Phillies shortstop Didi Gregorius blames the worst season of his career on an elbow condition he says developed after he was vaccinated for COVID-19. He claims the shots caused him to develop pseudogout — a form of arthritis characterized by sudden, painful swelling — in his right elbow which debilitated his performance.

“Some people say it’s from the vaccine. I will say it’s likely from that, too,” Gregorius told The Inquirer before Wednesday’s game. “But when you say that, everyone looks at you like you’re stupid because the vaccine is not supposed to be like that or give you that reaction.”

Paul Offit, a vaccine expert at Children’s Hospital of Philadelphia, said that no vaccines, including those for COVID-19, could cause pseudogout. “It has nothing to do with the vaccine,” he said. It is possible, however, that a vaccine could cause a flare of pseudogout if Gregorius already had it and didn’t know about it. However, the flare would only last a few days. A flare lasting months “doesn’t make any sense.”

Ravina Kullar, a spokesperson for the Infectious Diseases Society of America and an infectious diseases consultant for Los Angeles nursing homes, said she knew of two reports of short flares of rheumatoid arthritis after COVID-19 vaccination. She was not aware of any reports of gout or pseudogout after vaccination. Such a reaction might be possible, she said, but it likely wouldn’t last long. A patient’s doctor would have to rule out all other potential causes.

Gregorius was one of the Phillies’ top hitters last season and signed a $28 million contract in the offseason, but he has been one of baseball’s least productive offensive players in 2021 and is valued roughly the same as a replacement-level player in Wins Above Replacement.

Gregorius, 31, started experiencing elbow discomfort and swelling in April, which he said began shortly after receiving the second dose of the vaccine. Pseudogout is treated with medicine, but Gregorius said the discomfort has not gone away.

Pseudogout, also known as calcium pyrophosphate deposition disease or CPPD, is a type of arthritis that occurs when calcium pyrophosphate dihydrate crystals build up in cartilage. It most commonly affects knees but can affect other joints. It can last for days or weeks. Risk factors include joint injury, genetic predisposition, excessive calcium or iron or too little magnesium in the blood, and problems with thyroid and parathyroid glands, according to the Mayo Clinic. The crystal deposits can cause joint damage.

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Gregorius’ right elbow is his throwing arm and the lead arm of his left-handed swing. Gregorius said his doctor, not a member of the Phillies, told him the vaccine may have caused it.

“He didn’t give me like 100%,” Gregorius said. “Of course, this is the joint that I use the most and I get it on my elbow.”

The Phillies were one of the last remaining teams to meet Major League Baseball’s 85% vaccination rate until they crossed the threshold on Wednesday. They declined to comment on Gregorius’ claim about the vaccine.

MLB did not mandate players to be vaccinated this season but did not allow teams to relax their health and safety protocols until they vaccinated 85% of their players and staff members. The Phillies have tried to convince their players to get vaccinated but met some resistance due to stories like Gregorius’ and that of former reliever Brandon Kintzler, who was released in August but said his neck injury and two teammates’ injuries stemmed from the vaccine. That did little to help convince unvaccinated players to get the shot.

Asked if he regretted getting the vaccine, Gregorius said: “Kind of, yes.”

Gregorius had been unsure if he would get vaccinated but said his doctor told him he should since he has a chronic kidney disorder. People with preexisting conditions are at a greater risk of severe COVID.

“I had all types of reactions when I took the first and second shot. I know nobody knows because nobody talks about it,” Gregorius said. “... I had a really bad reaction. And then with the elbow, after the shot, I was nine days removed. But nobody knows because nobody talks about it. They just say, ‘Didi is having a bad year,’ but they don’t explain why I’m having a bad year and what I’m dealing with.”

The Phillies first thought Gregorius’ swollen elbow was from being hit by a pitch or from diving for a ball and believed the bruising lingered for weeks because his kidney ailment frequently slows his body’s ability to flush inflammation. Gregorius missed three games in April, tried to play through the discomfort, and landed on the injured list on May 14 with a “right elbow impingement.”

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“I couldn’t bend my elbow for at least two months,” Gregorius said. “They didn’t want to do anything about it in the beginning. They told me it was just inflammation, but it wasn’t just inflammation. I was mad that I missed like 50 games. It’s not a fair thing. I’m here to play. I’m not here to sit around and not do anything. It’s been frustrating basically the whole year with what’s going on. I didn’t get an answer until June. I got the answer.”

The Phillies diagnosed Gregorius three weeks later with pseudogout, “a pretty rare condition, but it’s one that is not particularly concerning,” general manager Sam Fuld said in June.

“They didn’t tell me what it is exactly. All they said was pseudogout. I didn’t know what the hell gout was. I didn’t know what the hell pseudogout was until I got it,” Gregorius said. “After waiting so many days for an answer, I finally got it. I don’t know for sure if it’s something that I’ll deal with for the rest of my life or not. Apparently, you get gout from drinking. I don’t drink. I don’t eat red meat. So how did I get it? I don’t drink alcohol. They tried to blame me and said it’s because you’re drinking. Everybody who knows me knows I don’t drink. That’s why it didn’t make sense. Those 50 days I was out, I was really [ticked] off because people told me I was doing something that I didn’t do.”

Gregorius returned to the Phillies on July 2 but said his elbow pain remained. He entered Thursday hitting .210 with a .667 OPS in 200 at-bats since being activated from the injured list. Gregorius said his doctors have recommended an arthroscopic procedure this offseason to repair his elbow, but he has not discussed that yet with the team.

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“It’s in our best interest that I’m at my best when I go out there. so if I have to do it so my elbow doesn’t flare up again and I can feel comfortable swinging and not feeling a pop every now and then when I swing, I should be fine,” Gregorius said.

Gregorius was the only free-agent shortstop last winter to land a multiyear deal, which will pay him $14 million next season. The second year of that contract looks like an albatross based on Gregorius’ performance this summer as he has been worth 0.3 Wins Above Replacement by FanGraphs and has the 16th-lowest OPS (.654) among all players with at least 350 plate appearances.

“Well, I think that the fact that he has bounced back before means he can do it again,” manager Joe Girardi said Wednesday when asked if Gregorius can be an everyday player in 2022. “He’s gone through somewhat of a difficult year, where we weren’t exactly sure what he was dealing with, why he couldn’t get rid of the swelling. He was late getting to spring training a little bit. It’s just been a difficult season for him, and I do believe he has played a better shortstop. I think reps are important. Consistent reps are important. But I do believe he’ll bounce back.”

Gregorius did just that after undergoing Tommy John surgery for the same elbow following the 2018 season. He returned to the lineup in early June of the 2019 season, playing 82 games and hitting 16 home runs for the Yankees.

Gregorius’ contract means he’ll be with the Phillies in 2022 unless they decide to release him and pay him $14 million to not play. It’s hard to imagine them finding a trade partner this winter. The Phillies have released players with guaranteed contracts but never cut ties with a player owed as much as Gregorius.

If he’s back in 2022, the Phillies will have to hope that an offseason provides a cure for his nagging elbow.

“One hundred percent,” Gregorius said when asked if he can play every day next season. “I’ll be feeling back to normal. My elbow is still bothering me. They’re not talking about it because I’m not on the [injured list] and I’m still playing.”

Inquirer health reporter Stacey Burling contributed to this article.