Your son may be having a procedure called chondral resurfacing using a microfracture technique. This means that the surgeon uses an arthroscope to find the defect.
Then a special tool called a curet is used to scrape the layer clear. Another tool called an awl makes holes in the subchondral bone plate. The subchondral layer is just above the cancellous or spongy bone where the blood supply to the bone is found.
These tiny holes or "microfractures" allow blood to seep down into the cartilage layer forming clots. A healing response is set up and tissue fills in the layer.
Your son's cooperation is very important for a good result. He must follow the surgeon's instructions very carefully. For example, putting too much weight on the knee can cause the clot to get displaced. Likewise, premature weight-bearing can limit attachment of the clot to the cartilage base.
Patients must also cooperate with the physical therapist. A postoperative program of exercises will be part of the rehab and recovery. Patients are guided step-by-step through the phases of activities. For example, a continuous passive motion (CPM) machine is worn for at least six hours a day for the first six weeks. The patient is unable to just get up and walk about when using the CPM.
Strengthening exercises followed by low-impact activities are slowly advanced. MRI testing and patient symptoms are used to guide the progression of rehab. Running is not allowed until about four months after surgery. If your son is an athlete, returning to high-impact sports activity takes up to six months or more.