Numbness is a lack of sensation or feeling in part of the body. Patients will often attend a Physiotherapist or Chiropractor complaining of numbness in the leg or arm. Generally, numbness is caused by a nerve compression which cuts off the normal nerve supply to an area. This presentation needs to be investigated immediately by a Physiotherapist.
Numbness in the leg is a common consequence of a nerve root compression from the low back. This is generally caused by a disc herniation in the lower back. Depending on the level of the nerve root involved, it can refer to different parts of the leg. The most common location for a disc herniation (slipped disc) is the lower two discs of the lumbar spine just above the pelvis. These segments are referred to as L4/5 & L5/S1.
The nerves from the lower part of the spine go on to form the sciatic nerve (L4-S3) which runs down the back of the thigh centrally. The sciatic nerve forms several branches in the thigh that supplies the back of the leg, outer part of the knee and the front & back of the shin.
Foot or Calf Numbness:
Although the primary source of leg numbness is a compression of the nerves in the spine, symptoms will often arise as far down as the calf or foot. It is possible to experience heel numbness with no back pain that can occur as a consequence of a disc herniation in the lower back.
Patients often find it difficult to comprehend that the location of their symptoms can be so far from the source. The nerve roots from the lower back supply different parts of the foot depending on the level involved, The part of the foot where numbness is experienced may indicate the probable level of the disc herniation.
The bottom 3 discs of the spine are known as L4, L5 & S1. These are the main levels for disc herniations
If the big toe is involved then it indicates an L5 (Lumbar nerve 5) involvement.
The outside of the foot typically indicates S1 (Sacral nerve 1) involvement.
The medial part of the shin, ankle & the inner aspect of the toe suggests an L4 involvement.
If the numbness is associated with weakness in the toes or leg then this would suggest a significant nerve compression is present. A physio/chiropractor may assess the reflexes in the ankle or knee to confirm the presence of a disc bulge & determine the level involved.
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