Let's clear up a little , the ligaments either side of the knee are the co-lateral ligaments of which the ones on the inner side of the knees are the medials they stabilise the knee in side to side movement, the medial can also pull the medial meniscus into a position where it can be damaged in extreme movement and leave fragments in the joint space, not nice.
The Cruciate Ligaments the anterior and posterior stabilise the knee in front to back movement , you most often hear of them being ruptured in footballers or high performance surfers.
Yoga, fitness , pilates , stretching and a whole range physical therapy can help but the dynamic nature of surf means even a perfect knee can be caught short.
Building up the balancing and structural muscle around the knee can be a great help, the more balanced the muscle groups around any joint the better.
In any clinical situation I would also look at how the injury first occurred. this would point out any deficiency of technique or unbalanced muscle strength. Without correcting these it can happen again. A tear on a tear is worse , a rupture worse still.
Go get thoroughly diagnosed.
