The acromioclavicular, or AC, joint is formed by the acromion process of a person's shoulder blade and the distal end of the collarbone. An injury to the AC joint may happen suddenly or may occur from repetitive movements such as lifting boxes over the head or throwing a baseball. An AC joint injury usually occurs along with an injury to a person's rotator cuff.
Types
AC joint injuries include sprains or separation, and arthritis. AC joint strains or separations are graded according to the degree of ligament damage. If a person suffers from a small amount of tearing to the ligaments around her AC joint, it is classified as a grade I injury while a complete tear of her ligaments is classified as a grade III injury, according to Sportsmed.org.
Features
A first-degree or grade I sprain of a person's AC joint elicits pain, tenderness and swelling over his affected joint. A person suffering from a second-degree or grade II sprain will complain of pain around his AC joint and the end of his clavicle may be elevated higher than his non-injured shoulder. If a person is suffering from a third-degree or grade III sprain, the ligaments holding his acromion and coracoids processes to his clavicle have been torn and the bones are completely separated, according to Sandra Shultz, Ph.D., and colleagues in the book "Examination of Musculoskeletal Injuries." Arthritis in a person's AC joint typically causes pain and swelling when the affected shoulder is in motion, such as during a bench press.
Effects
A person suffering from a first-degree AC joint sprain will not be able to raise her arm out to the side much beyond 120 degrees, according to Schultz. If she has a second-degree sprain, she will be unable to raise her arm above 90 degrees. If a person has a complete separation of her AC joint, she will be very unwilling to move her arm at all. The distal end of her collarbone will be obviously higher than her acromion process. Arthritis in a person's AC joint will limit her range of motion as her joint loses cartilage, becomes stiff and more difficult to move.
Prevention
AC joint injuries may be prevented if a person refrains from repetitive movements such as excessive bench pressing and shoulder pressing. A light warm up of the shoulders increases blood flow to a person's AC joint, improving his range of motion at his joints and therefore reducing his risk of AC joint injuries during sport and exercise.
Treatment
A person suffering from an AC joint injury should immediately immobilize her shoulder, apply an ice pack to the AC joint and take anti-inflammatory medicine to reduce pain and swelling, according to Sportsmed.org. If it is a complete separation, a person might consider surgery to repair her joint. Once pain and swelling are reduced and she has her doctor's permission, a person may do light stretching and strengthening exercises, gradually progressing the difficulty of each movement according to her comfort and pain level, according to Schultz.
References
- "Examination of Musculoskeletal Injuries"; Sandra Shultz, Ph.D., Peggy Houglum, Ph.D., and David Perrin, Ph.D.; 2005
- Sports Med: AC Joint Injuries
- MedlinePlus: Osteoarthritis
