Diagnosing a torn anterior cruciate ligament (ACL) of the knee joint is not difficult.
Most patients have some form of twisting or pivoting injury to the knee. This usually happens during sports such as football or basketball. There may or may not have been contact during the injury.
A typical story is twisting injury to the knee associated with a ‘pop’ or ‘crack’ sound. There is immediate onset of severe pain and the injured person is not able to continue playing. If one can continue playing after the injury, it is highly unlikely to be an ACL injury. The injured knee becomes swollen within the next 1 to 2 hours.
The ACL injured sportsperson will be limping over the next 3 to 7 days.
In such a situation, I am 70% confident that this patient has an ACL injury. The other 30% is confirmed by clinical examination of the knee joint.
Other things that he or she may notice is that of giving way of the knee when walking or jamming/locking of the knee.
During the physical examination of the ACL-torn knee, we look for increased laxity in the knee joint.
The anterior drawer test is shown in this short video clip.
The Lachman’s test is shown next. This is a very sensitive test for this condition.
The Pivot Shift test is confirmatory of rotatory instability of the injured knee but may be difficult to elicit in a person who is guarding or tensing the knee muscles.
MRI scans of the knee is not usually needed in order to diagnose an ACL tear. It is, however, useful to assess the status of other structures in the knee joint that may be injured as well. These include meniscus tears and tears to other ligaments such as the medial collateral ligament.