Closed kinetic chain alone compared to combined open and closed kinetic chain exercises for quadriceps strengthening after anterior cruciate ligament reconstruction with respect to return to sports: a prospective matched follow-up study. Knee Surg Sports Traumatol Arthrosc. 2000;8(6):337-42. Mikkelsen C1, Werner S, Eriksson E.
From the study:
Rehabilitation after anterior cruciate ligament (ACL) reconstruction has focused over the past decade on closed kinetic chain (CKC) exercises due to presumably less strain on the graft than with isokinetic open kinetic chain exercises (OKC); however, recent reports suggest that there are only minor differences in ACL strain values between some CKC and OKC exercises. We studied anterior knee laxity, thigh muscle torque, and return to preinjury sports level in 44 patients with unilateral ACL; group 1 carried out quadriceps strengthening only with CKC while group 2 trained with CKC plus OKC exercises starting from week 6 after surgery. Anterior knee laxity was determined with a KT-1000 arthrometer; isokinetic concentric and eccentric quadriceps and hamstring muscle torque were studied with a Kin-Com dynamometer before and 6 months after surgery. At an average of 31 months after surgery the patients answered a questionnaire regarding their current knee function and physical activity/sports to determine the extent and timing of their recovery. No significant differences in anterior knee laxity were noted between the groups 6 months postsurgery. Patients in group 2 increased their quadriceps torque significantly more than those in group 1, but no differences were found in hamstring torque between the groups. A significantly higher number of patients in group 2 (n = 12) than in group 1 (n = 5) returned to sports at the same level as before the injury (P < 0.05). Patients from group 2 who returned to sports at the same level did so 2 months earlier than those in group 1. Thus the addition of OKC quadriceps training after ACL reconstruction results in a significantly better improvement in quadriceps torque without reducing knee joint stability at 6 months and also leads to a significantly higher number of athletes returning to their previous activity earlier and at the same level as before injury.
The key to physical therapy after ACL reconstruction is to restore strength and function as fast as possible with minimal risk to the graft. Another key is to avoid dogmatism. When I was in PT school in the 90s all the talk was about closed kinetic chain (CKC) exercises (exercises done with the foot fixed to the floor or a plate) being safe for the repaired ACL while open kinetic chain (OKC) exercises (with the foot free to move) putting the repair at risk. The reason was stated that the quadriceps acting alone without cocontraction of the hamstrings would stretch the ACL graft and made the knee too loose, perhaps leading to graft failure and early arthritic changes. Since then considerable additional research has been completed providing sound answers as to what exercises are safe, what exercises are most beneficial, and what is good timing with regards to recovery. What this and a few other studies found was that a mixture of exercises including CKC and OKC are needed to improve the odds of full recovery. So while some of my favorite CKC exercises like squats, RDLs and lunges are great for restoring overall leg strength, physical therapy after ACL repair should include some resistive leg extensions as well to restore full active range of motion and strong knee extension.
This additional knee extension strength did in fact have a significant effect with regards to both strength and return to sporting activities. Adding resistive leg extensions to the rehabilitation program increased quad strength to ~80% of contralateral side at 6 months compared to ~70% in the group that did only CKC exercises, with no increase in ACL laxity. It should be noted that the ACL grafts used were bone tendon bone grafts from the patellar tendon which seems to tolerate earlier strain without stretch than does the hamstring tendon grafts. Also though the OKC group started leg extensions at 6 weeks, they performed the exercise through only 90 to 40 degrees of knee flexion at first and did not progress to 90-10 degrees until 12 weeks out. Per other research 12 weeks post-op seems to be where hamstring tendon graft ACL repairs can safely tolerate resistive OKC exercise.
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Chad Reilly is a Physical Therapist, obtaining his Master’s in Physical Therapy from Northern Arizona University. He graduated Summa Cum Laude with a B.S. Exercise Science also from NAU. He is a Certified Strength and Conditioning Specialist, and holds a USA Weightlifting Club Coach Certification as well as a NASM Personal Training Certificate. Chad completed his Yoga Teacher Training at Sampoorna Yoga in Goa, India.