Peripheral Nerve Injury
BRIEF ANATOMY ABOUT SPINAL NERVE:
The dorsal and ventral nerve roots arising from the spinal cord join at the intervertebral foramen to form a spinal nerve.
In the thoracic segments, these mixed spinal nerves retain their autonomy and supply one intercostals segment both dermatome and motomal.
In virtually all other segments, spinal nerves join with others to form a plexus.
There are 31 pairs of spinal nerves consisting of 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal.
Peripheral Nerve Injury
A spinal nerve has three components: motor, sensory and sympathetic.
The sympathetic components of all 31 mixed spinal nerves leave along the 14 motor roots (12 thoracic and 2 lumbar roots).
Each spinal nerve now divides into anterior and posterior rami.
The anterior rami of the upper four cervical nerves form the cervical plexus and the lower four cervical together with upper thoracic nerves form the brachial plexus.
The anterior rami of the first three lumbar nerves and part of the fourth lumbar nerve form the lumbar plexus.
The sacral anterior rami along with the anterior rami of the fifth lumbar and part of fourth lumbar form the lumbosacral plexus.
The posterior rami supply the para spinal muscles and the skin of the back. They are smaller than anterior Dermatome is an area of skin supplied by a single spinal root. Myotome represents a muscle unit supplied by a single spinal root.
GENERAL PRINCIPLES OF NERVE INJURY:
● Any part of the neuron detached from its nucleus degenerates and is destroyed by phagocytosis.
● This process of degeneration distal to a point of injury is called secondary or wallerian degeneration.
● Reaction in proximal end is called primary or retrograde degeneration.
● Time required for degeneration varies between sensory, motor, and is related to the size and myelination.
● In secondary degeneration, response is obtained to faradic stimulation up to 18-7hours.
● After 2-3 days, distal segment is fragmented and the myelin sheath starts degenerating.
● By seven days, macrophages clear the axon or debris and are completed within 15-30 days.
● Schwann cells undergo mitosis from seventh day onwards and start filling
the areas previously occupied by axon and its myelin sheath.
● Primary retrograde degeneration proceeds
for at least one internodes or more.Histological, it is identical to wallerian degeneration.
● More proximal the site of injury, more pronounced will be the changes.
● Axonal sprouting starts from 24 hours after the injury.
● Unmyelinated initially but later on it gets
myelinated.
● Now if the endoneurium is intact, sprouts will readily pass along their former courses and after regeneration may innervate their previous end organs.
● If the endoneurium is interrupted, then
the sprouting axons may migrate aimlessly
throughout the damaged area into the epineurial,perineurial regions forming a stump neuroma or neuroma in continuity or they may enter into the other empty endoneural tubes or newly formed endoneurial tubes only to terminate in myotomal or dermatomal areas of their own.
Hence, recovery is difficult if entire axon is transected and filled with scar tissue.
Classification of Nerve Injuries:
Seddon’s Classification (1943):
Seddon identified three types of nerve injuries: The
first one is a mere contusion;
the second is the transection of axons only,
and the third complete transection of the nerve.
This classification is less accepted clinically.
Sunderland’s Classification:
Accepted clinically and arranged in ascending order of severity from 1-5. Various degrees represent injury to myelin, axon, endoneurium, perineurium and the entire trunk.
Etiology:
General Causes:
Metabolic diseases, collagen diseases, malignancies, endogenous or exogenous toxins; thermal, chemical or mechanical trauma, etc. can cause injury to the peripheral nerves.
Local Causes:
Forty percent of bone and joint injuries are associated with peripheral nerve lesions.
TYPES:
Primary: This is due to injury of a peripheral nerve resulting from the same trauma that has injured a bone or joint.
Secondary: This is due to involvement of the nerve in infection, scar, callus, etc.
● It is largest branch of the medial cord of the brachial plexus with a root value of C8-T1. It arise at the level of pectoralis minor muscle, run through the axilla and lie in the medial compartment of the arm.
● pierce the medial intermuscular septum at the level of coracobrachialis and lie in the posterior compartment of the arm.
● pass over the posterior aspect of the medial epicondyle and enter the forearm through the two heads of flexor carpi ulnaris via the elbow.
● beneath the flexor carpi ulnaris muscle within the forearm.
● At the junction of middle and lower one-third of forearm, dorsal sensory branch, which winds round the forearm and passes dorsally to supply the dorsum of the ulnar border of the hand, the little finger and medial half of ring finger.
