Flexor carpi ulnaris (FCU) tendonitis



 Flexor carpi Ulnaris (FCU) is a common injury that causes ulnar sided wrist pain.  

This muscle is the primary flexor of the wrist, making wrist curls possible.  It is a major flexor and responsible for a large part of grip. In electrical studies of the wrist, the Flexor Carpi Ulnaris is very active throughout the day. It is likely the most active wrist muscle.  

People develop FCU tendonitis for a variety of reasons.  You can better understand the cause by “where” on the tendon it is injured.
• IF at the insertion (where the muscle attaches to the bone at the wrist) the cause is usually positional and load. 
• IF at the muscle-tendon juncture-(1/3 proximal to the wrist) it is usually repetitive.
• IF at the origin, at the elbow, it is likely a combination of both repetition and force. 

The flexor carpi ulna originates at the elbow and inserts at the palm side of the wrist, right at the base of the pinky in the wrist.  It anchors over and onto the pisiform. It is a relatively large tendon at the wrist compared to the others.   

This structure is on the underside of the forearm/wrist, while the ECU (extensor carpi ulnaris) is on the top side of the ulna. 

Take a look at Dr. Ebraheim's super quick anatomy presentation: 

   The FCU muscle is fairly easy to palpate and identify. 

Photo from: Paintotopia


People with FCU tendonitis often complain of slightly different sensations than a TFCC tear.
• deep ACHE
• pain with weight-bearing
• pain with rotational load
• pain to touch at the palmar ulnar side of the wrist. 

There is an important distinction between FCU and TFCC injuries: people with FCU tendonitis do not have a loss of weight-bearing tolerance.  When they perform the weight-bearing test, they are 90% of normal. Sharp pain does not limit their load, an ache does.  They also get a delayed ache 1-2 hours after the load test is performed. This is an important detail.  


The FCU rarely shows pathology on MRIs or Xrays, although I often suspect that the edema seen in the TFCC region is FCU swelling. 


Pain can be created when the wrist is supinated (palm up), hand in a fist,  and deviated towards the ulna. In addition to ulnar sided pain, the pain can radiate into your forearm.  FCU pain can indicate that there are trigger points to be massaged and released.  


 Common activities that cause pain or result in trigger points in the FCU include:

  • Scissor use (barbers, hairstylists, seamstresses)
  • Tennis
  • Rock/boulder climbing
  • Swimming



If there is no change in your weight-bearing test results with and without the WristWidget, then the TFCC is not involved. TFCC injuries will ALWAYS respond with a higher test result when the WristWidget is worn. 

Because the FCU is a dominant and strong flexor of the wrist, the treatment can be frustrating.   It is difficult to turn this muscle off so it can rest. When a splint or cast is applied to the wrist, we have learned that the FCU activity increases often against the resistance of the cast, making matters worse.  

Eastern medicine
The FCU in Chinese medicine is along the heart meridian.  This is of great interest to me. When patients are seen by an acupuncturist of Chinese training, they are often given minerals, hydration and herbs to calm the heart.  I have long recommended high dosages of magnesium, sodium, potassium, and calcium along with hydration to help the FCU tendonitis. Interestingly this is quite effective.   One could study the minerals with a simple annual CBC. With the increase of heat globally and the incidence of this in the athlete, minerals should be analyzed. We have a very informative Instagram LIVE session about Magnesium deficiencies.  You can find a topic index for episode 15 here:  https://www.wristwidget.com/blogs/blog-archive/wristwidget-live-topics-of-conversation 

The FCU also responds well to ice.  Icing the insertion of the FCU is helpful.  2 minutes of direct ice five times daily. This cools the wrist. 

It is valuable to go to a physician or occupational therapist twice weekly for 3 weeks to work on deep tissue massage, ultrasound, dry needling,  electrical stimulation.  

Strengthening is not recommended until the pain is gone in the am, no pain to touch, no pain with the composite stretch of the wrist and elbow, and the patient is symptom-free.  

There is rarely a loss of grip strength in patients with FCU tendonitis. 

Cortisone injections are extremely helpful.  I recommend one injection combined with 10 days of rest, then progressive stretching on day 14 only.  It is important not to load the wrist during the 10 days after the injection.  

Kinesiotaping is helpful. Here is a video demonstrating the technique. 

The FCU is often confused with a TFCC injury.  They are nearly the same except for a few distinguishing details.  If you have any questions, reach out. We’re here for you!



PS!  Wendy has Instagram LIVE segments devoted to FCU issues

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