Diagnosing an ACL tear: from clinical examination to MRI

The clinical examination: the first and often most decisive step

Before any imaging, the clinical examination guides the diagnosis. It consists of several stages:

• Patient history : the surgeon reconstructs the circumstances of the trauma (mechanism of injury, sensations felt, symptom progression) and assesses the level of instability experienced by the patient. ‍
• The Lachman test : this is the gold-standard clinical test for the ACL. The surgeon evaluates the forward displacement of the tibia relative to the femur with the knee slightly flexed. Excessive movement without a firm endpoint strongly suggests a tear. ‍
• The anterior drawer test and the pivot-shift test : two complementary examinations that assess anterior instability and rotational instability of the knee, respectively. ‍
• Repeating the examination at a later date In the first few hours following an injury, pain and swelling make the examination difficult to interpret. A clinical assessment performed 2 to 3 weeks later, once the swelling in the knee has gone down, is often more reliable and comprehensive.

MRI and other tests: mapping all injuries

Imaging complements and refines the clinical diagnosis. Each test has a distinct role.

Standard X-ray

It does not show ligaments, but it helps rule out an associated fracture. It can also reveal indirect signs of an ACL tear, such as a Segond fracture (a bone fracture on the outer edge of the tibia, which is indicative of a severe ligament injury).

MRI (Magnetic Resonance Imaging)

This is the gold standard test. It provides a direct view of the ACL and allows for the assessment of:

• the severity of the tear (partial or complete, one or two bundles)
• the condition of the menisci (medial and lateral)
• any potential cartilage damage
• other ligament structures (PCL, collateral ligaments, anterolateral ligament)
• bone bruises, which are common in pivot-type injuries

MRI is highly reliable for diagnosing ACL tears. However, interpretation can vary depending on the radiologist, particularly for partial tears or subtle cartilage lesions: a careful review of the raw images, rather than relying solely on the radiology report, provides valuable additional information.

Additional tests depending on the situation

• TELOS stress radiography (dynamic stress X-rays): objectively quantifies ligament instability and allows for a comparison between both knees. ‍
• CT arthrography : an alternative to MRI in cases of contraindications (metallic implants, claustrophobia), providing a clear view of the cartilage. ‍
• GNRB (instrumented arthrometer): measures tibial displacement in a reproducible way, useful for follow-ups or when in doubt. ‍
• EOS imaging : weight-bearing imaging of the lower limbs, useful for assessing limb alignment and guiding surgical planning.

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Why a comprehensive diagnosis changes the treatment plan

Therapeutic decisions cannot be based on an incomplete diagnosis. Three factors often make the difference.

• Partial vs. complete tear : a partial tear can, in some cases, be treated without surgery. A complete tear in an athletic patient more often points toward ligament reconstruction. This distinction requires high-quality MRI and a rigorous clinical examination. ‍
• Identifying associated injuries : an undiagnosed meniscal or cartilage injury can worsen long-term functional outcomes. When identified beforehand, it can be treated during the same surgical procedure as the ligament reconstruction. ‍
• Patient profile integrated into the interpretation : age, activity level, and perceived functional instability are all analyzed alongside imaging data. The same MRI result does not lead to the same conclusions for a 22-year-old soccer player as it does for a 55-year-old sedentary patient.

By analyzing the entire file—including raw MRI images, clinical assessment, and patient profile—a knee surgery specialist can provide a personalized opinion on the most appropriate strategy. This comprehensive approach provides greater clarity before committing to a treatment plan.

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