Computing Muscle, Ligament, and Osseous Contributions to the Elbow Varus Moment During Baseball Pitching

Abstract

Baseball pitching imposes a dangerous valgus load on the elbow that puts the joint at severe risk for injury. The goal of this study was to develop a musculoskeletal modeling approach to enable evaluation of muscle-tendon contributions to mitigating elbow injury risk in pitching. We implemented a forward dynamic simulation framework that used a scaled biomechanical model to reproduce a pitching motion recorded from a high school pitcher. The medial elbow muscles generated substantial, protective, varus elbow moments in our simulations. For our subject, the triceps generated large varus moments at the time of peak valgus loading; varus moments generated by the flexor digitorum superficialis were larger, but occurred later in the motion. Increasing muscle-tendon force output, either by augmenting parameters associated with strength and power or by increasing activation levels, decreased the load on the ulnar collateral ligament. Published methods have not previously quantified the biomechanics of elbow muscles during pitching. This simulation study represents a critical advancement in the study of baseball pitching and highlights the utility of simulation techniques in the study of this difficult problem.

Mechanical misconceptions: Have we lost the “mechanics” in “sports biomechanics”?

“…By interpreting a net joint force as a joint contact force, one may greatly underestimate the loads experienced by tissues at/within the joint, since forces from muscles and other internal tissues are not included (Figure 1). For instance, the net joint force on the elbow is about 1-1.5 body weights during baseball pitching (e.g., Fleisig et al [21,22]), whereas the elbow joint contact force peaks between 4-7 body weights [23]. Similarly, during squatting, net joint force calculated from inverse dynamics on the knee is about 1-1.5 body weights [24,25], whereas the joint contact force is much larger, about 2-3.5 body weights [25].…”

Mechanical Misconceptions: Have we lost the "mechanics" in "sports biomechanics"?

“…For instance, the net joint force on the elbow is about 1-1.5 body weights during baseball pitching (e.g., [21,22]), whereas the elbow joint contact force peaks between 4-7 body weights [23]. Similarly, during squatting, net joint force on the knee is about 1-1.5 body weights [24,25], whereas the joint contact force is much larger, about 2-3.5 body weights [25].…”

Valgus stability is enhanced by flexor digitorum superficialis muscle contraction of the index and middle fingers

“…Anatomical studies indicate that the FPMs lie in a good position to protect the UCL [6,8]. Biomechanical studies report that the flexor digitorum superficialis (FDS) muscle plays the greatest role among the FPMs as an active stabilizer against valgus stress [10,11,13,16]. Ultrasonographic (US) studies report that the FDS has significant effects on medial joint distance (MJD) through grip contraction [14,17].…”