A trigger finger, also known as stenosing tenosynovitis or trigger digit, is a condition where one of the fingers or the thumb gets stuck in a bent position and then suddenly straightens out with a snap, like a trigger being pulled and released. This condition is caused by inflammation or swelling of the tendon sheath, which surrounds the tendons that control the movement of the fingers.

Adhesive capsulitis, commonly known as frozen shoulder, is a condition that affects the shoulder joint, resulting in pain and progressive loss of motion. It is characterized by inflammation and thickening of the shoulder joint capsule, which leads to the formation of scar tissue in the joint.

Polymyositis is a rare autoimmune inflammatory myopathy characterized by chronic inflammation of skeletal muscles, leading to muscle weakness and fatigue. It is considered one of the idiopathic inflammatory myopathies, a group of disorders that involve the immune system attacking the body's own muscles.

The coronavirus disease 2019 (COVID-19) pandemic is resulting in a growing population of individuals recovering from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and accumulating observational data suggest that some of these patients may experience a wide range of symptoms after recovery from acute illness, referred to as "Long COVID" or "post-acute sequelae of SARS-CoV-2 infection". Some of these patients meet diagnostic criteria for fibromyalgia and/or chronic fatigue syndrome.