We’re taught that there are three grades of muscle strains and three grades of ligament sprains. However, we commonly name only two grades of joint disorders – subluxations and dislocations. Robin McKenzie proposed that joints commonly get tweaked (a “joint derangement”), filling the void at grade 1. While joint derangements can create signs and symptoms ranging from mild to severe, by definition, they are resolved with repeated movement in a specific direction. I agree with his discoveries that these mechanical joint derangements make up the bulk of orthopedic disorders. For more explanation, please see my video: