Is it safe to do knee extension after an ACL surgery?

Key Points

1. It is safe to do knee extensions after an ACL surgery.
2. Knee extensions isolate quadricep muscles which are essential for recovery after an ACL surgery.

What is the ACL and what does it do?

The Anterior Cruciate Ligament (ACL) is an important component of the knee joint that connects your femur to your tibia. The purpose of the ACL is to secure the position of your tibia (leg bone), preventing it from sliding too far forward on your femur (thigh bone).

Surrounding your knee joint are many muscles that maintain the normal function of your knee. In the event of an ACL injury, your body reacts by avoiding knee straightening movements in order to prevent the forward movement of your tibia. This compensatory movement results in the lack of use of your quadricep muscles, which in turn reduces its strength. Hence why it is common to see patients with weak quadricep muscles after an ACL surgery.

Post-ACL surgery, your quadriceps strength is an important muscle to address during recovery because it is linked to essential functions such as walking and running, return to sport, subsequent knee injuries, and long-term progression of knee osteoarthritis.

Knee extensions after ACL injuries – is it bad?

Is it safe to do knee extension exercise after an ACL surgery or injury? The belief that knee extensions are unsafe to do after an ACL repair stems from early reports that feared knee extensions would loosen the healing graft. These theories have been refuted since the 1990s. 

However, there are a few considerations to note when doing knee extensions after an ACL surgery:

1. Amount of resistance
   1. It is safe to do knee extension exercises at low loads in the beginning of rehabilitation. 
   2. Resistance should be increased as advised by your Physiotherapist because the ACL becomes increasingly strained at higher resistance levels.
2. Range of movement and timing of knee extension exercises 
   1. It is safe to do early knee extension after an ACL surgery from 90-45 degrees of knee flexion between weeks 4-12 post operation.
   2. Evidence shows that the ACL is placed at the highest amount of strain at the end range of knee extension. Therefore, it is advised not to do a full range of knee extension in the first 3 months following an ACL repair. 

Knee extension exercise after an ACL injury is not bad! Knee extensions are important in order to regain the essential quadricep strength, and are only harmful to the healing graft when used inappropriately. 

Why are knee extensions important after an ACL injury?

There is a belief that the best recovery happens when patients are given exercises that replicate the activities they will re-engage when they return to sport. However, these exercises do not work on building quadricep strength and can easily be compensated by other muscle groups, hence why there is emphasis on adding exercises that isolate and strengthen the quadriceps group. 

Therefore, the purpose of doing knee extension exercises is to isolate the quadricep muscles and strengthen it. When the quadricep muscles are isolated in exercise, it elicits strong activations that facilitate muscle regeneration and motor recruitment.

Higher levels of functional training and running should start after a strong foundation of quadricep muscle strength has been established.

Are you doing knee extension exercises?

The only way to isolate and load the quadriceps is by using the knee extension machine or an electromechanical dynamometer. These methods also provide instrumented strength testing that allow your therapist to properly gauge your progression, quadriceps strength, and discharge criteria. 

Other methods such as hop-testing are only able to infer and estimate your quadricep strength, running the risk of overestimating your recovery progress and criteria for rehabilitation progression or discharge.

Here at PhysioX, we don’t believe it’s a “one solution for all”. That is why our Physiotherapists conduct thorough assessments to formulate individualised plans for each patient. Through a journey of strengthening and education, PhysioX aims to get you back on your feet! An overview of a rehabilitation programme with us includes recovery, rebuilding your strength, and finally, returning to your sport. 

Keen to find out if we can help? Contact us to schedule an appointment to see our Physiotherapist today! 

Ref:

Noehren, B., & Snyder-Mackler, L. (2020). Who’s Afraid of the Big Bad Wolf? Open-Chain Exercises After Anterior Cruciate Ligament Reconstruction. Journal Of Orthopaedic &Amp; Sports Physical Therapy, 50(9), 473-475. https://doi.org/10.2519/jospt.2020.0609

Wilk, K., Arrigo, C., Bagwell, M., & Finck, A. (2021). Considerations with Open Kinetic Chain Knee Extension Exercise Following ACL Reconstruction. International Journal Of Sports Physical Therapy, 16(1). https://doi.org/10.26603/001c.18983

Kim, H., Lee, J., Ahn, S., Park, M., & Lee, D. (2016). Influence of Anterior Cruciate Ligament Tear on Thigh Muscle Strength and Hamstring-to-Quadriceps Ratio: A Meta-Analysis. PLOS ONE, 11(1), e0146234. https://doi.org/10.1371/journal.pone.0146234