Repetitive Youth Pitching/UCL Laxity

Elasticity of the ulnar collateral ligament increases with repetitive pitching in baseball, according to a new study.

The researchers in “Ulnar Collateral Ligament Laxity After Repetitive Pitching: Associated Factors in High School Baseball Pitchers,” published online on April 8, 2021 in The American Journal of Sports Medicine, sought to understand the changes in the ulnar collateral ligament (UCL) and forearm flexor-pronator muscles (FPMs) during repetitive pitching.

“Medial elbow injury is common in baseball pitchers, with evidence of elbow valgus instability after only 60 consecutive pitches. However, the tissue-specific effects of repetitive pitching on medial elbow stabilizers are largely unknown,” they wrote.

Thirty high school baseball pitchers were included in the study (mean ±SD age, 16.6 ±0.5 years). Each player pitched 100 times which broke down to 5 blocks of 20 pitches.

The researchers measured the strain ratio which indicates elasticity in the UCL and FPMs using ultrasound before pitching and after every 20-pitch block.

They found that that the strain ratio of the UCL after pitches was less than before pitching (3.59 ±1.35 vs. 4.83 ±1.70; p = .013), but the same level of reduction was not seen for the FPMS (0.43 ±0.18 vs. 0.57 ±0.24; p = .07).

In addition, the ratio of the strain ratio in the UCL and FPMS before pitching (β= -0.385; p = .031) and the elbow flexion range of motion before pitching (β= -0.352; p = .046) were independently correlated with the change rate of the UCL.

“Elasticity significantly increased for the UCL, indicating laxity, but not for the FPMs after 100 pitches. Furthermore, the ratio of elasticity (UCL/FPMs) and the elbow flexion range of motion before pitching were significantly related to the change rate of UCL elasticity,” they wrote.

“To reduce laxity of the UCL, pitchers should be limited to less than 100 pitches per game. Sustaining a lower level of relative FPMs to UCL elasticity at rest and maintaining a large muscle volume to avoid excessive elbow flexion range of motion may prevent UCL laxity that develops during repetitive pitching.”