Peripheral nerve injuries
Peripheral nerve injuries have been classified based on the degree of functional and structural integrity of the nerve trunk:
1. Neurapraxia--refers to a transient interruption in nerve function (impulse conduction) due to ischemia and/or mild paranodal demyelination.
There is no structural damage to the axons and their supportive connective tissue. Neurapraxia is the mildest form of nerve injury and it is commonly caused by blunt trauma or compression. The degree of proprioceptive and motor dysfunction can be variable, nociception is usually preserved. Neurogenic muscle atrophy is unlikely to occur. Recovery is usually spontaneous, complete and occurs within one to two weeks once the compression and edema resolve. Local demyelination may take 4 to 6 weeks to resolve.
2. Axonotmesis: few to several axons and surrounding myelin are disrupted (structural damage), but the Schwann cells, their basal lamina and the endoneurium remain intact. Wallerian degeneration occurs. Distally to the point of injury the axons and their myelin sheaths degenerate and undergo phagocytosis. Degenerative changes also occur in the axons proximal to the injury site but usually involve only one to three nodes of Ranvier.
Axonotmesis may result from severe stretching or crush injury of the nerve. The degree of proprioceptive, motor and nociceptive deficit is proportional to the number of axons that are damaged. In general, significant neurological dysfunction and Neurogenic muscle atrophy are expected. Axonal regrowth occurs spontaneously (1 mm/day) along the connective tissue scaffold, but the time until return to function depends on the extent of injury and the distance from the denervated end-organs.
3. Neurotmesis--is the most severe type of injury and is characterized by complete severance of the nerve trunk (axons, Schwann cells, supportive connective tissue). It is associated with complete proprioceptive, motor and nociceptive dysfunction (i.e., no deep pain perception). Neurogenic muscle atrophy is severe. As in Axonotmesis the distal segment undergoes Wallerian degeneration, but the proximal axons will not regrow to their end-organ since there is no guiding scaffold (Schwann cell basal lamina and the endoneurium have been disrupted). Scar tissue tends to interfere with sprouting axons and may result in neuroma formation. Consequently, surgical intervention is necessary to assist regenerating axons to reach and reinnervate their appropriate end-organs.
Axillary nerve injury
A condition involving dysfunction of the axillary nerve which normally supplies the deltoid and teres minor muscles and sensation to the lateral aspect of the shoulder.
This condition is a type of peripheral neuropathy that may manifest as the result of a variety of disease processes or injuries.
Conditions associated with axillary nerve dysfunction include mononeuritis multiplex, fracture of the humerus, abduction injury to the shoulder, pressure to the armpit from a cast, splint or crutches.
Symptoms include numbness over the outer portion of the shoulder, shoulder weakness and difficulty lifting arm or objects over your head. An EMG, nerve conduction جج or muscle biopsy can be helpful in making the diagnosis. Recovery is generally spontaneous if the underlying cause can
The Musculocutaneous nerve:
The Musculocutaneous nerve is formed from the lateral cord and contains the C5,6,7 nerve roots. The nerve enters the coracobrachialis muscle and passes through it to lie laterally between the biceps and brachialis muscles. The nerve supplies all three muscles and terminates as a sensory nerve which emerges from the lateral side of the tendon of biceps to form the lateral cutaneous nerve of the forearm.
The Musculocutaneous nerve is rarely injured. If the nerve is cut by a penetrating wound then sensation will be lost from a narrow strip of skin on the lateral side of the forearm. Supination and flexion of the forearm will be weakened but not lost since the supinator muscle will still be intact and innervated by the radial nerve, and the forearm flexors, innervated by the median and ulnar nerves, and the brachioradialis and extensor carpi radialis longus innervated by the radial nerve will still produce flexion.
