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Chris Kreider's season was interrupted abruptly, and seemingly without warning.
On Dec. 27, the Rangers forward was forced to leave the game against the Washington Capitals after the first period. He had pain in his right arm, but as far as anyone could tell, there was no hit or incident that led to the injury. That is, until the next day, when doctors discovered that the pain was being caused by a blood clot that had caused the arm to swell.
But as strange as it may sound to those outside the National Hockey League, Kreider's injury was no fluke. Blood clot diagnoses have become an alarming trend in the NHL. Though the league tends to hold back injury information, there are at least 11 players known to have been diagnosed with some form of the condition since 2008.
There are different causes of blood clots, but, doctors say, Kreider's is not typically associated with playing hockey.
"Classically, it's been considered a problem for athletes like baseball players, but we've seen four hockey players get this in the last three years, and this is a group we don't expect," said Dr. Karl Illig, professor of surgery and director of vascular surgery at the University of South Florida's medical center.
In broad terms, the clotting of blood is required for survival. Without the clotting factor, any injury that leads to the loss of blood could be fatal. According to the Centers for Disease Control, a blood clot becomes dangerous when it forms improperly or unnecessarily - clogging the blood vessel or, most worrisome, breaking off and traveling to the lungs, blocking a pulmonary artery.
According to the National Blood Clot Alliance, on average, 274 people die daily from blood clots in the U.S. and there are about 600,000 cases of non-fatal blood clots every year. Annually, blood clots kill more people than AIDS, breast cancer and car crashes combined, the alliance said.
Two types of blood have been clots associated with athletes:
THORACIC OUTLET SYNDROME
At least four players, including Kreider and Lightning star Steven Stamkos, have been diagnosed with upper-body clots tied to thoracic outlet syndrome (TOS), clots that occur when blood vessels are compressed in the space between the collarbone and the first rib.
Though there are different types of thoracic outlet syndrome, the one Illig said he's hearing more about in hockey players is the relatively less common venous TOS. This occurs when the vein under the collarbone gets compressed, sometimes through a combination of genetic predisposition (a narrower space in the area), muscle development and repetitive, over-the-head arm movement.
"Maybe it's a result of more stress placed on conditioning the upper body,'' Illig said. "I don't think anybody really knows, but I would guess it's time in the gym. Players have been playing hockey for a century without this happening."
Dr. Laith Jazrawi, chief of sports medicine at NYU-Langone Medical Center, also is studying why hockey players develop TOS-related clots. "Is it their slap-shot arm, and the extra rib and the slap shot is causing trauma?"
Hockey can be a taxing sport. Players learn to play hurt from a young age, and some players undergo numerous medical procedures to heal injury or lengthen their careers. "These hockey players are checking and constantly putting their shoulders ," said Dr. Natasha Desai, assistant professor of sports medicine at Columbia University Medical Center. "Who's to say that's not causing scar tissue leading to thoracic outlet?"
Kreider, 26, underwent a rib resection - or removal of part of the first rib near the clavicle - to alleviate the condition last Sunday, the Rangers announced Tuesday. It is the same surgery that was performed on the Lightning's Steve Stamkos and Andrei Vasilevskiy, along with the Islanders' Adam Pelech. The Rangers have said Kreider is out indefinitely.
Illig, who performed the surgery on Stamkos and Vasilevskiy, said the prognosis for athletes who have venous TOS and get the surgery is very good, with about 90 percent of athletes returning to form.
DEEP VEIN THROMBOSIS
A clot caused by deep vein thrombosis, which ended the careers of Cody McCormick, Pascal Dupuis and Tomas Vokoun, often can be more dangerous.
"When you get a lower-extremity clot , the obvious fear is that it will turn into a pulmonary embolism," said Jazrawi, who also heads the Hockey Center at Langone - a center devoted specifically to the treatment of hockey players. " has risks and he may opt not to continue his career."
Deep vein thrombosis often is caused by genetic factors but can be exacerbated by injury followed by immobility (say, a long flight between road trip games), Desai said.
It generally starts in the leg but also can be found in the arm. People who have it can experience pain or swelling or nothing at all, and the biggest risk is that the clot travels to the lungs or the heart.
Clots like these are alarmingly common in the population, though there are certain risk factors - old age, pregnancy and obesity.
So why hockey players? After all, NHL athletes are at the height of their physical abilities. They are neither obese nor bedridden, factors that can lead to deep vein thrombosis.
"They travel a lot," Desai said. "Any time there's a vascular injury with a sedentary flow, that can initiate a blood clot . . . This would be for anybody, but think about the volume that these players get injured; then there's surgeries and immobilization. is probably higher than the general population."
There are things players can do if they've had blood clots in their legs - blood thinners, or a sort of filter that stops the clot from traveling - but these things do involve risk, Jazrawi said.
"It's not something to be taken lightly," he said, noting that someone on chronic blood thinners "may be hit in the head and get a concussion and bleed out."
Former Flyer Kimmo Timonen, whose family had a history of blood disease, came back to win a Stanley Cup with the Blackhawks after recovering from blood clots in his leg and lungs, but cases of deep vein thrombosis often end careers - or worse.
The death of Montreal Canadiens center Howie Morenz in 1937 is a stark reminder. Morenz, a former Ranger, suffered a fractured leg in a game against the Chicago Blackhawks. He was laid up for weeks and suffered a fatal coronary embolism related to the deep vein thrombosis from inactivity.
On the other hand, players such as Kreider with TOC-related clots can expect to come back. Because they need to be on blood thinners for a few weeks, though, it's not recommended that they engage in activity that potentially could lead to further injury, like concussion.
Despite the long lag time - players can be out for two to three months after surgery - athletes generally can start skating shortly after surgery, Illig said, adding that Stamkos attempted slap shots only two weeks after his surgery.
Stamkos appears to be back at full strength for the Lightning after a TOC-related clot and ensuing surgery ended his 2016-17 season. He has 17 goals and 35 assists in 44 games.
"The worry in Tampa is that all the Lightning are going to get upper thrombosis," Illig joked. "From skating around and holding up the Cup."
According to the National Blood Clot Alliance, on average, 274 people die daily from blood clots, and there are about 600,000 cases of non-fatal blood clots every year. Annually, blood clots kill more people than AIDS, breast cancer and car crashes combined, the alliance said. Here are important terms:
BLOOD CLOT: A mass of coagulated platelets and plasma proteins that have thickened, forming a semisolid mass, according to the Mayo Clinic. Blood clots are generally helpful - they form in an effort to repair a damaged blood vessel - but can become dangerous if they block the vessel, or break off and travel.
PULMONARY EMBOLISM: A blood clot in one of the pulmonary arteries. It can cause death. Symptoms include shortness of breath and chest pain.
DEEP VEIN THROMBOSIS: A blood clot in a "deep" vein, usually the legs and sometimes the arm. It can cause pain or swelling, according to the Mayo Clinic, or have no symptoms at all. DVT can occur if you have certain medical conditions - for instance, hypercoagulability, which means your blood clots at an unusually high level. These clots can also be caused by injury followed by immobility. It can lead to pulmonary embolism.
THORACIC OUTLET SYNDROME: A disorder that can occur when either blood vessels or nerves are compressed in the space between the collar bone and the first rib, according to the Mayo Clinic. Certain types of thoracic outlet syndrome can lead to blood clots in the upper body, like the arm. It can lead to pulmonary embolism.
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