Are Japanese Pitchers at Greater Risk of Injury?

This past week it was announced that Rangers’ pitcher Yu Darvish will require Tommy John Surgery to repair a tear in his UCL and will miss all of 2015. It is a major blow to the Rangers and to the entire league as Darvish is another addition to the list of star pitchers who have undergone the operation. Prior to the 2012 season, Darvish was posted by his Japanese league team and made his way to the MLB after signing a record-breaking deal. Masahiro Tanaka, the most recent major Japanese star to make the transition over to the league, has also been in the news due to elbow issues. Tanaka missed a large chunk of his rookie season due to a partially torn UCL and many people think it is a matter of time before he needs Tommy John. The fact that the most recent big Japanese imports have both had elbow problems made me wonder if there could be a trend that exists with these imports.

There are currenty seven Japanese-born pitchers on MLB rosters, with Hiroki Kuroda returning to Japan for 2015 and Daisuke Matsuzaka doing the same. Among the seven pitching in the MLB this upcoming season, the pending Darvish surgery means that four of the seven will have had Tommy John. That does not include Matsuzaka who also previously had the operation. Additionally, by adding Tanaka’s partially torn UCL and the fact that Koji Uehara has previously landed on the DL with an elbow sprain, a common precusor to Tommy John, six of the seven pitchers have had previous elbow issues. Although the sample size is extremely small, the fact that so many of these Japanese arms have had these issues is alarming. The question that follows is whether we can find something in these pitchers that might be the reason for the increased prevalence of injury.

The first thought that came to mind was the widely reported fact that Japanese pitchers often throw a lot more innings at a young age than pitchers who grow up in American systems. As an 18-year-old in Japan, Tanaka threw over 180 innings — significantly more than the average 18-year-old in the minors or college would do. Additionally, over his last five seasons in Japan, Tanaka averaged more pitches per start than Justin Verlander, the MLB leader in that time. Looking at the others who have made the jump to MLB, however, that type of workload is not common. Darvish and Iwakuma had seasons above 200 innings pitched prior to coming over, but only Tanaka did it at such a young age. The issue with pitch counts and innings, however, might not be at the professional level, but at the high school level. Marathon pitching performances are common at the high school level and the pitchers often gain fame as a result of their efforts. As this article discusses, many young Japanese talents will throw well over 100 pitches in a game and return the next day and throw over 100 again. Daisuke Matsuzaka reportedly threw 250 pitches over 17 innings in one day as an amateur. Japanese coaches argue that if mechanics are correct, throwing that many pitches does not put the player at greater risk. Yet these Japanese pitchers are breaking down more frequently than the typical MLB pitcher, and this could be a result of the incredible amount of stress put on their arms as young players.

My next assumption was that there were some similarities in their pitch mixes that could signal a type of pitch that increases the risk of Tommy John. Looking at the PITCHf/x data for all seven of the active players, there is no pitch that each of them throws frequently enough to call it a cause of their elbow issues. I thought going in that the splitter would be a potential cause, but only Uehara, Iwakuma, and Tanaka have thrown more than 10% splitters over the past five seasons, and those three are the only ones who have actually not had surgery yet.

The only thing that these pitchers seem to have in common is the fact that they come from Japan, and while huge pitch counts and Japanese baseball are often synonymous, most of the active MLBers did not have huge innings numbers in comparison to starters who pitched their whole careers in MLB. The reason for the arm issues could actually be switching to American baseball. In the NBP, the Nippon Professional Baseball, teams employ a six man rotation instead of the five man common in the MLB. This allows for an additional day of rest that the pitchers have to get used to no longer having when switching over to MLB. This adjustment to less rest could be a reason why these pitchers are breaking down more frequently upon making the transition to MLB. So a fair argument to make from looking at these Japanese pitchers seems to be that limiting pitch counts is not a solution for the Tommy John epidemic, but giving pitchers more rest in between appearances could be the answer.

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