A study of bone metabolism and its abnormalities (Chapter 67: Diseases of Bones) should include a review of vitamin D metabolism (see Chapter 10: Nutritional Diseases) and the parathyroid glands (see Chapter 59: The Parathyroid Glands). Bone fractures are a common consequence of trauma. Bacterial infections and neoplasms of bone are discussed in Chapter 67: Diseases of Bones. Degenerative joint diseases, particularly osteoarthrosis (Chapter 68: Diseases of Joints & Connective Tissue), are a common cause of disability in elderly persons. Many inflammatory diseases of joints and connective tissue have their basis in immunologic hypersensitivity (see Chapter 8: Immunologic Injury). Neoplasms of connective tissue are considered in general here; many of the specific neoplasms have been discussed in other chapters, eg, vascular neoplasms in Chapter 20: The Blood Vessels and peripheral-nerve and skeletal-muscle neoplasms in Chapter 66: The Peripheral Nerves & Skeletal Muscle.