When it comes to ski injuries, the torn ACL is the most infamous: Surgeons repair 350,000 rips and ruptures each year. And, thanks to all that practice-plus new techniques using your own hamstrings, parts from cadavers, and, in the future, pig ligaments-recovery time is shrinking. Unfortunately, in 25 percent of all ACL tears, the soft articular cartilage that protects your bone ends is injured as well, and can even get dinged just from overuse. Around 900,000 Americans damage knee cartilage each year, leading to pain, poor performance, eventual arthritis, and, in some cases, knee replacement. “At times, it feels like you’ve got an ice pick jammed in there,” says ski-mountaineer Alison Gannett, who’s had eight knee surgeries since 1986. If your knees need fixing, here are your best bets.