A majority of patients have one question on their minds: Where the "heck" is that pain coming from? A red, painful swollen knee may hurt deep, on the side, in the middle, in the back, or just plain everywhere. A shoulder may hurt with the arm up, down or to the side. Although the question of "where" may seem simple enough, sometimes sorting out the exact location of the pain generator is an inexact science. Within the structure of a joint there exist three general areas of interest: the passive structures, the active structures and the nerves. Dissecting out the source of the pain involves the close examination of each of these areas. Once the location of the pain is found, the hope is that treatment can be directed, focused and effective.
By definition, a joint is where two bones join together to create a hinge joint, a ball-and-socket joint, a saddle joint, or one of the other types of joints found in the human body. Because the bones are not actively doing anything, just providing a hard, skeletal frame, the bones are considered passive structures. Binding the bones together is usually a system of ligaments that attach from one bone to the next. These anchoring ties are fixed in terms of length and location; thus, ligaments are considered passive structures of a joint. The protective joint cartilage that covers the bone is also considered passive.
All of these passive joint structures can become injured and become a source of pain. Deciphering whether or not a passive component is a source of pain and where exactly the pain is coming from may require special imaging or diagnostic injections. But before getting fancy, the first clues should come from a physical exam. Restricted and/or painful passive range of motion is the biggest indicator that a flaw in the passive structures may be cause of the pain. Range of motion must be tested passively, with no effort by the patient, in order to test the passive structures. Testing passive range of motion is then followed by testing the active structures with active range of motion.
The active structures are the muscles which are actively involved in joint movement, joint protection and joint stability. A pain in a joint might be solely related to sore muscles. The primary way to determine if a muscle is sore is to test its functional strength with active range of motion, resisted movement and manual muscle testing.
For example, a patient can try to bend the elbow while the doctor puts a downward, opposing force against the forearm. This maneuver would be testing the elbow flexing muscle, primarily the biceps muscle. If resisted active muscle contraction is painful, then the muscle is a source of pain, in this case the bicep muscle. Actively testing each muscle group that surrounds a painful joint is critical for determining where the pain is coming from.
Once both the active and passive structures of a joint are tested, then the nervous system should be tested as well. Measuring sensation like pinprick, light touch and vibration is important because sensation helps the joint to function properly. Additionally, testing nervous system sensitivity is also important (but rarely done) by examining neural tension signs, the most popular being the "straight-leg raise test." Many other neural tension signs exist but are not widely practiced or known, like the "slump test" or the "upper limb neurotension signs." More doctors need to become familiar with these tests because the nervous system can be a major source of joint pain.
Joint pain is often misdiagnosed as tendonitis, like some cases of "tennis elbow tendonitis," when in fact the nerves, not the tendons, are the source of pain. A skilled, thorough clinician should be able to know when the nervous system is the pain generator based on a good history and examination.
But even the best doctors can be baffled because all is not "black and white" when it comes to pain. Sometimes the entire joint (active, passive and nerves), is the source of pain. Such would be the case in a major joint injury like a crush injury. In these cases of major trauma, it would be nearly impossible to pinpoint one exact source of pain. In other complicated structures like the spine, many potential problems may exist and finding the exact pain generator may be a needle-in-a-haystack proposition. In such a case, the patient and doctor have to be comfortable with a bit of uncertainty. In these occasions, the question of "where is the pain" may not be as important as the question of "where is the pain relief going to come from?" But, that is a question for another day.
As for today's question of where that joint pain coming from, the answer is literally at the finger tips of a doctor who will take the time to examine a joint thoroughly.