Two tendons run through a tunnel, or compartment, along the thumb-side of the wrist. These are the extensor pollicis brevis (EPB) and the abductor pollicis longus (APL).
Inflammation in these tendons is called de Quervain’s disease. It seems to occur most often when the two tendons are separated by a piece of tissue called a septum. This means each tendon has its own space, or compartment.
There isn’t a single treatment known to be effective in all cases of de Quervain’s. Sometimes a steroid injection into the tendon tunnel helps. However, the doctor must know if there is a separate space for each tendon when giving this injection. In other cases, surgery is to release the tissue between the tendons is needed.
Doctors think that the patients who have a separate compartment for each tendon do better with surgery. Finding a test that will show which patients have the septum would be helpful. A group of doctors tested for this by resisting thumb motion. First the thumb was kept from outward movement. Then resistance was given as the thumb moved straight out from the palm.
This test was counted as “positive” when the patient had more pain with the thumb straight out away from the hand. There was less or no pain with downward motion away from the palm. This test is called the EPB entrapment test.
Patients with a positive EPB entrapment test are more likely to have a septum within the tunnel than those with a negative result. Knowing about this extra compartment can help direct the doctor’s treatment. When the septum is present, it must be fully released to allow for pain-free thumb motion.