A strain occurs when a muscle is stretched or torn. A sprain occurs when a ligament is stretched or torn.

Strains are often the result of overuse or improper use of a muscle, while sprains typically occur when a joint is subjected to excessive force or unnatural movements (e.g., sudden twists, turns, or stops). Sprains can be categorized by degree of severity:

• A first-degree sprain stretches the ligament but does not tear it. Symptoms include mild pain with normal movement.
• A second-degree sprain is characterized by a partially torn ligament, significant pain and swelling, restricted movement, and mild to moderate joint instability
• In a third-degree sprain, the ligament is completely torn with mild to severe pain, swelling, and significant joint instability.

In the low back, nerves join to form the sciatic nerve, which runs down into the leg and controls the leg muscles. Sciatica is a condition that may cause radiating pain, numbness, tingling, and/or muscle weakness in the leg but originates from nerve root impingement in the lower back. Nerve impingement is most often caused by a herniated disk or spinal stenosis.

Stenosis refers to a narrowing of the spinal canal, usually in the lower back (lumbar) region. This narrowing is often a result of the normal degenerative aging process. It occurs as the disks of cartilage that separate the spine’s vertebrae lose water and the space between the vertebrae become smaller, causing friction between the bones. The loss of water in the disks makes them less flexible and unable to act as shock absorbers in the spine. Daily wear and tear on the spine becomes more significant without these shock absorbers.

As the disks degenerate, vertebrae may shift, causing the spinal canal to narrow. In some cases, the nerves that travel through the spinal column to the legs become squeezed. This can cause back and leg pain, and even leg weakness. Arthritis and falls also contribute to the narrowing of the spinal canal, compressing the nerves and nerve roots and causing pain and discomfort.

Degenerative disk disease is a general term applied to back pain that has lasted for more than three months. It is caused by degenerative changes in the intervertebral disks in the spine and can occur anywhere in the spine: low back (lumbar), mid-back (thoracic), or neck (cervical).

Under the age of 30, these disks are normally soft, and they act as cushions for the vertebrae. With age, the material in these lumbar disks becomes less flexible and the disks begin to erode, losing some of their height. As their thickness decreases, their ability to act as a cushion lessens. The less dense cushion now alters the position of the vertebrae and the ligaments that connect them. In some cases, the loss of density can even cause the vertebra to shift their positions. As the vertebrae shift and affect the other bones, the nerves can get caught or pinched and muscle spasms can occur.

Degenerative disk disease is primarily a result of the normal aging process, but it may also occur as a result of trauma, infection, or direct injury to the disk. Heredity and physical fitness may also play a part in the process.

The rotator cuff is a group of tendons and their related muscles that help keep the shoulder and upper arm bone securely placed in to the socket of the shoulder blade. The rotator cuff stabilizes the shoulder joint and helps you to raise and rotate your arms.

There are three stages of rotator cuff tears:

• A stage 1 tear is a partial tear less than 1 cm in size. It is accompanied by some pain following overhead arm movements, but range of motion is not limited.
• A stage 2 tear is a partial tear greater than 1 cm but less than 5 cm in length. Pain is common during and after overhead arm movements, as well as at night. It may be accompanied by a slight decrease in range of motion.
• A stage 3 tear is a full tear greater than 5 cm in size. Stiffness, weakness, and pain occur during and after overhead arm movements and during sleep. There may be a slight to severe decrease in range of motion in the shoulder.

Impingement syndrome is a common disorder of the shoulder that refers to an improper alignment of the bones and tissues in the upper arm. Inflammatory conditions such as tendinitis, bursitis, and arthritis are all closely related to impingement syndrome, as are tears to the rotator cuff tendons.

If the rotator cuff becomes inflamed from overuse or there is a bone deformity or spur on the end of the shoulder blade, then the space between the upper arm bone and tip of the shoulder blade is narrowed, causing the rotator cuff and its fluid-filled bursa to be squeezed or pinched. This impingement causes irritation and pain to the rotator cuff when the shoulder is raised.

Frozen shoulder (adhesive capsulitis) is a condition in which the tissues around the shoulder joint stiffen, scar tissue forms, and shoulder movements become difficult and painful. It can develop when you stop using the joint normally because of pain, other injury, or a chronic health condition, such as diabetes. Any shoulder problem can lead to frozen shoulder if you do not work to maintain its full range of motion.e

A shoulder separation (acromioclavicular joint injury) occurs when the outer end of the collarbone separates from the end of the shoulder blade because of torn ligaments. This injury occurs most often from a blow to the shoulder or a fall on a shoulder or outstretched hand or arm.

A shoulder dislocation (shoulder instability) occurs when the upper end of the arm bone pops out of the shoulder joint. This injury may be caused by a direct blow to the shoulder, a fall on an outstretched hand or arm, or an exaggerated overhead throwing motion.

Shin splints are an inflammation of the periosteum, a fibrous sheath that surrounds bone. In this case, the affected bone is the shin bone, or tibia. Shin splints are usually accompanied by pain and swelling in the front of the lower leg. Most frequent in runners, this overuse injury is caused by the repetitive stress of running on hard surfaces.

There are four ligaments in the knee: the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL). The ACL and PCL stabilize front-to-back knee movements, while the MCL and LCL stabilize side-to-side movements.

The ACL can be sprained or torn if the knee is straightened beyond its normal limits (hyperextended), twisted, or bent side-to-side. A sprained or torn ACL is common in sports and usually results from a hard stop or aggressive twisting of the knee. The PCL is the least common ligament to be injured.

