Open Kinetic Chain Knee Extension After Articular Cartilage Repair in the Knee: Is it Safe?

Open Kinetic Chain Exercise After Articular Cartilage Repair in the Knee: Is it Safe?

After articular cartilage repair in the knee, specifically with the tibiofemoral joint, there is a period of protected weight bearing.  Early post-operatively we know that regaining range of motion, regaining quadriceps activation, and decreasing excess inflammation and swelling is important.  Commonly weight bearing is progressed to full by about 8 weeks, sometimes a little longer or shorter depending on the surgeon, the surgery, and lesion factors.  

Deficits in quadriceps strength are seen far beyond discharge from rehabilitation and have been seen up to 7 years post op.  Knowing this, it is easy to want to get after quadriceps strengthening early.  There has been a lot of talk in the physical therapy community about "underdosing" our patients when we claim that we are "strengthening" them.  We are aware that we should be cautious with weight bearing exercise with these patients, but what about non-weight bearing exercises?  

In this post, we will explore tibiofemoral joint compression forces with open kinetic chain knee extension and compare the forces to those sustained while walking and performing closed kinetic chain exercises. The goal is to help improve decision making in exercise prescription for patients who have undergone articular cartilage repair of the tibiofemoral joint.  

A study by Steele et al. examined the tibiofemoral forces during various levels of a "crouch gait."  The greater amount of average knee flexion during gait increased the amount of tibiofemoral force but unimpaired gait produced peak tibiofemoral compressive forces of approximately 3.0 times body weight (x BW) with a mean BMI in the unimpaired gait group of 17.3 walking at an average speed of 2.56 mph (1.146 m/s).

A study by Kumar et al. demonstrated peak knee tibiofemoral compressive forces in the medial compartment of healthy subjects to be about 2.4 x BW (1860 N) and lateral compartment peak tibiofemoral compressive forces of about 1.3 x BW (1001 N) during the first half of gait.  During the second half of gait, they found peak medial forces to be 1.8 x BW (1369 N) and .45 x BW (320 N) in the lateral compartment.  Less force during the second half of the gait cycle makes sense since the limb is either in shared stance or swing during the second half of gait.  Total joint forces during the first half of gait are 2860 N.

A study by D'Lima et al. reported that level ground walking resulted in peak tibial forces of 2.1 x BW at 1-3 mph and up to 2.8 x BW at 4 mph.  Peak tibial forces during an open kinetic chain knee extension of 0.2 x BW resulted in peak tibial forces of 1.5 times body weight (x BW).  .2 x BW is not very much weight (30# for a 150# individual) and it can be assumed that increasing this weight just a few lbs will create similar tibiofemoral compression to walking.  

In a study by Bini, he looked at tibiofemoral compression and shear forces with an open kinetic chain knee extension exercise.  If this study he was comparing forces between different Cam placements on various OKC knee extension machines, but consistently, tibiofemoral joint compression force had a sharp spike between 45 degrees and 60 degrees with a drop off from 60 degrees to 90 degrees.  Shear forces at the tibiofemoral joint were greatest near full extension and were the least as the knee approached 90 degrees of flexion.  Resistance in this study was set at 46 netwons, and compressive force was found to peak at > 15,000 N even with the most ideal Cam placement and even when the compression was lower, it was still around 5000N. The figure below summarizes the results of the effect of joint angle on tibiofemoral compression and shear.  

Of note: Peak tibiofemoral compressive forces in this model are far greater than in any other study cited in this blog

In a study by Escamilla et al. the authors found that OKC knee extension produced greater tibiofemoral compressive forces than did the squat or the leg press.  In this study, exercises were performed in a slow, continuous manner (1.5 - 2s ecc / 1 - 1.5 s con) to help mitigate the effects of inertia.  Assessment for each exercise was performed at the patients 12 RM (likely much higher than what we would be performing early on during rehab since these are healthy subjects).  Peak tibiofemoral compressive forces during an OKC knee extension exercise occurred at approximately 30 degrees during the eccentric portion of the exercise and at about 80 degrees during the concentric portion of the exercise.  Peak force during knee extension was 3285 N compared to 3017 N when the knee was flexing.  The big take away from this article for me was the fact that tibiofemoral compression was actually greater in the OKC knee extension group.  

Take Home Message: 

If we are avoiding high loads, or even any load with squatting leg press or other CKC exercise due to excess compression of the tibiofemoral joint, then we need to take the same precautions with OKC knee extension when addressing quadriceps strength deficits.  It may also be beneficial to think about early "weight bearing restrictions" as "tibiofemoral loading restrictions" as weight bearing restrictions does not factor in the stresses that our non-weight bearing rehab exercises may place on the joint.

Citations:

Steele, K. M., DeMers, M. S., Schwartz, M. H., & Delp, S. L. (2012). Compressive tibiofemoral force during crouch gait. Gait & posture, 35(4), 556-560.

Kumar, D., Manal, K. T., & Rudolph, K. S. (2013). Knee joint loading during gait in healthy controls and individuals with knee osteoarthritis. Osteoarthritis and cartilage, 21(2), 298-305.

D’Lima, D. D., Fregly, B. J., Patil, S., Steklov, N., & Colwell Jr, C. W. (2012). Knee joint forces: prediction, measurement, and significance. Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine, 226(2), 95-102.

Bini, R. R. (2017). Patellofemoral and tibiofemoral forces during knee extension: simulations to strength training and rehabilitation exercises. Fisioterapia em Movimento, 30, 267-275.

Escamilla, R. F., Fleisig, G. S., Zheng, N., Barrentine, S. W., Wilk, K. E., & Andrews, J. R. (1998). Biomechanics of the knee during closed kinetic chain and open kinetic chain exercises. Medicine & Science in Sports & Exercise, 30(4), 556-569.