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 part of 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 medical professional to rule out a serious condition.
Numbness in the leg is a common consequence of a nerve root compression from the low back. This is generally caused by a lumbar 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 joints of the lumbar spine. These segments are referred to as L4/5 & L5/S1. L refers to the lumbar spine which is the part of the spine directly above the pelvis. S refers to the sacrum which is part of the pelvic girdle. When the disc bulges it can place pressure on the nearby nerve root.
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. A person in their thirties reporting heel numbness may actually have a disc herniation in their low back. This may arise with or without pain or symptoms in the low back itself. 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.
If the big toe is involved then it indicates a probable 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 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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