Knee Loading Deficits During Dynamic Tasks in Individuals Following Anterior Cruciate Ligament Reconstruction.

Pratt KA, Sigward SM. J Orthop Sports Phys Ther. 2017 Jun;47(6):411-419. doi: 10.2519/jospt.2017.6912. Epub 2017 May 12.

* cliff notes version of the article above, intended for clinicians. For the full article please click on the link below:


  • Patients s/p ACL reconstruction exhibit deficits in sagittal plane loading 6 – 24 months after surgery. The loading strategies are often shifted away from knee extensors per previous studies. The knee extensor moment deficits can be as large as 35% within 6-15 months of surgery during deceleration tasks such as running, landing, and hopping.
  • Orishimo et al have identified individuals that at 7 months post op still exhibit 43% decrease in knee joint power absorption and 6% decrease in ability to perform single limb hopping. Kline et al found that post-ACLR, during running tasks the surgical limb is slower to reach peak knee extensor moment. This equates to slower knee flexion during deceleration following surgery
  • This is of concern as running can increase forces 3 to 30x a person’s body weight within a short period of time 10-40 milliseconds.
  • Running training often occurs early in ACL rehab, with running beginning as early as 8-12 weeks post op in most protocols.
  • The authors’ purpose of the study is to investigate how individuals with ACLR perform dynamic knee loading tasks in comparison with controls at similar time frames that running tasks are initiated in rehab protocols.  


  • 30 Participants were recruited age 16-39 and were separated into ACLR and non ACLR group and were matched by similarities in age and activity level. The ACLR group had been attending PT and had began a running program within 1.5 months of testing.
  • ACL R group consisted of 7 female, and 7 male who had unilateral ACL R using a patellar tendon bone autograft or an allograft at 4.6 +/- 1.4 months prior to testing and a range of 2.9 – 7.6 months. (Unfortunately there can be a large difference between someone at 2.9 months and 7.6 months post ACLR)
  • Prior to testing participants warmed up for 5 minutes on the bike.  
  • Participants performed single limb loading (SLL) and running tasks. SLL task involved leaping to a target that was the length of the participants tibia away from the take off spot. Participants were instructed to lower themselves as low as they can before returning to a 2 limb stance. 3 trials were performed at participants own pace.
  • For running participants ran a self selected pace for 15 M and analyzed using a Brower Timing System


  • The nonsurgical limb exhibited greater ROM, peak knee extensor moment, peak knee flexion angular velocity, rate of knee extensor moment, and peak knee power absorption during both tasks.
  • In the ACLR group there was a greater difference noted for ROM deficits in SLL than during running tasks, however greater differences were noted with peak knee extensor moment and rate of knee moment during running.
  • No differences in the ACL R nonsurgical leg and the control group were found. (The nonsurgical limb has been questioned in its ability to be a control in previous studies, this study suggests it may be suitable)


  • Patients S/P ACL reconstruction exhibit deficits in magnitude of knee loading and impairments in dynamic loading. When compared to the nonsurgical leg there were impairments observed in all knee loading tasks
  • The knee extensor moment and ROM deficits were similar to those described in previous studies in ACL R patients at 3-5 months post op.
  • Interestingly, there were no differences in peak knee flexion angular velocity between tasks in the control group, suggesting that SLL may be used to work on improving knee flexion angular velocity with a smaller knee extensor moment.
  • “Individuals modulate knee angular velocity to reduce dynamic demands regardless of loading demands. While this may be influenced by the differences in range-of-motion requirements between tasks, it may also be indicative of an underlying impairment in dynamic control.”

Clinical Relevance

  • “Knee flexion contributes nearly 40% and 55% of the lower extremities power absorption when running 2 m/s and 5 m/s, respectively.  During a drop landing, the knee goes through a greater knee flexion range, and its contribution to lower extremity power absorption is nearly 56%.21 Furthermore, dynamic tasks require force attenuation across the knee at high angular velocities (nearly 455°/s and 600°/s during running and landing, respectively).6,10 Therefore, restoration of proper dynamic knee loading mechanics, such as rate of knee extensor moment and knee flexion angular velocity, may be imperative for those looking to return to high-level activities and should be considered as individuals progress to dynamic tasks in rehabilitation.
  • Results may be due to decreased quadriceps strength, decreased rate of force, or fear of loading. 
  • During ACL R it is important to incorporate tasks that involve rapid knee flexion prior to dynamic load such as running or single leg hopping.
  • Despite the average time frame of 4.6 months ACL R still exhibits deficits with dynamic loading, ACL R should be a goal based progression rather than a time based.

*all citations can be found in the original article

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