Researchers uncover risk of shoulder injury…

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While existing data on the effect of spaceflight on the bones and tendons is available, there is little information about how soft tissue in the shoulder is affected throughout spaceflight. A team of orthopedic surgeons at Baylor College of Medicine studied the risk of shoulder injury during and post spaceflight to determine preventative measures for astronauts. Their findings were published in JSES International.

The research team worked with NASA to acquire data from astronauts that have flown into space (242 astronauts) and reviewed their preflight, intra-flight and postflight data with a particular focus on upper extremity and shoulder injuries or complaints.

"The main finding of the study was that astronauts who have been in spaceflight, especially the longer duration they have been in spaceflight, experience higher rates of shoulder injuries, particularly rotator cuff tears - even those that require surgery," said Dr. Adil Ahmed, corresponding author and assistant professor in the Joseph Barnhart Department of Orthopedic Surgery at Baylor.

The six-month time point appeared to be the threshold level. Astronauts in space for six months or longer had much higher rates of shoulder injuries that needed intervention compared to astronauts in space for a shorter duration. They also had higher rates of shoulder injuries and rotator cuff tears compared to non-astronauts. While most people do not go into space for over six months, commercial spaceflight companies aim to increase the presence of humans in space, and NASA has goals to establish a base on the moon and send astronauts to Mars and beyond, which are long-duration missions.

"The biggest issue that has historically been the focus of research regarding orthopedics and space is that bone mineral density decreases in microgravity. However, the soft tissues like the rotator cuff have received relatively little attention," Ahmed said.

The shoulder is important in space because there is only microgravity, making it challenging for astronauts to use their legs to move and propel forward. All motion and ambulation requires increased activity, use and demand of upper extremities more than on earth due to the lack of gravity. Injuries in the shoulder girdle can make astronauts ineffective at their job and jeopardize not only their own life, but the mission. If astronauts go to Mars to build an installation, they need to be functional as soon as they land.

"If they have an injury, there is no way to perform surgery or fix it in space, so we need to identify the risk factors and make counter measures for them now before someone gets injured in space and becomes a liability to other astronauts," he said. "There has to be something that can be done to decrease the impact of spaceflight on the shoulder to lower the risk that it poses with the combination of microgravity and the increased demand placed on the upper extremity."

Astronauts are extremely fit and typically do not have preflight issues in the upper limbs, but they are sustaining these injuries at a much higher rate than the normal population despite being in shape. Most of their exercise at the space station targets preventing bone mineral density loss and maintaining bone density, but the exercises are not dedicated for the rotator cuff and scapular muscles. One current action item is to improve the spacesuit design. Older spacesuits are not well-designed for normal shoulder motion as they are restrictive. The arm and shoulder do much more work in space than on earth while the spacesuit restricts their motion and flexibility.

Ahmed explains the importance of reviewing the biochemical profiles of each astronaut because even on earth, nutritional factors such as high cholesterol predispose patients to rotator cuff tears and impact healing after injury.

"Having the appropriate mix of amino acids and protein is very important in the rotator cuff muscles and tendons, especially when they have increased demand in space," he said.

The team hopes to conduct further studies with astronauts in real time to prevent further spaceflight injuries.

"There is a big push to make sure we can find a way to adequately assess these soft tissues intra-flight and in real time. As those longer-term space missions become real, we can have a plan for it," Ahmed said.

Benjamin Fiedler, Meghana Jami, Srikhar V. Chilukuri, Abdullah Ghali, and Todd Phillips also contributed to this work.

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