Pitching places quite a bit of stress on the shoulder and elbow. While Tommy John surgery gets most of the attention from fans and media as far as elbow injuries go, the pitching motion can cause other injuries as well. In my latest Ask Dr. Geier column, I discuss one of these elbow injuries – flexor pronator injury.

Jack Zee in Bixby, Oklahoma writes:
My 21 year old son is a pitcher who has been diagnosed with a flexor carpi ulnaris muscle tear. What can we expect as far as treatment and return to pitching? He has rested two weeks and started to throw, but when he throws with any velocity, it still feels like it is pulling and aches. He has had Tommy John surgery, and there is no damage to the UCL.

Also read:
Ask Dr. Geier: Partial UCL injuries of the elbow
Ask Dr. Geier – Biceps tendon ruptures

Location of flexor pronator injury
The flexor pronator muscle are a source of medial elbow pain in throwing athletes. Note the location of the flexor pronator origin (orange arrow).

What is a flexor pronator injury?

Thanks for the question, Jack! The flexor carpi ulnaris (FCU) is one of a group of muscles that originate on the medial epicondyle. That is the bony prominence along the medial border of the elbow. This group of muscles is often called the flexor-pronators. They flex the wrist and pronate the forearm, or turn the forearm so that the palm faces down.

The FCU sits right over the ulnar collateral ligament (UCL), the ligament injured leading to Tommy John surgery. It and the other flexor muscles are thought to provide dynamic stability to the elbow against the repetitive valgus stress of the pitching motion. Fatigue of these muscles is believed to place more stress on the UCL and contribute to those injuries.

Mechanism of injury

The FCU and other flexor muscles or their tendon attachments to bone can be injured with a single traumatic event. The pitcher might feel a sharp pain after a single pitch. These injuries can also occur with repetitive stress to the arm. He might develop increasing pain along the medial side of the elbow while pitching, decreasing velocity or difficulty locating his pitches.

Also read:
Ask Dr. Geier – Tommy John injuries
Ask Dr. Geier – Shoulder Labral Tears

Treatment of a flexor pronator injury

Fortunately most flexor pronator injuries can be treated without surgery. A period of rest from throwing – anywhere from a few days to six weeks or more, depending on the extent of the injury – can help the muscle heal. Occasionally a pitcher will pull the tendon completely off the bone. In these cases, the orthopaedic surgeon might repair the tendon by reattaching it with sutures and/or anchors.

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