syndrome

Anterior Cruciate Ligament (ACL) Tear

ACL tears are among the most common and devastating sports injuries, particularly in pivoting sports like soccer, basketball, and skiing. The ACL is critical for knee stability, preventing anterior tibial translation and rotational instability. Tears often require surgical reconstruction.

Anatomical Basis

The ACL runs from the anterior tibial plateau (between the intercondylar eminences) to the posterior aspect of the lateral femoral condyle. It prevents anterior translation of the tibia relative to the femur and resists rotational movements. It has poor healing capacity due to its intra-articular location and limited blood supply.

Relevant Structures

Anterior cruciate ligamentFemoral condylesTibial plateauIntercondylar notchMenisci (often injured concurrently)MCL (may be part of "unhappy triad")

Mechanism

Non-contact: Sudden deceleration, pivoting, or landing from a jump with the knee near extension and foot planted. The knee often collapses into valgus and internal rotation. Contact: Direct blow to the lateral knee causing valgus stress. Athletes often hear/feel a "pop."

Clinical Presentation

•Immediate knee swelling (hemarthrosis within 2-4 hours)
•Sensation of "pop" at time of injury
•Knee instability ("giving way")
•Difficulty bearing weight
•Loss of range of motion
•Often unable to continue activity

Physical Examination

→Lachman test: Knee at 20-30° flexion, anterior tibial translation - MOST SENSITIVE test
→Anterior drawer test: Knee at 90° flexion, anterior tibial translation
→Pivot shift test: Demonstrates rotational instability - MOST SPECIFIC test
→Joint effusion (ballotable patella)
→Check MCL stability (valgus stress)
→Check menisci (joint line tenderness, McMurray test)

Treatment

✓Initial: RICE (rest, ice, compression, elevation), protected weight bearing, pain control
✓Physical therapy: Prehabilitation to restore range of motion and strength before surgery
✓Surgical reconstruction: Standard of care for active individuals, especially athletes
✓Graft options: Bone-patellar tendon-bone autograft, hamstring autograft, quadriceps tendon, allograft
✓Non-operative: May be appropriate for sedentary individuals, partial tears, or those unwilling to undergo surgery
✓Rehabilitation: 6-12 months post-surgery before return to sport

Prognosis

Good with reconstruction and proper rehabilitation. 85-90% return to sport at some level. Re-tear rate 5-15%. Without reconstruction, chronic instability leads to meniscal and cartilage damage. Osteoarthritis develops in 50-70% within 10-20 years, regardless of treatment.

Study Tips

💡ACL = prevents Anterior tibial translation (named by tibial attachment)
💡Lachman at 20-30° flexion is most sensitive (hamstrings relaxed)
💡Pivot shift is most specific - tests rotational instability
💡Unhappy triad: ACL + MCL + medial meniscus (valgus force)
💡Poor healing: intra-articular, bathed in synovial fluid, limited blood supply