how mobile (or immobile) the joint is and whether there is any crepitation, or grinding in the joint, as the joint surfaces move past one another. Again, this is not a finding which can be picked up any other way than manually, although in the neck you can often hear very loud chafing from the joints as you turn your head. These palpatory findings are the preserve of professionals but they give a deeper understanding.

Figure 3.4 There is no better tool than the human thumb to feel facet joints and gauge their function.

Once the joint surfaces become involved in the degenerative process, the changes stand out more clearly, even on X-rays. Because bone is radio-opaque, bony erosion can be seen, as can excess bone growth around the margins of the joint.

The pain is different in the various phases of the condition. Capsular pain is angry and mercurial, sometimes causing pain in different parts of the leg as the nerve is compressed by the swollen capsule, with changes in the body's position. By the time it has progressed to bony breakdown it is a deep-seated, gnawing ache which goes through like a meat cleaver in the side of your back, or across to the other side too if both joints of the segment are affected.

capsule

Figure 3.5 Capsular inflammation and swelling can readily irritate a nearby spinal nerve root.

angry swollen facet inflamed spinal nerve

Figure 3.5 Capsular inflammation and swelling can readily irritate a nearby spinal nerve root.

angry swollen facet inflamed spinal nerve

There has never been a clear correlation between imaging and degrees of pain. Sometimes the films show nothing at all and yet a patient is genuinely crippled by pain. Somebody else's images can look like a snow storm, with white, roughened bone surfaces and strange knobbled outgrowths around margins of the joints, yet there has never been a day of pain. Hence the maxim of our practice: treat the patient not the pictures.

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Responses

  • fethawit
    What is facet arthropathy?
    2 years ago

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