Low back pain - A clinician's perspective

Lower back pain is a common complaint that causes many to seek the aid of a skilled physiotherapist. 

The structure of the spine consists of a series of bones called vertebrae, between which sit sacs of fluid called discs that act as shock absorbers and allow for movement and flexibility. At the top of the spine in the neck, these bones and discs are thin as they need only to support the load of the head and neck above each level respectively. However, as humans evolved and began to walk upright as opposed to all fours, the weight on top of the lower spine became considerably greater, and as such requires larger, stronger bones, and thicker discs to support the added weight. However, despite natures best attempts to counteract this substantial load, the structures of the lower back remain vulnerable to injury and dysfunction, often resulting in pain.

Identifying the factors leading to the pain is important as it helps to identify the structures likely to be involved. An accident resulting in sudden trauma and pain may be an obvious cause, however it is often more difficult to decipher the causative factors when the pain presents gradually. Things to take into consideration may be posture, work activities and the time of day when the pain presents. Once identified, aggravating factors should be avoided to enable healing and recovery.

It is important to consider how the body regulates movement to appreciate why dysfunction occurs. During most movements, spinal stability is largely created by very specific and ordered contraction of muscles surrounding the spine. However when the muscles become fatigued, or have too much stress placed on them, they can fail resulting in a muscle strain, or offload the stress to surrounding structures such as bones, ligaments and discs. Generally speaking, when the force applied to the back becomes too much for the body to take, injury occurs at the weakest point.

A sound understanding of the human anatomy is necessary to identify the structures responsible for the pain, as its location does not always correlate with where the pain originates. The best known example of this is pain down the back of the leg that can stem from dysfunction in the lower back or bottom musculature. Many people refer to this as sciatica.

Below is a summary of some of the more common lower back injuries and symptoms that may be associated with them.

What is a Disc injury?

Each disc in the human spine consists of a soft, gelatinous centre called the ‘nucleus’, surrounded by network of tough, interwoven fibrous bands called the ‘annulus’. When standing up straight, forces generated by the weight of the body are evenly distributed throughout the annulus. However certain movements of the spine such as bending and twisting can place increased stress on certain areas of the disc structure. Add the weight of any object being carried and the stress can become so large it causes considerable damage. If only a few annulus fibres are damaged, the disc may maintain its shape and pain may not present until a day or two after the incident when the body tries to heal the damage using the inflammatory response. However, more significant damage may cause the disc annulus to stretch or even rupture, known as a disc bulge/protrusion and a disc prolapse/herniation respectively. This can move parts of the disc into space normally reserved for the nerves that supply the pelvis and lower limbs. The pressure on the nerve can be interpreted by the brain as pain at that site and/or into the leg/s. In very severe instances, the annulus may break into fragments when it ruptures generating floating pieces of disc within the spinal canal that can cause significant pain and nerve damage depending on where they lodge themselves. This is called a ‘sequestration’.  

Following a disc injury, patients often report significant pain bending forward and twisting. Prolonged sitting is also likely to increase the back or leg pain, particularly when first standing up. It is important to regain full movement into back extension as early as possible, whilst limiting all sitting and bending activities. These activities can be gradually re-introduced once healing has enabled sufficient strength in the disc annulus. In very severe cases, disc injuries may require surgery to free up space for the spinal nerves. Medical advice should be sought promptly if there is a loss of bladder or bowel control, severe pins and needles or numbness into the leg or legs, or a significant loss of power in one or both legs.       

What is muscle strain?

When a force is applied to a muscle beyond its capabilities, damage occurs to the muscle fibres. Repeated overload in a controlled manner such as in bodybuilding can lead to the body generating larger, stronger muscles to deal with the increased load. However when the overload is too great at a single point in time, significant damage can occur. We may commonly see this on the sporting field, as a calf strain or hamstring tear to give two examples. However a muscle strain can occur anywhere in the body including the back. Commonly all movement is painful and the patient may only feel comfortable when well supported at rest. Symptomatic relief is an important aspect of early treatment including pain relief, rest, ice if caught early and anti-inflammatory medication if deemed appropriate by the pharmacist or physician.

