Orthopedics 101 - The Bare Bones by L. Matthew Jones, M.D. Sports medicine physician and board certified orthopedic surgeon Until their late teens, athletes are vulnerable to injury because the skeletal and muscular systems are not fully developed. A basic understanding of the musculoskeletal system may help you understand common sports injuries. Your brain sends signals along nerves to a muscle, telling it to contract. This pulls the bone to create movement. Your skeleton consists of over 600 muscles. Gradual increase in frequency and intensity of exercise works the muscles to make them bigger and more powerful. Adolescent hormones are needed for large muscle development. Warm ups get blood flowing to muscles and ligaments to make them more flexible to prevent injury, and improve the athlete's reaction time.

A muscle stretched when it is not warmed up, overstretched from excessive force, or not rested, can tear. Bleeding and swelling may be noticed. This is strain, commonly called a pulled muscle. Muscles of the neck, back, thigh or calf are commonly strained. Muscle cramps are painful, involuntary contraction, and usually caused by dehydration.

Your skeleton has 206 bones. Bone growth occurs at the ends of the bone, the growth plates. These are not calcified until growth ceases, so they're susceptible to injury, and the bone may not grow properly. About 90% of bone growth is complete by age 18, and bone loss begins about age 30. The young person that includes 1500 mg of calcium in the diet and avoids carbonated beverages builds bone density and helps prevent osteoporosis in the later years. Growing bones are more flexible in childhood, but too much force causes a fracture - a crack, a chip, or a complete break in the bone. About 50% of children sustain a fracture, usually of a finger, forearm, collar bone, foot or elbow. When the skin is broken, a fracture is open and often needs surgery soon to decrease the incidence of infection. The bone has blood vessels and nerves, so it bleeds and hurts when broken. An ice pack reduces pain because it constricts blood vessels to decrease bleeding, swelling and inflammation. Also, ice causes the nerves to send a cold signal instead of a pain signal.

Each muscle is connected to the bone by a strong cord-like tissue called tendons. The largest tendon is the Achilles' tendon above the heel. When tendons are overused, you have tendinitis. During rapid growth, the bones grow faster than the muscles and tendons, so these tight muscles must lengthen to keep up with bone growth. Tighter muscles pull on the tendons that attach to the bone. Gentle stretching can decrease the pain.

Bones are held together by strong tissue bands called ligaments. They limit the range of motion of the bones. A ligament stretched beyond its limit is a sprain. A torn ligament causes the joint to be loose. Ankle sprains are common.

Bones are linked together at flexible joints. Bones slip out of a joint in a dislocation. The ends of each bone are cushioned by pads of smooth rubbery cartilage. As sections of cartilage are worn away, the bone ends rub against each other, and create the pain of osteoarthritis. Common joints affected are the ones that bear weight - the hips, knees and spine. A slippery synovial membrane produces fluid to lubricate the joint.

• Stretch and warm up before playing.
• Wear proper protective equipment.
• Gradually increase physical activity.
• Use proper technique, such as throwing the ball correctly.
• Stretch and cool down after playing.