BCP crystals, or basic calcium phosphate crystals, are hydroxyapatite crystals that can accumulate in joint tissues and synovial fluid, often associated with conditions like osteoarthritis and periarthritis. Their presence is clinically significant as they can provoke inflammatory responses, leading to pain and joint dysfunction. A key association is with calcific tendinitis, where BCP crystals contribute to tendon inflammation and degeneration, complicating patient management.