PCL

**Anatomy** - Attachments: it originates from the lateral surface of the medial femoral condyle and inserts on the posterior intercondylar area of the tibia. - Function: it is the primary restraint to posterior tibial translation. It is the strongest knee ligament and the central stabilizer of the knee. - Bundles: the larger anterolateral bundle is tight in flexion. The smaller posteromedial bundle is tight in extension. - Blood supply: the middle genicular artery, a branch of the popliteal artery. - Mnemonic: "PCL = Posterior tibial displacement; ACL = Anterior tibial displacement." The cruciate ligaments are named by their tibial insertion. The ACL attaches to the anterior tibia and the PCL to the posterior tibia. They cross each other, hence "cruciate." - Mnemonic: the ACL runs from the lateral femoral condyle to the anterior tibia ("Lateral-Anterior"). The PCL runs from the medial femoral condyle to the posterior tibia.

**Mechanism of injury** - Dashboard injury: in a motor vehicle collision, the flexed knee strikes the dashboard and the tibia is forced posteriorly. This is the classic mechanism. - Fall onto a flexed knee with a plantarflexed foot. - Hyperextension or knee dislocation, often with multiligament injury. - Sports injuries are common, such as football and soccer. - PCL injuries are less common than ACL injuries (ACL is the most commonly injured knee ligament). Isolated PCL tears are less common than combined injuries.

**Clinical presentation** - Pain and swelling, often milder than with an ACL tear. Many isolated tears are subtle or missed. - A feeling of instability, especially going down stairs or inclines. - Pain at the posterior knee, or anterior knee pain from patellofemoral degeneration with chronic injury.

**Physical exam** - Posterior drawer test: with the knee at 90° flexion, a posterior force on the tibia produces excess posterior translation. This is the most sensitive and specific test. - Posterior sag sign (Godfrey test): with the hip and knee flexed to 90°, the tibia sags posteriorly. - Quadriceps active test: the quadriceps contracts and the tibia reduces anteriorly from its posteriorly subluxed position. - Compare with ACL tests. The anterior drawer and Lachman test (most sensitive for ACL) show anterior tibial translation. The "unhappy triad" (O'Donoghue) is ACL + MCL + medial meniscus.

**Imaging and diagnosis** - X-ray: rule out fractures, including tibial avulsion. - MRI is the diagnostic study of choice. The ligament appears as a thick, low-signal band with disruption when torn. - Stress radiographs can quantify posterior laxity.

**Management** - Isolated grade I-II tears: nonoperative treatment with a hinged knee brace, rehabilitation, and quadriceps strengthening. Quadriceps strengthening protects the knee because the quadriceps pulls the tibia anteriorly. - Grade III tears or combined ligament injuries: surgical reconstruction. - Avulsion fractures with displacement: surgical fixation. - Always check neurovascular status in knee dislocations. Popliteal artery injury is a limb-threatening complication. Common peroneal nerve injury can also occur, with foot drop. Obtain an ankle-brachial index (ABI) and, if abnormal, CT angiography.

**Complications** - Chronic instability. - Early-onset osteoarthritis, particularly of the medial compartment and patellofemoral joint. - Associated meniscal and cartilage injuries.

**High-yield pearls** - PCL = posterior drawer; ACL = anterior drawer and Lachman. - Dashboard injury suggests PCL. A pivoting or non-contact injury with a "pop" suggests ACL. - Knee dislocation: consider popliteal artery injury and perform vascular assessment. - Other abbreviations: "PCL" can also mean "pericardial/pleural" in some contexts, but on boards it nearly always means posterior cruciate ligament. In ophthalmology, "PCL" can denote posterior chamber lens, and in dentistry/biomaterials, polycaprolactone.