++
++
An injury involving an audible pop when the knee buckles
Acute swelling immediately (or within 4 hours)
Instability occurs with lateral movement activities and going down stairs
ACL tears are common with sporting injuries
Can result from both contact (valgus blow to the knee) and non-contact (jumping, pivoting, and deceleration) activities
++
Acute swelling of the knee, causing difficulty with motion
After the swelling has resolved, the patient can walk with a 'stiff-knee' gait or quadriceps avoidance gait because of the instability
Patients describe symptoms of instability while performing side-to-side maneuvers or descending stairs
++
Stability tests assess the amount of laxity of the knee while performing side-to-side maneuvers or descending stairs
The Lachman test is performed with the patient lying supine and the knee flexed to 20–30 degrees (Table 41–7)
The anterior drawer test is performed with the patient lying supine and the knee flexed to 90 degrees (Table 41–7)
The pivot shift test is performed with the patient lying supine with the knee in full extension and is used to determine amount of rotational laxity of knee (Table 41–7)
Plain radiographs are usually negative in ACL tears but are useful to rule out fractures
MRI is the best method to diagnose ACL tears
++