Shearwave elastography : a prospective study on short term changes in UCL health of college baseball pitchers

The rate of ulnar collateral ligament (UCL) reconstruction surgery, or "Tommy John" surgery, has risen dramatically in baseball pitchers over the last decade. Throughout the baseball pitching motion, the UCL undergoes tremendous tensile stress, placing it at increased risk of injury in overhand throwing athletes. Because of these demands placed on the medial elbow, morphological adaptations have been shown to occur in the throwing arm of baseball pitchers such as increased UCL cross-sectional area and increased joint laxity. It is currently unknown if the material properties of the tissue are changing as well. Ultrasound shearwave elastography (SWE) is a relatively new tool for the quantitative evaluation of the material properties of connective tissue in vivo. It has been recently used to assess differences in ligament stiffness in patients exhibiting symptoms of frozen shoulder, as well as achilles tendon stiffness while recovering from surgery. The hypothesis of this thesis is that UCL stiffness increases after a pitching bout and returns to baseline throughout the following days. The purpose of this study is to observe the material properties of the UCL after a pitching bout and evaluate change in stiffness compared to baseline. 6 collegiate baseball pitchers between the ages 18-25 participated in this study. SWE measurements were collected the day prior (Baseline), and the 4 days following the pitching bout (Days 1-4). Ulnohumeral joint space was measured in both supported and stressed conditions, the difference between the two representing joint laxity. Participants also completed the Kerlan-Jobe Orthopedic Clinic Overhead Athlete questionnaire as a measure of self-reported arm health. No significant changes in stiffness were observed within the study timeframe. Mean stiffness increased by 30.7kPa (12.8% of Baseline) after the pitching bout (Day 1), and 5 of the 6 participants experienced an increase in stiffness. One participant exhibited a severe drop in stiffness (63.4kPa; 29.5% of baseline), who also reported the lowest cumulative KJOC score of the participant pool (indicating increased risk of injury). The removal of this outlier increases the effect size of the change in stiffness between Day 1 and Day 4 from small (ES = 0.37) to moderate (ES = 0.56). No significant changes in the joint space were observed. This prospective study suggests ultrasound SWE may have practical application as a biomarker of UCL health. The direction of the change in UCL stiffness may be related to the current health status of the tissue. Limitations included a small sample size, varying pitch counts and types among participants, and a wide range of pitcher skill level and arm health. Although more research is needed, this thesis provides insight into the material property changes of the ligament during the 4 days following pitching