Arthrofibrosis can occur after total knee replacement or partial knee replacement. The common pathway for the development of arthrofibrosis (AF) is excessive collagen fibril deposition in and around the knee. This can be accompanied by shortening of the patellar tendon (patella baja/infera) which can also contribute to limited flexion. The rates of AF after TKA vary widely in the literature as there is no standard definition. One study's definition is a total range of motion (ROM) <90 degrees constitutes AF, another definition is flexion contracture >10 degrees, or inability to flex the knee >100 degrees. AF is a diagnosis of exclusion; before making a final diagnosis of arthrofibrosis, other causes of stiffness following knee replacement should be excluded (ex: infection, malposition of the implants, or mechanical block to motion). In the case of AF after total knee arthroplasty (TKA) management typically consists of attempt at aggressive physical therapy, and in the case that fails manipulation under anesthesia (MUA). The rates of MUA after TKA vary widely. There are several reasons for this: there is no definite consensus to when a MUA is required (different surgeons follow different indications), there is no standardized definition of arthrofibrosis (see above), and depending on how and when it is performed MUA is not always a reliable treatment. For these reasons treatment patterns vary widely. Successful MUA depends on many variables. MUA after TKA has been found to be most successful if performed in the first 8-12 weeks after surgery. After 12 weeks manipulation is much less likely to have an acceptable outcome. If the fibrosis is chronic (more than 12 weeks) there is a decreased likelihood of success with MUA and an increased chance of success with open lysis of adhesions or revision surgery, however this carries with it the attendant risks of another open procedure (i.e., infection, blood clots, blood loss, etc).  http://kneearthrofibrosis.com  http://www.kneeguru.co.uk/KNEEnotes/primers/complications-rehabilitation/key-arthrofibrosis-resources-kneeguru-site