This patient presents with knee pain, swelling, decreased range of motion, skin changes, and vasomotor changes after a recent injury consistent with complex regional pain syndrome (CRPS). This syndrome was previously known as reflex sympathetic dystrophy, algodystrophy, causalgia, Sudeck atrophy, transient osteoporosis, and acute atrophy of bone. Usually occurring after an injury, CRPS presents with pain out of proportion to the injury, temperature change, edema, and abnormal skin color. Type I CRPS (90% of CRPS cases) occurs without a definable nerve lesion, while type II occurs with a definable nerve lesion. The pathogenesis is likely due to an injury causing increased sensitivity to sympathetic nerves, an abnormal response to and sensation of pain, and increased neuropeptide release causing burning pain to light touch (allodynia).
Typically, CRPS occurs in 3 stages. Stage 1 includes burning pain, edema, and vasomotor changes in a limb after injury. Stage 2 includes progression of edema, skin thickening, and muscle wasting. Stage 3 is the most severe and includes limited range of motion and bone demineralization on x-ray. Diagnosis can be confirmed by either autonomic testing that measures increased resting sweat output or magnetic resonance imaging that looks for the above changes. The treatment for CRPS is regional sympathetic nerve block or intravenous regional anesthesia. This patient appears to have Stage 3 disease and would benefit from a local nerve block.