THE LATERAL COMPARTMENT
The Lateral Collateral Ligament
The lateral collateral ligament originates from the lateral femoral condyle and proceeds distally 5-6 cm between the deep and superficial laminae of the joint capsule to insert into the fibular head.
The Lateral Capsuloligamentous Complex
Like the medial side, the lateral complex is separated into three layers numbered I, II, and III.
Deep Layer (III)
This layer consists of the joint capsule and the lateral collateral ligament. It can also be conceptualized as anterior, middle, and posterior portions. The anterior 1/3 attaches to the meniscus, and is reinforced by the lateral extension of the quadriceps retinaculum. The middle 1/3 avulsion results in a Segond’s fracture. The popliteus tendon perforates through the posterior 1/3. Posterior to the iliotibial band, the deep layer divides into a superficial and a deep laminae, between which the lateral collateral ligament runs.
More posteriorly, the deeper laminae condenses into the arcuate ligament, which also originates from the styloid process of the fibular head. The arcuate ligament interdigitates with and crosses over the popliteus muscle and inserts into the posterior capsule near the termination of the oblique popliteal ligament in the posterior capsule. The “arcuate complex” is the combination of the arcuate ligament, the popliteal tendon, the lateral collateral ligament, and the lateral head of gastrocnemius. The superficial laminae forms the fabellofibular ligament. Both the arcuate ligament and fabellofibular ligament connect the styloid process of the fibula to the femoral insertions of the lateral gastrocs and oblique popliteal ligament. In knees without a fabella, the fabellofibular ligament is obviously absent; the arcuate ligament becomes correspondingly robust. In knees with a large fabella, the fabellofibular ligament may be robust and the arcuate ligament absent.
The popliteus muscle originates on the posterior tibia; the tendon courses beneath the LCL and around the lateral femoral condyle to insert into the lateral condyle just anterior and inferior to the LCL insertion. The tendon travels along the side of the lateral meniscus, passing through a defect in the coronary ligament attachment.
The popliteofibular ligament is felt to be an important part of the posterolateral capsuloligamentous complex. It originates from the posterior fibula and inserts into the tendon of popliteus just proximal to the musculotendinous junction. It is called the popliteofibular ligament because it connects the fibula to the femur through the popliteus tendon, making the popliteus muscle-tendon unit into a Y-shaped structure with one limb inserting into the fibula and one limb inserting into the femur.
Intermediate Layer (II)
This layer consists of the quadriceps/patellar retinaculum, originating from the iliotibial tract and capsule and running medial to the patella. It is incomplete posteriorly.
Superficial Layer (I)
This layer consists of the deep fascia of the thigh and leg, enveloping the iliotibial tract in the anterolateral position and surrounding the biceps femoris tendon posterolaterally. The common peroneal nerve lies just deep to this layer
The “Posterolateral Corner”
The posterolateral corner refers to the capsuloligamentous structures of the posterolateral knee, with the most significant structure being the arcuate complex. Tears through the posterolateral capsule lead to posterolateral rotatory instability, usually associated with disruptions of the lateral collateral ligament or the PCL or with knee dislocations