Medial Knee Ligament Tear

William in Belfast, Northern Ireland asks:

"I've torn my medial ligament and stretched my anterior cruciate ligament on the inner part of my knee. I was wondering if I will tear my cruciate now that I have stretched it?"

Dr Christopher Piller, MD, Orthopedic Fellow, American Sports Medicine Institute and Dr Lawrence Lemak, MD reply:

"The diagnosis of a 'stretched' or partially torn anterior cruciate ligament (ACL) is controversial. This diagnosis is difficult to make accurately based solely on physical exam findings or an MRI scan. Increased knee laxity with a soft endpoint found in an ACL on manual testing after an injury almost universally means a complete tear. Increased laxity with a solid endpoint (the so called 'stretched' ACL) can be due to a portion of the fibers being torn while some remain intact, or result from a complete tear that has managed to scar down or heal in such a way that it can still provide some stability in preventing abnormal forward movement of the tibia (shin bone).

"Many surgeons base the diagnosis of a partial ACL tear on the findings at arthroscopy, and the incidence in published studies ranges from 10 to 50% of all ACL injuries. The incidence is most likely closer to 10% if all diagnostic tools are utilized, including consideration of injury mechanism and concurrent injuries, objective manual laxity testing, MRI results, examination under anesthesia and arthroscopic findings. An exam under anesthesia, demonstrating abnormal pivoting (where the knee joint virtually subluxes due to instability), and anterior translation of a knee, is probably the single most accurate way to distinguish a partial tear from a complete tear.

"Injuries to the medial collateral ligament (MCL) occur in approximately 20% of all ACL injuries. Initially, depending upon the severity of the injury to the MCL, the knee will be more prone to instability than if the ACL was torn by itself. However, with proper rehabilitation and management, even completely torn MCLs have been shown to heal well without surgery and should not affect the long term stability and functional abilities.

"That being said, there are few studies that tried to predict the risk of residual instability and further knee injury with a half torn ACL found at arthroscopy. One study found a 50% incidence of instability and a 75% incidence of further knee injuries with a partial tear. Another study, however, demonstrated a very low incidence of instability, limitations with sports or work activities, or the development of arthritis. Out of 21 patients, none went on to require ACL reconstructive surgery. This discrepancy is most likely due to a difference in the demands and expectations of the patients studied.

"Although it is very difficult to predict the likelihood of completely rupturing your partially torn ACL, general guidelines have been established for addressing a situation such as yours. For the person who has sustained a true partial ACL tear, treatment must be customized. If the tear is estimated at greater than 50% of the ligament fibres; if there are symptoms of instability present (buckling or 'giving way' of the knee); or the patient is in a high-risk or high demand category (athlete, manual laborer) then early ACL reconstruction should be considered to prevent later problems of re-injury or arthritis. Patients with a tear less than 50% of ligament fibres, or patients with a sedentary lifestyle and no symptoms of instability, can be treated conservatively. Of this group, perhaps 10% of patients may later go on to require ligament reconstruction due to re-injury or onset of instability."

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Article published: 20th December 2003