"strained ligaments" may be indicative of your GP's ignorance, as there's no such thing. "Sprain" is used to describe a ligament injury, "strain" for muscle or tendon. And it's denial to think of it as nothing permanent. Ligaments heal with a more disorganized deposition of collagen than what was there originally, so even a sprain means you have a substantially higher risk of recurrence. A torn meniscus or bone crack often means surgery, hopefully an arthroscopy but data published in the last six months now argues against doing meniscus surgery if the knee has significant arthritis seen in the MRI, as the procedure is ineffective. The point again is that playing as much as you evidently do is simply asking for trouble, as you don't allow your body enough rest periods to heal.