Multiple sources are confirming what essentially amounts to a worst-case scenario for Joel Zumaya. His MRI this morning revealed a torn UCL, which means the only alternative for Zumaya is Tommy John surgery. Best case scenario at this point: He can start throwing sometime next summer.
The ulnar collateral ligament can become stretched, frayed or torn through the stress of repetitive throwing motions. If the force on the soft tissues is greater than the tensile strength of the structure, then tiny tears of the ligament can develop. Months (and even years) of throwing hard cause a process of microtears, degeneration, and finally, rupture of the ligament. The dominant arm is affected most often. Eventually the weakened tendon my rupture completely causing a pop and immediate pain. The athlete may report the injury occurred during a single throw, but the reality is usually that the ligament simply finally became weakened to the point that it finally ruptured.
Zumaya has suffered so many setbacks in his career, and this moment has to be particularly heartbreaking. One could hope that this kind of surgery might allow him to come back in a couple of years and throw with an arm that is finally ready and strong enough to hold up under the pressures and torque required of a pitcher. But right now, after as many issues as he's had, it's hard to say anything with much certainty.
We feel for you, Joel. Good luck.