Struggling A’s Lose Trevor Rosenthal to Thoracic Outlet Syndrome

After pitching his way back from the outskirts of oblivion last year, Trevor Rosenthal fared relatively well via free agency, landing a one-year, $11 million deal from the A’s. Unfortunately, he has yet to take the mound for the team, and now it appears that it could be awhile before he does, even in a best-case scenario. On Thursday, Rosenthal underwent surgery to alleviate thoracic outlet syndrome, a loss that hardly helps an A’s pitching staff that’s off to a rough start this season.

The 30-year-old Rosenthal spent 2020 with the Royals and Padres, notching 11 saves while tossing 23.2 innings with a 1.90 ERA and 2.22 FIP; both his 41.8% strikeout rate and 33.0% strikeout-walk differential ranked sixth in the majors among relievers with at least 20 innings. He made an impressive rebound from a rough 2 1/2-year stretch that began with late-2017 Tommy John surgery that cost him the last quarter of that season and all of ’18; when he returned, he struggled greatly with his control, walking 26 batters in 15.1 innings while being rocked for a 13.50 ERA, and getting released in mid-season by both the Nationals and Tigers.

Rosenthal agreed to a deal with the A’s on February 18, making him the last reliever from among our Top 50 Free Agents (where he was 36th) to find work. Among free agent relievers, only the pitcher he was expected to replace, Liam Hendriks, received a contract with a higher average annual value, and only Hendriks, Blake Treinen, Trevor May, and Pedro Báez received larger guarantees. Though slowed by a groin strain in early March, Rosenthal appeared to be on track to open the season with the A’s until a bout of shoulder inflammation led to his placement on the injured list on April 1.

On April 7, the San Francisco Chronicle’s Matt Kawahara reported that Rosenthal had visited vascular surgeon Dr. Gregory Pearl in Dallas and was considering surgery to alleviate thoracic outlet syndrome, a condition caused by a compression of the nerves and/or blood vessels somewhere between the neck and the armpit. Symptoms of TOS commonly include numbness or tingling in the fingers and hands, or fatigue or weakness that doesn’t go away with physical therapy and rest. Pitchers tend to be particularly vulnerable to TOS because of their repetitive overhand movements and the way their arm muscles build up. The condition is generally remedied by the removal of a cervical rib and two small scalene muscles.

As Kawahara reported, A’s head trainer Nick Paparesta said that Rosenthal told the team that he had experienced numbness in his fingers, pain in his neck and chest, and difficulty maintaining velocity during his March 29 exhibition outing. Dr. Pearl diagnosed him with “severe neurovascular compression” and performed the surgery at the Baylor Scott and White Heart and Vascular Hospital in Dallas on April 8.

Rosenthal will be re-evaluated by Dr. Pearl in eight weeks, and his recovery time is expected to be about 12 weeks, though and Paparesta said that from past experience in dealing with A’s pitchers who have undergone the surgery, his expectation was that Rosenthal could be throwing around the four-month mark, which at best points to a late-season return.

Alas, the history of TOS returnees is not a sunny one. Picking up the baton from research Craig Edwards did in connection with Matt Harvey’s TOS diagnosis in 2016, I’ve been tracking the pitchers who have undergone the surgery here at FanGraphs, most recently checking in last year when Chris Archer was diagnosed. While there are certainly a handful of success stories such as Kenny Rogers, Aaron Cook, Alex Cobb, Mike Foltynewicz, and Jaime García — all of whom threw over 500 major league innings post-surgery, and weren’t any worse than about league average — 15 of the 32 players we’ve identified as having undergone the surgery after reaching the majors have thrown fewer than 50 major league innings thereafter, with four never making it back at all. That total was five until Archer returned earlier this season, but alas he made just two appearances totaling 4.1 innings before landing on the Injured List with a minor forearm injury.

