Diagnosis
Torn ACL symptoms and what happens next
The pop, the swelling, the giving way. What an ACL tear typically feels like, what the exam and the MRI add, and what the first two weeks in the American system look like.
Most people who tear an ACL know something significant happened within about ten seconds. The classic story is a non-contact pivot, deceleration or landing, an audible or felt pop, immediate loss of confidence in the knee, and a joint that swells within a few hours.
The typical presentation
- A pop or snap at the moment of injury, often heard as well as felt.
- Immediate swelling, usually within two to six hours, because the tear bleeds into the joint.
- A feeling that the knee gave way or shifted, and reluctance to trust it.
- Inability to continue playing, even when the pain settles quickly.
- Loss of full extension, sometimes from swelling and sometimes from a displaced meniscus fragment.
- Later, instability with cutting or turning rather than with straight-line walking.
Pain is a bad guide here
Plenty of complete ACL tears hurt sharply for a few minutes and then settle to an ache. Being able to walk to the parking lot proves very little. The swelling within hours and the loss of trust in the knee are more informative than the pain score.
What is often torn with it
An isolated ACL tear is common but so are combinations. Meniscus tears frequently accompany it, and a repairable meniscus tear can change the surgical decision and the rehabilitation restrictions considerably. Medial collateral ligament injuries and bone bruises are also common. This is why the MRI answers more than one question, and why the answer to whether to operate is not decided by the ACL alone.
How the diagnosis is made
- Clinical examination
- The Lachman test is the most sensitive manual test for ACL integrity, with the pivot shift and the anterior drawer adding information. An experienced examiner gets a long way before any imaging.
- X-ray
- Does not show the ACL. It is done to rule out fracture, which matters more in adolescents with open growth plates.
- MRI
- Confirms the ACL and, more usefully, shows the meniscus, the cartilage and the other ligaments. This is the study that shapes the plan.
- Instrumented laxity testing
- Used in some centers to quantify anterior translation. Not required for a diagnosis.
The first two weeks, practically
Get seen
Urgent care or an orthopedic office. A locked knee that will not straighten, a deformity, an inability to bear any weight, or numbness is an emergency department problem.
Control the swelling and get the knee straight
Compression, elevation, cryotherapy, and gentle motion. This is the start of prehab, not a waiting room.
Expect an MRI and a wait
Prior authorization for the MRI, then for the surgery, is standard. Two to six weeks between injury and operation is normal in the United States, and it is usable time.
Start rehabilitation before you have a surgery date
In the comparison of two cohorts, 72% of patients who did extended preoperative rehabilitation returned to their preinjury sport against 63%, with better IKDC and KOOS scores at two years.
Ask the network questions early
Whether the surgeon, the facility, the anesthesiologist and the physical therapy clinic are in network, and what your plan authorizes. It is much easier to ask now than to appeal later.
When it is not an ACL tear
A pop with swelling can also be a patellar dislocation, a meniscus tear, an MCL injury or a bone bruise. Swelling that appears over two days rather than two hours points away from an ACL tear. None of that is something to settle by reading; it is what the examination is for. What is worth knowing is that ACL reconstruction is not a rare operation: it rose from 86,687 in 1994 to 129,836 in 2006 in the United States, and the largest increases were in patients under 20, patients 40 and older, and in women.