The Hook Test: Don’t Miss A Rupture of the Biceps Tendon at the Elbow!

Most of us are familiar with the biceps muscle, particularly those who are into weight training. Unfortunately, the lower end of the biceps at the elbow can rupture as a result of certain injuries. For most individuals, surgical repair of the torn biceps has the highest chance of restoring strength. Interestingly, ruptures of the biceps at the elbow are commonly missed, even by experienced physicians. This becomes a problem, since surgery performed late is more complicated and potentially less successful. There is a relatively simple and reliable test, called the “hook test”, used to diagnose distal biceps tendon ruptures. You can even test it on yourself!


The muscles in the front of the arm

There are two muscles in the front of the arm: the biceps and the brachialis. The brachialis is deeper and connects to the forearm through a flat tendon that attaches to the ulna, one of the two bones in the forearm. The biceps is more superficial. It is call bi-ceps (“two heads”) because it has two portions. One portion arises from the socket of the shoulder joint, whereas the other arises from a finger-like prominence of the shoulder blade called the coracoid. Both portions merge as they approach the elbow, and connect to the forearm through a single tendon: the distal biceps tendon. This cord-like tendon wraps around the other bone of the forearm, the radius, attaching to it.

How does the biceps tendon rupture?

Most of the times, the distal biceps tendon ruptures as a result of an injury. Often the injury is caused by a sudden extension of the elbow while the biceps muscle is contracting. Imagine you are carrying a heavy object with your arms, like a big box. If the box were to fall, and you tried stopping it from falling, the weight of the box will take your arm down while your biceps is still contracted, (trying to hold the heavy box). Typically, the tendon rips cleanly off the bone, and a tearing sensation may be felt. This results in pain and weakness, and sometimes the arm and forearm will turn black and blue. However, pain subsides in a few days, and the other muscles in the arm and forearm compensate to some extent for the biceps injury. The injured person may choose not to go to the doctor, thinking the arm was just strained. And as mentioned, even experienced doctors can miss this injury when they are not specifically looking for it.


The hook test

Do you want to feel your own biceps tendon? Place the palm of your hand in front of your face as if you were holding a cellphone to read its screen. Your elbow will be bent 90 degrees. Try to hook the index finger of the opposite hand behind a cord-like structure in the front of your elbow: that is your biceps tendon. You can actually pull on it with your hooked finger. If the biceps is ruptured, a finger cannot be hooked behind any structure, since the brachialis tendon is flat. Thus, if someone gets injured as described above, and there is no way to hook a finger behind a cord-like structure in the front of the elbow, you can bet that person just suffered a rupture of the distal biceps tendon. If hooking a finger behind the distal biceps tendon is painful, there may be a partial tear.

Other helpful tests

When the distal biceps is ruptured, other observations can be made. As mentioned before, the arm and forearm may have black and blue discoloration after the injury. If the injured person tries to make a muscle with both arms, the contour of the biceps on the injured side looks funny: the muscle belly is high and the lower part of the arm looks flat in the front. The distance between the skin crease in the front of the elbow and the lowest part of the muscle belly may be measured in finger breaths, and it will be longer on the side of the rupture. Strength in elbow bending may feel close to normal, however, weakness in turning the palm up (supination) is more evident. Radiographs are commonly obtained to rule out other injuries, but these tendon tears cannot be seen on x-rays. Magnetic resonance imaging (MRI) shows ruptures best, especially when the MRI is performed with the arm overhead (flexion-abduction-supination or FABS position).

Abnormal biceps tendon on the right side of a patient
Abnormal hook test
Normal hook test

What  happens next?

Without surgery, distal biceps tendon ruptures do not heal. Some individuals may adapt to it, but most find it bothersome: the arm cramps with repetitive use and especially with certain activities such as shaving, using a screw-driver, or turning a doorknob. Most elbow surgeons recommend surgical repair of the torn tendon, and the best results are typically obtained when surgery is performed soon after the injury. After surgery, a short period of protection is recommended, weight-training is initiated soon, and most people are allowed unrestricted activities at most by three months after surgery.

If you want to learn more about distal biceps tendon tears… Distal Biceps Tendon Injuries