The Orioles were dealt a devastating blow on Tuesday morning when closer Zach Britton ruptured his right Achilles tendon during a post-throwing sprinting session in his native California.
"It felt like something punched me in the leg," Britton said. "I went down. It was probably the most painful thing I've ever experienced."
Dr. Kenneth Jung of the Kerlan-Jobe Orthopaedic Clinic in Los Angeles confirmed the rupture via MRI and performed surgery to repair Britton's Achilles on Thursday morning. Britton, who will likely be out of action for at least six months, gave a status update on Twitter on Thursday afternoon.
"Surgery went really well," Britton tweeted. "Want to thank everyone for their support."

The Achilles tendon is the thickest tendon in the human body, about four centimeters at its narrowest point. It connects the gastrocnemius and soleus muscles of the calf to the calcaneus bone, or heel. When the calf muscles flex, the Achilles tendon pulls on and lifts the heel, boosting us forward onto our toes when walking, running and jumping. Though the Achilles tendon is capable of absorbing a large amount of force, it is also vulnerable to injury due to its limited blood supply and the sheer amount of tension placed upon it.
Britton's Achilles injury is to his landing leg, which, on the surface, seems better than if it were to his push-off leg. But while Britton's lead leg may not be responsible for generating velocity at the beginning of his delivery, it is certainly required to absorb all of the force generated by the 6-foot-3, 195-pound Britton at the end of it. And it must do so on the sloped, uneven surface of the pitcher's mound.
"At the time of landing, there is a lot of impact the body has to absorb, and also as you come forward over your front side, you get an explosive gastrocnemius contraction, which pulls up on the Achilles," said former Red Sox trainer Mike Reinold, now of Champion Physical Therapy and Performance in Waltham, Mass. "The tissue has to be able to accept that load again, and in the landing leg at ball release with all that weight and force coming over the front side, that's a big deal for the tissue."
Upon his return, Britton will also have to field his position, and while he's not an outfielder whose bread-and-butter is running and cutting, navigating the sloped pitcher's mound, explosively moving to field ground balls and breaking sideways to cover first base all also put significant stress on the Achilles tendon.

Though Achilles surgeries are not done arthroscopically with tiny incisions and a miniature camera to guide surgical instruments, there are two main options for an Achilles repair. First is an open repair, in which an incision or incisions are made exactly over the rupture, as shown by an MRI. If a more traditional technique is used, the incision will be several inches long. Another open-repair technique utilizes what foot and ankle specialist Dr. Norman Waldrop at the Andrews Sports Medicine & Orthopaedic Center in Birmingham, Ala., refers to as "mini-opens," which are several incisions of roughly three centimeters each.
The second option for Achilles repair is the newer, more minimally invasive PARS technique, which utilizes smaller, two-centimeter incisions and has successfully been done in several NFL players.
It is unclear which surgical option was used by Jung on Britton's Achilles.
"As long as you can do the repair and do it strong, it's a little bit of dealer's choice, as far as how the surgeon feels most comfortable," Waldrop said. "But no matter how you do it, really what we try to do is tie the two ends of the hose back together."
Waldrop said that when the Achilles tendon ruptures, the torn ends of the tendon unravel into many little strands, resembling a mop. He uses sutures to bring the strands back together, then runs more sutures around the tendon to make it tubular again. While doing the repair, Waldrop will use the patient's healthy tendon to gauge the tightness of his repair, so it will not be too loose after surgery.
"The three things you worry about with an Achilles repair are wound problems, the tendon stretching out and the tendon re-rupturing," Waldrop said. "Stretching it out is a much bigger problem than being too tight, because when the tendon is too loose, an athlete will lose their power and their strength."
Following surgery, the patient will be immobilized for anywhere from two to six weeks, depending on the doctor's wishes, and according to Reinold, the process is tricky.
"If we immobilize them for too long, they can get too stiff, but if we mobilize too fast, they get too loose and they have lack of end-range strength to really push off and explode and exert force through that tendon," Reinold said. "It's a very fine line."
Waldrop immobilizes patients for up to four weeks, but has them start therapy and motion at two weeks. While Britton will have to be careful with his Achilles repair until the four-month mark -- that is the point at which the chance of re-rupture finally begins to drop -- he will be able to work out the rest of his body.
"I let all my athletes work out from the knee up on the affected side, and everywhere else," Waldrop said. "I also let guys throw, and there is a ton of throwing stuff that can be done on one knee, in a special brace or with other modifications. The goal is that when I say, 'Go,' right around that four-month mark, we can minimize the amount of time between then and when the athlete is ready to play."

If all goes well and Britton begins a real throwing program at the four-month mark, a return in six months is not out of the question. However, there are few Major League pitchers who have had Achilles repairs, so there are not a lot of comparable situations. In 2015, Adam Wainwright missed five months, while Jason Grilli missed nine. In '14, Johan Santana's comeback bid was ended by his ruptured Achilles.
"If you look at data from other professional athletes with Achilles tendon ruptures, you're really looking at eight months to return, and their return to play typically is not at the level it was previous to the Achilles rupture," Waldrop said. "The data is not out there in pitchers, because we just don't have the numbers, so it may be different, but it is certainly not an insignificant injury."
Not insignificant, and incredibly difficult for Britton, who struggled with forearm and knee issues throughout the past season, to stomach.
"I was about to throw bullpens. I was right where I wanted to be," Britton said. "It's probably the most frustrating thing I've experienced."