TEST: Open Kinetic Chain Exercises after ACL Reconstruction

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Open Kinetic Chain Exercises after ACL Reconstruction:
Science Says You Can Do It

There is heated discussion among medical professionals about whether or not to do open kinetic chain (OKC) exercises after anterior cruciate ligament (ACL) reconstruction surgery. Many in sports medicine and physical rehabilitation already include OKC exercises in their post-surgical regimens. Others are resistant to the idea, though, and may be relying on old science.

A mountain of new information supports the safe use of open-kinetic chain (OKC) knee extensions after ACL reconstruction (ACLR). More sports medicine and physical rehabilitation professionals will embrace the use of OKC exercises once they learn about the research supporting its use.

In other words, when it comes to OKC following ACLR, you can do it. And you can do it with confidence because a mountain of science backs you up.

ACL Injury and OKC Knee Extensions Research

ACL injury affects as many as 250,000 individuals in the United States annually and these injuries lead to 80,000 to 100,000 surgical ACLRs each year. Surgeons and therapists are often reluctant to have these patients perform OKC knee extensions out of concern that the exercise could tear the ACL or increase laxity. Other research suggests that omitting OKC knee extensions may even be a disservice.

ACLR does not always lead to successful outcomes and return to sport. In fact, research shows that 20 to 50 percent of patients with ACLR do not return to the same sports following their surgery. About 12 percent of patients who had undergone ACLR had a repeat ACL injury within five years.

A mountain of new information supports the safe use of open-kinetic chain (OKC) knee extensions after ACL reconstruction (ACLR).

A number of factors can prevent a patient from returning to the same levels of activity as he or she enjoyed prior to the ACL injury. Fear of reinjury, lack of training, and incomplete rehabilitation can effect outcome and return to sport. Proper rehabilitation should improve a patient’s return to pre-injury levels of activity by restoring quadriceps strength as early as possible post-surgery. Sadly, this does not always happen.

Quad Strength Following ACL Reconstruction

Decreased strength in the quadriceps (quad) muscles is one of the most commonly reported and well-researched impairments following ACLR. The reports and research look at decreased quad strength immediately after surgery and years later.

Quad strength is a good predictor of function. In fact, a study published in the Journal of Orthopaedic and Sports Physical Therapy shows that patients with less than 85 percent quadriceps muscle strength demonstrated decreased function at the time of return to sport, regardless of the graft type, presence of meniscal injury, and knee pain or other symptoms.

One study shows that recovery of quad strength significantly influences physical function at the time of return to sport. Other research shows that greater than 80 percent quad strength after ACLR is associated with less severe cartilage damage in the short term. In another study, researchers found that ACLR patients with weaker quads demonstrated altered landing patterns at the time of return to sport.

Researchers are also investigating the importance of quad strength in regards to functional outcomes in a variety of patient populations. In one study, the scientists found that quad strength is a major determinant of self-report mobility measures in patients with osteoarthritis (OA) of the knee.

Increasing quad strength is imperative to improve function after ACLR. OKC exercises are one of the best ways to isolate and strengthen the quadriceps.

In short, decreased quad strength is a reliable predictor of decreased function following ACLR. Increasing quad strength, then, is imperative to improve function after ACLR. OKC exercises are one of the best ways to isolate and strengthen the quadriceps.

Worry Over OKC Exercises Post-ACLR         

Unfortunately, a number of clinicians are reluctant to add these exercises to the treatment plan of ACLR patients because they worry that OKC exercises will increase strain to the ACL. Some point to outdated studies, like the 1985 Henning study that associated increased shear forces with OKC exercise. The authors concluded their study by saying patients should not perform full range of motion exercises during the first year following ACL injury or ACLR.

While often cited now, the study has flaws: the researchers enrolled only two patients into the study and then used the data from only one participant. Furthermore, the two patients enrolled into the study had partially torn ACLs, so the data may not actually reflect the effects of OKC exercises on intact ACLs.

Some therapists cite the 1997 Beynnon study in which the scientist inserted a gauge directly into the ACLs of participants to assess ACL strain during exercise. The participants then performed the closed kinetic chain (CKC) exercise of squatting, and OKC exercise of active flexion-extension of the leg. The results of the study suggest that both OKC and CKC produce ACL strain.

Science Supporting OKC Post-ACLR

Research suggests both OKC and CKC play a beneficial role in the early rehabilitation following ACLR. One study found that the direct ACL strain measurements for OKC and CKC may not be clinically significant. The authors of another study conclude their paper by saying that the “great concern about the safety of OKC knee extensor training in the early period after ACLR may not be well founded.”

Clinicians that do use knee extensions often wait at least 12 weeks after surgery to start, citing concerns about laxity. This may be too late! Research now shows no difference in knee laxity in patients who started OKC knee extensions at 4 weeks versus 12 weeks.

While the debate will likely continue, clinicians can safely implement OKC knee extensions into their early rehabilitation for patients following ACL reconstruction. With science behind you, you can do it!


Interested in learning more? Download Simple Decision Rules Can Reduce Reinjury Risk by 84% After ACL Reconstruction: The Delaware-Oslo ACL Cohort Study





Shannon Wiggins, Senior Sales Representative
Biodex Medical Systems, Inc.

Content reviewed by Jennifer Hunnicutt, PhD, ATC – Emory Sports Medicine