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Nerve Damage and Classification
Nerves may be damaged by compression, stretching, thermal injury or chemical injury. In transient ischaemia, there is short-term low-level compression with no long-term effects. Axonal hypoxia may give rise to a prolonged conduction block. In situations where compression is more forceful, there may be both mechanical segmental demyelination and focal ischaemia. Seddon classified three different types of nerve injury as neurapraxia, axonotmesis and neurotmesis. Sunderland’s classiﬁcation comprises of five degrees of injury i.e. 1st, 2nd, 3rd, 4th, and 5th degree injury.
Nerve Recovery and Function Assessment
Clinical features of acute nerve injuries include vascular injury, signs of abnormal posture, changes in sensibility, and sudomotor changes. In chronic nerve injuries, skin may be smooth and shiny, diminished sensibility, median nerve palsy, postural deformities. For assessment of nerve recovery, the history and Tinel’s sign are important. If a muscle loses its nerve supply, the EMG will show denervation potentials by the third week. For assessment of nerve function, two-point discrimination is a measure of innervation density.
Principles of Treatment
Nerve exploration is indicated if the nerve was seen to be divided and needs to be repaired, if the type of injury suggests that the nerve has been severely damaged, and if recovery is inappropriately delayed and the diagnosis is in doubt. A clean cut nerve is sutured without further preparation. A ragged cut may need paring of the stumps with a sharp blade. The stumps are anatomically orientated and ﬁne sutures are inserted in the epineurium. Delayed repair may be indicated because a closed injury was left alone, the diagnosis was missed, or primary repair has failed. Free autogenous nerve grafts can be used to bridge gaps too large for direct suture.
Lower Limb Nerve Injuries
The plexus may be injured by massive pelvic trauma. These lesions are usually incomplete and often missed. The patient may complain of no more than patchy muscle weakness and some difﬁculty with micturition. The femoral nerve may be injured by a gunshot wound or by pressure. Clinically, the knee reﬂex is depressed. The common peroneal nerve is often damaged at the level of the ﬁbular neck by severe traction when the knee is forced into varus. The tibial nerve is rarely injured except in open wounds. The distal part is sometimes involved in injuries around the ankle.
Sciatic Nerve Injury
In sciatic nerve, traction lesions may occur with traumatic hip dislocations and with pelvic fractures. Intraneural haemorrhage in patients receiving anticoagulants is a rare cause of intense pain and partial loss of function. In a complete lesion the hamstrings and all muscles below the knee are paralysed; the ankle jerk is absent. Sensation is lost below the knee. The patient walks with a drop foot and a high-stepping gait to avoid dragging the insensitive foot on the ground. If sensory loss extends into the thigh and the gluteal muscles are weak, suspect an associated lumbosacral plexus injury.