Posterolateral Corner Of The Knee

There has been much confusion about the proper description of the posterolateral corner (PLC).
Seebacher and associates (Seebacher 1982) provided a detailed layer concept by dividing the structures into three layers. The first, being the most superficial, contains the iliotibial tract (ITT) and the biceps femoris. While the ITT is fundamentally thought of as inserting into Gerdy’s tubercle, there are actually three insertions. One insertion blends into the intermuscular septum and inserts onto the supracondylar tubercle via Kaplan’s fibers. The second inserts onto the patella and patellar ligament and the third inserts onto Gerdy’s tubercle. The first layer is also composed of the superficial aspect of the biceps femoris. The biceps consists of a long and short head and also has numerous insertions. The major insertion runs posteriorly to the ITT and inserts on the fibular head. The second layer is deep to the first and consists of the quadriceps retinaculum, anteriorly, as well as the patellofemoral ligaments, posteriorly. The third layer, the deepest, can also be divided into a superficial and deep lamina. Superficial are the lateral collateral ligament (LCL) and the fabellofibular ligament. The deep lamina of the third layer contains the popliteofibular ligament (PFL), arcuate ligament, and the popliteus muscle and tendon complex.

The LCL originates from the lateral distal femoral condyle and inserts onto the lateral aspect of the fibular head. The femoral site of origin is posterior to the popliteus origin and the fibular site of insertion is distal to the insertions of the arcuate and PFL. The popliteus originates from the posterior aspect of the proximal tibia and passes through a hiatus in the coronary ligament (capsular attachment to the outer edge of the meniscus) as it inserts onto the lateral femoral condyle, inferior to the LCL origin. In addition, less than 20% of the population has attachments between the popliteus tendon and the lateral meniscus, which may aid in lateral meniscal movement and stabilization (Tria 1989). The PFL connects the popliteus tendon to the posterior,
proximal region of the fibular head. The arcuate ligament is a Y-shaped ligament with medial and lateral limbs. Additional structures that may contribute to stability include the middle third of the capsular ligament, the lateral head of the gastrocnemius tendon, the lateral meniscus, and the posterolateral joint capsule.

Another description (Richetti 2008) states the PLC can be described as consisting of 5 structures (2 muscles and 3 ligaments); the lateral head of the gastrocnemius, the popliteus, the popliteofibular ligament, the lateral collateral ligament (LCL), and the arcuate ligament­fabellofibular ligament complex. The arcuate ligament­fabellofibular ligament complex consists of the arcuate and fabellofibular ligaments in 67% of knees, the fabellofibular ligament alone in 20% of knees, and the arcuate ligament alone in 13% of knees (Seebacher 1982). The biceps femoris tendon and iliotibial band also contribute to the stability of the PLC of the knee, and may be damaged with injuries in this region.

Biomechanically, the PLC acts in concert with the PCL in providing stability by resisting posterior translation and external and varus rotation of the tibia on the femur (Chen 2000; Larson 2003). The PLC serves as the primary restraint to both varus and external rotation forces, with the PCL acting as a secondary restraint (Covey 2001; Shahane 1999; Veltri 1996; Veltri 1995). The LCL plays the greatest role in resisting varus stress, while the other components of the PLC play a larger role in resisting external rotation of the lateral side of the tibia on the femur. The popliteus and popliteofibular ligament, in particular, have been shown to be the most important structures in resisting external rotation (Maynard 1996; Shahane 1999; Veltri 1996; McGuire 2003; Sugita 2001; Nau 2005; Stannard 2005). Therefore, repair or reconstruction of the PLC typically attempts to recreate the LCL for varus stability and the popliteus and/or popliteofibular ligament for stability in external rotation. The PLC also acts as a restraint to posterior translation of the tibia on the femur, secondary to the PCL. Therefore, disruption of the PLC with an intact PCL results in increased varus and external rotation of the knee, most pronounced at 30° of knee flexion, while disruption of the PCL with an intact PLC results in increased posterior translation of the tibia, most pronounced at 90° of knee flexion. Disruption of both the PLC and PCL causes increased varus angulation, external rotation, and posterior translation at all angles of knee flexion (Covey 2001, Larson 2003). PLC and PCL disruption also increases medial, lateral, and patellofemoral compartment pressures that can lead to early degenerative joint disease in these compartments if the biomechanical integrity of these structures is not restored (Anderson 1995; Skyhar 1993).

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