Pathophysiology of nerve compression syndromes: response of peripheral nerves to loading.

Nerve compression syndromes involve peripheral-nerve dysfunction that is due to localized interference of microvascular function and structural changes in the nerve or adjacent tissues. Although a well known example is compression of the median nerve at the wrist (carpal tunnel syndrome), other nerves, such as the ulnar nerve at the wrist or the elbow and the spinal nerve roots at the vertebral foramen, are vulnerable. This paper focuses on studies in which the physiological, pathophysiological, biochemical, and histological effects of biomechanical loading on the peripheral nerves were evaluated in humans and animals. When tissues are subjected to load or pressure, they deform and pressure gradients are formed, redistributing the compressed tissue toward areas of lower pressure. Nerve compression syndromes usually occur at sites where the nerve passes through a tight tunnel formed by stiff tissue boundaries. The resultant confined space limits movement of tissue and can lead to sustained tissue pressure gradients. Space-occupying structures or lesions (for example, lumbrical muscles, tumors, and cysts) can cause nerve compression injury, as can conditions associated with accumulation of fluid (for example, pregnancy, congestive heart failure, and muscle compartment syndromes) or accumulation of extracellular matrix (for example, acromegaly, myxedema hypothyroidism, and mucopolysaccharidosis)76. Although nerve injuries related to vibration occur near the region of exposure, the symptoms may be manifest at another site, where the nerve may be constricted. Other conditions, such as diabetes mellitus, may increase the likelihood that a compressed nerve will undergo a pathological response. In addition, there may be an inflammatory reaction that may impair the normal gliding of the nerve. Basic knowledge of the microanatomy of peripheral nerves and neurons and of their complex reactions to compression is essential to understanding, preventing, and treating nerve compression injuries. ### Microanatomy The neuron consists of the nerve cell body, located in the …