Medial Elbow Joint Space Decreases with Forearm Flexor Contraction – Implications for Elbow Joint Stability & Ulnar Collateral Ligament Injury

Research Team Members: Brett Pexa (PhD Student in Human Movement Science), Dr. Eric Ryan and Dr. Joseph Myers

elbow valgusWhy did you do this study?

Ulnar collateral ligament (UCL) tears, or commonly called ‘Tommy John’ is the tearing of the ligament on the medial portion, or inside, of the elbow. This injury is becoming more common in baseball players, and happening in younger and younger athletes. The ulnar collateral ligament is commonly injured during baseball participation due to the high loads and repetitive stress it experiences during throwing. Baseball pitching exerts a tremendous amount of force on the ulnar collateral ligament and the entire medial elbow. The forces during baseball pitching are up to three times higher than what the ulnar collateral ligament can withstand before tearing. The muscles in the forearm contract to help absorb this force, and previous research in cadaveric and computer models support this hypothesis. The use of diagnostic ultrasound is a quick and reliable way to image living tissue, we are able to look at the medial elbow joint in living tissue to assess how finger and forearm flexor activity can assist in protecting the medial elbow joint.

What did you do and what did you find in this study?

Pexa1

Ultrasound image of medial elbow. Dotted line represents the medial elbow joint space, which was the main measure in this study. (ME = medial epicondyle; TR = trochlea; ST = sublime tubercle; UCL = ulnar collateral ligament)

We measured the medial elbow under 3 different loading conditions: unloaded, loaded, and loaded-contracted. For the unloaded condition, the elbow was at rest. For the loaded condition, we added a cuff weight to the wrist to create stress on the medial elbow joint that mimics baseball pitching. Finally, for the loaded-contracted condition, we added a cuff weight and had the participants grip against a handgrip dynamometer. Our main outcome measure was medial elbow joint space, and this variable was the distance between the humerus (upper arm bone) and the ulna (lower arm bone). The ultrasound machine was placed in a specific location over the medial elbow and 4 specific structures were identified: The medial epicondyle, the ulnar collateral ligament, the trochlea of the humerus, and the sublime tubercle of the ulna (Figure below). Once all 4 of the structures were identified, an image was captured on our ultrasound machine. During the loaded-contracted condition, we made sure all 4 structures were present and the participant was maximally contracting against the grip dynamometer in their hand. The distance from the trochlea to the sublime tubercle was then measured and assessed across conditions. We found that the medial elbow joint space during the loaded condition was larger than the unloaded condition, and the joint space was smaller in the loaded-contracted condition than the loaded condition. This confirmed our hypothesis that the medial elbow joint does assist in absorbing force from the UCL to protect it and prevent it from tearing.

Pexa2

Elbow joint space across 3 loading conditions. The loaded-contracted condition was significantly lower than the loaded condition, indicating that the forearm muscles decrease the medial elbow joint space and subsequently the amount of stress on the medial elbow.

How do these findings impact the public?

These findings help stress how the forearm flexor muscles helps protect the ulnar collateral ligament. With UCL injuries on the rise in professional baseball and happening to younger athletes, rehabilitation and training regimens should address strength of this muscle group. Exercises that address grip strength, wrist strength, and even elbow strength should be added in preseason programs. High function of this muscle group is imperative to health of the UCL and medial elbow joint in baseball pitchers. Future research will investigate how fatigue of this muscle group affects its protective capability of the UCL.

 

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