Musculoskeletal Overview (38 CFR 4.71a)

The musculoskeletal system is the largest system in the body. About 25% of body weight is attributed to connective tissue and bony structures, and about 50% of the body weight is attributed to muscle mass. The musculoskeletal system is closely related to the neurologic and vascular systems, and there is an interdependent relationship with the rest of the body systems. This system includes bones, joints, muscles, tendons, ligaments and bursae. The functions of the musculoskeletal system include: protection; support; locomotion; mineral storage; production and development of blood cells; and heat production. The bony structure and skeleton protect vital organs, e.g., brain, lungs and heart. The strong framework supports body structures, and body movement is made possible by muscles attached to the skeleton. Minerals are deposited and stored in bones, and the marrow in bones is responsible for the production of red and white blood cells. When muscles contract heat is produced in addition to mechanical actions.

The range of movement of a joint is termed, range of motion (ROM). Common movements performed by muscles and joints are described below:

• Flexion/Extension-"Flexion decreases the angle between two adjacent body structures; extension increases the angle."

• Abduction/Adduction-"Abduction is movement of a part away from the midline, either of the body or of the hand or foot. Adduction is movement toward the midline (toward the anatomical position)."

• Lateral/Medial Rotation-"Medial rotation means torsion of the distal bone so that a point on the lateral aspect of the distal bone is moved anteriorly or medially toward the body midline. Lateral rotation is the opposite".

• Circumduction-"A combination of flexion, abduction, extension, and adduction." (C&P Training Letter 00-05 on Muscle Injuries and Related Problems; July, 2000)

The 206 bones comprising the skeleton are categorized as follows: long bones (e.g., the thigh bone); short bones (e.g., the ankle); flat bones (e.g., the sternum); and small bones (e.g. the vertebrae). Bones are covered by a membrane called periosteum which serves in the nutrition and growth of bone, and provides for the attachment of tendons and ligaments. Nerves, blood vessels, and lymphatics are contained in the periosteum. When two or more bones are joined together, joints are formed which provide for movement of the body. The joint capsule is lubricated and protected from pressure by a membrane called the synovium. Ligaments and muscle tendons passing over a joint provide stability of the joint. Types of joints include: ball and socket (e.g., hips and shoulders); hinge (e.g., elbows and knees); condyloid (e.g., wrists); saddle (e.g., thumbs); pivot (e.g., radius and ulna); and gliding (e.g., the carpals). Associated with some joints are bursae. These structures are located at points of friction, and are filled with synovial fluid. Bursae serve as cushioning structures in movement of tendons, ligaments, and bones at the elbow, shoulder, knee, and at other joints.