Full Knee Extension After ACL Surgery – 3 Exercises To Help You Straighten Your Knee


You need to ensure that you can fully extend and lock your knee within the first three weeks post ACL surgery

A question that is often asked by patients is how do I fully extend (straightening) and lock my knee after ACL surgery?

Recovering from an ACL reconstruction is an emotionally sensitive time for many people, especially after the surgery when the end of the journey to recovery appears far away.

The early phases of your rehabilitation can also be particularly challenging as your knee movement and functionality is initially limited by pain and swelling.

Locking your knee out straight by using the quadriceps muscles at the front of your thigh is very important in the early stages of your ACL rehabilitation.

Knee straightening is fundamental to your knees progression in the early phases of your ACL recovery timeline.

This includes both achieving and subsequently maintaining full extension of your knee.

Fully extending your knee within approximately two weeks after ACL surgery is a very important goal that will help you restore your knee’s range of motion in a timely manner.

Practice locking your knee as often as possible by sitting on a flat table or couch with legs extended out straight, placing a rolled towel under your heel.

Do this for 25-30 minutes, 3 to 4 times per day.

You need to ensure that you can fully extend and lock your knee within the first three weeks post ACL surgery.

Otherwise you run the risk of developing scar tissue in the joint and requiring an arthroscopy to restore knee extension.

3 primary ACL knee extension exercises to be completed 3 to 4 times a day after surgery

You need to do your exercises 3 to 4 times a day where progress should be gradual and guided by the level of pain and swelling in your knee.

Beginning from the day after surgery, start your ACL recovery with knee locking (knee extension) and knee slides (bending and flexion) exercises.

These exercises, when performed consistently each day, are highly effective for achieving knee straightening and restoring quadriceps functionality plus also help to progress your walking after ACL surgery.

Introduce prone leg hangs at about 2 weeks after surgery to help achieve and maintain full knee extension.

ACL Knee Extension Exercise 1 – Knee Locking


As noted above, knee locking exercises should begin the day after ACL surgery.

With a rolled towel or pillow under the heel, contract the quadriceps muscle to push the knee further down into the bed/couch holding for 5 seconds then return to the relaxed extension.

You can perform this exercise by either lying on your back or sitting with legs extended horizontally on a bed, couch or table (refer to picture above).

Repeat this exercise 20 times 3 to 4 times a day.

As mentioned earlier, it is also important to commence heal slide (knee bending) exercises on day 1 simultaneously with your knee locking exercises to help restore knee flexion after ACL surgery.

ACL Knee Extension Exercise 2 – Prone Leg Hangs

Add prone leg hangs after approximately 2 weeks post operation to help further straighten your knee.


Lie on your stomach with knees just overhanging the edge of a table or bench with knee caps just off the end.

Hang your legs for 2 minutes in a fully extended/straight position.

You can use a weight or the heel of your good leg to push down on the heel of your operated leg if struggling with full extension.

Try to relax and apply pressure as long as it is comfortable to do so.

ACL Knee Extension Exercise 3 – Use a towel or band to pull foot back

As noted above it is very important that you can lock knee within 3 weeks after ACL surgery to avoid the risk of further complications and possibly additional surgery to restore knee straightening.

In addition to the above 2 exercises, the following exercise uses a towel or band to straighten the knee by pulling the foot back and therefore assisting with achieving a lock of your knee after ACL surgery.



To perform this exercise, sit on a bench or couch and wrap an exercise band or towel around the foot of the bad leg.

Followed by pulling your foot backwards toward the body and slightly raising your heel off the ground to bring your knee into full extension.

Whilst your other hand can be positioned on your thigh or the bench for stability.

Holding for 5 seconds before returning to a relaxed position.

There should be little or no pain and as per all ACL recovery exercises your progress should be guided by the level of pain.

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How long after ACL surgery do you need to continue with your knee extension exercises?

As you progress your recovery after surgery and move into the next stage of rehabilitation it is important to continue your knee extension exercises.

In the first 2 to 3 weeks of your recovery, there is an immediate requirement to restore and maintain knee straightening – to ensure you can lock your knee straight.

As you progress your ACL recovery into more advanced stages, it remains important to continue with knee extension exercises and importantly maintain your knee’s ability to fully straighten and lock.

Before ACL surgery, do I need to restore knee extension?

Leading up to surgery one of your key ACL prehab goals will be to ensure that knee extension is fully restored in the injured knee.

In other words, it is very important to do your knee locking exercises in the lead up to an ACL reconstruction and to reduce swelling by applying RICER and NO HARM.

After tearing your ACL it is common for many people to experience significant amounts of knee swelling and a loss of knee functionality as a result of the injury.

This includes for many people the loss of the ability to fully extend their knee.

Leg extension exercises to avoid after ACL surgery

Open-kinetic chain leg extensions such as a seated quadriceps extensions on the gym machine are often avoided in the early stages of ACL recovery for at least 3 months post surgery.  As this exercise may lead to loosening or stretching of the new ACL graft.

However, some therapists will recommend modified range open-kinetic chain leg extension exercises from about 4 weeks post surgery.  This should only be considered with proper instruction and guidance from your therapist on how to complete the exercise safely.

Conclusion – The role of knee extension exercises to your ACL recovery

Overall, it is essential that you achieve full knee extension and locking within 3 weeks after ACL surgery and continue to maintain your knee extension exercises throughout the entire course of your ACL rehabilitation period.

Completing your exercises within the first 2-3 weeks after surgery is a critical window for the ongoing success of your ACL recovery.

Your initial ACL recovery goals include restoring knee extension, reduce the knee swelling and restore your quadriceps function.

The exercises recommended by your surgeon and physio in the first 2 to 3 weeks after returning home from surgery, will include specific exercises targeted at restoring knee extension such as those exercises illustrated above.

If you cannot perform the basic action of extending and locking your knee at 3 weeks post-surgery your chances of requiring an arthroscope, to restore extension in your reconstructed knee, are significantly increased.

The success of your ACL recovery may be compromised as a result of poor rehabilitation in the first 2 to 3 weeks after surgery.

After approximately 2 weeks post surgery you will progress your exercise program to include additional strength and mobility exercises.

Swimming after ACL surgery is also generally recommended at about 3 weeks which is highly encouraged for improving your knee’s range of motion.

Although starting your post-surgery pool workouts with basic water exercises is recommended.

Also see ACL recovery timeline for further information regarding your 2 week post-surgery rehabilitation.


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