Ulnar nerve injury
Injury or damage to the ulnar nerve which runs down the length of the arm. The site of the damage is usually at the elbow or wrist. The nerve can be injured by a physical trauma (cut, broken elbow) or by certain activities such as cycling and throwing which cause repetitive mild stress on the ulnar nerve leading to inflammation. Ulnar nerve inflammation can result in neurological symptoms in the lower arm such as pain, weakness, tingling and paralysis of the muscles controlled by the nerve.
Lesion of ulnar nerve at or near wrist or base of palm will result in paralysis of Hypothenar muscles, all interosseous muscles, 1/2 of FPB, the Palmaris brevis, & adductor pollicis;
Also it will result in loss of sensation in the small finger and half of the ring finger
The median nerve supplies the muscles of the volar forearm except two, the flexor carpi ulnaris and the ulnar half of the flexor digitorum profundus. In the hand it supplies the thenar muscles, and two lumbrical muscles. It supplies sensation to the thumb, index, long and one-half of the ring fingers.
Injuries to the median nerve result in severe disability. High median nerve injuries, in the proximal forearm or above, lead to loss of wrist flexion strength, ulnar deviation of the wrist, loss of thumb opposition, and loss of finger flexion of the thumb, index and long finger interphalangeal joints. When making a fist, the ring and small fingers flex while the long and index tend to stay straight. In low median nerve injuries the fingers are still able to flex, but thumb opposition is often los
Radial Nerve Anatomy
The radial nerve arises from the posterior cord of the brachial plexus and travels around the posterior aspect of the humerus in the spiral groove with the profunda brachial artery. The nerve distributes branches here to the triceps muscle. In severe humeral fractures, the radial nerve is often injured at this level. The nerve travels distally where it enters the anterior compartment of the arm as it pierces the lateral fascial septum just proximal to the elbow. The nerve then divides in the forearm and gives off branches to the brachialis, brachioradialis and extensor carpi radialis longus.
It often then divides into a sensory and posterior interosseus branch that provides motor function the rest of the dorsal forearm extensor muscles. Injury to the radial nerve results in loss of extension of the wrist, fingers and thumb. The resulting difficulty in grasping objects leads to significant disability. When the nerve is injured to the extent that it will not recover and nerve repair or grafting is not possible, tendon transfers can provide some return of function.
Ideally however, acute injuries resulting in nerve transection are primarily repaired or grafted
The Femoral Nerve
The femoral nerve enters the thigh below the inguinal ligament, lying on the iliacus. Before entering the thigh the nerve supplies iliacus and pectineus. The femoral nerve in the thigh divides into anterior and posterior branches. The anterior branch supplies the Sartorius muscles and gives off medial and intermediate cutaneous nerves of the thigh. The posterior division gives off the saphenous nerve and muscular branches to rectus femoris and the vastus muscles. The saphenous nerve and the nerve to vastus medialis lie in the subsartorial or adductor canal. At the knee the saphenous nerve emerges from behind Sartorius and accompanies the greater saphenous vein along the medial side of the leg and foot.
The femoral nerve is rarely injured. Injury results in loss of knee extension and loss of cutaneous sensation on the medial side of the leg and foot. Pain may be felt over the femoral nerve distribution due to compression of the L2,3,4 nerve roots by an intervertebral disc
The Obturator Nerve
The Obturator nerve from anterior branches of L2,3,4 anterior primary rami leaves the pelvis through the superior part of the Obturator foramen as anterior and posterior divisions. The anterior branch, lying anterior to adductor brevis supplies the adductor brevis, pectineus, adductor longus and gracilis. It supplies cutaneous branches to the medial thigh. The posterior branch supplies Obturator externus, adductor brevis and adductor magnus. The nerve supplies innervation to the knee joint. Pain from the hip joint might be referred to the medial side of the thigh or to the knee joint since the Obturator nerve supplies all three.
