Compartment syndrome is a painful, potentially dangerous build-up of pressure within a compartment of the body defined by connective tissue — the “sausage wrapping” around a muscle or group of muscles. This usually occurs in the lower legs as a reaction to injury. When it’s acute, it’s dangerous — never ignore steadily escalating lower leg pain, especially if the leg seems swollen.
A milder, chronic form often afflicts runners. It’s one of the main causes of stubborn shin pain, for instance. And that’s a basic description of a seemingly simple, “mechanical” disorder. But nothing is simple in musculoskeletal medicine …
There are problems with common assumptions made about compartment syndrome, mainly that pressure is the problem. In 2014, Franklyn-Miller et al argued persuasively in the British Journal of Sports Medicine that excessive compartment pressure does not seem likely to be involved:
To date, no conclusive evidence exists to demonstrate cellular hypoxic damage or decreased capillary perfusion.… no evidence of a direct association between this rise in compartment pressure and the pain and reduced muscle function.
In fact, it’s not even clear that we can measure pressure in the muscle compartment in the first place. There are some concerns with a classic paper on the topic, and “there is clear evidence that intracompartmental pressure measurement should no longer be considered a valid diagnostic tool for compartment syndrome.”
It’s possible that only acute compartment syndrome actually exists — the only condition that involves excessive pressure — and the chronic version is just something else altogether. It may have been misunderstood and mislabelled all along.
So, if not pressure, then what?
Franklyn-Miller et al propose a muscle overuse syndrome caused by poor running form (exaggerated heel strike):
Muscle overuse syndromes are not new. They are well described in the literature, significantly in musicians and office workers (occupational overuse syndrome) and there is a clear synergy with the predisposing factors in repetitive exercise: increasing frequency and the intensity or load of work and practice; and, altered limb biomechanics alongside limited rehabilitative intervention. We believe that in patients with exertional leg pain related to the myofascial compartments we are simply observing a phenomenon seen commonly in other patient groups; that of muscle overload. As the aetiology in these patients is biomechanical we have described their condition as a ‘biomechanical overload syndrome’ (BOS).
So their opinion is that what’s really going on is basically just painfully exhausted, irritated muscles.
This post is an adapted excerpt from a major update my shin splints book. In the book, I go into greater depth about compartment syndrome and the implications of Franklyn-Miller et al.