What Should You Do the First Week After an ACL Tear?

During the first week after an ACL tear, protect the knee from another injury, start controlling swelling, and get assessed so you can begin restoring motion and quadriceps function. Don’t spend the week simply waiting for an MRI or surgery date. Early losses in knee extension and quad activation can affect what comes next.

How Do You Know If You Tore Your ACL?

A pop, rapid swelling, pain, and a knee that feels unstable can raise suspicion for an ACL tear, but symptoms alone cannot confirm it.

ACL tears often happen during cutting, landing, sudden deceleration. It also can occure when contact forces the knee out of position. Some people can still walk afterward, while others have trouble putting weight on the leg.

The ACL may not be the only structure injured. The meniscus, cartilage, other ligaments, or bone can also be involved. That’s why an examination matters even when the injury felt or sounded like a classic ACL tear. Treatment decisions depend on the specific injury and patient rather than the ACL tear alone.

What Should You Do in the First 48 Hours After an ACL Tear?

In the first 48 hours, stop sport, protect the knee from another twisting injury. You should also manage the swelling and arrange for an assessment.

Avoid cutting, pivoting, jumping, and repeatedly testing whether the knee “still works.” If you can’t walk safely, use crutches or another support recommended by a clinician. You can use compression and elevation to help manage swelling, and ice can be used for comfort if it helps.

Don’t force the knee through severe pain. At the same time, don’t assume the safest plan is to leave it completely still for the next several weeks.

Swelling after an ACL tear can make it harder to activate your quad. Researchers have shown this by adding fluid to otherwise healthy knees. As the knee became more swollen, quadriceps activation dropped. In other words, they did not need to injure the ACL or damage the muscle to make the quad work less effectively. Swelling alone was enough.

The combination of the injury and that swelling can make your quad feel weak. It can also make it difficult to “turn on” even though the muscle itself hasn’t suddenly lost all its strength. This is one reason controlling swelling and restoring quad activation are early priorities in ACL rehab. 

Should You See a Doctor or Physical Therapist First After an ACL Tear?

You need a prompt assessment after a suspected ACL tear, and the right first stop depends on your symptoms.

A physical therapist can assess swelling, range of motion, walking, quad activation, and early function. A sports medicine physician or orthopedic surgeon can evaluate the full injury, order imaging when needed, and discuss whether surgery may eventually be part of the plan.

Those roles should work together. If the knee is deformed, locked, impossible to bear weight on, or showing signs of nerve or blood-flow problems, urgent medical evaluation comes first.

If there are no emergency signs, starting PT early can help you address swelling, motion, walking, and quad function while the diagnosis and longer-term plan are being clarified.

Do You Need an MRI Right Away After an ACL Tear?

Not always. An MRI is useful for identifying ACL, meniscus, cartilage, and other internal knee injuries, but it doesn’t always need to be the first test after acute knee trauma.

The American College of Radiology recommends X-rays first in some acute knee injuries, especially when fracture is a concern. If no fracture is found but an ACL or other internal injury is suspected, MRI is often the next step.

However, waiting for an MRI appointment doesn’t mean you should do nothing with the knee. Swelling, motion, walking, and quad activation can often be assessed and addressed while you wait, provided your clinician has ruled out reasons for a different approach.

Why Does the First Week After an ACL Tear Matter?

The first week matters because swelling, loss of knee extension, and quadriceps inhibition can develop before you have decided whether surgery is part of your plan.

Swelling Can Shut Down Your Quad

Quad shutdown after an ACL tear is not simply a strength problem. The injured knee can reduce the nervous system’s ability to fully activate the quadriceps, a process called arthrogenic muscle inhibition, or AMI.

A study of 300 people with acute ACL ruptures found that 170, or 56.7%, had AMI at their first outpatient assessment. Knee swelling, associated injuries, and higher pain were linked with a greater likelihood of inhibition.

Getting Your Knee Straight Matters

Restoring full knee extension is another early priority because going into surgery with an extension deficit can make recovering full extension afterward harder.

