Decreased knee motion following ACL reconstruction is expected. Over the next 3-9 months this motion normally improves to your normal level before surgery. In 5-10 out of 100 patients, a long-term decrease in knee motion occurs. This usually occurs in patients with decreased or poor knee motion before the surgery. It can also occur because of scar formation inside the knee. Most of the time this can be corrected with aggressive therapy and knee bracing, but may require an operation if therapy and bracing are unsuccessful.