Arthralgia is the name for pain afflicting the joints. Myalgia is the name for pain affecting the muscles. Arthralgia and myalgia both have Greek roots in name, with arthro- meaning joint, myo- meaning muscle, and –algos meaning pain. Both are also symptoms of other conditions, of which there are a great number that can result in joint or muscle pain.
Characterized by pain at a joint and often accompanied by tenderness, swelling, warmth, or stiffness, arthralgia can be caused by a multitude of diseases, injuries, or other ailments. Common in the synovial or movable joints like those in the shoulders, elbows, wrists, spine, knees, and ankles, arthralgia can be caused by chronic inflammatory conditions like osteoarthritis, rheumatoid arthritis, and bursitis. These involve a degeneration and/or inflammation of joint structures, namely the disks, the synovial membrane lining the joint, or the fluid-filled sac within the synovial membrane. Similarly, inflammatory repetitive-strain injuries like carpal tunnel syndrome and tennis elbow can cause joint pain and often are felt as both arthralgia and myalgia.
Acute injury to a joint is another cause of arthralgia and, often, arthralgia and myalgia. As joints contain ligaments connecting the articulating bones, ligament damage in the form of sprains, partial tears, or complete ruptures, can cause pain at a joint. A torn ACL in the knee is a common cause of knee joint pain, for example. Fractured bones can also lead to arthralgia, as bones absorb weight at joints and damaged bones cannot effectively perform this job.
Also, joint pain can be the result of a dislocation, in which a bone is pulled out of its joint, such as the humerus into the glenoid cavity of the scapula in the shoulder joint. Often the repair of such an injury leads to a greater degree of arthralgia than the injury itself. An example of this might be the inflammation resulting from pushing a dislocated humerus back into its socket.
Other causes of arthralgia include disease. These can include a wide range of ailments from Lyme disease to scleroderma to sarcoidoisis. As joints are made of bone, cartilage or other fibrous tissue cushioning the bones from one another, a sac containing synovial fluid enclosed within a membrane, and penetrating blood vessels to nourish the joint, many ailments that affect bones, connective tissue, and blood can lead to joint pain.
Many bodily systems are involved at a joint. For this reason, many conditions can create both arthralgia and myalgia as symptoms. One condition like this is fibromyalgia, a disease characterized by muscle pain, sensitivity to pressure, and joint stiffness among other symptoms.
Myalgia can also be caused by a range of ailments and injuries. Diseases resulting in myalgia include viruses like influenza, other infections like malaria, and chronic illnesses like lupus. Simple electrolyte imbalances are another cause of muscle pain. Chronic and acute muscle injuries are the most common causes of myalgia. These include overuse injuries like tendinitis, as well as those resulting from a blunt trauma like a hamstring pull or tear. Often these injuries lead to both arthralgia and myalgia as the tendons of damaged muscles place stress on the joints to which they attach.
