Diagnosis Process

May 23, 2025

Tests and procedures used to diagnose ACL injuries accurately.

Initial Evaluation

The diagnosis of an ACL injury begins with a detailed patient history. Your healthcare provider will ask about the mechanism of injury, whether you heard or felt a “pop,” the timing of swelling, and any sensation of knee instability. This history often provides valuable clues about the nature and severity of the injury.

Physical Examination

Several clinical tests are used to assess ACL integrity:

Lachman test: Considered the most reliable clinical test (sensitivity >90%), it assesses anterior tibial translation while the knee is flexed 20-30 degrees
Anterior drawer test: Evaluates forward movement of the tibia while the knee is bent at 90 degrees
Pivot shift test: Assesses rotational stability of the knee
Examination for associated injuries: Including meniscal tears, other ligament damage, and cartilage injuries

Imaging Studies

Diagnostic imaging confirms the diagnosis and assesses for associated injuries:

X-rays: While they cannot visualize ligaments directly, they can identify associated fractures or avulsions
MRI (Magnetic Resonance Imaging): The gold standard for diagnosing ACL tears, with approximately 95% accuracy. MRI can also reveal meniscal tears, cartilage damage, bone bruises, and other ligament injuries. However, the MRIs don’t necessarily show everything. Or even if they indicate issues, they may not be definitive in terms of degree.
Ultrasound: Sometimes used for dynamic assessment but less common than MRI

Grading ACL Injuries

ACL injuries are typically categorized as:

Grade 1: Mild damage; the ligament is stretched but still provides knee stability
Grade 2: Partial tear of the ligament; rare in ACL injuries
Grade 3: Complete tear; the ligament is split into two pieces and the knee is unstable

Time

Orthopedists may want to have some time in between injury and imaging studies or after imaging studies and making surgical decisions to see how things progress. Since surgery isn’t likely to happen immediately if there are major swelling issues and such, it’s likely useful to to to physical therapy for awhile and see how things progress. (If there were other associated injuries, those might have to be dealt with earlier of course.) The point is, it might be useful to take some time in between initial consult and more definitive tests to do some “prehab” to see how things develop.