The Biomechanics of Pitcher's Elbow

Despite everything we know about and are developing in the area of sports medicine – not to mention the enormous financial investment that the Major League Baseball teams have in their pitchers – the elbow injuries for the horsehair hurlers continue to be on the rise. What is known about the actual variables that cause “pitcher's elbow?”

The nexus of the ailment is in the ulnar collateral ligament (UCL or internal lateral ligament), a thick triangular band at the medial aspect of your elbow. It consists of two portions, an inner and outer section joined by a thinner middle section.

Elbow varus is the name given to the force that pushes a pitcher’s forearm and hand toward the medial side of the elbow when he releases a baseball. The rotational expression of that force is known as varus torque.

Now that those terms are defined, you can appreciate a recent study from the Hospital for Special Surgery that set out to find the relationship between elbow varus torque and the variables of arm speed, arm slot, and shoulder rotation. The study examined 81 professional major or minor league pitchers who took 81,999 throws while wearing a Motus baseball sleeve, designed to track and analyze in-game biomechanical data.

Previous studies had been done only under laboratory conditions. This research evaluated a combination of baseball throws in real settings such as structured long tosses and live game play. It was the largest analysis of throwing biomechanics to date.

"Obtaining this comprehensive, individualized analysis of on-field throwing activity was made possible by technological advancements that give us the ability to accurately measure body motions outside the lab," said Joshua Dines, MD, sports medicine surgeon at HSS and primary investigator. "Capturing data during the pitchers’ normal activities provided us with robust, baseline biomechanical performance metrics."

The study found that arm slot, arm speed and shoulder rotation all have a significant relationship with elbow varus torque. There was a 1 nanometer increase in elbow varus torque associated with a 13 degree decrease in arm slot, 116 percent increase in arm speed and 8 degree increase in shoulder rotation.

Increased arm speed and shoulder rotation were found to be associated with increased elbow stress as well as decreased arm slot. Height and weight were also positively correlated with elbow varus torque.

"Now that we know these modifiable risk factors, we have a foundation to develop evidence-based rehabilitation programs. Additionally, these findings can be utilized to prevent injury and help to identify potential pitchers at risk," said David Altchek, MD, sports medicine surgeon at HSS.

The research was presented at the 2017 nnual meeting for The American Academy of Orthopedic Surgeons.