When knee discomfort arises, healthcare professionals use various diagnostic tests to assess knee stability. The varus stress test is one such method, specifically designed to evaluate the lateral side of the knee.
Understanding Knee Ligaments
The knee joint relies on a complex network of ligaments for stability and controlled movement. Ligaments are strong, fibrous bands of connective tissue that connect bones, preventing excessive motion. The major ligaments include the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL). The LCL, located on the outside of the knee, resists forces that push the knee inward, preventing excessive sideways movement.
Purpose of the Varus Stress Test
The varus stress test assesses the lateral collateral ligament (LCL) and other structures on the outer side of the knee. It determines if the LCL has been stretched or torn, helping diagnose sprains or complete ruptures. Doctors typically perform this test when a person reports pain, swelling, or instability on the outer knee. LCL injuries often result from a direct blow to the inside of the knee, which forces the lower leg outward.
Performing the Test
A healthcare professional performs the varus stress test with the patient lying on their back. The examiner positions themselves next to the injured knee, supporting the leg to ensure the muscles are relaxed. The test involves applying force to the knee joint.
The test is typically performed in two positions: with the knee fully extended and again with the knee flexed to about 30 degrees. In both positions, the examiner places one hand on the inside of the knee and the other hand around the ankle. They then apply a gentle force to the outside of the knee, pushing the lower leg inward, while simultaneously stabilizing the thigh.
Testing at full extension assesses the LCL along with the posterior cruciate ligament (PCL) and the posterolateral capsule. Flexing the knee to 30 degrees isolates the LCL more effectively. Any excessive gapping or pain during this maneuver indicates a potential injury to the LCL or surrounding lateral structures.
Interpreting Test Findings
During the varus stress test, a healthcare professional observes the degree of gapping on the lateral side of the knee. A “positive” test result means noticeable laxity or excessive gapping compared to the uninjured knee. This gapping, along with reported pain, suggests an injury to the LCL or other lateral knee structures.
The extent of gapping helps classify the severity of the ligament injury. A Grade I sprain involves microscopic tearing of ligament fibers with minimal gapping and pain. A Grade II sprain indicates a partial tear, causing some noticeable gapping but a firm endpoint. A Grade III injury signifies a complete rupture, characterized by significant gapping and no firm endpoint.
Next Steps After Testing
Following a varus stress test, the healthcare professional discusses the findings. If the test suggests an LCL injury, further diagnostic imaging, such as a magnetic resonance imaging (MRI), may be recommended. An MRI provides detailed soft tissue images, confirming ligament damage and identifying any other associated injuries.
Based on test results and imaging, a personalized treatment plan is developed. Minor sprains (Grade I or II) often respond to conservative management, including rest, ice, compression, elevation (RICE), and physical therapy to restore strength and range of motion. More severe injuries, such as Grade III tears, might require bracing or surgical repair to restore knee stability.