Lateral Collateral Ligament Knee Injury

Excerpt

The lateral collateral ligament (LCL), also known as the fibular ligament, is one of the knee joint's key stabilizers (see Image. Left Knee Ligaments). This fibrous structure originates from the lateral femoral epicondyle and inserts on the fibular head. The LCL is part of the knee's "posterolateral corner" (PLC) along with the biceps femoris tendon and fibular collateral, fabellofibular, popliteofibular (PFL), and arcuate ligaments, though this region's anatomy is variable. The LCL primarily prevents excess varus stress and posterolateral knee rotation. LCL and PLC injuries are the least frequent of all knee injuries but still warrant high suspicion during knee exams.

Anatomy

The LCL's origin is located 1.4 mm proximal and 3.1 mm posterior to the lateral epicondyle of the femur. The LCL inserts anteriorly on the fibular head, 28.4 mm distal to the fibular styloid tip, covering nearly 38% of the fibular head. The common fibular nerve innervates the LCL. The ligament's blood supply arises from the popliteal artery, primarily from the anterior tibial recurrent arteries and branches of the superior and inferior lateral genicular arteries.

Unlike the MCL, which is fan-like, the LCL has a cord-like shape. Additionally, the LCL lacks the meniscal and joint capsule attachments the MCL has. The LCL has a thickness of 2 to 3 mm, a width of 4 to 5 mm, and a length of 69.9 mm.

Deep to the LCL lies the popliteus tendon (PLT), which originates 18.5 mm anterior and distal to the LCL and measures 55 mm long on average. Superficial to the LCL is the superficial layer of the iliotibial band (ITB), which inserts along the knee's anterolateral portion at Gerdy's tubercle. However, the LCL is exposed in its distal quarter anteriorly and laterally in a location often serving as a surgical entry window.

Biomechanics

The LCL is the primary stabilizer of varus stress in all degrees of knee flexion, with the PLT, ITB, cruciate ligaments, and biceps and lateral gastrocnemius tendons acting as secondary varus stabilizers. The LCL combines with the fabellofibular, popliteofibular, and arcuate ligaments to become the static PLC stabilizer. The LCL also secures the knee posterolaterally, preventing medial tibial translation.

The LCL helps restrain external tibial rotation and posterior tibial displacement in 0° to 30° of knee flexion. Typically, the PFL resists external tibial rotation as knee flexion increases past 60°. Beyond 60° of flexion, the LCL contributes to limiting knee external rotation but to a lesser degree than the PFL.

Studies show that the LCL and PLC structures play minor roles in stabilizing anterior and posterior tibial translation when the cruciate ligaments are torn.