How to diagnose a pinched nerve in the back/sciatica?
A pinched nerve in the back is a common condition in our practice. It usually results from disc herniation causing pressure on the lower spine's nerves. The patient usually presents with pain, numbness and possibly weakness in the leg. The condition is also called “sciatica” and "radiculopathy". The article describes the causes of sciatica and the role of imaging in establishing the diagnosis.
What is sciatica?
Sciatica refers to back pain symptoms that extend into the thigh and leg. This is usually secondary to pressure or pinching of the nerves as they leave the spine, resulting in pain, numbness and sometimes weakness in the leg muscles. The site of symptoms depends on the level of nerve pinching within the spine.
The spine is formed by multiple bones (called vertebrae) separated by special structures (called discs). These give the spine flexibility, allowing for different movements during our daily activities. They also act as shock absorbents, reducing the forces that go through the spine. The spinal cord is the main central nerve bundle within our body that runs from the brain into the lower back through a special canal (called the spinal canal) and gives off smaller nerves during its course. These nerves supply different body parts, including the arms and legs. They are responsible for the movement and sensation within our body. When leaving the spinal cord, these nerves run very close to the discs, and therefore they are susceptible to pressure or irritation secondary to any “disc herniation”. Disc herniation is a term used to describe focal bulging of the intervertebral discs; it can happen acutely particularly secondary to an injury or sudden movement, or more slowly over time due to degenerative (wear and tear) disc changes.
What are the causes of a pinched nerve within the spine?
By far, the most common cause we see for a pinched nerve within the spine is disc herniation. More rare causes include trauma and tumours.
How can I tell if I have a pinched nerve?
The clinical features of a pinched nerve usually include:
Pain- this can be felt at the back and usually goes down the thigh or leg. The exact distribution of pain depends on the site of nerve impingement. The lower part of the spine is called (the lumbar spine), and the nerves are numbered according to the level at which they exit the spine from L1 to L5 nerves (L stands for lumbar). The pain can be sharp or burning in nature and sometimes described as a sensation of pins and needles.
Leg weakness- again, the level of weakness will depend on the level of the pinched nerve.
In severe cases, the pinching of the nerves can affect other functions like bowel and urinary bladder control. This is an important sign as it can indicate large disc herniation causing significant pressure on the nerves within the lower spine, “a condition known as cauda equina syndrome”. If you have such symptoms, you need to seek urgent medical attention.
How to diagnose a pinched nerve within the spine?
MRI spine is usually the best test to assess for any pressure on the spine's nerves. It will assess the degree and level of neural impingement.
Normal disc (no disc herniation)
What conditions can mimic a pinched nerve within the spine?
The most common conditions that can be mistaken for a pinched nerve within the spine are:
Hip osteoarthritis refers to wear and tear changes within the hip joint. Pressure on the first or second lumbar nerves (L1 or L2) can cause pain at the front of the hip and can be mistaken for hip arthritis.
Trochanteric bursitis (greater trochanteric pain syndrome)- This condition is characterised by pain at the outer aspect of the hip. Pressure upon L3, L4 or L5 nerves can also cause pain at the outer aspect of the hip and is confused with this condition.
Proximal hamstring tendinosis. This condition can cause pain in the buttock area. It can be mistaken for pressure upon S1 (the first sacral nerve).
Piriformis syndrome can cause deep pain in the buttock and be mistaken for sciatica.
What are the treatment options for a pinched nerve within the back?
The treatment depends on the severity of the condition. If a large disc herniation causes significant pressure on multiple nerves within the spine, this might require an urgent operation to relieve the pressure on the nerves.
Surgical treatment to remove the disc bulge can also be considered if the conservative management described below is not helping. Conservative management includes physiotherapy to strengthen the back muscles and reduce the tension within the muscles and lifestyle modification, including weight reduction if appropriate. Treatment may include tablets to reduce nerve-type pain (like amitriptyline) and anti-inflammatory tablets or creams (like Ibuprofen and Voltarol). You need to speak to your doctor before starting any treatment.
If the conservative management is not helping, then an image-guided cortisone injection to target the area of nerve pinching can be considered. This aims to reduce the swelling and inflammation around the nerve and may provide prolonged pain relief. This can also be used as a test if a surgeon is trying to confirm the nerve impingement before any surgical treatment. This will confirm the diagnosis if you notice a significant improvement in your symptoms. Given the deep location and complex bony anatomy, spinal injections are usually done under X-ray or CT guidance. Using ultrasound guidance to perform these injections is usually limited.
Hip conditions and treatments