Caught Looking examines articles from the academic literature relevant to baseball and statistical analysis. This review examines a recent article from the Journal of Shoulder and Elbow Surgery on Tommy John revision surgeries.
In 1974, Dr. Frank Jobe performed ulnar collateral ligament reconstruction surgery on Los Angeles Dodgers pitcher Tommy John. At the age of 31, John was 13-3 with a 2.59 ERA in the midst of his 12th big-league season when he tore the UCL in his left elbow. This marked the end of his season, and for everyone who had previously torn a UCL, it had marked the end of their career. The procedure performed by Dr. Jobe was seen as a longshot, but it was a longshot that paid off. John missed the 1975 season, but returned in 1976 and went on to pitch in the majors for 14 more seasons that included two runner-up finishes for the Cy Young Award.
Since then, Tommy John surgery, as it has come to be known, has been performed over 300 times on major-league players and becomes more common over time. There has also been a corresponding rise in revision surgeries, where the same pitcher has gone under the knife twice. Some, including Jason Isringhausen, have even had the surgery three times. In their article, Outcomes in Revision Tommy John surgery in Major League Baseball pitchers, Joseph Liu and co-authors examine the performance of Tommy John repeaters to find out just how likely it is to come back successfully from a second UCL reconstruction procedure.
Before digging in to what they find about recovery rates for Tommy John revisions, it’s worth a quick look at what academics and medical practitioners have found about what happens the first time a pitcher has the procedure. Nowadays, it is more likely than not that a pitcher who undergoes the surgery will return to pitch in the majors. The procedure has been honed over time, and improvements in technique have corresponded with increases in frequency. In general, pitchers who undergo the surgery miss a full season during rehabilitation, though recovery time can vary. However, pitchers on average do not return to their pre-surgery level of performance, nor do they reach the level of performance obtained by a control group that has not had the procedure.
The current study focuses on 26 pitchers who underwent revision Tommy John surgery between 1999 and 2012, and examines their results two and three years after surgery. Seventeen of these pitchers eventually returned to pitch in the major leagues and four more returned to pitch in the minors, but only 11 returned to pitch in at least 10 games. In some sense, the surgery has been effective, because a torn UCL without surgery is generally a career-ender and any return to pitching is an improvement. In general, however, pitchers have seen some drop in effectiveness relative to pre-revision surgery. The number of innings pitched and total pitches decline substantially as many starters are converted to relievers. Performance metrics such as ERA and fastball velocity also declined, though the sample size is not large enough to find statistical significance in these measures.
To really measure effectiveness, however, it’s not sufficient to simply observe that a pitcher is not as good after surgery as he was before. The trick in studies like this is to identify an appropriate control group to allow you to determine how the pitcher performed relative to what might have been expected absent the surgery. If the only pitchers who get the surgery are on the downward-sloping part of their aging curve, for instance, then perhaps age, rather than surgery is to blame. To deal with this problem, the study’s authors created a control group by matching pitchers with others at the same age and position (starter versus reliever). First, they identified a control group of potential matches for each pitcher with Tommy John revision surgery, then matched each pitcher in the treatment group with a randomly selected pitcher from their potential control group. Again, the pitchers who underwent revision surgery under-performed their control group in terms of innings pitched, pitches thrown and fastball velocity, though the authors do not report on other performance measures.
A control group is necessary to provide a baseline for measuring how pitchers performed relative to what could be expected, and the authors here have used a relatively simple and straightforward method of forming one. However, it seems possible to improve the comparison group by including more information. An obvious use for the information in this study is to inform contract negotiations, and building a better baseline will improve projections for agents and front offices.
One concern is that there are differences in usage rates and injury histories among pitchers who undergo surgery versus those who do not, and that we can improve on our baseline estimates by including this information. The pitchers in the treatment group have all had one Tommy John surgery already, so if nothing else, perhaps it is possible to choose matches from this group, rather than from among all pitchers. In addition, PECOTA-style or other matching may provide a better control group than what is chosen here. Such methods allow for matching on multiple dimensions beyond age.
Another use of the results of this study may be to guide players who need to decide between surgery and retirement. Unfortunately, the sample of players who undergo revision surgeries is not likely to be entirely random. Introspection suggests that older players may be more likely to choose retirement, for instance. One interesting extension of this paper would be to examine how this selection bias affects the observed results.
In just a few more years, the authors will be able to add many more cases to their study, as UCL reconstruction surgery spiked rapidly in 2012 and results will be available for those who had the treatment in 2013 and beyond. Soon, we will have nearly double the sample size to examine and can develop an even clearer picture of what happens to pitchers who have Tommy John surgery more than once.
Michael Wenz is Visiting Professor at Politechnika Czestochowa in Poland. Comments and suggestions for future articles are appreciated.