Acromioclavicular joint (ACJ) arthritis is a common source of shoulder pain. Manifestations of the arthritis may include inferiorly projecting spurs that predispose an individual to impingement and rotator cuff tears and can result in permanent impairment due to shoulder weakness or motion loss. Rotator cuff tendinopathy generally is multifactorial, and tears usually result from a combination of intrinsic factors (loads transmitted, local blood supply, and age) and extrinsic factors (impingement, primarily). Surgery to eliminate impingement collectively is termed subacromial decompression. The AMA Guides to the Evaluation of Permanent Impairment provides no impairment rating for cheilectomy about acromioclavicular or other joints, and, because removal of this liability is beneficial, it results in no (and perhaps even negative) impairment. An individual whose job involves repetitive shoulder elevation and who develops impingement probably has a legitimate workers’ compensation claim, even if predisposed by preexisting bony prominences; in this scenario, the proximate cause was repetitive shoulder elevation. A case example demonstrates that if an individual with preexisting osteoarthritis of the ACJ is injured and disabled at work, the rotator cuff tear, although preexisting, was worsened during employment and probably will be covered under the claim. In legal terms, findings of disability associated with ACJ injuries may differ depending on the jurisdiction.