Three seasons ago, Matt Harvey was one of the best pitchers in all of major-league baseball. Over 26 starts, his 2.00 FIP was the best among all starters. His 2.27 ERA placed behind only Clayton Kershaw and Jose Fernandez’s marks by that measure. Despite a relative deficit of innings, Harvey’s 6.5 WAR was third among pitchers behind only Clayton Kershaw and Adam Wainwright.

The reason for that low-ish innings total? A partially torn UCL that ended Harvey’s season in August and ultimately required Tommy John surgery. Rehab kept Harvey off the mound for the entire 2014 campaign, as well, but he came back strong in 2015, posting a 2.71 ERA (82 ERA-) and 3.05 FIP (80 FIP-), and proved instrumental in getting the New York Mets into the World Series.

The 2016 campaign has been an up-and-down one for Harvey — and will feature much more down than up going forward, as reports indicate that the right-hander will undergo surgery for thoracic outlet syndrome. For the Mets, the loss of Harvey is a threat to their postseason odds. For Harvey himself, it’s a threat to his career.

On May 20, Eno Sarris wondered, What’s Wrong with Matt Harvey? His conclusion: that maybe the slider wasn’t quite as good as it had been, by movement or location, and that a little bit of work on that pitch might right the ship. For a time after that, Harvey appeared to have gotten things in order. In five starts beginning May 30, Harvey went at least six innings in every start, striking out 25 against five walks with a 2.25 ERA and 2.08 FIP. His strikeouts were down a bit from last year in that stretch (25% to 21%), but his walks also decreased (7% to 4%).

Unfortunately, that encouraging period was short-lived. In his next two starts, Harvey failed to complete four innings, and he was placed on the 15-day disabled list due to shoulder discomfort. With surgery now a certainty, it’s time to take stock of the implications of Harvey’s injury on his long-term prospects.

For reference, we can look at other pitchers who’ve undergone similar procedures, beginning with Chris Young. Simply because he’s been able to pitch at all, it’s unlikely Harvey’s condition has deteriorated to the degree Young’s had. Still, Young’s case provides a sample of the debilitating symptoms that accompany the problem:

Young outlined his fruitless regimen of physical therapy, soft-tissue exercises, massage therapy and chiropractic adjustments. He could not complete push-ups. When he exercised on an elliptical machine, his arm ached. He could not fall asleep on his right side. He gave his toddler son a piggy-back ride and felt his hand go numb.

Those symptoms were a part of a longer decline than what Harvey is likely experiencing, although it is possible that, if left untreated, Harvey’s current malaldies are a precursor to the symptoms Young described. For a bit of nuts and bolts on the condition, the Mayo Clinic has this to say:

Thoracic outlet syndrome is a group of disorders that occur when the blood vessels or nerves in the space between your collarbone and your first rib (thoracic outlet) become compressed. This can cause pain in your shoulders and neck and numbness in your fingers. Common causes of thoracic outlet syndrome include physical trauma from a car accident, repetitive injuries from job- or sports-related activities, certain anatomical defects (such as having an extra rib), and pregnancy. Sometimes doctors can’t determine the cause of thoracic outlet syndrome. Treatment for thoracic outlet syndrome usually involves physical therapy and pain relief measures. Most people improve with these approaches. In some cases, however, your doctor may recommend surgery.

“Repetitive injuries from job- or sports-related activities”? You mean like throwing a baseball at speeds near 100 mph 100 times every five days for six or seven months? Seems pretty credible. Unfortunately, tracking those who’ve had the surgery is slightly more difficult than simply checking disabled list transactions, as players are often placed on the disabled list with something a bit more vague prior to an eventual surgery.

From the list we were able to compile, it appears as though 18 MLB players have had the surgery, 16 of those pitchers. The first we found was Kenny Rogers, back in 2001, and Rogers was able to return successfully to the majors.

Of the 16 pitchers, four had previously undergone Tommy John surgery: Chris Carpenter, Shaun Marcum, Jaime Garcia, and Drew VerHagen. Carpenter and Marcum were unable to return successfully while VerHagen just had the surgery and Garcia is currently pitching in an effective manner after a very good 2015 season. The table below shows the pitchers who had the surgery and the number of MLB innings pre- and post-surgery.

There are not any real patterns or signals to be divined here. This piece from Beyond the Box Score discusses a few of the players above and their effectiveness after the surgery. It’s a difficult procedure from which to return, but there are success stories. Most of the players who’ve had the surgery are relatively young like Harvey, but all had varying levels of success even before the surgery. While we usually think of a 14-month recovery for Tommy John surgery, thoracic outlet surgery doesn’t require the same time frame for recovery and, provided everything goes according to plan, Harvey will likely be ready for next season.

As for the Mets, the absence of Harvey hurts their chances in 2016. The club currently sits three games back of the Nationals in what could be a competitive race going forward. In the wild-card race, the Mets find themselves in the top spot, half a game ahead of the Dodgers, three games ahead of the Marlins and Cardinals and 3.5 games ahead of the Pirates. FanGraphs’ playoff odds give them a 69% chance of making the playoffs with Harvey’s 1.9 projected WAR. Without Harvey, those numbers will take a bit of a dive. Zack Wheeler is still a month away from returning. Bartolo Colon could shoulder more innings than he is currently getting in the Depth Charts, but neither Logan Verrett, nor Rafael Montero or Seth Lugo are likely to pitch at better than a replacement level. An interesting playoff race could get more interesting without Harvey. If the team wants to weather the loss, they might need to add a starter from outside the organization, which could prove difficult given the lack of available pitchers.