Symptoms of ACL Injury
ACL injuries typically present with knee instability during activities involving cutting, pivoting, and landing, though some patients experience instability even with routine daily tasks 1.
Acute Presentation
At Time of Injury
- Audible "pop" or crack: Reported by approximately 30% of patients at the moment of injury 2
- Shifting sensation: A feeling of the tibia and femur shifting relative to each other, noted by 61% of patients 2
- Immediate functional impairment: Only 17% of patients can continue sports activity immediately after injury, and those who do experience significant difficulty 2
Early Post-Injury Symptoms
- Pain: Acute knee pain that is particularly severe with movement through full range of motion 3
- Swelling: Joint effusion develops rapidly, often making clinical assessment difficult in the acute setting 4
- Limited mobility: Painful movement throughout the full range of motion 3
Functional Impairment
The hallmark symptom is knee instability, particularly during dynamic activities 1. This manifests as:
- Difficulty with cutting and pivoting movements: Most pronounced in younger, active patients 1
- Problems with landing from jumps: Common mechanism of injury and ongoing symptom 1
- Variable severity: While younger athletes are most affected, some patients experience instability even with mundane daily tasks 1
Clinical Examination Findings
Physical examination reveals positive findings on specific maneuvers 3:
- Lever sign test: Highest diagnostic accuracy (sensitivity 0.92-1.00, specificity 0.94-1.00)
- Lachman test: Sensitivity 0.63-0.93, specificity 0.55-0.99
- Pivot shift test: Sensitivity 0.18-0.48, specificity 0.90-0.99
- Anterior drawer test: Sensitivity 0.18-0.92, specificity 0.78-0.98
Important Clinical Pearls
The mechanism of injury is critical to recognize: 70% of ACL injuries occur at footstrike during non-contact situations, with 53% involving internal rotation of the tibia with the knee in slight flexion 2. This non-contact mechanism is particularly common in female athletes and during landing maneuvers 5, 6.
Associated injuries are common and should be suspected, including meniscal tears and other ligamentous injuries 4. These can be subtle and require careful evaluation, as they significantly impact treatment decisions and return to sport 4.