Posterior Sag Sign

What is a posterior cruciate ligament tear?

A posterior cruciate ligament (PCL) tear is a significant knee injury, often resulting from trauma or sudden force applied to the knee. The PCL is one of the key stabilizing ligaments in the knee joint, preventing the femur from moving too far forward over the tibia. Although less frequently injured than the anterior cruciate ligament (ACL), a PCL tear can severely impact knee stability and function.

In the case study by Ermer, Sharma, and Saxena (2019), a 55-year-old man presented with worsening knee pain and instability. Despite having no recent trauma, his history of playing sports like football and baseball could have contributed to the chronic nature of his PCL tear. Diagnostic tests, including physical examinations and an MRI, confirmed a complete tear of the PCL along with a torn medial meniscus.

One key physical examination finding for diagnosing a PCL tear is the Posterior Sag Sign, where the tibia sags backward when the knee is bent. This sign is highly specific and sensitive to posterior cruciate ligament injuries. Other tests, like the posterior drawer and Lachman tests, also help confirm the diagnosis (Ermer et al., 2019).

Symptoms of this tear

A posterior cruciate ligament tear manifests through several key symptoms that can significantly affect daily activities and overall knee stability.

• Pain
• Instability
• Swelling
• Limited mobility
• Tenderness

What can tear posterior cruciate ligaments?

PCL tears can occur due to several common causes. Understanding these can help with prevention and treatment. According to Ermer, Sharma, and Saxena (2019), the main causes include:

• Direct impact
• Sports injuries
• Hyperextension
• Hyperflexion
• Rotational forces
• Combined injuries

What is the Posterior Sag Sign?

The Posterior Sag Sign is a clinical test for diagnosing a posterior cruciate ligament injury. It involves observing the position of the tibia (shinbone) in relation to the femur (thighbone) when the knee is bent. The assessment of the medial femoral condyle in the Posterior Sag Sign serves as a visual indicator of PCL laxity or injury. A noticeable posterior sag of the tibia relative to the femur, accompanied by a depression of the medial femoral condyle, suggests a positive test result and indicates potential PCL pathology. This observation guides further diagnostic evaluation and treatment planning for individuals suspected of having PCL injuries.

How is this assessment conducted?

The patient is lying on their back with their hips flexed and knees bent to 90 degrees, known as the "tabletop" position. The examiner observes the patient's knee profile from the side and looks for the posterior displacement of the tibia in relation to the femur. A positive Posterior Sag Sign indicates that the PCL is not functioning properly, allowing the tibia to slide backward.

To confirm a PCL tear, the examiner may perform tests like the posterior drawer test, where the patient's knee is bent to 90 degrees and the tibia is pushed backward. A positive test occurs if the tibia moves excessively backward, indicating a PCL tear.

Benefits of conducting this test

Conducting the Posterior Sag Sign test offers several benefits in the evaluation of PCL injuries, facilitating precise diagnosis and targeted management strategies to optimize patient outcomes. HEre are the benefits:

Accurate diagnosis

The Posterior Sag Sign test enables healthcare professionals to accurately diagnose posterior cruciate ligament tears, ensuring appropriate treatment and management for patients experiencing knee instability or pain.

Differential diagnosis

By assessing for a posterior sag in the knee joint, clinicians can differentiate between PCL injuries and other conditions affecting the knee, such as posterolateral corner injuries or tibial plateau fractures. This aids in providing targeted treatment strategies.

Assessment of PCL Integrity

Conducting the test allows clinicians to evaluate the integrity of the PCL, a crucial ligament in stabilizing the knee joint during activities involving flexed knee positions. Identifying a positive sag sign indicates a potential PCL injury that requires further investigation.

Confirmation of acute PCL injuries

In the case of acute PCL injury, the Posterior Sag Sign test can confirm the presence of ligamentous damage, aiding in prompt diagnosis and timely intervention to prevent further complications.

Complementary to the posterior drawer test

When used with the posterior drawer test, the Posterior Sag Sign provides a comprehensive assessment of PCL laxity and stability, enhancing diagnostic accuracy and guiding treatment decisions for patients with suspected PCL tears.

References

Ermer, J., Sharma, A., & Saxena, S. (2019, December). The Sag Sign: Posterior Cruciate Ligament Injury of the Knee. Consultant360.com. https://www.consultant360.com/photoclinic/sag-sign-posterior-cruciate-ligament-injury-knee