ACL Tear Grades Explained: Grade 1, 2, and 3

Grade 1 ACL Injury: Ligament Sprain

A Grade 1 ACL injury is a mild sprain where the ligament fibers are stretched but not torn. The ligament remains intact and continuous, and the knee joint retains its structural stability. On clinical examination, the Lachman test and anterior drawer test show a firm endpoint (the knee stops moving at the appropriate point), indicating the ACL is still functional. There may be mild swelling and tenderness, but no sensation of the knee giving way.

On MRI, a Grade 1 sprain appears as increased signal (brightness) within the ligament on T2-weighted images, indicating edema and microtrauma, but the ligament fibers remain continuous without a visible gap. Treatment is conservative: rest, ice, compression, and elevation followed by physical therapy. Recovery typically takes 2-4 weeks, and most patients return to full activity without restrictions.

Grade 2 ACL Injury: Partial Tear

A Grade 2 ACL injury involves a partial tear of the ligament fibers. Some fibers are disrupted while others remain intact, resulting in partial loss of structural integrity. This is the least common grade — most ACL injuries are either mild sprains or complete tears, with true partial tears accounting for only 10-28% of ACL injuries.

On clinical examination, the Lachman test may show increased laxity compared to the other knee, but with a soft or delayed endpoint. On MRI, a partial ACL tear shows disruption of some ligament fibers with other fibers remaining intact. The overall ligament contour may be irregular or thinned, but a continuous portion can be traced from origin to insertion. Treatment is individualized — many partial tears respond to intensive physical therapy, while patients with persistent instability may benefit from surgical reconstruction or augmentation.

Grade 3 ACL Injury: Complete Tear

A Grade 3 ACL injury is a complete rupture of the ligament. All fibers are torn, and the knee has lost this critical stabilizer. This is the most common ACL injury presentation, often occurring during pivoting, cutting, or landing from a jump, and frequently accompanied by a pop sensation and rapid swelling. On clinical examination, the Lachman test shows significantly increased anterior translation with a soft or absent endpoint.

On MRI, a complete ACL tear shows complete discontinuity of the ligament fibers. The ACL may appear as a mass of disorganized, bright signal rather than the normal taut, dark band. Common secondary findings include bone bruising on the lateral femoral condyle and posterolateral tibial plateau (present in over 80% of acute ACL tears), anterior tibial translation, and meniscal tears (present in 50-65% of ACL injuries). For guidance on interpreting these findings, see our article on how to read knee MRI.

Treatment Decisions by Grade

Grade 1 sprains almost always respond to conservative treatment and rarely require surgery. Grade 2 partial tears require individualized assessment — the decision depends on the percentage of fibers torn, the patient's activity level, functional instability symptoms, and the presence of associated meniscal or cartilage injuries. Grade 3 complete tears in young, active patients who participate in pivoting sports are generally recommended for ACL reconstruction.

Older, less active patients or those who do not participate in cutting and pivoting activities may function well without surgical reconstruction (known as copers) with appropriate rehabilitation. For a comprehensive overview of post-surgical rehabilitation, see our article on ACL rehabilitation.

Key Takeaways

• Grade 1 (sprain): ligament stretched but intact, firm endpoint on Lachman test, 2-4 week recovery
• Grade 2 (partial tear): some fibers disrupted, soft endpoint, treatment is individualized
• Grade 3 (complete tear): all fibers torn, absent endpoint, usually requires surgery in active patients
• MRI is the gold standard for confirming ACL tear grade and identifying associated injuries
• Bone bruising on MRI is present in over 80% of acute complete ACL tears
• Meniscal tears accompany 50-65% of ACL injuries and affect the treatment plan

Frequently Asked Questions