The MCL is injured when a force is exerted on the outside of the knee, pushing it inward, while the LCL is injured by a force exerted on the inside of the knee that pushes it outward. This type of hit is frequent in contact sports like football or hockey.

A torn knee ligament is usually accompanied by feeling or hearing a pop in the knee at the time of injury, severe pain and swelling, and joint instability.

When muscles become inflamed, they can also spasm, or contract tightly, as a response to injury. While they are the body’s way of protecting itself from further injury, they often produce excruciating and often debilitating pain. Muscle spasms are common in the low back (lumbar) muscles.

The medial and lateral menisci (plural of meniscus) of the knee are two crescent moon-shaped disks of tough tissue that lie between the ends of the upper leg bone and lower leg bone that form the knee joint. Meniscus tears commonly occur during sports when the knee is twisted while the foot is planted firmly on the ground. In people over the age of 40 whose menisci are worn down, a tar might occur with normal movement, minimal activity, or minor injury.

Tendinitis is inflammation of a tendon, a band of tissue that connects muscle to bone. It is most commonly the result of overuse during physical activities. Repetitive motions can stretch and irritate the tendon, causing pain and swelling. Tendinitis occurs around joints such as the elbow, shoulder, wrist, ankle, or knee.

Bursitis is inflammation of a bursa or bursae (more than one bursa), small fluid-filled sacs that cushion areas of friction around joints. Bursae contain synovial fluid that lubricates the joints. Bursitis typically occurs as a result of overuse during physical activities or infection of the synovial fluid. If a bursa becomes infected or irritated from repetitive stress, it will cause pain and limited movement. Bursitis is most common in the shoulder, knee, hip, elbow, or heel.

The most common form of arthritis, osteoarthritis, can affect any joint in the body, but most often afflicts the knees, hips, and fingers. Most people will develop osteoarthritis from the normal wear and tear on the joints through the years. Joints contain cartilage, a rubbery material that cushions the ends of bones and facilitates movement. Over time, or if the joint has been injured, the cartilage wears away and the bones of the joint start rubbing together. As bones rub together, bone spurs may form and the joint becomes stiff after long periods of activity or inactivity.

A stress fracture is a microscopic crack in a bone that occurs from overuse. Muscles normally absorb the shock of physical activities, but when they become too fatigued to do so, they transfer the stress to the bones which results in a hairline-sized fracture.

Stress fractures usually develop in the weightbearing bones of the feet and lower legs, often after a rapid increase in the duration or intensity of exercise or from wearing improper or worn out athletic shoes.

Carpal tunnel syndrome is the term used to describe a specific group of symptoms (tingling, numbness, weakness, or pain) in the fingers or hand and occasionally in the lower arm and elbow. These symptoms occur when there is pressure on a nerve (median nerve) within the wrist (carpal tunnel). Carpal tunnel syndrome develops over time because of repetitive hand motions that damage muscle and bone in the wrist area.

Lateral epicondylitis, commonly known as tennis elbow, is inflammation of the tendon that connects the muscles of the forearm, wrist, and hand to the upper arm at the elbow. The tendon on the bony outside (lateral) part of the elbow (the epicondyle) is most often irritated by overuse during physical activity.

Plantar fasciitis is the most common cause of heel pain. It is commonly referred to as a heel spur, although a heel spur, or bony growth on the heel bone, develops as a result of plantar fasciitis. The condition occurs when the long, flat ligament on the bottom of the foot (plantar fascia) stretches irregularly and develops small tears that cause the ligament to become inflamed. This inflammation is most often caused by walking with an abnormal inward twisting of the foot, called pronation. Over time, this slightly abnormal step may increase tension on the plantar fascia and cause it to become inflamed.

The Achilles tendon is the largest tendon in the body. It connects the muscles in the lower leg (calf) to the heel bone. With every movement of the foot, the Achilles tendon stretches and tightens. Because it is under so much stress, it can partially or completely tear (rupture) from excess force or overuse. Ruptures usually occur about two inches above where the tendon attaches to the heel bone.

An Achilles tendon rupture is most common in middle-aged “weekend warriors” who are not conditioned for athletics and who neglect to properly warm up and stretch prior to exercise. Ruptures frequently occur from sudden movements that stress the calf muscles, such as jumping or quick stops; from overstretching; from vigorous exercise after a long period of inactivity; or from untreated Achilles tendinitis/tendinosis (overuse).

The spinal vertebrae are separated by flexible disks of shock absorbing cartilage. These disks are made of a supple outer layer with a soft jelly-like core (nucleus). If a disk is compressed, so that part of it intrudes into the spinal canal but the outer layer has not been ruptured, it may be referred to as a “bulging” disk. This condition may or may not be painful and is extremely common.

Herniated disks are often referred to as “slipped” or “ruptured” disks. When a disk herniates, the tissue located in the center (nucleus) of the disk is forced outward. Although the disk does not actually “slip,” strong pressure on the disk may force a fragment of the nucleus to rupture the outer layer of the disk.

If the disk fragment does not interfere with the spinal nerves, the injury is usually not painful. If the disk fragment moves into the spinal canal and presses against one or more of the spinal nerves, it can cause nerve impingement and pain.

If the injured disk is in the low back, it may produce pain, numbness, or weakness in the lower back, leg, or foot. If the injured disk is in the neck, it may produce pain, numbness, or weakness in the shoulder, arm, or hand.

Radiculopathy refers to a condition in which the spinal nerve roots are irritated or compressed. Many people refer to it as having a “pinched nerve.” Lumbar nerve impingement indicates that the nerve roots in the lower spine are involved, while cervical radiculopathy is associated with nerve roots in the neck. Nerve impingement is most often caused by a herniated disk or spinal stenosis.