Here’s an updated version of my age-based summary, for which I sorted the pitchers into three buckets. The data now includes 2020 performance, and so Daniel Bard (who underwent the surgery in 2014) is no longer among those who never made it back; I’m not counting Archer as not returning, but I haven’t included anyone’s 2021 data yet. The data now includes three current or former A’s pitchers who were previously unaccounted for among the TOS ranks, namely Frankie Montas, Andrew Triggs, and Bobby Wahl:

Pitchers who underwent the surgery before their age-27 seasons have fared the best, with the other two groups taking significant hits in performance, and the oldest group’s numbers somewhat distorted by the presence of Rogers, who underwent the surgery at age 36, then made three All-Star teams thereafter over the course of 1,253.1 post-surgical innings while pitching through his age-43 season. Without him, the post-surgical performance of the 31-plus group falls to an average of just 80 innings, with a 102 ERA- and 129 FIP-. By comparison, removing Cook, who threw 1,150 innings after undergoing surgery during his age-25 season, doesn’t have as drastic an effect on the youngest group, lowering the average to 247 innings, with a 102 ERA- and 106 FIP-. Given the extent to which one pitcher can distort these findings, I’m not sure we should go overboard in putting stock in them except to note that the range of outcomes is wide.

On a different note, the first of those two Kawahara articles cites a study done by Pearl of 13 pitchers who underwent the surgery between 2001 (Rogers) and July ’14, which took a look a performance in the three years before the surgery and three years after and found “no significant differences” on the basis of a broad suite of both traditional and advanced metrics (including some involving PITCHf/x data). While its three-year time frame does limit the distortions caused by Cook and Rogers, that study might reasonably be considered outdated given that the number of pitchers who have undergone the surgery since then is more than double the total in the original study.

It doesn’t feel as though we’ve seen many positive outcomes lately, with the likes of Matt Harvey (319 post-surgical innings with a 145 ERA- and 131 FIP-, Tyson Ross (234 innings, 122 ERA-, 118 FIP-), and Phil Hughes (86.1 innings, 142 ERA-, 137 FIP-), all of whom underwent surgery in 2016, looming large. Hughes officially retired in January, having not pitched since August 2018. Harvey is now pitching for the Orioles, his fifth team in four seasons, and hasn’t shown much to make anyone optimistic, while Ross, who opted out last season, signed a minor league deal with the Rangers and was assigned to the alternate site. I may revisit my data using a three-year window in the near future, along with a velocity-based look.

As for the A’s bullpen, like the rest of a team that lost its first six games and is just 3-7 at this writing, the unit has been dreadful thus far. In fact, its 5.72 FIP and -0.5 WAR are AL worsts, while its 5.95 ERA is the second-worst mark. Because neither the rotation (6.39 ERA, 5.38 FIP) nor the offense (.189/.278/.307 for an AL-worst 71 wRC+) have been any better, the A’s haven’t had a save opportunity yet. While lefty Jake Diekman was presumed to be the top closer candidate before the team signed Rosenthal — that despite his having just seven career saves — and Sergio Romo has ample experience at closing, manager Bob Melvin said that Lou Trivino is first in line for the job.

The 29-year-old Trivino has just four saves in his four-season major league career and is still trying to recover the form that made him a standout as a rookie in 2018; last year, he pitched to a 3.86 ERA and 3.92 FIP in 23.1 innings. Thus far this season, he’s allowed just one hit and one run in 6.2 innings while striking out eight.

“It’s not ideal to use Jake in the ninth inning,” Melvin told reporters last week. “A lot of times, his spot comes up before that in the eighth. If we can keep moving forward with Lou, he gives us an option to close as well. He’s pitched really well for us. We’ve seen what he can accomplish when he’s feeling good.”

Unfortunately for the A’s, Rosenthal is hardly the only one of their hurlers on the IL. Righty Mike Fiers, expected to be part of the rotation, was slowed by back stiffness and inflammation in his right hip during spring training; he’s been building up his pitch count via simulated games at the A’s alternate site. Lefty A.J. Puk, who lost out for a rotation job in Fiers’ absence, suffered a biceps strain last week during his first outing of the season and will miss more than the minimum 10 days. Righty Burch Smith suffered a groin strain after making two appearances and will apparently miss significant time, and lefty Reymin Guduan sprained his left thumb after making three appearances. Somehow the A’s, who have made the playoffs in each of the past three seasons, will make do amid the injuries as always, but having to dig themselves an early hole won’t make their jobs any easier.