● Later, pass through the Guyon’s canal at
the wrist formed by the pisohamate ligament and thehook of the hamate. On the exit from the canal, split into a superficial and deep branch.
● supply the following muscles during my course:
• In the arm—Nil.
• In the forearm—Flexor carpi ulnaris and medial half of flexor digitorum profundus supply
both these muscles at the proximal third. give off a dorsal sensory branch at the distal third.
• In the hand—superficial branch supply palmaris
brevis and digital branches to volar aspect of little
finger and medial half of ring finger.
. Role of lumbricals: Mainly flexes the metacarpophalangeal joints and extends the proximal interphalangeal joint.
. Role of interossei: Palmar interossei adducts the fingers and dorsal abducts the fingers. Through the dorsal digital expansion, they aid the action of lumbricals.
.Role of hypothenar: Abducts and helps in the movement of apposition of little finger
Local Causes:
These are more important and could be in the
following areas:
Causes in the axilla:
• Crutch pressure.
• Aneurysm of the axillary vessels.
Causes in the arm:
• Fracture shaft of humerus.
• Gunshot and penetrating injuries.
Causes at the elbow:
• Compression by the accessory muscle (anserina
epitrochlearis).
• Fracture lateral epicondyle of humerus.
• Repeated occupational strains.
• Recurrent subluxation of the nerve.
• Compression by the osteophytes as in rheumatoid and osteoarthritis.
• Cubitus valgus deformity due to various causes
results in repeated friction of the nerve giving
rise to tardy (late) ulnar nerve palsy.
Causes in the forearm:
• Fracture both bones forearm.
• Incised wounds, gunshot wounds and penetrating injuries of the forearm.
Causes at the wrist:
• Compression by osteophytes.
• Fracture hook of the hamate.
• Compression by ganglion.
• Wrist injuries.
Causes in the hand:
• Blunt trauma.
• Penetrating injuries.
• Occupational—people operating high-speed drills in rock mining, etc.
• Associated ulnar artery aneurysm.
Ulnar nerve injuries give rise to claw hand
deformity either true type or ulnar claw hand.
Claw Hand:
Two varieties are described:
1) One is a true claw hand involving both median and ulnar nerves
2) second an ulnar claw hand or claw-like hand due to ulnar nerve injury.
Claw Hand deformity can be:
Complete: when it involves all the digits and therefore results from both Ulnar and Median Nerve Palsy.
Incomplete: or Partial where it involves only ulnar 2 digits and is referred to as an isolated Ulnar Nerve Palsy.
Pathomechanics:
Loss of intrinsic muscle function due to ulnar nerve injury results in loss of flexion at MP joints and extension of IP joints of the fingers.
In a bid to bring about the flexion of the MP joints, the long finger flexors overact pulling the IP joints and wrist into more flexion.
This causes a tenodesing
(pulling) effect on the long finger extensors. The extensors cannot extend the IP joints without the stabilization of the MP joint in neutral or slightly flexed position, which is normally brought about by the intrinsic.
This along with the compensatory over action of the long finger extensors to bring about the lost extension of the MP joints results in hyperextension of the MP joints and the classical deformity.
This is called the intrinsic minus hand: The thumb is also adducted by its long extensors because the
intrinsics and the abductors are paralyzed.
Problems of claw hand:
Hyperextension of MP joints (not the only primary or most disabling deformity).
Grasp decreased by 50 percent due to loss of power of flexion at MP joints.
Pinch decreased due to loss of stabilizing effect from the intrinsics.
Roll up maneuver lost.
Many surgical procedures are devised to block hyperextension of MP joints as it is still considered as the primary deformity.
Risk Factors:
Some activities are considered as risk factors due to their nature:
External compression at the elbow.
Applying upper body weight to push down on the tool can cause nerve damage over time.
Prolong movements causing the elbow to lean as seen among cyclists, motorcyclists or people with desk jobs.
Symptoms of Nerves:
● The continuation of the posterior cord of the brachial plexus and its largest branch. root value is C5-8 T1. In the axilla, lie behind the axillary artery, pass posterior to the humerus beneath the teres major, and enter in the interval between the long and
medial head of triceps.
● wind round the spiral groove, pierce the lateral intermuscular septum at the junction of the distal third and the middle third, and come to lie in the anterior compartment of the arm.