What is a joint injury?

At each level of the spinal column, there are a number of joints, each positioned and orientated in a strategic manner. In the lumber spine for example, we see the facet joints aligned vertically from front to back. As such they allow for movement bending forwards or backward, and to a lesser extent leaning from side to side, however they act to restrict rotational movements. Ligaments and a capsule surrounding each joint further limit range of movement and hold the joint surfaces in place. When the joints are forced beyond this predefined movement range, damage occurs to the ligaments, capsule, bones, or all three. This can be complicated by the close proximity of the spinal nerves to the facet joints. As the inflammatory chemicals are sent to the damaged area to begin the healing process, they can act on nearby structures such as the nerves generating a painful stimulus in the back or down the leg. Patients often report an increase in pain when leaning backward, twisting, reaching for high objects, or walking for longer periods. Treatment involves symptomatic relief initially, but moves quickly to restoring range of movement at the affected joint and those surrounding it. Core strength and stability is important to compensate for the weakened ligaments and joint capsule.

What fractures can cause low back pain?

Although bones are normally considerably strong, they are at times vulnerable to injury. As we age, bone can become brittle and prone to fractures. This results from a decreased bone density and is referred to as osteoporosis. As a result of this, spinal bones can become so weak that they can collapse in on themselves with relatively minor force, known as a ‘crush fracture’. This would be unlikely in the majority of patients, but may warrant investigation in the form of an x-ray when osteoporosis is suspected in the older individual.

Pain can also result from a slip of one spinal bone forward with respect to the one below it, a condition known as ‘spondylolisthesis’. This often occurs from a fracture that commonly occurs very early in life (around 5-7 years old), but which may not cause back pain and dysfunction until the middle to later parts of life. A small slip may be managed conservatively with physiotherapy and a structured exercise program; however surgical options may be suggested in the event of larger slips.      

What is spinal degeneration?

Wear and tear takes its toll on all structures of the human body including the lumber spine. Osteoarthritis occurs in the joints in the spine just like those in the hands, hips and knees. This can lead to rough joint surfaces, prone to inflammation when activity levels increase. It can also lead to small protrusions of bone away from the edges of joints, known as ‘osteophytes’. Considerable dysfunction occurs in the spine when the osteophytes begin to encroach on the space where the nerves exit the spine. Changes in spinal bone shape can also cause a reduction in space in the spinal canal itself, known as ‘spinal stenosis’.

The discs themselves also degenerate with age, losing volume and thus height. This can reduce the strength of the disc itself, or place an increased load on the joints throughout the spine. Although there is no real cure for degeneration, a regulated exercise based approach in the form of an osteoarthritis class or hydrotherapy can help to limit symptoms and improve quality of life. Anti-inflammatory and/or pain relief medication may be prescribed to assist during peak pain periods. Certain health supplements on the market such as glucosamine and chondroitin sulphate are also believed to assist by improving joint surfaces and function.   

Due to the complex workings of the human body, it is at times difficult to suggest that pain results from dysfunction in a single structure. As an example, it can be complicated by the associated muscular spasm and inflammation that often occurs following injury. It is impractical and unsafe to expose the majority of patients experiencing lower back pain to the radiation omitted from many of the scanning procedures such as x-rays and CT-scans. Therefore most of the time patients rely on the practitioners’ clinical diagnostic and problem solving skills to determine the factors at play. At times it may even be suggested that a patient has non-specific lower back pain, usually with a mixture of presenting symptoms and a varied response to treatment.

This complexity highlights the benefits of seeking the advice of a skilled physiotherapist, and utilising the many adjuncts to proficient physiotherapy including clinical Pilates and hydrotherapy.