Cartilage tears are they common and what is the best way to fix it especially. in the knees?

Pretty Common: I would have a lengthy discussion with your orthopoedic surgeon and review your MRI results in detail. Depending on the extent and location of the tear there are multiple modalities available for treatment....Surgical and conservative.

Knee pain: Cartilage tears and cartilage degeneration are extremely common, especially in the knees. Cartilage lays over the knee bones and lines the joint. It also produces synovial fluid which acts as a lubricant and reduces friction inside the joint (think oil inside your engine). Fix: consider physical therapy, relubricating hyluronic acid injections, regenerative treatment(prp, stem cells), or surgery.