● lie between the brachioradialis and extensor carpi radialis longus and at the level of the lateral epicondyle, split into superficial branch and posterior interosseous nerve.
● Superficial branch is direct continuation, which runs distally in the forearm under cover of brachioradialis and about two inches above the wrist it pierces the
deep fascia, turns dorsally and laterally and reachesthe dorsum of the hand supplying three and half fingers until the level of middle phalanges.
● posterior interosseous branch penetrates the supinator muscle through the arcade of Frohse, runs distally in the forearm, and lies on the interosseous membrane. It ends as a pseudo ganglion over the wrist joint.
● supply the following muscles course
• Above the spiral groove: All the three heads of triceps and anconeus.
• In the spiral groove: I give off three cutaneous branches, posterior cutaneous nerve of the arm, posterior cutaneous nerve of the forearm and lower
lateral cutaneous nerve of the arm.
• Between the spiral groove and lateral epicondyle: supply brachialis, brachioradialis and extensor carpi
radialis longus.
• Before piercing the supinator: supply extensor carpi radialis brevis and part of supinator.
• In the supinator supply the rest of it. After emerging out of the supinator, supply all the remaining extensor muscles of the forearm and abductor pollicis longus.
Local causes:
In the axilla:
• Aneurysm of the axillary vessels.
• Crutch palsy.
In the shoulder:
• Proximal humeral fractures.
• Shoulder dislocation.
In the spiral groove 5’S:
• Shaft fracture.
• Saturday night palsy
• Syringe palsy.
• Surgical positions (Trendelenburg).
• ‘S’march‘s (Esmarch) tourniquet palsy.
Saturday night palsy (Also called weekend palsy):
● In this condition, there is compression of the radial nerve between the radial spiral groove and the lateral intermuscular septum.
● It is known after an event which typically
happens on a Saturday night weekend when in an inebriated condition, a person slumps with his midarm compressed between the arm of the chair and his body .
● Saturday Night syndrome so named because it can be acquired by sleeping with the arm over back of a chair whist in a drunken stupor, compressing the plexus.
● Between Spiral Groove and Lateral Epicondyle:
• Fracture shaft humerus
• Supracondylar fracture humerus.
• Lateral epicondyle fracture of the humerus.
• Penetrating and gunshot injuries.
• Cubitus valgus deformity.
At the elbow
• Posterior dislocation of the elbow.
• Fracture head of radius.
• Monteggia fractures.
Causes in the forearm
• Fracture both bones forearm.
• Penetrating and gunshot injuries
● The lesion is high, the patient will present with wrist drop, thumb drop and finger drop. He will be unable to extend the elbow.
● If the lesion is low the elbow extension is spared; but the wrist, thumb and the finger extensions are lost, but the patient can extend the IP joints of the fingers because of the action of the intrinsic muscles of the hand.
● Sensation along the posterior surface of the arm and forearm is lost in high lesions and in low lesions the above sensations are spared, but there is loss of sensation over the first dorsal web space.
● In acute injuries, it is difficult to evaluate the injury to the radial nerve. In such situations, the Hitchhiker’s sign (inability to extend the thumb) is used as the screening test.
● It is thickest nerve in the body with a root value of L4,5 S1,2,3.
● It enter the glutei region through the greater sciatic notch and pass between the greater trochanter of femur and ischial tuberosity.
● From here, enter the thigh and in the middle, divide into common peroneal
and the tibial part. Before doing so, supply biceps, semitendinosus, semimembranosus and adductor magnus.
● The common peroneal part is the smaller of my two terminal divisions. This runs along the medial border of biceps, leaves the popliteal fossa at the lateral angle, passes behind the head of the fibula,
winds round the neck and divides into superficial (musculocutaneous nerve) and deep peroneal nerve.
● The superficial nerve descends in the substance of peroneus longus and supplies the peroneal muscles,
● skin over the lower part of front of the leg, whole of the dorsum of the foot except the first web space and most of the toes.
● The deep peroneal nerve supplies all the
four muscles of the anterior compartment and divides into medial terminal branch and lateral terminal branch.The former supplies the first web space and the latter ends as a ganglion after supplying
extensor digitorum brevis and second dorsal interosseous.
● The medial terminal branch also supplies
the first dorsal interossei. The tibial component of mine supplies muscles of
the posterior compartment of the leg and provides cutaneous distribution to the entire sole of the foot.
