The lumbar spine is that part of the skeleton below the rib cage and above the pelvis, commonly called the low back. Like the cervical spine in the neck it is a common spot to develop problems due to the relative high range of motion that occurs here and also due to the forces across the spine that result from carrying around the body weight in the upright human skeleton.
Like the rest of the vertebral column the lumbar spine consists of individual bones (or vertebra) connected to each other via ligaments, muscles and specialised cartilages called intervertebral discs. With the exception of segmentation anomalies there are usually five separate vertebrae in the lumbar spine, with those lower down the spine being exposed to progressively greater forces due to body weight so that the lower segments tend to be more commonly affected by degenerative changes or injury.
The pattern is very similar to that described in the cervical spine with the major exception however being that the spinal cord generally does not extend any further down the spinal column past the L1 or L2 levels. This is because of the so-called differential growth between the spinal cord itself and the spinal column. Although both of these structures grow and get larger in the developing human foetus and baby the spinal column grows more and at a faster rate than the spinal cord so that in early foetal life the spinal cord extends all the way down the spinal canal, but by the time of birth it has apparently “ascended” to L3 and then by skeletal maturity rests at somewhere between L1 and L2 in most people. Some rare congenital or developmental disorders (e.g. spina bifida) can interrupt this apparent ascending pattern of the cord and lead to the condition of “tethered spinal cord” that, if present, not uncommonly causes symptoms during childhood or adolescent growth spurts.
In the adult spine the significance here is that although all parts of the spine are by definition delicate parts of the human body the lack of the spinal cord in the spinal canal means that conditions in the lumbar spine may not be as serious or are more forgiving than those in the cervical or thoracic regions. Although spinal nerves can cause significant problems if they are compressed, for example, they have a higher ability to heal and seem to be more resilient than the spinal cord itself.
Common conditions that may require surgery include lumbar radiculopathy and neurogenic claudication from intervertebral disc herniation and spinal canal stenosis.
The term “claudication” refers to the Roman Emperor Claudius I who was said to have a limp (claudicare in Latin means “to limp”). Whenever this term is used in medicine it generally refers to a problem that is experienced or made worse when the patient walks. The term “neurogenic” means caused by or related to the nerves.
The syndrome of neurogenic claudication refers to a combinations of some or all of nerve-sounding symptoms (such as pain, pins and needles, numbness, burning, weakness, unsteadiness, a sense that the legs won’t do what they are being asked to do) that tend to start in the low back and spread down one or both legs characteristically getting worse the longer a person tries to stand up or the further they try to walk. Bending forward can help, but as the condition progressed most people find that they need to sit down (or sometime lie down) to gain any relief, only to find that when they get up and go again the symptoms come back.
By far the most common cause of neurogenic claudication is nerve compression in the lumbar spine (low back) due to spinal canal stenosis.
Early in the condition it can be managed with non-surgical treatments such as life-style modifications, medications, or spinal injections. Most cases however will progress over a time frame of months to years, often at an ever increasing rate. This leads to more and more difficulty in managing basic activities such as walking down the street, doing the grocery shopping, standing in the kitchen preparing meals etc. People suffering from this condition commonly describe that they need to walk from chair to chair, bend forward and lean heavily on the shopping trolley to relieve some of the symptoms, and prepare meals or shower while sitting down on stools.
Unfortunately, unlike disc herniations which may spontaneously heal with time, spinal stenosis due to spondylosis only tends to get worse as time passes and so often it is more a question of when rather than if someone will need surgery. Since the underlying problem is structural (i.e. no longer enough space for the nerves), eventually a structural solution will be necessary (i.e. surgery to decompress the spinal canal).
This refers to symptoms that develop if there is a problem affecting one of the nerve roots in the lumbar spine such as compression of the nerve by a herniated disc, spinal or foraminal stenosis, inflammatory cysts, etc. Although patients may experience some low back pain the characteristic symptoms are felt in that part of the body looked after by the specific nerve involved. In the lumbar spine this is generally one or other part down the leg. Symptoms can include pain, pins & needles, numbness, or even weakness depending on the degree of the problem involved. The term “sciatica” is often used to describe the pain that seems to spread down the leg, since it was once thought to relate to the “sciatic nerve” (one of the large nerves that runs out of the pelvis into the back of the thigh and then branches further down the leg). Although we still use this term it is now understood that the majority of cases of sciatica are caused by lumbar radiculopathy and do not in fact relate to an issue with the sciatic nerve itself.
