Chapter 49: Disorders of Musculoskeletal Function – Metabolic Disorders

The core focus of this chapter is the spectrum of disorders affecting bone structure, growth, and metabolic function, concluding with an analysis of activity intolerance and fatigue. Skeletal growth and remodeling, initiated during embryonic development and continuing through childhood via the epiphyseal growth plate, are susceptible to alterations resulting in developmental deformities. Common growth-related issues covered include torsional deformities, such as toeing-in (metatarsus adductus) and internal femoral torsion, as well as angular alignment problems like genu varum (bowlegs) and genu valgum (knock-knees). More severe congenital conditions detailed are Osteogenesis Imperfecta (OI), a hereditary disorder defined by defective type I collagen synthesis leading to extreme skeletal fragility, Developmental Dysplasia of the Hip (DDH), which encompasses unstable or dislocated hips, and congenital clubfoot (talipes). The chapter also examines juvenile conditions affecting growth centers, such as the osteonecrotic Legg–Calvé–Perthes disease (affecting the proximal femoral epiphysis) and Osgood–Schlatter disease (involving microfractures at the tibial tubercle), along with Slipped Capital Femoral Epiphysis (SCFE) and various forms of scoliosis (idiopathic, congenital, neuromuscular). Moving into metabolic pathology, the text defines osteopenia as a general reduction in bone mass, often preceding osteoporosis, the most prevalent metabolic bone disease, characterized by porous bone structure due to bone resorption exceeding formation. The pathogenesis of osteoporosis is heavily influenced by hormonal factors, particularly estrogen deficiency in postmenopausal women, mediated through the RANKL/OPG system. In contrast, osteomalacia (in adults) and rickets (in children) involve inadequate mineralization of the bone matrix, typically caused by deficiencies in Vitamin D, calcium, or phosphate. Paget disease (osteitis deformans) presents a distinct pathology marked by localized, excessive, and disorganized bone turnover, which can lead to complications like cardiovascular disease. Finally, the chapter differentiates between acute fatigue (rapid onset, often relieved by rest) and chronic fatigue, which is frequently associated with complex illnesses like cancer or heart failure. A specific, complex condition explored is Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), defined by debilitating, persistent fatigue and characteristic postexertional malaise, requiring clinical evaluation based on established criteria from the Centers for Disease Control and Prevention (CDC).