Acute Musculoskeletal DI

Although they have similar blood supply, joints, and musculo-tendinous attachments, it is noteworthy that 'bends' pain only appears to affect long bones of the appendicular skeleton - not the axial skeleton. Adult long bones contain a fatty marrow cavity that could be a reservoir for inert gas and predispose to DI. Axial bones largely contain haemopoietic tissue which appears to be unaffected by decompression.

Another interesting feature of 'bends' pain is that it is influenced by premorbid hyperbaric activity. In a review of more than 19,000 cases, Sowden found that bounce divers and pilots primarily developed shoulder pain, whereas saturation divers and caisson workers developed knee pain 103. There are many theories but little evidence to explain this phenomenon.

There are four theories for bubble-related pain in bones and joints. They involve stretching of nerve endings or inflammation occurring (1) within joints; (2) around the joints, such as within tendons and muscle; (3) within bone, due to gas expansion within fatty marrow, the medullary cavity and bone sinusoids (a phenomenon also associated with cancer-pain), and; (4) as a result of referred pain, either due to an injury to the nerves or nerve roots associated with the joint, or due to a generalized release of inflammatory modulators with flu-like symptoms and poliarthralgia.

Intra- and periarticular pain associated with decompression can usually be localized and is of a non serious nature. There is a trend towards treating these conservatively although they respond well and promptly to recompression. Referred pain is part of the neurological spectrum of DI that has been considered elsewhere. What remains, is medullary pain.

The discovery of sinusoid innervation has led to the concept of a venous congestive mechanism for cancer and osteoarthritic bone pain 104,105. This sinusoid congestion pain theory is also attractive as an explanation for 'bends' pain as it addresses several clinical phenomena: (1) the deep, poorly localized, boring pain; (2) relief achieved by the local application of pressure (e.g., a BP cuff); and (3) a gravity-related distribution of manifestations in the various patient subgroups.

Although there is no scientific association between medullary pain and dysbaric osteonecrosis, it is usually viewed as a more serious form of musculoskeletal DI and recompression is recommended.

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