The musculoskeletal system comprises bones, muscles, joints, ligaments, tendons, and bursae (see Introduction to Biology of the Musculoskeletal System). Any of these components can be injured or affected by a number of disorders.
Some disorders affect primarily the joints (such as osteoarthritis), causing arthritis. Other disorders affect primarily the bones (such as fractures, Paget disease of bone, and tumors) or muscles or other soft tissues (such as fibromyalgia and tendinitis).
Different diagnostic tests are available to diagnose musculoskeletal disorders (see Tests for Musculoskeletal Disorders), but the most important elements of diagnosis are the doctor's medical history and physical examination.
During a musculoskeletal evaluation, doctors ask people about musculoskeletal symptoms but also look for other symptoms, such as fever, chills, weight loss, rash, eye pain or redness, and symptoms of heart, lung, and gastrointestinal disorders. These other symptoms may be caused by or associated with various musculoskeletal disorders.
Pain is the most common symptom of musculoskeletal disorders. Doctors ask people to describe the character, location, and severity of the pain. They ask people to list factors that aggravate or relieve the pain and describe whether the pain is new or recurring. Doctors want to know whether the pain is worse when first moving a joint or after prolonged use and whether it is present upon waking or develops during the day. Doctors also ask people to describe what the pain feels like, for example, whether it is sharp or dull or whether it is aching or burning. They need to know whether people feel the pain deep in a joint or whether other musculoskeletal structures seem to be affected by it. Knowing the type and location of the pain can help doctors figure out the cause.
People who have musculoskeletal disorders often have stiffness of their joints (that is, people feel resistance when trying to move a joint). Doctors ask people to specifically describe their stiffness because people often use the word "stiffness" to describe weakness or extreme tiredness (fatigue), but, to doctors, "stiffness" means difficulty moving the joints. Doctors distinguish stiffness from a reluctance to move because of pain that occurs with movement.
Doctors also ask people to describe when they feel stiffness. In some joint disorders (such as rheumatoid arthritis and osteoarthritis), stiffness occurs after people first start to move after a period of rest or when awakening in the morning. Doctors also need to know where people feel stiffness and how long stiffness lasts. For example, in disorders that cause inflammation (such as rheumatoid arthritis), stiffness is prolonged (for example, longer than an hour), whereas in disorders that do not cause inflammation (such as osteoarthritis), stiffness is short-lived (for example, about 10 minutes) even though it may be severe and pain may persist.
Fatigue is another symptom doctors ask about. Fatigue is when a person feels a strong need to rest and has so little energy that starting and sustaining activity is difficult. It differs from weakness or an inability to move, and doctors evaluate people to distinguish it from sleepiness. Fatigue may mean people have a disorder that affects more than one system in the body and causes inflammation, or that there is a disorder disrupting normal sleep.
People may have joint instability (for example, wobbliness or buckling of a joint), which suggests weakness of the ligaments or other structures that stabilize the joint. Buckling occurs most often in the knee.
A doctor looks for certain things during a physical examination depending on what disorder or injury is suspected.
When evaluating bones, if a fracture is suspected, the doctor may notice that the affected part (such as an arm or a leg) is abnormally shaped, suggesting that the segments of bone are out of alignment.
A doctor may feel (palpate) the surfaces of the bones and joints to detect any tenderness, warmth, fluid in the joints, or abnormal shape, particularly if a fracture, a tumor, or a bone infection (osteomyelitis) is suspected. Compression fractures of the spine caused by osteoporosis and stress fractures may be very painful at first, but no abnormal shape may be detected. Abnormal bumps in bones occasionally indicate a tumor. If osteomyelitis is suspected, a doctor or nurse checks for a fever.
When a person complains of muscle weakness, the doctor feels muscles for bulk, tone (how relaxed the muscle is when it is not being used), strength, and tenderness. Muscles are also checked for twitches and involuntary movements, which may indicate a nerve disease rather than a muscle disease (see Motor Nerves). Doctors look for wasting away of muscle (atrophy), which can result from damage to the muscle or its nerves or from lack of use (disuse atrophy), as sometimes occurs with prolonged bed rest.
Doctors also look for muscle enlargement (hypertrophy), which normally results from activities or exercises that repeatedly stress the muscle, such as weight lifting. However, when a person is ill, hypertrophy may result from one muscle working harder to compensate for the weakness of another. Muscles can also enlarge when normal muscle tissue is replaced by abnormal tissue, which increases the size but not the strength of the muscle. Abnormal tissue can replace muscles in amyloidosis and in certain inherited muscle disorders, such as Duchenne muscular dystrophy.
Doctors try to establish which (if any) muscles are weak and how weak they are. The muscles can be tested systematically, usually beginning with the face and neck, then the arms, and finally the legs. Normally, a person should be able to hold the arms extended, palms up, for one minute without their sagging, turning, or shaking. Downward drift of the arm with palms turning inward is a sign of weakness. Strength is tested by pushing or pulling while the doctor pushes and pulls in the opposite direction. Strength is also tested by having the person perform certain maneuvers, such as walking on the heels and tiptoes or rising from a squatting position or getting up and down from a chair rapidly 10 times. The person is asked to look in all directions; if double vision develops, one or more eye muscles may be weak.
The doctor tests a person's active range of motion. The active range of motion is the maximum range through which people can move a joint by themselves. Limited active range of motion may indicate weakness, pain, or stiffness as well as mechanical abnormalities (such as scarring and swelling). The doctor then tests a person's passive range of motion. The passive range of motion is the maximum range through which the doctor can move the person's joint while the person is completely relaxed. The doctor also checks muscle tone by moving the limb passively. Resistance to passive movement (called passive resistance) may be decreased when the nerve leading to the muscle is damaged. Resistance to such movement may be increased when the spinal cord or brain is damaged.
If a person is weak, doctors also tap the person's muscle tendon with a rubber hammer to check reflexes. Reflexes may be slower than expected when the nerve leading to the muscle is damaged. Reflexes may be more rapid than expected when the spinal cord or brain is damaged.
Doctors note which joints or limbs are affected. Finding a pattern of affected joints and limbs can help doctors figure out the cause.
Doctors also examine affected joints in more detail. For example, they examine the joints to determine whether fluid is in the joint (called a joint effusion). They may test specific active or passive motions. They may pull or apply force to see whether the joint is stable.