Review Question - QID 5839

The politeus tendon (C) and the popliteofibular ligament (D) are the lateral knee structures that provide the most rotational stability in knee flexion. The lateral collateral ligament (B) provides varus stability and rotational stability in knee extension.

The lateral knee is stabilized by 28 unique static and dynamic structures. These structures work in concert to resist varus gapping and rotational knee instability. The three primary stabilizers include the fibular or lateral collateral ligament (LCL), the popliteus tendon (PT) and the popliteofibular ligament (PFL). Injury to these ligaments results in increased forces seen on ACL and PCL ligament reconstruction grafts with combined posterolateral corner (PLC) injuries, which can result in graft failure if the PLC is not reconstructed as well.

James et al reviewed the anatomy and biomechanics of the lateral knee stabilizers, detailing the specific functional contributions of the individual structures. The LCL is the primary restraint to varus instability, the highest forces occurring at knee extension (0°-30°). The PT and PFL serve as restraints to rotational instability, the highest forces occurring at knee flexion (60°-90°).

LaPrade et al reviewed the anatomy and biomechanics of the medial knee stabilizers. The three key static stabilizers are the superficial medial collateral ligament (sMCL), the deep medial collateral ligament (dMCL), and the posterior oblique ligament (POL). The sMCL is the primary restraint to valgus instability (proximal sMCL) and secondary restraint to rotational instability (distal sMCL) at all knee flexion angles. The dMCL is a secondary restraint to valgus and rotational instability. The POL is the primary restraint to rotational instability.

Figure A depicts the lateral knee structures in a cadaver specimen (A = lateral meniscus, B = LCL, C = PT, D = PFL, E = lateral head of gastrocnemius). Illustration A is a labeled picture of the lateral knee structures. Illustration B is a table from James et al demonstrating the change in forces experienced by the different lateral stabilizers at varying degrees of knee flexion. You see the LCL resists rotation at 0°-30° (extension) while the PT and PFL resist rotation at 60°-90° (flexion).

Incorrect Responses:
Answer 1: The lateral meniscus (A) is a secondary restraint to anterior translation and does not provide significant rotational stability.
Answers 2 + 3: The LCL (B) provides minimal rotational stability in knee flexion, as compared to the PT and PFL.
Answer 5: The lateral head of the gastrocnemius (E) does not provide significant rotational stability.