In this blog, we will discuss why leg extensions are safe, and why they are essential in anterior cruciate ligament reconstruction or ACLR.

Before getting into what we should be doing and before explaining why leg extensions are safe, let’s address some arguments or myths about OKC or the open kinetic chain exercise post ACLR.

Myth number one: leg extension or OKC is harmful post ACLR

We used to believe that OKC exercises, like leg extension, post-ACLR, or the rehab plan will place a lot of stress on the ACL graft and lead to ligamentous laxity.

Let’s first take a look at the amount of strain on the ACL put during leg extension exercise CKC exercises, and some daily life functional tasks.

The function of the ACL is to restrain anterior tibial translation on the femur. During walking, the peak shear force found was 335N at 16.8 degrees of knee flexion. When doing seated leg extension, 0-90 degrees of knee flexion the shear force was found to be 248N at 14 degrees of knee flexion. We used to postpone leg extension 2 to 3 months post-operation, and we directly start to begin gait training retrain. If the studies have shown that there is more shear force during walking than there is during OKC exercise and specifically leg extension, as well as they found that there is a similar amount of strain on the ACL if we perform a bodyweight squat that we physical therapists tend to use earlier in the rehab program.

So why should we hesitate to implement leg extension as early as possible in the rehab journey?

Another study found that a Lachman Test, which is usually performed by the surgeon after the reconstruction performed at 30 degrees of knee flexion with 150N of force causes about a 3.5% strain on the ACL. A leg extension exercise from 0-90 degrees of knee flexion causes a maximal amount of strain on the ACL at 10 degrees, and the tension found was only 2.8% and this was without resistance. And only 3.8% when we 4.5 kg were added. The same question repeats itself again. If we are okay with Lachman test, why aren’t we okay with leg extensions?

It has been shown that the strength of a native ACL is 2000 N. when the amount of ACL loading during isokinetic knee flexion-extension at 60 degrees per second was 349N at 35-40 degrees of knee flexion. Which is far from reality, since no one would be able to actually put that stress directly after the operation. This would be implemented further down the road in the rehab plan. This shows that the overall amount of ACL loading during OKC is low.

Moreover, neither of the prescribed exercises in the rehab plan put too much strain on the ligament, whether it’s an open or closed kinetic chain. When the knee is about 10 and 30 degrees, we can notice more strain on the ligament and almost no strain on the ACL when the knee flexion is greater than 60 degrees.

Finally, recent systematic reviews have shown that there is no difference in knee laxity between patients who performed open kinetic chain exercises and those who did not. That’s because there is a similar loading of the ACL in both ways, open and closes kinetic chain.

A snaeak peak into our ACL rehab session at the clinic:

https://www.instagram.com/reel/CY4US8PLBcF/?igshid=YmMyMTA2M2Y%3D

https://www.instagram.com/reel/CjlY001jkCt/?igshid=YmMyMTA2M2Y%3D

References:

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8. Escamilla RF, Macleod TD, Wilk KE, Paulos L, Andrews JR. Anterior cruciate ligament strain and tensile forces for weight-bearing and non-weight-bearing exercises: a guide to exercise selection. J Orthop Sports Phys Ther. 2012;42(3):208-220.
9. Pandy MG, Shelburne KB. Dependence of cruciate-ligament loading on muscle forces and external load. J Biomech. 1997;30(10):1015-1024.
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11. Jewiss D, Ostman C, Smart N. Open versus Closed Kinetic Chain Exercises following an Anterior Cruciate Ligament Reconstruction: A Systematic Review and Meta-Analysis. Journal of Sports Medicine. 2017;2017:1-10. doi:10.1155/2017/4721548
12. Grindem H, Snyder-Mackler L, Moksnes H, Engebretsen L, Risberg MA. Simple decision rules can reduce reinjury risk by 84% after ACL reconstruction: the Delaware-Oslo ACL cohort study. British Journal of Sports Medicine. 2016;50(13):804-808. doi:10.1136/bjsports-2016-096031