One study of 102 ACL reconstruction patients found that among people missing at least 5 degrees of extension before surgery, 33% still lacked at least 5 degrees six months afterward. Only 7% of patients who entered surgery with full extension had that degree of extension loss at six months.

That doesn’t mean you should aggressively force a painful or blocked knee straight at home. A knee that won’t straighten physically because something is blocking the joint needs medical assessment.

Why Start ACL Prehab Before Surgery?

Prehab helps reduce swelling, restore motion, rebuild quadriceps function, and normalize movement before ACL reconstruction instead of entering surgery with deficits you have already accumulated.

A small randomized trial of 20 patients found that six weeks of progressive prehab improved single-leg hop performance and quadriceps strength before ACL reconstruction. Improvements in knee function were still present 12 weeks after surgery, although the small sample means the results should be interpreted carefully.

Longer-term research points in the same direction. In a comparison of the Delaware-Oslo ACL Cohort and the MOON cohort, 72% of patients who completed extended preoperative rehabilitation returned to their preinjury sport at two years compared with 63% in the MOON comparison group. Because this was a cohort comparison rather than a randomized trial, it can’t prove that prehab alone caused the difference.

Prehab doesn’t replace surgery when reconstruction is needed. It changes what condition your knee is in when you get there.

BPR’s ACL Prehab program focuses on swelling, quad activation, range of motion, and walking before surgery, which reflects the priorities already established for the program.

When Should You Go to Urgent Care After a Knee Injury?

Get urgent medical assessment when an acute knee injury includes signs that a fracture, displaced tissue, major ligament injury, or nerve or blood-vessel problem may be present.

Seek urgent care or emergency evaluation if:

• Your knee is visibly deformed.
• Your foot or lower leg becomes numb, unusually weak, cold, pale, or discoloured.
• Your knee is locked and you can’t straighten it.
• You can’t bear weight after the injury.
• Your knee becomes very swollen very quickly, especially with severe pain.
• Your pain, swelling, or function is rapidly getting worse.

Where Can You Get Help After an ACL Tear in the Tri-Valley?

Bax Performance Rehab provides one-on-one ACL physical therapy in Pleasanton for athletes and active adults who need help in the days and weeks after an ACL injury.

You don’t need to wait until after surgery to begin PT. We can assess swelling, extension, quad activation, walking, and what your knee needs next while working alongside your orthopedic plan.

We serve Pleasanton, Dublin, Livermore, San Ramon, Danville, and the wider Tri-Valley. No referral is required, and we can usually get you in this week.

If you just injured your ACL and don’t want to lose the first few weeks waiting for the next appointment, book your free discovery call with Bax Performance Rehab in Pleasanton.

FAQs

Should you use crutches after an ACL tear?

Crutches can help if pain, swelling, or instability makes it difficult to walk safely. You may not need them if you can walk with good control and without a significant limp, but a clinician should help determine what level of support is appropriate.

Should you ice an ACL tear?

Ice can help with pain and comfort during the first few days, but it doesn’t repair the torn ligament. Swelling management may also include compression, elevation, and appropriate movement based on your assessment.

Can you walk with a torn ACL?

Some people can walk after an ACL tear, while others can’t put weight on the leg safely. Being able to walk doesn’t rule out an ACL tear, and inability to bear weight after an acute knee injury should be medically assessed.

Why can’t I straighten my knee after an ACL tear?

Swelling, pain, muscle guarding, and quadriceps inhibition can all make extension difficult after an ACL tear. A true mechanical block can also prevent the knee from straightening, which is why a locked knee should be assessed promptly.

Clinically Reviewed by Dr. Rob Bax

Dr. Rob Bax, PT, DPT, OCS, CSCS

Dr. Rob Bax is a Doctor of Physical Therapy, Board-Certified Orthopedic Clinical Specialist, and Certified Strength and Conditioning Specialist. He leads Bax Performance Rehab in Pleasanton, California, serving athletes and active adults throughout the Tri-Valley.