PATHOLOGICAL PROCESSES FOLLOWINGS INJURY OF THE

PERIPHERAL NERVOUS SYSTEM

Prepared ByAhmed Shawky Ali

contents INJURY TO THE NERVOUS SYSTEM Sites of injury Kind of injury Intraneural and extraneural

pathology PATHOLOGICAL PROCESSES Vascular factors in injury Mechanical factors in nerve injury

INJURY TO THE NERVOUS SYSTEM

A definition of adverse neural tension is abnormal physiologIcal and mechanical responses produced from nervous System structures when their normal range of movement and stretch capabilities are tested’.

The term adverse neural tension’ includes both movement and tension.

Sites of injury

I. Soft tissue, osseous or fibro-osseous tunnels. The median nerve in the carpal tunnel, spinal nerve in the intervertebral foramen

2. Where the nervous system branches. This is particularly so if the branch leaves the main trunk at an abrupt angle.

Sites of injury 3. Where the system is relatively

fixed. Examples of this are, the common peroneal nerve at the head of the fibula, the dura mater at the L4 vertebral segment), the attachment of the radial nerve to the head of the radius and the suprascapular nerve in the scapular notch. Neurovascular bundles such as in the popliteal fossa, may also fix the nervous system to some degree.

Sites of injury 4. in close proximity to unyielding

interfaces. The cords of the brachial plexus passing over the first rib, the radial nerve in the radial groove of the humerus

Sites of injury 5. Tension points such as the T6

vertebral level and the tibial nerve at the posterior aspect of the knee seem anatomically and clinically vulnerable in adverse tension disorders.

Sites of injury Some areas of the nervous system

have many vulnerable features. For example, the tibial nerve posterior to the medial malleollus is in the posterior tarsal tunnel and branches into the lateral and medial plantar nerves while within the tunnel.

Sites of injury Areas where the nervous system has

previously been traumatised appear to be susceptible to further trauma and irritation.

Sites of injury Clinically, it appears that a patient can

carry a subclinical injury for years. Symptoms from the old injury site may be activated by re-injury or trauma which mechanically sensitises the old injury sites

Kind of injury The most common nerve traumas

encountered by physiotherapists are the mechanical and physiological consequences of friction, compression, stretch and occasionally disease.

Kind of injury Nerve anomalies, or anomalies of

interfacing tissues, are likely to predispose the system to injury.

The clinical presentation of a nervous

system injury will differ depending on whether the injury is acute or chronic.

Kind of injury With the development of a chronic

injury, such as an entrapment syndrome, the system has time to allow at least some adaptive measures such that conduction may only be minimally affected.

Kind of injury With an acute injury, such as

compression of the radial nerve in ‘Saturday night palsy’ or an epidural haematoma, the consequences may be more severe due to the sudden alternation in blood and axoplasm flow together with the sudden mechanical deformation of nerve fibers

Intraneural and extraneural pathology Pathological processes that lead to

adverse tension syndromes and positive tension tests can be classified as extraneural , intraneural or both.

Physiotherapists are encouraged to ascertain not only the site of the disorder, but also the kind and extent of the pathological process at that site.

Intra neural pathology Intra neural pathology involves the

consequences of injury involving any of the structures of the nervous system. Intraneural pathology can be considered in two ways. The first is as affecting the conducting tissues such as demyelination, neuroma formation or hypoxic nerve fibers. The other is pathology affecting the connective tissues such as scarred epineurium, arachnoiditis or irritated dura mater.

Extraneural pathology Extraneural pathology involves the nerve bed or the mechanical interface. Blood in a nerve bed or epidural space, epineurium pathologically tethered to an

interface, dura pathologically adhered to the posierior

longitudinal ligament, and swelling of bone and muscle adjacent to a nerve

trunk are examples. The narrow spinal canal is a commonly

encountered extraneural situation which may lead to an adverse tension syndrome.

Both extraneural and intraneural processes often occur together. However, identification of the predominant process will direct treatment.

Extraneural and intraneural pathology can be linked to the movement adaptive mechanisms of the nervous system. If the location of a pathology is extraneural, it will probably affect the gross movement of the nervous system in relation to its mechanical interface. With an intraneural pathology, while the system may be free to move, the elasticity of the nervous system will be affected.

A broad link can now be made between neurobiomechanics and neuropathology

The clinical consequences from both extra- neural and intraneural processes can be broadly considered as either pathophysiological (i.e., symptoms) or pathomechanical (i.c., loss of range of movement and elasticity).

Pathophysiology, if not attended to, can lead to pathomechanics.

There will be overlap in that it is unlikely a pathomechanical situation can exist without pathophysiology.

