Non-neutral joint positions + external load

Very important to keep this in mind when performing tasks at work or exercises that require non-neutral joint positions for extended periods of time:

Excerpts taken from an excellent review paper entitled: Pathophysiology of Nerve Compression Syndromes: Response of Peripheral Nerves to Loading.

“The findings that non-neutral joint positions and external load (for example, during pinch grip) can affect extraneural pressure, combined with the findings from the animal studies, can guide our understanding of the pathogenesis of nerve entrapment related to loading. On the basis of the animal studies, it appears that if elevated extraneural pressures are maintained for an adequate duration the initial injury, remodeling, and repair mechanisms, which are constantly ongoing, may be overwhelmed, leading to persistent extraneural or intraneural edema and eventually to synovial or intraneural fibrosis and loss of nerve function. However, the precise characteristics of this critical time-pressure threshold remain to be determined.”

“Edema was visible in the subperineurial space within four hours in all compression subgroups, and it persisted for the entire duration of the study. Inflammation and fibrin deposits occurred within hours after compression, followed by proliferation of endoneurial fibroblasts and capillary endothelial cells. Vigorous proliferation of fibrous tissue was noted within days, and marked fibrosis and sheets of fibrous tissue were seen extending to adjacent structures at twenty-eight days. Endoneurial invasion of mast cells and macrophages was noted, especially at twenty-eight days. Axonal degeneration was noted in the nerves subjected to 10.7 kilopascals of compression and, to a lesser extent, in those subjected to 4.0 kilopascals of compression. It rarely was seen in the nerves subjected to 1.3 kilopascals of compression. Axonal degeneration was associated with the degree of endoneurial edema. Demyelination and Schwann-cell necrosis at seven and ten days was followed by remyelination at fourteen and twenty-eight days. Demyelination was prominent in the nerves subjected to 4.0 kilopascals of compression and, to a lesser extent, in those subjected to1.3 kilopascals of compression. The sham intervention in which the cuff was applied but not inflated also led to demyelination in regions close to the surface of the cuff; this was thought to be due to the tense but uninflated rubber cuff pressing on the nerve. The sham operation in which no cuff was applied did not cause any lesions. This study62 and another16 demonstrated that relatively brief periods of extraneural compression result in very long-lasting subperineurial edema, which later is accompanied by degeneration and regeneration of nerve fibers and initiation of the permanent changes of the laying down of fibrous tissue. Again, there was a dose-response relationship between the amount of pressure and the severity of the effects”