As for chronic compartment syndrome (the name may not be accurate, but that's by the by) there's various theories, but it isn't clear what the exact cause is. It is true that it requires an increase in the intracompartmental pressure to the degree where perfusion is compromised, resulting in pain. Initially compartment pressure exceeds venous pressure, inhiniting drainage and causing oedema. If the intracompartmental pressure continues to be high, eventually reduced areteriolar supply can give localised (but reversible) ischaemia and pain.