An accessory Obturator nerve may be present, arising from L3,4 and passing into the thigh over the superior pubic ramus. The nerve may supply pectineus, the hip joint and may communicate with the anterior branch of the Obturator
The nerve might be injured in pelvic surgery since it lies on the lateral wall of the pelvis. In that case the adductors would be paralyzed, and there would some sensory loss on the medial side of the thigh
The Sciatic Nerve
The sciatic nerve is formed in the pelvis by fibers from the lumbosacral trunk (L4,5) and by fibers from S1,2,3. This thick nerve immediately leaves the pelvis through the greater sciatic notch, below the piriformis muscle (P on diagram). The nerve may divide immediately, or may pass either above the piriformis or through the piriformis. In the gluteal region the nerve lies deep to gluteus maximus, between the greater trochanter (GT) and the ischial tuberosity (IT). The nerve then passes down the back of the thigh to the apex of the popliteal fossa. In the thigh the nerve divides into lateral common peroneal and medial tibial divisions. In the upper part of its course the sciatic nerve supplies the semimembranosus, semitendinosus,
the ischial head of adductor magnus and long head of biceps femoris from its tibial division. The common peroneal division supplies fibers to the short head of biceps femoris
The Tibial Nerve
The tibial nerve passes through the popliteal fossa to pass below the arch of soleus. In the popliteal fossa the nerve gives off branches to gastrocnemius, popliteus, soleus and plantaris, and the sural nerve. The sural nerve is joined by fibers from the common peroneal nerve and runs down the calf to supply the lateral side of the foot. Below the soleus muscle the nerve lies close to the tibia and supplies the tibialis posterior, the flexor digitorum longus and the flexor hallucis longus. The nerve passes into the foot below the medial malleolus.
Here it is bound down by the flexor retinaculum in company with the posterior tibial artery. The nerve and artery divide into medial and lateral plantar branches. The medial plantar nerve supplies the abductor hallucis, the flexor digitorum brevis, the flexor hallucis brevis and the first lumbrical. Cutaneous distribution of the medial planter nerve is to the medial sole and medial three and one half toes, including the nail beds on the dorsum (like the median nerve in the hand). The lateral plantar nerve supplies quadratus plantae, flexor digiti minimi, adductor hallucis, the interossei, and three lumbricals. and abductor digiti minimi. Cutaneous innervation is to the lateral sole and lateral one and one half toes (like the ulnar nerve)
The Common Peroneal Nerve
The common peroneal nerve leaves the popliteal fossa between the tendon of biceps femoris and the lateral head of gastrocnemius. It crosses behind the head of the fibula and passes laterally around the neck of the fibula (where it may be palpated). The nerve gives of the sural communicating branch to the sural nerve, and the lateral cutaneous nerve of the calf. The nerve pierces the peroneus longus muscle to divide into deep and superficial branches
The deep peroneal nerve supplies the muscles of the anterior compartment - the tibialis anterior, extensor hallucis longus, extensor digitorum longus, peroneus tertius and extensor digitorum brevis. The deep peroneal nerve supplies cutaneous branches to the cleft between the big toe and the second toe. The superficial peroneal nerve supplies the muscles in the lateral compartment (peroneus longus and brevis) and the skin over the anterior lower leg and dorsum of the foot.
The sciatic nerve is commonly injured during intramuscular injections into the buttocks. The nerve may also be injured by posterior dislocations or fracture dislocations of the hip joint. Injury to the nerve might result in loss of the hamstrings and calf muscles resulting in loss of knee flexion, and loss of the muscles of the anterior and lateral compartments of the leg resulting in foot drop. Cutaneous sensation would be lost over the calf and dorsum, sole and lateral side of the foot.
The common peroneal nerve may be injured as it winds around the neck of the fibula, resulting in foot drop (anterior compartment muscles), and loss of sensation on the lower anterior leg and dorsum of the foot. The nerve is also at risk in anterior compartment syndrome.
The roots of the nerve may also be compressed by a prolapsed disc, giving pain over part of the distribution of the nerve - sciatica.