Joint laxity refers to how tight or loose a joint is. Laxity is determined naturally by your genetic makeup. Sometimes people are naturally loose or tight. In other cases one or more ligaments has been stretched or even torn with use and age. This can increase the joint laxity causing problems. Uneven wear and tear on the joint is one such problem. It can lead to degenerative arthritis and the need for a joint replacement.
The surgeon tries to mimic the normal knee as much as possible when putting in an artificial joint. Matching your natural laxity is the goal but can be difficult.
A recent study of knee joint laxity before and after total knee replacement made some interesting discoveries. The researchers found that the lateral or outside edge of the knee joint is more lax than the medial or inside joint line. On testing, this is called the joint gap. They also reported less lateral laxity after joint replacement.
There's no way to change joint laxity without surgery. Muscle strengthening helps protect the joint when the ligaments don't hold the joint stable. It sounds like you're already working on that. Your surgeon will balance the joint laxity during the operation.