Knee Extensor Mechanism Injuries

Extensor mechanism knee injuries are a common clinical entity seen by physicians in a variety of clinical settings. The extensor mechanism is critical for normal gait, activities of daily living, and sports. Injuries to this process can be divided into traumatic and non-traumatic mechanisms.  It is critical to understand the anatomy of knee extension. From proximal to distal, the primary extensors anatomy of the knee includes the quadriceps muscle, the patella, and the patellar tendon. The quadriceps muscle group includes the rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis. The rectus femoris originates from the anterior inferior iliac spine, the vastus lateralis from the lateral greater trochanter, the vastus medialis from the femoral neck, and the vastus intermedius from the femoral body. These muscles converge to form the quadriceps muscle tendon, which attaches to the superior pole of the patella. Synchronous contraction of these muscles results in lower leg extension. The patella fits within the trochlear groove of the femur and acts as an anchor for the quadriceps and patellar tendons. The patellar tendon originates at the inferior pole of the patella and inserts into the tibial tuberosity. The retinacula of the extensor mechanism are composed of connective fibers from the quadriceps muscle group and are divided into medial and lateral portions. They include the patellofemoral, vastus medialis, medial collateral, patellotibial, and medial patellomeniscal ligaments. These ligaments provide stability to the osseous components of the knee. The soft tissue structures of the knee include the quadriceps, prefemoral, and infrapatellar fat pads. Lastly, the suprapatellar, pretibial, and prepatellar bursae provide a cushion against friction and assist in movement. The blood supply to the knee structures is provided by the lateral and inferior genicular arteries, which are branches of the femoral artery. The nerve supply is provided by branches of the tibial, femoral, obturator, and common peroneal nerves.