Kinesiology THURSDAY – Lacertus Fibrosis (The Other Carpal Tunnel)

Hand numbness and weakness are common symptoms attributed to carpal tunnel syndrome, a compression of the median nerve beneath the transverse carpal ligament at the wrist. Median nerve compression results in numbness, tingling and weakness of the first four digits of the hand, often limiting grip strength.

The lacertus fibrosis is a band of tissue extending from the bicep brachii tendon to the medial forearm fascia. It overlies the median nerve proximally at the elbow. Studies show it increases the lever arm of the biceps, improving strength of elbow flexion and supination. Resection of this band, often used in treating chronic compression of the median nerve at the elbow, may result in upwards of 50% reduction in supination and 28% reduction elbow flexion strength.

Here is an illustration of the normal median nerve anatomy as it traverses through the elbow.

Notice the pronator teres also underlies this structure.

I recently evaluated a patient diagnosed with golfer’s elbow (medial epicondylitis). He complained of medial elbow pain with gripping and resisted pronation. He also presented with a severe trigger point in the biceps brachii muscle belly.

Release of the trigger point resulted in immediate elimination of symptoms with manual muscle testing.

Why does this matter?

The lacertus fibrosis is a key connection of the biceps brachii to the medial elbow. It’s function serves to enhance bicep strength, so resection is not a favorable treatment (though the surgery has proven to eliminate pain in over 90% of cases).

As manual therapists, it is important to evaluate other causes of lacertus fibrosis tightening. This structure doesn’t just get tight due to age. Trigger points in the bicep brachii muscle belly may increase tension on this structure causing symptoms that mimic medial epicondylitis and carpal tunnel syndrome. Remember, trigger points set up in muscles that are chronically short. For instance, holding a cell phone (which we all do a lot) could be a cause of prolonged elbow flexion and increased biceps trigger points.

Next time you see a patient with medial elbow pain or numbness or weakness in the hand/wrist, think of the lacertus fibrosis and hunt for a trigger point in the biceps brachii. You just might save someone’s golf game and more importantly, prevent a surgery.

Because nobody has time to be in pain.

Until next time…