Chapter 50: Disorders of Musculoskeletal Function: Rheumatic Disorders

Osteoarthritis represents the degenerative category, characterized by progressive cartilage breakdown and bone remodeling that produces clinical manifestations including joint swelling, audible crepitus during movement, and structural deformities such as varus alignment. The chapter then transitions to systemic autoimmune rheumatic diseases, establishing diagnostic and classification criteria for conditions like Rheumatoid Arthritis and Systemic Lupus Erythematosus. Rheumatoid Arthritis involves chronic joint inflammation driven by autoimmune mechanisms, while Systemic Lupus Erythematosus represents a multisystem autoimmune condition with diverse clinical presentations affecting multiple organ systems. Additional inflammatory conditions receive detailed analysis, including Polymyalgia Rheumatica, which presents with constitutional symptoms such as fever and generalized malaise alongside pronounced muscular stiffness and pain, particularly affecting proximal muscle groups. The chapter also covers Idiopathic Inflammatory Myopathies, a group of conditions characterized by primary muscle inflammation and dysfunction; this category includes Polymyositis, affecting skeletal muscles with inflammatory infiltration, and Dermatomyositis, which combines muscle inflammation with characteristic dermatological manifestations. Throughout the chapter, the distinction between mechanical joint degeneration and immune-mediated inflammatory processes is emphasized as fundamental to understanding disease pathogenesis, clinical presentation, and treatment approaches. The various conditions are contextualized within broader frameworks of autoimmune dysfunction, tissue damage mechanisms, and systemic versus localized disease manifestations.