Leg weakness is a serious symptom which is commonly ignored by many people. Leg weakness is highly based on ones own perception, so many people may not even realize that they have leg weakness. However, for practical purposes it is the first sign of paralysis because of nerve compression in the lower back. Leg weakness is frequently accompanied by loss of touch sensation and shooting pain, which generally come before the leg weakness. Thus, loss of sensation or shooting pain can be taken as an alarming signals, which tell us that leg weakness is on its way. Hence, it should be taken very seriously and any prompt medical help should be sought. This is especially important for people having low back problems, who have a greater chance of getting leg weakness.
What is leg weakness ?
Leg weakness should not be confused with tiredness or a heavy feeling that one gets after a long day of work. It is the weakened strength of the leg muscles, which is manifested by inability to do certain movements with the foot or leg. Leg weakness should also not be confused with a muscle cramps or arthritis which cause a painful inability to move the foot or leg. Leg weakness also interferes with walking especially when it is involving the foot muscles. This is known as foot drop, in which a person unable to lift the foot upwards.
How does leg weakness occur ?
The leg is supplied by nerves which come out of the spinal cord and back bone in the lower part of the back. These nerves travel all the way from the lower back to the various parts of the leg, imparting it touch sensation and movement. The vertebrae in the lower part of the back are a common site of diseases like slip disc (slipping of cartilage intervertebral disc (Picture 1, 2) which normally lies between two vertebrae causing compression of nerves or spinal cord), sciatica (compression of a nerve bundle as it comes out of the hip bones), and leprosy (fibrosis of superficial nerves near the skin). The nerve damage caused by these diseases results in abnormal functioning of the parts supplied by the nerves (generally muscles and touch sensation). Consequently, when a large part of the leg looses its nerve supply, like a major muscle, it makes the person unable to do the movement performed by this part (muscle) or makes the part insensitive to touch.
Picture 1: Intervertebral disc, top view
(source: Chiro Org Images)
Picture 2: Intervertebral disc, side view
(source: Chiro Org Images)
Why is leg weakness an emergency ?
Nerve damage is almost always permanent as nerve tissue does not grow back easily. One can only prevent further damage by identifying its cause and taking treatment, but the damaged nerve can not be repaired. There is a window period of a few days between getting leg weakness and the nerve being permanently damaged. Thus, if leg weakness is treated during this period, the permanent damage to nerves can be avoided and leg movements can come back. So it is very important to seek medical attention and perform the diagnostic tests early, to complete treatment within this window period.
Diagnosis of Leg weakness
Leg weakness most commonly arises from nerve compression in the lower back. Hence, pain in the lower back region should not be ignored, especially if it is longstanding. The shooting pain, which travels from the lower back to the knee or the ankle, is because of the irritation of the nerves caused by compression. This is also called sciatica because the nerve coming out of the hip bone is called the sciatic nerve, which divides into smaller nerves which supply the leg muscles and also provide touch sensation.
The initial evaluation consists of evaluation of the leg muscles by a doctor or a physiotherapist. The doctor would ask you to do several simple movements and measure the strength of your movements by opposing the movement with his hand. The touch sensation is also tested with a cotton wisp or a pin to find out the exact region of sensory loss.
This helps in locating the probable site of the nerve compression so that further tests can be directed towards that region.
The common diagnostic tests employed for investigation of causes of leg weakness are:
Picture 3: Spondylolisthesis on X-ray
- X-rays of lower back, which rule out bony abnormalities like fractures or spondylolisthesis (forward or backward slipping of a vertebra)(Picture 3). This is the primary investigation for all causes and is especially important when one has had a traumatic incident like a fall or a road accident.
- MRI helps in diagnosis of injuries and abnormalities like slip disc, intervertebral disc protrusion, nerve compression, and so on. Soft tissues which cannot be seen on x-rays can be seen on MRI so the causes related to them can be accurately diagnosed.
- Nerve conduction studies are used in diseases, which are difficult to visualize on X-ray or MRI like leprosy, syphilis, etc., and which are confined to the nerves. In this test, small electrodes are stuck to the different parts of the body and measurements are made of the electrical activity of the nerves of that part.
After these investigations and the physical examination, leg weakness can be attributed to compression of spinal cord (Picture 4), compression of spinal nerve (Picture 5 ), or local nerve disease.
Picture 4: Spinal Cord Compression
Picture 5: Spinal nerve compression
Compression of spinal nerve or spinal cord is mostly due to intervertebral disc protrusion. However, some other causes for the same are spinal tumor, sciatica, dislocation of vertebra (spondylolisthesis), fracture of vertebra, and spinal stenosis.
Local nerve diseases are leprosy, syphilis, nerve cut injury, or neurofibroma.
Treatment of Leg weakness
Leg weakness due to local nerve disease is treated as per the disease condition. Most of these diseases are treated with medicines and do not require surgery. However, the medicines have to be continued for many months, or sometimes even a couple of years.
Leg weakness caused by spinal cord or nerve compression are treated by surgery more often than by medicines. The diseases like sciatica and fracture of vertebra are generally treated with bed rest and painkillers for a period of 6 weeks. This is followed by gradual exercises and physical therapy which strengthen the muscles. The other medicines which are helpful in reducing the pain are muscle relaxants and neurovitamins. As long as the treatment program is religiously followed there are no complications. However, if not followed, one may end up being a paraplegic for life.
The surgery for spinal tumor or intervertebral disc protrusion should be taken only when leg weakness or loss of sensation is present. A person also has to wear an orthosis (a belt for the back which gives support and restricts some movement)(Picture 6) after surgery for a period of 6-8 months until the bones and muscles regain their strength. Simple low back pain or shooting pain should not be taken as an alarming sign for surgery. They should only be pointers towards a medical evaluation for leg weakness.
Picture 6: Orthosis for lower back
The surgery of spinal cord or vertebral column is not at all risk-free. There are chances that one may end up in paralysis after the surgery. It is also expected from the patient in writing that one is aware of this disastrous consequence and is still ready for the surgery. In the presence of leg weakness, surgery is a logical choice as one is eventually going to end up in paralysis without the surgery. But in the absence of leg weakness, there is still time and one can try medicines and physical therapy for improvement.