A torn ACL is formally diagnosed with MRI (Magnetic Resonance Imaging) of the knee; however, the Lachman test is a good predictor. For this test the knee is bent slightly, the doctor or trainer applies gentle traction to the leg bone while stabilizing the knee cap; if the leg moves excessively forward on the thigh, then the ACL has an 86% chance of being torn. ACL injuries typically swell up in the hours after an accident; performing the Lachman test before the swelling sets in is helpful and is on par with the MRI (87%) for demonstrating a torn ACL.
Sometimes it is not as clear what happened. A lot of weekend warriors have knee pain during a sport and are not sure what to do next. The most common cause of knee pain is arthritis, which comes on gradually as you age and can be made worse during exertion. Other than arthritis, the most common issues are a torn ACL or meniscus injury. The meniscus is a horseshoe shaped cartilage. There are two menisci in the knee which support the thigh bone. If you have knee pain it can be hard to tell at first whether it is a torn ACL or meniscus. To see how you can tell the difference in your own knee without an MRI our video here:
Magnetic Resonance Imaging
The decision to get an MRI of the knee after an injury is automatic in the case of high-profile athletes; however, knowing when to get an MRI for knee pain in regular life is more complicated. The first consideration is whether you may have a serious illness. Knee pain can be a sign of a more serious underlying condition if you have any red flags (sudden onset of pain so severe you cannot walk; deformity of the knee; a red, hot, swollen knee; the history of cancer; unexplained weight loss; blood in your urine, stool, or vomit). If you have a red flag, then you need an urgent evaluation by a doctor. Assuming you have no red flags, then an MRI can usually wait a few weeks to see if the pain resolves. If not, then see a medical or chiropractic doctor.
Your doctor will examine you, get blood work, and order an x-ray. The main thing on the examination is the Lackman test. The blood work is to look an elevated WBC (white blood cell) count, or elevated CRP (c-reactive protein). These are signs of infection. Arthritis shows up well on x-ray; so, if the x-ray shows arthritis, you may have a good diagnosis without needing an MRI. So, you need an MRI if the red flag history, blood work and x-ray are do not suggest the cause, but your knee still hurts like heck.
To preview an MRI of the knee and learn more about how to decide if one is needed check out this video:
A torn ACL will not heal itself. However, not everyone depends on an intact ACL. Biomechanical studies suggest the ACL is responsible for around 85% of the strength of your knee. However, your knee is held together by the muscles and other ligaments as well as the ACL. In some people the knee is stable, despite having a torn ACL. A functioning ACL is absolutely required for strenuous work or sports. So, the next step for the Heisman trophy winner is arthroscopic ACL reconstruction.
There are some situations where surgery is not recommended. Surgical repair involves placing a graft across the knee joint and anchoring it to the leg and thigh bones; this can disrupt the growth plate in children. A pediatric orthopedic surgeon may elect to wait until a child reaches skeletal maturity to recommend repair. On the other end of life older folks with chronic medical problems who are not highly active and can walk despite the tear, may be better off without surgery.
During surgery, the torn ACL is not actually repaired, it is replaced. While you would think the torn ligament could be sewn back together experience has shown that the ligament does not heal well enough the be functional afterward. The better approach turns out to be reconstructing the torn ligament in its entirety. This surgery should be done by an orthopedic surgeon specializing in Sports Medicine through tiny incisions using an arthroscope. The ACL is replaced by a graft that comes from the kneecap tendon, hamstring tendon, quadriceps tendon, or even a cadaver, depending on the exact situation.
To get a better sense of how this is done, check out this animation of an arthroscopic ACL repair with a patellar tendon graft:
Surgery and Recovery
Arthroscopic ACL reconstruction surgery takes 1-2 hours and is done as an outpatient in an ambulatory surgery center (ASC). The surgery is performed under general or spinal anesthesia. Orthopedic surgeons who perform this procedure typically have a year of specialized training in arthroscopic surgery and are certified in Sport’s Medicine. A brace is placed on the knee in the recovery room, and you can walk out of the ASC 1-2 hours after surgery on crutches. Since the surgery is not done in a hospital you do not have to worry about COVID-19, hospital errors, or staph infection.
Full recovery from arthroscopic ACL repair surgery takes 6-9 months for regular activity and 9-12 months for athletic competition. For your knee to fully recover the graft must heal into position. The excessive activity could dislodge the graft and ruin the repair. Right after surgery, you will wear a brace to protect your graft. Your surgeon will supervise your recovery and involve a physical therapist.
The good news is that once you are fully recovered from arthroscopic ACL reconstruction surgery the new graft will be strong enough that you can return to full activity, including sports, without restriction.
You can walk with a torn ACL, but you shouldn’t. The ACL is the main ligament holding the knee together, and biomechanical studies show that the ACL provides 85% of the strength of the knee. Tearing the ACL may leave the knee unstable, that mean the knee does not have the internal strength to hold itself together without additional damage. The additional damage may be tears to other ligaments, or even injuries to the menisci.
Partial tears of the ACL often heal on their own in 6-12 weeks. If the ACL is partially intact, then it may provide enough strength to keep the knee stable. Here the word stable means the knee has enough internal strength to function without causing additional damage.
It depends on the injury. A partial tear may heal just fine on its own without additional trouble. Since the ACL provides 85% of the force holding the knee together, tearing it often leaves the knee unstable. That means not treating the knee with a complete tear can result in additional damage to the knee such as other ligament tears, or meniscal injuries. In these setting of these additional injuries and an untreated ACL tear rapidly advancing arthritis and ultimately the need for total knee replacement becomes more likely.
When compared to major procedures such as hip or knee joint replacement surgery ACL reconstruction is generally considered minor surgery. Arthroscopic ACL reconstruction surgery takes 1-2 hours and is done as an outpatient in an ambulatory surgery center (ASC). The surgery is performed under general or spinal anesthesia. Orthopedic surgeons who perform this procedure typically have a year of specialized training in arthroscopic surgery and are certified in Sport’s Medicine. A brace is placed on the knee in the recovery room, and you can walk out of the ASC 1-2 hours after surgery on crutches. Since the surgery is not done in a hospital you do not have to worry about COVID-19, hospital errors, or staph infection.
Most patients do not require narcotic medications after ACL reconstruction and rely on non-steroidal anti-inflammatory medications for relief.
Once fully healed ACL reconstruction is expected to be permanent.