Kris Medlen and the history of returning from a second Tommy John surgery

Yesterday the Royals signed Kris Medlen to a two year deal, one year for each Tommy John surgery he has had (snap!). The history of have two Tommy John surgeries isn't very long. According to Jeff Zimmerman's Tommy John data (found here) there are about 50 players who have twice gone under the knife. From that data I sorted through players who I felt had enough pre and post Tommy John data that would be useful to look at. I eventually widdled it down to 10 names. Many of the names on the list either never played in the MLB, didn't enough in their MLB career, or didn't pitch enough after surgery. I wanted to look at pre-velo and post-velo levels, but the data just wasn't big enough as Pitch F/X is only tracked back to 2007. Briefly we'll look at just a few things here.

One thing to note, the list includes both starters and relievers so the comparisons aren't exact or transitive.

First off, here is the group of 10 players and their innings pitched before and after their 2nd TJS.

Upon returning the group has only pitched 37% of the amount of innings prior to surgery. Everybody except for Wilson, Soria, Kelley, and Capuano are retired or unofficially retired. That means those guys would all need to pitch another 2900 innings combined to get back to pre-TJ innings level.

Next we can look at the pre-fWAR and post-fWAR of those players:

Only really Capuano returned to his pre-2nd TJ/post-1st TJ level, while Isringhausen fell off a cliff while others just couldn't pitch enough innings to accrue more wins.

Here is the K/9 for each pitcher for the cumulative innings prior to surgery in the 2nd column. Next to it is each pitchers group adjusted (scaled to 100) K/9. So for instance, Soria's pre-TJ K/9 is 19% better than the group average pre-TJ K/9 (8.15). In the final column is the league adjusted (again scaled to 100) K/9 using the average K/9 from 1994 to 2014. Overall the group had a better than league-spanned average K/9 prior to surgery by 20%.

This is BB/9 expressed in the same style as the K/9 table with group adjustments and league-spanned adjustments. In this case the group had a 6% worse walk rate than the league-spanned average.

Now we have the post-TJ data. As a whole, the group almost unanimously increased their strikeout rate over the league-spanned average.

In the opposite of the previous table, the group increased their walk rate (or decreased their % better than the league-spanned average, which is bad).

This is an admittedly imperfect study given the sample size and the lack of innings distributed to the post-TJ level data. Having said that, there seemed to be a pattern here. The group almost as a whole increased their strikeout rate after their 2nd Tommy John, but that also came with an increase of walks.

You probably can't just assume a similar pattern will emerge for Kris Medlen once he hits the mound though. In the meantime though, here's Medlen's data in the same format as above.

Medlen does have a very good walk rate, but a below average strikeout rate in today's environment. Perhaps if the trend from the earlier group were to continue with Medlen once he returns from his second Tommy John then he could see an increase in his K/9 at the cost of his BB/9 where he has some room to give.