My bf showed me something interesting about his left knee today. He is now 32, but had a hyper extension injury in HIGH SCHOOL during a basketball game and has had this issue ever since:
When he fully extends his left leg, the proximal head of the tibia pops backwards quite noticeably. (He had me put my hand on the posterior aspect of his knee as he did it, and I jumped back in disgust when it popped back at me.) He claims it's not that painful, just after he runs or if it randomly hyper extends during the day.
In my profession (veterinary medicine), this indicates some lax or torn ligaments...either of which aren't good.
Would you agree? Obviously he needs to see an orthopedic doctor, but immobilization therapy wouldn't work well 14+ years after the fact, would it?
He is actually performing a posterior drawer test on his knee. This is indicative of a torn posterior cruciate ligament. You can do the same test on his knee by bending it to 90 degrees, sit on his foot, then gently push the proximal tibia posteriorly (be sure the tibia starts at neutral, because in PCL injuries the knee may naturally sag backwards. Many ortho residents are fooled by this and think the person has an ACL injury when they reduce a sagging tibia to neutral.) You can also look for a posterior sag sign or have him do a quad active test (these are both described in the Wheeless Orthopedic Site online).
The mechanism of injury is consistent with a PCL injury. Many people do very well, playing sports, performing manual labor with a torn PCL. Many never have it fixed. The only reason to have it surgically repaired, is if it is significantly impairing his ability to work or perform his chosen recreational activities. Many also do well with a PCL sports brace if it only bothers them occasionally.
And you are correct, bracing or immobilization will not do anything. The cruciates will not heal, due to the fact that they are intasynovial. This is also true in canine ACL's. As one of my partners helps a local vet do ACL reconstructions on many dogs (Labs, Goldens, and Shepards mostly). It was actually research on canine's that allows us to do many of the knee procedures now done on humans.
He should see an orthopedic surgeon for a firm diagnosis, to make sure that there is nothing else going on (torn meniscus, OCD, etc). But, again, if it is not bothering him now, and at his age, most PCL's do not need to have anything done. Be wary of being pressed into something that may not need to be performed. Good luck.