Cite This Article

Do, M. Martin, P. Tomesch, A. Notch Your Average Sign. Ortho Pearls. July 3, 2024; Available: https://www.orthoempearls.com/articles/notch-your-average-sign

What is the diagnosis?

Anterior Cruciate Ligament (ACL) Tear. The imaging on a plain radiograph shows a lateral femoral notch sign, which is an indirect sign of a torn ACL. 

Image 2. Plain radiograph in lateral view of left knee. Author’s own images. Specifically showing the lateral femoral notch sign suggestive of an ACL tear. The depth of the lateral notch is measured by drawing a line from the normal articular surface of the lateral femoral condyle and measuring the depth of the depression. In this case, the depression is 1.9mm deep. 

• Pearl: The lateral femoral notch is due to an abnormal deepening of the lateral condylopatellar sulcus from an osteochondral impaction fracture.

• Pearl: A lateral femoral notch sign with a depth of greater than 1.5 mm is a reliable sign of a torn ACL [1]. 

What is the mechanism of injury?

ACL tears often result from a pivoting injury in which the tibia translates anteriorly while knee is slightly flexed and in valgus [2]. 

What physical exam findings are expected?

History: 

• Patient describes a sudden “pop” with immediate pain and swelling after an injury involving sudden changes in the direction of movement. 
• Injury can be a contact or non-contact injury.
• Patients typically have difficulty ambulating after the injury [2]

Physical Exam Findings:

• Significant effusion and joint line tenderness on palpation 
• Reduced knee range of motion 
• Positive provocative maneuvers: Lachman test, anterior drawer test, pivot shift test, lever sign test

Which imaging modalities can be used?

Although the lateral femoral notch sign can be appreciated on plain radiography and is an indirect sign of ACL tear, an MRI is the primary imaging modality to diagnose ACL pathology. 

Additionally, knee arthroscopy can differentiate between partial and complete tears of the ACL. 

What is the management in the ED?

There is typically no need for emergent intervention in an isolated ACL injury. However, the ED physician may discharge the patient home in a hinged knee brace or ACE wrap with crutches to aid in non-weight bearing or protected weight bearing [4], recommend “RICE” therapy, and refer the patient to an outpatient orthopedics appointment. 

When do you consult Orthopedics? What do you do to follow up?

Orthopedics can be consulted on an outpatient basis once there is suspicion for ACL injury. An MRI can help differentiate the decision to pursue nonoperative vs operative management, which can also be performed in the outpatient setting. The physician also considers the patient's age, activity level, comorbidities, and sports participation [2]. Non-operative management consists primarily of physiotherapy, yet physiotherapy is also recommended with operative management. Surgical options are repair or reconstruction of the ruptured ACL. 

• Pearl: In higher level athletes sooner orthopedic evaluation and subsequent surgery is better.