Pain that starts in your lower back may not stay there. It often spreads to other nearby areas, moving further up your back or down to your buttocks, pelvis and legs.

Pain in your legs may be due to:

1. Pinching or irritation of your nerves (radicular pain)

2. A problem in the deeper structures of your back (somatic pain).

It’s not always easy to work out where the pain is coming from. Sometimes, we can reproduce it by pressing on various tender spots in your lower back and pelvis area. Usually targeted local anaesthetic injections under X-ray guidance are required to make a diagnosis.

Figure 1a, 1b, 1c & 1d: Key structures of the lumbar spine

1. Nerve Root Pain (Radicular Pain)

Typical nerve pain is a shooting, electric shock-like pain that runs down to your lower leg or foot. Usually the leg pain is much more severe than the local back or buttock pain. Squashing or compressing a nerve initially is not painful at all, until inflammation sets in.
Radicular pain is often associated with pins and needles, numbness and weakness. The pain comes from a chemical inflammation of the nerve and does not cause local back pain.

2. Somatic Referred Pain

Somatic referred pain is characteristically a deep, vague, diffuse pain, but it can be sharper in a well-defined area, usually in the back or hip area. The pain is usually worse in your back, closer to its point of origin, and less severe in the leg.

Somatic referred pain is the most common form of pain that traces back to your spinal structures. It can arise from any structure that contains a nerve supply, such as from inside the disc, the facet joint or the muscles. It does not come from pressure on a spinal nerve.

You know where the pain hurts most but our job is to find its source, which may be:

• One of the discs between your vertebrae – the source of about 40% of all chronic low back pain problems.

• Your sacroiliac joint in your pelvis – the source of about 15% of chronic low back and buttock pain

• The facet joints in your spine – responsible for about 15-40% of lower back pain (rising with age).

Your discs and other structures sit deep within your back, meaning we can’t diagnose the problem by palpating (feeling) the disc. Nor can this diagnosis be purely based on your symptoms and movement patterns.

It was previously thought that pain on bending forwards was most likely due to disc pain and that pain on bending backwards and twisting was more likely to be due to facet joint pain. However, this generalisation has been disproved.

Discogenic Pain

Discogenic pain means pain that’s due to a problem with your intervertebral discs. These are spongy, shock-absorbing cushions that sit between each of your spinal vertebrae.

If your pain is mostly in your midline, it is more likely to be due to your discs. The pain may spread out to both sides and down both buttocks and thighs (somatic referred pain). Alternatively pain may only be on one side radiating down one leg.

The only definitive test to determine if a disc is painful is a discogram. These are usually comfortable procedures done with some sedation in an operating theatre.

If a discogram shows that your discs are the source of your pain, then we have to decide on the right treatment. Options include:

• Surgery, such as spinal fusion and disc prosthesis

• Percutaneous techniques, such as intradiscal electrothermal therapy (IDET) and disc nucleoplasty.

These treatments may lead to excellent results in 20% of cases, and good to substantial improvement in about another 50%.

Facet Joint

Your facet joints connect your vertebrae together. The facet joints are more likely to be the cause of pain if bending backwards and to one side reproduces the pain.

If pain is from a facet joint on one side of your back, it is likely to be more concentrated on that side, and refer down that leg.

If pain is from facet joints on both sides of your back, it spreads across your back and feels more widespread.

We diagnose facet joint pain using X-ray guided painkilling injections into the facet joint (intra-articular injection) or its nerve supply. If the pain disappears with the anaesthetic, then it’s likely that your facet joints are responsible for your pain.

Facet joint pain can be treated with percutaneous radiofrequency neurotomy, which may relieve pain for at least 9-12 months.

Sacroiliac Joint

Sacroiliac joint pain is another example of referred somatic pain.

Your sacroiliac joint (SIJ) connects the sacrum and ilium bones of your pelvis. Pain usually starts in the sacrum and can spread as far as your foot.

We diagnose SIJ pain using X-ray guided injections. It can be a difficult process as the joint sits deep in your pelvis and is often hard to access. We usually need C-arm fluoroscopy or CT injection to confidently access the joint.

To relieve SIJ pain, we may use cortisone injections for a few weeks or sometimes longer. Other treatments for ongoing pain include a pelvic brace, sclerosant injections, radiofrequency neurotomy  of the nerve supply to the joint and joint fusion.

Hip Joint

Recent research has implicated the hip joint as a source of low back, buttock and somatic referred pain.

And What About Your Muscles?

All of the above conditions may present with features that seem as if the muscles are affected.

Your muscles are unlikely to be the problem if your pain is chronic (long lasting).

Muscles are commonly implicated in acute back pain. Treatment options include stretching, massage, heat, local anesthetic injections and acupuncture.