The largest articulating joint in the body, the knee is comprised of the medial and lateral femoral condyles, medial and lateral tibial plateaus, and the patella. Soft tissue structures include the anterior cruciate (ACL), posterior cruciate (PCL), medial collateral (MCL), and lateral collateral (LCL) ligaments; the medial and lateral menisci; the joint capsule; and the tendons associated with the knee musculature.

The knee ligaments provide stability. The ACL and PCL prevent anterior and posterior displacement of the tibia on the femur, respectively, attaching to the intra-articular portions of the femur and tibia. The MCL, originating below the adduction tubercle of the femur and attaching to the upper medial tibia, limits abduction and assists in controlling knee rotation. The LCL controls adduction, attaching to the lateral epicondyle of the femur and head of the fibula. The menisci are semilunar crescent-shaped structures on the tibial plateaus. They increase joint stability

Meniscal The medial meniscus is three times more likely to tear than is the lateral.⁵ The meniscus is usually injured by a noncontact rotational force on a partly or completely flexed knee, an injury commonly seen in tennis players. Patients may report hearing their knees “pop” but are able to continue with their activities, noting an effusion more than 12 hours after injury. Patients commonly experience stiffness, painful locking, or clicking and sometimes describe the knee as “giving way.” They may report pain and difficulty with squatting and/or climbing and descending stairs.¹

MCL This is the most commonly injured knee ligament. The damage usually results from a valgus blow but may also occur with external rotation while the foot is planted. Patients experience localized swelling and tenderness over the injured area within 12 hours of the injury. Football, soccer, hockey, and rugby players typically damage the MCL by a direct sideways blow. Skiers and wrestlers may also hurt the MCLs by twisting the knee.⁶

ACL ACL injuries have a presentation that is more than 70% accurate for diagnosis.⁷ The ACL is the second most commonly injured knee ligament, and damage is usually caused by a noncontact pivoting/twisting movement with the foot planted, a sudden deceleration, or hyperextension.^5,8 The patient will notice an audible “pop” at the time of injury, experience extreme pain, and be immediately disabled. The history includes swelling a few hours after the injury and the patient’s sense that the knee will give way. This injury is seen in skiers, gymnasts, and football, basketball, and soccer players.

PCL and LCL The PCL is three times stronger than the ACL,⁷ so an anterior blow to the tibia with the knee flexed has to occur in order for it to be damaged. Patients may report pain at the back of the knee that worsens when they kneel and a mild effusion within a few hours after injury. Football, basketball, soccer, and rugby players suffer from this type of injury. The mechanism of LCL injury is a varus blow or rotational force on a planted foot or extended knee. In addition to a mild effusion within a few hours after injury, there is tenderness along the lateral joint line. The LCL is the ligament least likely to be injured because the blow to the medial aspect of the knee would be to an area that is usually shielded by the opposite leg.

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