Chapter 49: Disorders of Musculoskeletal Function: Developmental and Metabolic Disorders, Activity Intolerance, and Fatigue

Developmental disorders such as torsional deformities, pes planus, and juvenile osteochondroses represent structural variations that emerge during skeletal growth and maturation. Conditions including Legg-Calvé-Perthes disease and slipped capital femoral epiphysis disrupt the normal ossification process at the hip joint, potentially leading to long-term functional impairment if not managed appropriately. Genetic skeletal dysplasias such as osteogenesis imperfecta compromise bone integrity through defective collagen synthesis, while developmental dysplasia of the hip reflects abnormal acetabular and femoral head formation during fetal development. The chapter provides extensive coverage of osteoporosis, a metabolic bone disease characterized by decreased bone mineral density and microarchitectural deterioration. The pathophysiology of osteoporosis centers on dysregulation of the receptor activator of nuclear factor kappa-B ligand and osteoprotegerin system, which governs osteoclast activation and bone resorption. Pharmacological interventions including bisphosphonates and parathyroid hormone analogs work through distinct mechanisms to enhance bone formation or suppress resorption. Idiopathic scoliosis represents a progressive three-dimensional spinal deformity of unknown etiology that predominantly affects adolescents and requires monitoring for cardiopulmonary compromise. The chapter concludes by examining chronic fatigue syndrome as a multisystem condition with emerging evidence implicating dysregulated inflammatory and immune signaling pathways in its pathogenesis. Understanding these disorders enables healthcare providers to implement timely interventions, optimize functional outcomes, and educate patients about disease trajectory and management strategies.