Both situations can affect neurobiomechanics and both are treatable by appropriate movement.

the term adverse mechanical tension in the nervous system’ (Breig 1978, Butler 1989, Butler & Gifford 1989) is not entirely correct. It belittles the physiological mechanisms occurring with nerve injury. In this text, ‘adverse tension’ or ‘tension’ could refer to either pathophysiology, pathomechanics or both.

PATHOLOGICAL PROCESSES Two major factors in the development

of nervous system pathology can be identified: vascular factors and mechanical factors.

PATHOLOGICAL PROCESSES There is disagreement about which

factor predominates, especially in the early stages of nerve compression. The current view is that vascular factors predominate (Sunderland 1978, Lundborg 1988) Mackinnon & Dellon 1988).

In man;’ Situations both factors may co-exist.

PATHOLOGICAL PROCESSES In the more minor injuries, vascular

factors related to altered pressures in tissues and fluids around nerve are probably more important (Powell & Myers 1986, Lundborg 1988, Lundborg & Dahlin 1989).

Vascular factors in injury Nerve fibres are dependent on an

uninterrupted supply of blood for normal function

Vascular factors in injury The requirement for nerve nutrition is

that blood must flow into the tunnel, the nerve fiber and then out of the tunnel again. A pressure gradient must therefore be maintained

Vascular factors in injury Sunderlànd (1976) details three distinct

stages that may occur with persistent tunnel pressure hypoxia, oedema and fibrosis

With venous stasis and consequent hypoxia, nerve fibre nutrition is impaired. Neuro-ischaemia is a likely source of pain and other symptoms such as paraesthesia.

Vascular factors in injury With continuing hypoxia, damage to

capillary endothelium follows and results in leakage of protein rich oedema. Mechanical pressure could also injure the capillaries (Rydevik et a! 1981).

An abnormal impulse generating mechanism may be set up

Vascular factors in injury Clinical signs and symptoms may be more

evident if immature axons or a neuroma are caught in the scar.

One possible consequence of a segment of scarred nerve is that sites of nerve friction could develop elsewhere along the tract, most likely at vulnerable tunnel sites.

SunderLand (1978) considers that a ‘friction fibrosis’ may be more painful and damaging than the original lesion.

Vascular factors in injury Nerve traction injury (Nobel 1966,

Meals 1977) can damage blood vessels associated with that nerve.

Vasoconstriction could also be induced by irritation of the sympathetic trunk. The perineunum and epineurium are sympathetically innervated (Lundborg 1970, Selander cc al 1985).

Vascular factors in injury Uninterrupted CSF flow is a necessary

condition to minimise subarachnoid scarring and spinal cord compression post injury (Oiwa 1983).

Altered blood supply to the spinal cord, in association with chondro-osseus spurs and a narrow spinal canal, is considered a significant component in the development of cervical spondyliotic myelopathy (Robinson et at 1977).

Functional loss began at approximately 40 mmHg with motor and sensory responses, completely blocked at 50 mmHg. Functional loss in the hypertensive group began at 60 mmHg. In normotensive and hypertensive subjects the tissue pressure threshold was consistently 30 mmHg below diastolic blood pressure. The night pain of nerve entrapments may be due to blood pressure being lower at night.

Mechanical factors in nerve injury

The nervous system can be damaged via physical force and both the connective and neural tissues are at risk. Studies by Haftek (1970) and Sunderland (1978) have found that the connective tissues of peripheral nerve require large forces before they rupture.

such studies are of little use when considering the more minor traumas encountered clinically by physiothcrapists.

Mechanical factors in nerve injury

The epineurium is not difficult tissue to injure, and it is a particularly reactive tissue. Slight trauma) such as mild compression or friction may result in an epineural oedema (Triano & Luttges 1982, Rydevik er al 1984).

(Lundborg 1970). Epineurial tears are common in injuries such as ankle sprains Nitz et al 1985).

Mechanical factors in nerve injury most nerve fiber injury occurred at the

edge of the tourniquet where the shearing forces were the greatest. On analysis, the myelin sheath was found to be stretched on one side of the node of Ranvier and invaginated on the other side with the displacement towards uncompressed parts of the nerve. (Fowler & Ochoa 1975, Ochoa 1980) (Fig. 3.5).

Mechanical factors in nerve injury All tissues of the body are under some

pressure. In a structure such as the nervous system, Uniform pressure is not damaging. Hence, a deep sea diver can work safely at pressures which would cause injuries, such as myelin slippage and nodal distortion if they were applied locally to a segment of nerve (Gilliat 1981).

Mechanical factors in nerve injury Mechanical stresses could also

cause nerve damage by rupture of intraneural and extraneural blood vessels.

With injury, both mechanical and vascular factors are likely to occur.

Mechanical factors in nerve injury Overstretch of axons during

movement seems likely only if there is a co-existing pathological state such as a stenotic ridge of bone in the canal or the cord is pathologically tethered.

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