Bursa is a medical term referring to fluid filled sacs most commonly found around different joints of the body. The function of these fluid filled sacs or the bursa is to protect the bones from knocking against each other.

The most likely cause of Deltoid Bursitis is any kind of injury around the shoulder joint. This injury can be in any form like an injury sustained during any sporting activity like football or rugby.

Repetitive stress to the shoulder joints may also result in Deltoid Bursitis as repetitive movements of the shoulder such as when lifting or moving heavy items repetitively can inflame the subdeltoid bursa and can result in Deltoid Bursitis.