Forelli et al. (2024)

The addition of open kinetic chain post-ACLR to conventional closed chain kinetic rehabilitation alone

This study examined the safety and benefit of adding exercises of open kinetic chain post-ACLR to a conventional closed kinetic chain rehabilitation program alone

The results showed no significant increase in anterior knee joint laxity, which was the primary outcome

When the requirements of open kinetic chain exercises are met, it is safe to add it to a closed kinetic chain program


The debate on the use of open kinetic chain exercises post-ACL reconstruction (ACLR) surgery is still ongoing. Several studies to date, however, point to the safety of doing these exercises of open kinetic chain post-ACLR. They indicate that these exercises have the potential to increase early muscular activation of the quadriceps muscles, which are crucial in the knee’s stability, and lead to a subsequent earlier functional recovery. Others are concerned that such exercises increase the laxity of the graft in the knee joint, especially when a hamstring tendon graft is used. This study consequently wanted to elaborate on this topic and compare the addition of open kinetic chain post-ACLR to a traditional closed kinetic chain rehabilitation program to closed kinetic chain exercises alone.



To make this comparison between open kinetic chain post-ACLR and closed kinetic chain rehab, 53 recreational athletes (21 females, 32 males) were retrospectively reviewed. They were between 18 and 40 years of age and underwent ACLR using a hamstring graft. Their ACL injury resulted from a non-contact trauma. Only ACL tears with concomitant meniscal injuries were allowed for inclusion, but other complex ligamentous injuries or osteochondral lesions were excluded.

The intervention group received a mix of closed and open kinetic chain exercises for the hamstrings and quadriceps muscles. The open kinetic chain exercises were introduced two weeks after the ACLR surgery. At first, these were performed without resistance. Before resistance to the open kinetic chain exercises was added, participants had to meet the following requirements:

  • A stroke test score less than 1+
    • How to grade the stroke test?
    • 0: produces no wave with the lateral downward stroke
    • Trace: produces a small wave with the lateral downward stroke
    • 1+: a large wave returns with the lateral downward stroke
    • 2+: the effusion spontaneously returns to the medial side after upstroke (without a lateral downward stroke)
    • 3+: it is impossible to move any of the effusion out of the medial aspect
  • Knee ROM from 0° to 110°Active straight leg raise without lag
  • The difference in between-leg laxity less than 1.5 mm on a 134N laximetry test using a GNRB device.

The open kinetic chain exercises in the intervention group consisted of isokinetic isolated leg extensions and seated leg curls. They performed these isokinetic exercises 3 times per week with visual feedback and during 10 sets of 8 repetitions at a speed of 60° per second. The resistance was at 60% of their MVIC. The open kinetic chain exercises were performed at the end of the first month after ACLR. The range of motion was limited to exercise between 0° and 30°. This was progressively increased 45 days post ACLR.

The control group participated in a 3 times weekly program of early weight-bearing and closed kinetic chain exercises.

Both groups were evaluated at 1, 3 and 6 months and the primary outcome was the anterior knee laxity. This was measured using a GNRB device on both the ACLR and non-operated knee. The isokinetic dynamometer was used to calculate the muscle strength of the quadriceps and hamstrings.



The characteristics of the included participants were not normally distributed and there was a significant difference in age between the intervention and control groups. The time of assessments 1 and 2 was not normally distributed.

open kinetic chain post-ACLR
From: Forelli et al., Phys Ther Sport (2024)


The primary outcome analysis revealed that there was no significant difference in anterior knee laxity between the groups.

From: Forelli et al., Phys Ther Sport (2024)


Individual participant data was also analyzed and revealed again no significant between group differences in anterior knee laxity.

open kinetic chain post-ACLR
From: Forelli et al., Phys Ther Sport (2024)


In terms of quadriceps strength, the results show that there was a significant difference of 0.5Nm/kg in favor of the intervention group at 3 months. This was not the case at 6 months. Similarly, the hamstring strength was significantly greater in the intervention group at 3 months, and this difference was still present at 6 months.

open kinetic chain post-ACLR
From: Forelli et al., Phys Ther Sport (2024)


Questions and thoughts

By measuring the strength of the participants weekly, the authors could carefully adapt the resistances of the exercises based on the required percentage of the MVIC. Assessing and reassessing are crucial to knowing where to start from and where to aim in rehabilitation.

The timing of the measurements taken in this study was not normally distributed. Table 1 displays the means and standard deviation of the timings of the assessments (T1, T2, and T3). Despite being non-normally distributed, the assessment timings appear to be quite similar between the groups. This could be due to a variety of factors, including some individuals being tested sooner or later than others. Because of the uneven timing, how the results are understood and compared between the two groups may differ. To guarantee the quality and dependability of their study findings, researchers must be aware of these variations in assessment scheduling. Unfortunately, this was not better explained. If there was a large difference in the timing of the assessments between the groups, this could have led to differences in strength gains and knee laxity.


Talk nerdy to me

There was no difference in anterior laxity between the groups. The amount of laxity observed in this study was lower than the minimally clinically important difference of 2mm. The authors thereby confidently stated that adding these open kinetic chain exercises post ACLR are safe and even beneficial in terms of strengthening goals. To reduce strain during the open kinetic chain exercises post ACLR, the authors used double-point leg support on the tibia during the isokinetic exercises.

The primary outcome was the anterior knee laxity. The strength gains are thus secondary outcomes that seem promising, but we cannot fully rely on this finding. Since the participants performed the exercises on an isokinetic dynamometer, the strength gains may reflect familiarization effects. Also, because the strength was not measured at baseline, we cannot conclude anything about this finding.

Of course, an isokinetic dynamometer is expensive and specialized equipment that not every clinic can afford. What we can learn from this study is that by weekly assessing the minimal isometric voluntary contraction (MVIC) and adjusting the loads of the open kinetic chain exercises post ACLR accordingly, we can confidently add open kinetic chain training to the rehabilitation plan. This was also concluded by the Aspetar clinical practice guideline on rehabilitation after anterior cruciate ligament reconstruction by Kotsifaki et al. (2023).

A limitation of this study is that the groups were different based on age and that this was not examined as a covariate. Furthermore, it was a non-randomized and retrospective study. Two different rehabilitation centers were used and it is possible that this influenced the findings. It may have recruited different populations for instance. As such, this study sheds light on the importance of open kinetic chain exercises post ACLR, but these findings should be further examined to be definite.


Take home messages

The primary finding of this study is that we don’t have to fear increasing anterior knee joint laxity when prescribing early kinetic chain exercises. Especially when it is gradually introduced after the athletes reach certain requirements (as stated above). It seems that adding these open kinetic chain exercises may facilitate strength gains at 3 and 6 months in the hamstrings, but this should be further examined. It is however important because the hamstrings act as a posterior tibial translator, which helps the ACL in preventing anterior translation of the tibia relative to the femur. Furthermore, when one of the hamstring tendons is used for the reconstruction of the ACL, strength gains in the hamstrings are particularly important to regain its normal function.



Forelli F, Mazeas J, Zeghoudi Y, Vandebrouck A, Duffiet P, Ratte L, Kakavas G, Hewett TE, Korakakis V, Rambaud AJM. Intrinsic graft laxity variation with open kinetic chain exercise after anterior cruciate ligament reconstruction: A non-randomized controlled study. Phys Ther Sport. 2024 Mar;66:61-66. doi: 10.1016/j.ptsp.2024.01.009. Epub 2024 Feb 6. PMID: 38335650. 



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