The ACL is the most commonly torn knee ligament, and is the ligament often torn by footballers or skiers. In about 50% of patients with an ACL tear, other structures (such as the meniscal cartilages) are also damaged at the same time. The ACL sits in the middle of the inside of the knee like a taught bungie cord surrounded in joint fluid. If the ligament ruptures, then the ends tend to ping apart and fray. Direct repair of a rupture in the middle of the ligament is never normally possible. Some patients will do well without surgery, through intensive physiotherapy to build up the strength of the muscles around the knee to compensate for the absent ACL. However, a large proportion of patient do not do well, and their knee will feel wobbly and will give way on a regular basis. In these patients, surgical reconstruction is recommended.
Ruptures of the PCL are rarer than ACL tears. If the PCL does rupture, then other knee structures are normally also damaged at the same time, particularly the posterolateral corner complex. Isolated PCL tears often do well treated conservatively. However, combined ligament tears, eg the PCL and the Posterolateral Corner, normally require surgical reconstruction.
Sprains (partial tears) or even complete tears of the MCL are normally best left alone, and treated conservatively with a knee brace. This is because the MCL is a wide broad ligament with a very good blood supply, and it therefore has the ability to heal up well on its own.
The LCL is a thinner cord-like ligament. Ruptures of the LCL are frequently associated with damage to the Posterolateral Corner, and often require surgical reconstruction.
The Posterolateral Corner (PLC) is an area of the knee that has been the focus of much attention over recent years. It is now appreciated that a significant percentage (perhaps as high as 10%) of ACL tears are associated with concomitant PLC tears. A missed PLC tear is a common reason for a poor outcome after isolated reconstruction of the ACL, as the ACL reconstruction on its own will not correct the rotational instability caused by deficiency of the PLC. PLC injuries also occur very frequently in association with PCL tears. Deficiency of the PLC with significant rotational instability is an indication for surgical reconstruction.
Article written by
Mr Ian McDermott
Consultant Knee Surgeon and Hip Surgeon, London & Northwood
Last updated 13/01/10
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