According to Dr. Jonathan Cluett, Berkman's knee water is troubling.
Draining the fluid just means it will come back, as we've seen from the previous post that Berkman has had the knee drained twice in under two weeks.
For example, meniscus tears and ligament injuries can cause fluid to collect. Furthermore, tearing of small blood vessels can cause fluid to accumulate within the knee, this is commonly seen in patients with an ACL tear.
Excess fluid around the joint can accumulate in the bursa, a condition called prepatellar bursitis. While the fluid is not actually within the knee joint itself, prepatellar bursitis also causes swelling, or water on the knee.
Ultimately Berkman's knee will need surgery, as it's pretty much syringes (for draining - don't get any ideas) and cortisone shots from here on out.