Tunnel Syndromes

Compression-ischemic neuropathies include all cases of mononeuropathies, united by a common pathogenetic factor-local compression of the nerve. It is possible most often in those places where the primary trunk passes inside natural morphological formations in the form of openings, canals or tunnels (bone, muscle, fibrous), and also in situations where the nerve changes its course, making a sharp turn, either a ligament or a tight fibrous margin of the muscle.

Vegetative disorders in compression-ischemic lesions of the limbs are associated with a damaging effect not only due to mechanical traumatization of the nerve by surrounding tissues. Violations of the functions of the nerve are also largely due to ischemia of the nerve and venous stasis, developing swelling of the tissues. In this case, the ischemia factor may follow the primary compression of the tissues surrounding the nerve, as occurs in carpal tunnel syndrome. Another sequence is possible: ischemia acts as the initial link of the pathological process, then intrachannel edema develops, secondary compression of the nerve. There is also a third option, which simultaneously compresses the neural stem and the accompanying arterial vessel.

There are some types of tunneling compression-ischemic neuropathies, for which vegetative disturbances are most characteristic.

Neuropathies of the median nerve

Neuropathies of the median nerve are possible with lesion at three levels: in the distal part of the forearm, in the proximal part of it and in the lower third of the shoulder. Compression-ischemic lesion of the median nerve in the distal part of the forearm occurs in the carpal canal; in the proximal part of the forearm - its upper third (syndrome of the round pronator, the syndrome of Veinsart), the lesion occurs when the nerve is pinched by two bundles of a round pronator, usually after considerable muscle tension, for example in pianists (pronation with simultaneous flexor flexors). Clinical manifestations of the syndrome of the round pronator are composed of sensory and motor disorders.

Compression-ischemic neuropathy of the median nerve in the lower third of the shoulder occurs when the nerve is damaged in the canal formed by the medial intermuscular septum, the distal and anterior surface of the medial condyle, and the so-called Strasher ligament. Vegetative disorders in neuropathy of the median nerve are characterized by diversity and severity. The pains are acute, burning, sometimes occur as seizures and are accompanied by bright vasomotor disorders in the form of cyanosis, puffiness of the fingers and expressed subjective sensations of numbness and paresthesia.

Neuropathies of the ulnar nerve

Neuropathies of the ulnar nerve arise with compression in the distal part of the hand - ulnar tunnel carpal tunnel syndrome (Guyon bed syndrome) and in the proximal part at the elbow level (cubital tunnel syndrome).

Neuropathies of the radial nerve

Neuropathies of the radial nerve most often develop due to infringement of the nerve in the spiral canal at the levels of the middle third of the shoulder.

On the lower limbs, the following compression-ischemic neuropathies are distinguished: the external cutaneous nerve of the thigh (the parietal Ralma); of the common peroneal nerve (Guillain de Céza, Blondin-Walter syndrome); plantar nerves; interdigital nerves (Morton's metatarsalgia); the distal part of the tibial nerve (tarsal canal syndrome, Rishe canal syndrome).

Etiology and pathogenesis of tunnel syndromes. Tunnel neuropathies are congenital, genetically determined. However, more often the cause of compression of nerves is the acquired factors, which last for a long time or for a short time, general and local diseases, traumas and their consequences, occupational diseases. Significant importance in the etiology of compression neuropathies have endocrine displacements, as evidenced by their frequency in elderly women in the climacteric period, in pregnant women, in women with ovarian failure. Of decisive importance in this case is the weakening of the inhibitory effect of sex hormones on the secretion of the growth hormone of the pituitary gland, which in these situations is released in excess, stimulating the swelling and hyperplasia of the connective tissue, including inside the tunnel. Similar changes may result from the narrowing of the receptacles of the nerves observed in collagenosis due to the proliferation of connective tissue. This factor takes on special importance in the elderly, when there is a regular fibrosis of the muscles.

Among the local causes that affect the formation of compression-ischemic neuropathies are the effects of injuries to bones, muscles and tendons, overstrain of the musculoskeletal system, iatrogenic effects due to improper application of the hemostatic tourniquet, deaf plaster bandage, due to gross manipulations during the repositioning of bone fragments during osteosynthesis. A frequent reason can be repeated mechanical nerve trituration in the area most fixed by surrounding tissues.

The pathogenesis of compression-ischemic neuropathies is rather complicated. Nerve compression in tunnels is caused by pathological changes in the surrounding nerves of ligaments, tendons and their vagina, muscles, bones forming the corresponding canal: an increase in the volume of perineural tissues (mechanical phenomenon), increased intracanal pressure (physical phenomenon), impaired blood supply to the nerve (ischemia and impairment venous outflow), hyperfixation of the nerve in a certain section of the tunnel with restriction of its mobility along the long (compression-traction mechanism).

In all cases of peripheral neuropathies, the severity of autonomic disorders in the limbs depends on the amount of vegetative fibers in the peripheral nerve, with the compression of which the corresponding neuropathic syndrome is formed. The most vivid clinical picture is revealed with lesions of the median nerve on the arm and peroneal on the leg, which determines the richness of the vegetative accompaniment of the corresponding tunnel neuropathies.