The terms sciatica and piriformis syndrome are commonly heard, but how much do you know about it?
Taking a look at some anatomy helps us to understand the structures involved in sciatica and piriformis syndrome.
The sciatic nerve is the longest and largest nerve in the body. It originates in the sacral plexus, a network of nerves in the lower back (lumbosacral spine). The lumbosacral spine refers to the lumbar spine (lumbo) and the sacrum (sacral) combined, way down at the base of your spine and above the tailbone (coccyx).
The sciatic nerve has several smaller nerves that branch off from the main nerve. These nerves are the peroneal and tibial nerves which enable movement and feeling (motor and sensory functions) in the thighs, knees, calves, ankles, feet, and toes.
The sciatic nerve has an intimate relationship to the piriformis muscle, exiting the pelvis usually inferior to the muscle at the greater sciatic notch. The piriformis muscle originates on the front surface of the sacrum, and its tendon attaches to near to the middle aspect of the greater trochanter. Its principal action is to externally rotate the hip. It additionally acts as a weak abductor and flexor. It is innervated by the spinal nerves L5 to S2.
Sciatica
The term “sciatica” is not clearly defined and it is often used inconsistently by clinicians and patients. Radicular pain and lumbosacral radicular syndrome have been suggested as alternatives, whereas radiculopathy describes involvement of the nerve root, which causes neurological deficit including weakness or numbness.
Sciatica is commonly used to describe radiating leg pain. It is caused by inflammation or compression of the lumbosacral nerve roots (L4-S1) forming the sciatic nerve. Sciatica can cause severe discomfort and functional limitation.
Compression of the nerve root and resultant inflammation play a role in pathogenesis of sciatica. Disc herniation resulting from age related degenerative changes, and rarely trauma, is the most common cause. The inflammatory response induces resorption of the herniated disc material, and is thought to be the reason why most people improve without surgery. Foraminal stenosis (a bony opening around a nerve root becomes narrow) and, less commonly, soft tissue stenosis caused by cysts, tumours, or extraspinal pathology are other causes. Rarely, extraspinal pathology in the lumbosacral nervous plexus such as neoplasm, trauma, infection, or gynaecological conditions, or muscle entrapment such as piriformis syndrome can mimic symptoms of disc herniation. Smoking, obesity, and manual labour are modifiable risk factors for the first episode of sciatica.
People with sciatica usually describe aching and a sharp leg pain radiating below the knee and into the foot and toes. The pain can have a sudden or slow onset and varies in severity. Most people report coexisting low back pain. Disc herniations affecting the L5 or S1 nerve root are more common and cause pain at the back or side of the leg and into the foot and toes. If L4 root is affected, pain is localised to the front and lateral side of the thigh. Tingling or numbness and loss of muscle strength in the same leg are other symptoms that suggest nerve root involvement.
Piriformis Syndrome
Edwards defines piriformis syndrome as neuritis (inflammation of a nerve) of branches of the sciatic nerve caused by pressure of an injured or irritated piriformis muscle. Several authors attribute piriformis syndrome to a shortening or “spasm” of the piriformis that results in compression of the sciatic nerve. The cause of spasm of the piriformis muscle has been most attributed to direct trauma, postsurgical injury, lumbar and sacroiliac joint pathologies, and overuse.
Symptoms associated with piriformis syndrome typically consist of buttock pain that radiates into the hip, back of the thigh, and the upper part of the lower leg. In general, pain increases with sitting or squatting, but person with piriformis syndrome may experience difficulty with walking or other functional activities. Piriformis syndrome typically does not result in neurological deficits such as decreased deep tendon reflexes and myotomal weakness (muscle weakness served by a spinal nerve root).
It is important to note that in severe cases of the nerve compression can cause symptoms to extend down into the thigh – which is where the similarities lie with sciatica. However, this is not true sciatica. The cause of the pain is the piriformis muscle being compressed or tight with primary symptoms of localized buttock pain which in turn puts strain on the sciatic nerve causing secondary symptoms.
In conclusion, the main difference between piriformis syndrome and sciatica is that piriformis syndrome is mostly characterized by localized buttock pain and some leg pain in worse cases. Sciatica is typified with lower back pain, buttock pain and leg pain which tracks down the back of the leg, following the areas supplied by spinal nerves.
References:
1. Jason C. Tonley, Steven M. Yun, Ronald J. Kochevar, Jeremy A. Dye, Shawn Farrokhi, Christopher M. Powers. 2010. Treatment of an Individual With Piriformis Syndrome Focusing on Hip Muscle Strengthening and Movement Reeducation: A Case Report. Journal of Orthopaedic & Sports Physical Therapy 40(2): 103-111.
2. Rikke K Jensen, Alice Kongsted, Per Kjaer, Bart Koes. 2019. Diagnosis and Treatment of Sciatica. BMJ 367: 1-6.