Complications
Bone bruising may accompany ACL tears and is thought to set in motion a biochemical cascade, which, even in reconstructed knees, may lead to posttraumatic arthrosis.[109]
Concomitant MCL tears have been found in up to 21% of ACL tears, with the classic unhappy triad (i.e., ACL tear, MCL tear/sprain, medial meniscus tear) being less common. Also, multiple ligament knee injuries may occur as the result of substantial trauma. The ACL, PCL, and MCL may all be ruptured, sometimes along with the lateral ligamentous complex. These devastating injuries usually result in a frank knee dislocation, which can be limb-threatening.[110]
The etiology of PTA is likely multifactorial, including direct chondral injury, meniscal tearing with altered joint loading, and recurrent instability episodes. Pain, instability, and impaired proprioception can result in disuse, muscle atrophy, and weight gain, which all increase the risk for arthrosis.[113] There is also evidence that the initial injury disturbs the normal milieu of the cartilage and joint fluid, setting in motion an inflammatory and apoptotic cascade.[114][115] Over time, this may lead to further cartilage degeneration. Many options exist for treating PTA, but prompt diagnosis and expert, individualized treatment of the initial injury is perhaps the best way to minimize the chance of this complication.
ACL tears are frequently complicated by injuries to other structures in the knee. A meniscal tear occurs in up to 81% of ACL injuries, with the lateral meniscus more likely to be injured acutely and the medial meniscus more likely to be torn in a patient with a chronic ACL tear.[106]
A meniscal tear may occur at the time of the initial ACL injury, as the meniscus is ground between the femur and tibia. This injury is more likely to affect the lateral meniscus. The tear may also develop over time as a result of recurrent instability (more likely for medial meniscus).[107][108] Meniscal tears can be repaired or excised and trimmed at the time of reconstruction. If a tear develops later, it can be addressed at that time. However, fixing a torn meniscus without reconstructing the torn ACL may be fruitless as recurrent instability can lead to repeated meniscal injury.
Mild chondral injury often occurs at the time of ACL tearing, as the femur and tibia bang against each other.[111] Increasing age, height, weight, and body mass index may also increase the risk for meniscal and articular cartilage injury.[112] Over time, recurrent instability episodes may cause further cartilage damage. Although no method yet exists for fully restoring normal articular cartilage, techniques can be combined with ACL reconstruction to address full-thickness chondral defects.
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