Lateral Collateral Ligament of the Knee
Insertion: Fibula head
At the proximal level this ligament is closely related to the joint capsule, without having direct contact, as it is separated by fat pad, The insertion is augmented by the iliotibial band. The popliteus tendon is deep to the LCL, seperating it from the lateral meniscus. The LCL further splits the biceps femoris into two parts.
The LCL stabilizes the lateral side of the knee joint, mainly in varus stress and posterolateral rotation of the tibia relative to the femur. The LCL acts as a secondary stabilizer to anterior and posterior tibial translation when the cruciate ligaments are torn. 
It is primary restraint to varus rotation from 0-30° of knee flexion. As the knee goes into flexion, the LCL loses its significance and influence as a varus-stabilizing structure. When the knee is extended, the LCL is stretched.
The incidence of LCL injuries are relatively low (6%) when compared to other knee injuries. It is commonly associated with other knee ligament injuries, thus LCL tear can be easily overlooked as a result of that.
- A direct blow to the anteromedial knee and posterolateral corner
- Non-contact hyperextension
- Non-contact varus stress
Patient position: Legs crossed with ankle resting on opposite knee (90° knee flexion, hip abduction and external rotation)
In this position the iliotibial band relaxes and makes the LCL easier to isolate. The ligament lies laterally and posteriorly along the joint line. Ocassionally, the LCL is congenitally absent.  When LCL is injured or torn, this cordlike band is not as noticeable as on the unaffected side.
Adduction (varus) stress test
Purpose: The varus stress test shows a lateral joint line gap.
Performance: A varus stress test is performed by stabilizing the femur and palpating the lateral joint line. The other hand provides a varus stress to the ankle. The test is performed at 0° and 20-30°, so the knee joint is in the closed packed position. The physiotherapist stabilize the knee with one hand, while the other hand adducts the ankle.
Interpretation: If the knee joint adducts greater than normal (compared to the unaffected leg), the test is positive. This an indication of a LCL tear.
Other structures involved:
- 0°: Posteriolateral capsule, arcuate-popliteus complex, anterior and posterior cruciate ligaments, lateral gastrocnemius
- 20-30°: Posteriolateral capsule, arcuate-popliteus complex, iliotibial band, biceps femoris tendon
Reliability and validity:
- Sensitivity: 25%. Specificity: not reported. Varus stress testing was performed in 20° of flexion, and testing in extension was not done.
- Sensitivity: 25% . The reliability of this test in extension is 68% and in 30° flexion only 56%. The test is fairly solid.
- If the varus stress test is positive at 20°, but negative at 0°, only the LCL is torn. A positive result at both 0° and 20° indicate cruciate ligament involvement.
Additional tests for detecting LCL injury with other knee ligaments:
- External Rotation-Recurvatum Test
- Reverse Pivot Shift Sign of Jakob, Hassler, and Stäubli
- Dial Test
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