A 20-yr-old, left-handed, college baseball pitcher sustained an injury to his forearm while throwing a fastball during a game. On release of the ball, the pitcher noted difficulty gripping the ball and significant pain within the forearm. He was subsequently removed from the game and referred for evaluation. On physical examination, there was no swelling or ecchymosis but significant tenderness in or about the flexor bundle on the involved left limb. There were no deficits in sensation, reflexes, or strength, except for a noticeable weakness of the short- and long-finger flexors. In addition, the athlete demonstrated general weakness of his abdominal and hip musculature, with appreciable weakness of the shoulder external rotators on the left. Magnetic resonance imaging was ordered in light of the significant weakness and pain and to better prognosticate return to play. As noted within the rectangular box on the coronal, T2-weighted, spin-echo, magnetic resonance image of the left elbow (Fig. 1), edema is present within the muscle belly of the flexor digitorum profundus. This finding is consistent with a clinically significant strain of this muscle group.
The throwing athlete generates most of his throwing power through a complex sequence of muscle activation, which begins in the lower limbs and translates through the hips and trunk (core musculature) into the arm, with eventual release of energy through the fingers. The significant interrelationship of muscle activation and translation of forces within the system is referred to as the kinetic chain theory. We hypothesize that this injury occurred as a result of overload of the most distal musculature (flexor digitorum profundus) of the kinetic chain secondary to underlying core musculature weakness and improper throwing mechanics. The athlete had a gradual return of muscle strength in the flexor digitorum profundus, though he missed the remainder of the competitive season. Rehabilitation strategies included not only addressing local pain and weakness, but also a focus on conditioning the core musculature, rotator cuff, and a comprehensive evaluation of throwing motion.