Often an injury can cause inflammation to a knee and the body may respond by producing extra synovial due to the inflammation . Doctors often use a syringe and large bore needle to drain excess synovial fluid while providing whatever medical attention is necessary to help the joint heal. Corticosteroids can be injected at the same time to help relieve the inflammation. If X Rays or MRI indicate any fractures or ligamentous tears, these may require surgical repair.