text: if you tear your acl, is surgery necessary? acl stands for anterior cruciate ligament.  i'd rather hear from people who have experienced, or knows about the topic. thanks! i was in a bad auto accident where my acl was severed in 2 places and underwent surgery.   treatment of an acl tear is most dependent on how much knee instability is caused by the injury. therefore, there is no critical cutoff (i.e. 50%) for determining when acl reconstruction surgery is necessary in the setting of a partial acl tear. rather, the decision should be based on a combination of symptoms (instability, episodes of 'giving way,' etc.) and physical examination findings (lachman test, pivot-shift). if there is instability perceived by the patient, and physical exam findings consistent with laxity of the acl, then reconstruction is a reasonable option.  unfortunately, incomplete tears of the acl are difficult to assess. when looking at an injured acl during an arthroscopy, your surgeon can assess the look and feel of the ligament to make an assessment on the extent of the injury.   good luck!   by the way, after surgery and my rehab, i was able to go back to my love of the martial arts for a while!!