0.5 contact hours (30 min)
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Orthopedics · 9 min · September 27, 2026
From the course: Open vs. Closed Kinetic Chain Exercise After ACL Reconstruction: What the Evidence Shows · 0.5 contact hours
A systematic review and meta-analysis examines open versus closed kinetic chain quadriceps work after ACL injury, including post-reconstruction and nonoperative cases, with outcomes like strength, pain, function, hop tests, and knee laxity.
The authors found very low to low certainty evidence overall, with open chain exercise often matching or outperforming closed chain work for strength and laxity, while functional results were inconsistent.
Pamboris GM, Pavlou K, Paraskevopoulos E, Mohagheghi AA. Effect of open vs. closed kinetic chain exercises in ACL rehabilitation on knee joint pain, laxity, extensor muscles strength, and function: a systematic review with meta-analysis. Frontiers in Sports and Active Living. Published 03 June 2024. https://doi.org/10.3389/fspor.2024.1416690. Review protocol registered with PROSPERO (CRD42023475230). Distributed under a Creative Commons Attribution License.
Is open or closed kinetic chain exercise better after ACL reconstruction? In a systematic review with meta-analysis published in Frontiers in Sports and Active Living in 2024, Pamboris and colleagues pooled nine randomized trials and reported that open kinetic chain exercise was associated with better quadriceps strength around three to four months after injury, both after surgery and in conservative care. Knee laxity was either lower or no different with open chain work, while self-reported function results were inconsistent. The authors graded every outcome as very low or low certainty and asked readers to interpret their conclusions with caution.
The authors describe open kinetic chain exercise as movement in which the distal segment is free and unweighted, as in seated leg extension or hamstring curls. Closed kinetic chain exercise fixes the distal segment, as in squats and lunges, and promotes co-contraction of the muscles around the joint.
The preference for closed chain work rested on concern about graft strain. The authors cite earlier work reporting minimal hamstring activity during isotonic open chain knee extension between roughly 40° and 0° of knee flexion, a range in which the quadriceps force needed to extend the knee was thought to raise strain on the ligament. In current practice, the authors note, open chain work often begins within the first days or weeks after surgery, because several research groups have reported that an early start does not appear to worsen anterior tibial translation.
Earlier systematic reviews had concluded that neither mode was superior after reconstruction. Pamboris and colleagues widened the question beyond post-surgical comparisons to ACL-deficient knees, and to the timing and loading of open chain work.
The protocol was registered in advance with PROSPERO (CRD42023475230). The reviewers searched five databases from March 2005 to March 2024. Of 480 records, nine trials met the criteria. Participants had to be aged 15 to 60 with an ACL injury and no other pathology in either limb. The trials were published between 2007 and 2015 and enrolled 433 participants, 79% of them men. They covered four comparisons:
The reviewers scored trial quality with the PEDro scale and graded the certainty of each outcome with the GRADE approach.
| Comparison | Outcome | What the authors reported |
|---|---|---|
| Open vs. closed chain after reconstruction | Quadriceps strength | Better with open chain at 12 weeks, from a single trial |
| Open vs. closed chain after reconstruction | Knee laxity | No clear difference at 14 weeks |
| Open vs. closed chain after reconstruction | Self-reported function | Inconsistent between two questionnaires at the same early assessment |
| Open vs. closed chain after reconstruction | Pain | Lower with closed chain at three months, with no clear difference later |
| Open vs. closed chain, ACL-deficient knees | Laxity and strength | Less laxity with open chain at 10 weeks; strength better with open chain at four months |
| Early vs. late start of open chain after reconstruction | Graft laxity | No clear difference for patellar or hamstring grafts, out to 17 months |
| Early vs. late start of open chain after reconstruction | Pain | Lower with an early start at every follow-up in one trial; no difference in the other |
| Open chain resistance loads, ACL-deficient knees | Laxity | Less laxity with high load than control at six weeks but not at 12 |
The authors reported no clear difference on hop or jump tests in any comparison that measured them, and graded all of these outcomes as very low or low certainty.
Both early function findings after reconstruction came from one trial, in which Lysholm scores were better with closed chain exercise and IKDC scores were better with open chain exercise at the same assessment. The authors write that this disagreement raises doubt about claiming either mode is better for early knee function.
In the comparison of an early and a later start, the trial that reported less pain with an early start used a numeric pain rating scale. The other trial used a modified anterior knee pain score and reported no effect on anterior knee pain.
Laxity with open chain exercise was lower than or no different from laxity with closed chain exercise. In the early-versus-late comparison, the largest gap between groups in either trial was 1.4 mm. The authors note that this is below the 2 mm threshold they describe as clinically meaningful and associated with graft rupture, and within the measurement error of the arthrometer used.
Eight of the nine trials were rated at high risk of bias, and their PEDro scores averaged 5.6 out of 10. No trial blinded participants or treating therapists, and only one used intention-to-treat analysis. Because most comparisons rested on a single trial, very low certainty was the most common grade.
Participants were mostly men, which the authors say limits how far the findings generalize and may hide differences between men and women. Exercise protocols varied in sets, repetitions, resistance and progression, and graft type and individual patient characteristics were not accounted for.
On very low certainty evidence, the authors concluded that open chain exercise appears superior to closed chain exercise for quadriceps strength at three to four months after injury, in conservative or post-surgical rehabilitation. They wrote that open chain exercise appears either superior or equally effective for knee laxity, which they say supports including it from the initial phase of rehabilitation. They also state that concerns about graft strain call for cautious implementation of open chain work from four weeks after reconstruction.
They add that the pooled laxity results should not be read as an endorsement of any open chain quadriceps exercise for every patient after reconstruction, regardless of graft type, because the trials followed distinct protocols and responses differed by graft. They call for larger trials with longer follow-up and for further work on the timing and dosage of open chain exercise.
Pamboris and colleagues concluded that open chain exercise appears superior for quadriceps strength at three to four months after injury. After reconstruction, that finding came from a single trial, and the authors graded the evidence as very low certainty.
The authors state that concerns about graft strain call for cautious implementation of open chain work from four weeks after reconstruction. In the two trials that compared an earlier with a later start, they reported no clear difference in graft laxity at any follow-up.
The results were inconsistent. In one trial, early scores after reconstruction were better with closed chain exercise on the Lysholm questionnaire and better with open chain exercise on the IKDC form, which the authors say raises doubt about claiming either mode is better for early knee function.
Pamboris GM, Pavlou K, Paraskevopoulos E, Mohagheghi AA. Effect of open vs. closed kinetic chain exercises in ACL rehabilitation on knee joint pain, laxity, extensor muscles strength, and function: a systematic review with meta-analysis. Front Sports Act Living. 2024;6:1416690. doi:10.3389/fspor.2024.1416690
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