Causes for joint and muscle pain
Bone pain is usually a deep, penetrating, boring, or dull pain. It commonly results from injury. Other causes of bone pain include infection and tumors. Muscle pain is often less intense than that of bone pain but can be very uncomfortable. For example, a muscle spasm or cramp (a sustained painful muscle contraction) in the calf is an intense pain that is known as a charley horse. Pain can occur when a muscle is injured as a result of an athletic injury, an autoimmune reaction, loss of blood flow to the muscle, infection, or involvement with a tumor. Almost all joint injuries and diseases produce a stiff, aching pain, often referred to as "arthritis" pain. However, because joint pain is so common, doctors usually base a specific diagnosis on the presence of other symptoms and results of laboratory tests. For example, Lyme disease is characterized by joint pain and a bull's eye skin rash; blood tests show antibodies to the bacteria that cause Lyme disease. Gout is characterized by a sudden attack of pain in the joint at the base of the big toe; blood tests generally show high levels of uric acid. A similar condition can occur in pseudogout which is due to crystals of calcium pyrophosphate. Sometimes pain can affect the tendons of the palm; this condition is called tenosynovitis or trigger finger. Inflammation causes swelling, warmth, redness, and tenderness, along with pain, and impairment of function. If a large part of the musculoskeletal system is inflamed, a low-grade fever may be present. Inflammation is a very common reaction of joints to a variety of abnormal circumstances, such as infection or autoimmune disease. Rheumatoid arthritis is one of many autoimmune diseases that cause joint inflammation. For joints, the swelling is often the result of fluid inside the joint. Loss of function occurs as a reduced range of motion. Sometimes, the area where the tendon meets the bone, the “enthesis” becomes inflamed in conditions such as psoriatic arthritis, Reiter’s disease, or ankylosing spondylitis. Muscle inflammation (myositis) can result from a number of diseases, including a viral infection. Like any inflammation, muscle inflammation can cause pain and tenderness, swelling, warmth, and impairment of function, occurring as muscle weakness. Weakness can occur when any part of the musculoskeletal system is abnormal. If the muscle itself cannot contract, weakness occurs. If a nerve does not adequately stimulate the muscle, the muscle contractions are weak. If a joint is frozen and unable to move normally, the muscle may not be adequately able to cause movement. Even pain, due to inflammation, prevents normal movement, causing weakness. Weakness may be limited to one joint or limb, as is typically the case when a nerve, joint, or single muscle is diseased, or diffuse, as occurs in widespread neurologic or muscular diseases. Muscle strength may also be limited by pain in the muscles, tendons, bones, or joints, giving the impression of weakness. Weakness is a common symptom of muscle injury or disease. Muscle weakness can also result from many diseases affecting the whole body. Although many people complain of muscle weakness when they feel tired or run down, true muscle weakness means that full effort does not generate normal strength. True muscle weakness can be caused by problems in the muscle itself; by problems in the nervous system, which helps to control movement such as following a stroke or after a spinal cord injury, or by disease affecting the connection between the nerve and the muscles, called the neuromuscular junction (such as myasthenia gravis). Muscle weakness can occur in old age because of an age-related reduction in muscle mass called sarcopenia. The word "asthenia" is sometimes used by doctors to describe weakness, but in the sense of feebleness or infirmity (debility) rather than simply muscle weakness.
Joint stiffness is common with arthritis. Disorders of joints often interfere with joint movement sufficiently to produce stiffness. A common example is the morning stiffness that occurs with rheumatoid arthritis, in which stiffness typically occurs on arising and gradually improves with activity only after an hour or two. This stiffness is also present during the day if one sits for too long. Some conditions, such as injuries that stretch or tear ligaments, may increase joint looseness (laxity), usually allowing excessive or abnormal bending of joints and thereby making the joints unstable. Joint looseness may occur in a connective tissue disease called cutis laxa. Joint crepitus or noises, such as creaks and clicks, are common in many people, but they can also occur with specific problems of the joints. For example, the base of the knee cap may creak when it is damaged by osteoarthritis, and the jaw may click in a person who has temporomandibular joint disorder. The range of motion in a joint may be reduced because it hurts to move the joint (such as when the joint is inflamed), because the joint itself has been damaged by disease, or because long-term lack of movement has allowed the joint to become fixed. For example, when a person's arm is paralyzed by a stroke, the joints in the shoulder and elbow may freeze in place if the arm is not regularly flexed and stretched.
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