I've not heard of this or read it in any of my journals. Enlighten me if you would.

Part of the exam is to determine laxity in the knee. The patient is sedated and the tibia is advanced forward while holding the femur in place. If the tibia advances past a certain point then the likelyhood of the ligament being torn is great, this is called cranial drawer sign. There are other portions of the exam, but as far as veterinarians rupturing ligaments during the exam, I don't think it is a common problem, not one I was ever warned about anyway.

I played sports for years and had my knees evaluated for ligament tears by human doctors, their exam was similar (without the sedation, because a human can be asked to totally relax the leg).