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Peripheral Nerves

Nerves carry information from the brain to the rest of the body, and vice versa. The arm and leg contains numerous nerves that transmit information for muscle contraction, sensation, and reflexes. The nerves that innervate the arm leave the central nervous system (spinal cord) through several areas in the neck, and form a complex structure called the Brachial Plexus. The same occurs for the leg. The nerves are larger near the neck / lumbar spine, and eventually divide to form smaller branches in the upper arm, forearm, and hand and thigh, calf and foot.

Injuries to the nerves can be one of the following:

  • neurapraxia – the nerve is stretched and damaged but not torn
  • rupture – the nerve is torn at a point along its length
  • axonotmesis – the nerve is partially damaged. Natural recovery is possible, so these injuries can often be managed conservatively with support and physiotherapy.
  • neurotmesis – the nerve is completely severed. There is no prospect of natural recovery, so this type of injury requires surgery to restore function.

There are 3 different nerves in the arm. When these nerves are injured they present differently:

The Median Nerve

The median nerve runs from the armpit, down the front of the arm to the wrist and into the hand.

If the median nerve is damaged near the elbow, then the index, middle finger and the thumb, are unable to flex (bend) to make an “OK” sign. Thus, they present with the Benediction sign.

Fig 1:Benediction sign – median nerve injury

If the injury is near to the wrist (Carpal Tunnel Syndrome) or in the hand, you may get pain, weakness of the thumb and fingers leading to dropping items (like cups) and a feeling of swelling in the hand.

Sensation is normally decreased in the thumb, index and middle fingers, and palm on the thumb side.

The Ulna Nerve

The ulna nerve runs from the armpit, passes at the back of the elbow (funny bone) and enters the wrist on the little finger side. The ulna nerve is most commonly damaged at the elbow or wrist or due to a fractured humerus.

If the injury is at the elbow (Cubital tunnel), then the person generally presents with pain / pins and needles and a weak grip.

If the injury occurs at the wrist, then weakness of grip, and sensory loss mainly over the ring and little finger is evident.

Where there has been significant injury due to a fracture, then an ulna claw is evident. This is where the ring finger and little finger, predominantly, are unable to straighten.

 

Fig 2: Claw hand with an ulna nerve injury

The Radial Nerve

The radial nerve passes from the armpit, at the back of the arm, close to the humerus, and into the top surface of the forearm. The most common cause of radial nerve injuries is a humerus fracture, a direct blow or sustained pressure (i.e. from incorrect use of a crutch).

Injuries to the radial nerve result in a wrist drop (unable to lift the hand), inability to lift/open the fingers and a small area of decreased/lost sensation on the top of the hand (over the thumb, and index and middle fingers).

 

Fig 3: Drop wrist with radial nerve injury

Other Nerves

Sciatic Nerve (leg)

This nerve is the largest nerve in the human body and the continuation of the sacral plexus

It is most commonly injured due to the following:

  • Direct trauma
  • Stretch
  • Compression due to hematoma (serious bruising)
  • Unknown (40%)
  • Uncommon (0-3%), complication following THR
Peroneal Nerve

30% of peroneal nerve palsies are from knee dislocations. The following signs and symptoms may be evident:

  • Decreased sensation, numbness, or tingling on the top of the foot or the outside border of the upper or lower leg
  • Foot drop
  • Toes drag while walking
  • Weakness of the ankles or feet
  • Prickling sensation
  • Pain in shin
  • Pins and needles sensation
  • Slapping gait. This is when the foot cannot lift off the ground properly, so when one tries to put the heel down first, it slaps onto the ground.

Femoral Nerve

The Femoral nerve is the major nerve supplying the front of the thigh.

The following is a number of reasons for femoral nerve injuries:

  • Direct injury
  • Tumor or other growth
  • Prolonged pressure / immobilization
  • Pelvic Fracture
  • Radiation to the pelvis
  • Haemorrhage into the retroperitoneal space
  • Catheter placed into the femoral artery
  • Diabetes may cause femoral neuropathy.

The following signs and symptoms may be present

  • Numbness / tingling in the front and inner aspect of the thigh
  • Dull aching pain in the genital area
  • Weakness of hip movements
  • Difficulty straightening the knee due to quadriceps weakness
  • Sensation that leg or knee is going to buckle
Treatment of peripheral nerve injuries in general:

Imaging:

To test the nerves in the arm or leg, the doctor may request an Electromyelography (EMG). This test uses needles and electrodes to test the electrical conductivity of nerves. If more information is needed, a CT Scan or an MRI may be requested. This will help explain what type of injury has occurred and the prognosis for recovery.

Therapy:

Depending on what type of nerve damage has occurred, the therapists can help with splinting, exercises and strengthening, pain management or compensatory strategies if function doesn’t improve. Treatment and recovery will depend on the severity of the injury.

The therapists will educate you with regards your specific nerve injury and resulting treatment plan.

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