Depending on the cause this condition can often be treated non-surgically with rest over time, medications, physical therapies (e.g. physiotherapy, osteopathy, chiropractic therapy etc), and sometimes spinal injections. To have confidence that an individual patient will respond to these non-surgical treatments we usually need to see a meaningful improvement over the first two to three months. If the condition is not improving over this time frame then the risk of non-surgical treatment starts to increase since the longer the nerve remains jammed and not improving the greater the chance the symptoms may entrench and persist even after the nerve becomes un-jammed (with so-called neuropathic or “memory-like” pain developing).
Surgery may therefore be needed if these treatments are not helping, the condition is persisting, or particularly if there are concerns that the nerve function may be at risk (e.g. if symptoms such as weakness or numbness in the leg are evolving). The type of surgery required will depend on the exact cause of the problem with the nerve but not uncommonly involves one of the minimally invasive procedures such as microdiscectomy.
This is a particular type of deformity that refers to the situation where one vertebra does not properly line up on top of the one below it. Most commonly this involves the higher vertebra seeming to have slipped forward (so-called “anterolisthesis”), less commonly backwards (“retrolisthesis”). We sometimes refer to spondylolisthesis as a “slip” for this reason. In doing so the nerves or spinal cord may become trapped and jammed as a result of the deformity.
It is not uncommon to see this in the lumbar spine where the normal lordosis in combination with the upright human posture results in the lowest two disc spaces having a “down-hill” type angle. This means that the body weight will tend to result in a vector of force promoting the one bone to “slide” down over the one below. In the normal situation this is prevented by the health of the intervening disc and the strength and integrity of the “guy-ropes” at the back of the spine, most notably the joints and the bone at the back of the spine itself which is called the lamina.
The process of spondylosis may compromise this integrity. The disc spaces can dehydrate and collapse, the ligaments become lax, and the joints become arthritic and potentially incompetent meaning they are not as able to prevent abnormal movement.
The various joints in our body do not simply allow movement to occur but restrict that movement in range and direction. If these joints become incompetent due to arthritis it can lead to deformity across the joint with the result of, for example, knees that are abnormally angled with advanced knee arthritis or fingers that point in bent directions with hand arthritis. In the spine, incompetence of the facet joints located at the back of the spine can lead to reduced ability to resist the force of gravity as we stand and walk around in turn leading to spondylolisthesis as one vertebra slips forward on the other. We call this type of slip a spondylotic spondylolisthesis.
In a different situation there may be some loss of integrity to the lamina itself either as a developmental problem or as a result of injury (or potentially surgery). The part of the lamina in between the joint above and the joint below (called the “pars interarticularis” meaning the bit in between the joints) can be particularly prone to this and may develop a “false joint” or so-called “pars defect”. If this leads to a slip the condition is somewhat confusingly referred to as a spondylolytic spondylolisthesis (not to be confused with the spondylotic spondylolisthesis as described above).
Cauda Equina Syndrome
The cauda equina is the name given to the collection all of the spinal nerves that run down the lumbar spinal canal. Each nerve will exit the spine under its co-named vertebra (i.e. the L1 nerve under the L1 vertebra, L2 under L2, etc) all the way down into the sacrum.
The lowest nerve to contribute any meaningful sensation to the leg is the S1 nerve. S2 and lower run mostly to the pelvis and, among other things, are involved in the neurological aspects of bladder function, erectile function, conscious control of the anal sphincter and sensation to the region of the body in between the legs called the “perineum”. These are somewhat smaller and more delicate nerves and therefore they can be prone to injury that may then result in difficulties with these functions and numbness in the perineum.
In some situations a large central disc herniation may compress all of these nerves at once particularly if the congenital dimension of the spinal canal is on the narrow side of normal. For various reasons related to anatomy this is most likely to occur in the low lumbar spine and particularly at the lumbosacral disc level. The dysfunction of these nerves results in somewhat sudden bladder and bowel dysfunction, erectile loss, and perineum numbness and is referred to as the “acute cauda equina syndrome”. Since the S1 nerve may not be compressed there may be no symptoms in the leg at all and also not much in the way of pain. It should be stressed however that the vast majority of disc protrusions are somewhat off to one side or another (therefore potentially jamming the exiting nerve but not all of the cauda equina), or if the disc protrusion is central the spinal canal is wide enough to accommodate the nerves so that they don’t develop dysfunction. Thankfully therefore this syndrome is relatively rare compared to the much more common pattern of acute lumbar radiculopathy.
The acute cauda equina syndrome is a neurosurgical emergency that usually requires an immediate operation since the longer the delicate sacral nerves are compressed the more likely the damage will not recover even after the nerves are decompressed. This may result in the need for permanent bladder catheterisation etc.