Anterior and Posterior Cruciate Ligament

The anterior cruciate (ACL)and posterior cruciate ligaments are two of four  ligaments that are very important to the stability of the knee joint. A ligament is made of tough fibrous material and functions to control excessive movement in the joint. The ACL and PCL are positioned in the centre of the knee joint and connects the base of the thigh bone (femur) with the top of the top of the shin bone (tibia). The ACL mainly resists forward movement of the shin bone relative to the thigh bone and the PCL backwards movement.  When the ligaments are overly stretched it can result in injury, inflammation and pain on the inside ACL or outside PCL  of the knee. This results in varying degrees of instability depending on the extent of the injury.  Clinicians often refer to a grading system which classifies the extent of the injury:

  • Grade I A mild injury that causes only microscopic tears . Although these tiny tears may stretch the ligament out of shape, they do not affect the overall ability of the knee joint to support your weight.
  • Grade II A moderate injury in which the A/P CL are partially torn. The knee can be somewhat unstable and can “give way” periodically when you stand or walk.
  • Grade III A severe injury in which the ACL or PCL are completely torn through and the knee feels very unstable.



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