Dynamic knee joint stiffness during bilateral lower extremity landing 6 months after ACL reconstruction

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Background: Anterior cruciate ligament (ACL) reconstructions are associated with long-term functional impairments. Improved understanding of dynamic knee joint stiffness and work may provide insights to help address these poor outcomes. Defining the relationship between knee stiffness, work and quadriceps muscle symmetry may reveal therapeutic targets. The purposes of this study were to investigate between-limb differences in knee stiffness and work during early phase landing 6-months after an ACL reconstruction. Additionally, we investigated relationships among symmetry of knee joint stiffness and work during early-phase landing and quadriceps muscle performance symmetry. Methods: Twenty-nine participants (17 M, 20.0 ± 5.3 years) were tested 6-months after ACL reconstruction. Motion capture analysis was used to assess between-limb differences in knee stiffness and work during the first 60 ms of a double-limb landing. Quadriceps peak strength and rate of torque development (RTD) were assessed with isometric dynamometry. Paired t-tests and Pearson's product moment correlations were used to determine between-limb differences of knee mechanics and correlations of symmetry respectively. Findings: Knee joint stiffness and work were significantly reduced (p < 0.01, p < 0.01) in the surgical limb (0.021 ± 0.01 Nm*(deg*kg*m)−1, −0.085 ± 0.06 J*(kg*m) −1) compared to the uninvolved limb (0.045 ± 0.01 Nm*(deg*kg*m)−1, −0.256 ± 0.10 J*(kg*m) −1). Greater knee stiffness (51 ± 22%) and work (35 ± 21%) symmetry were significantly associated with greater RTD symmetry (44.5 ± 19.4%) (r = 0.43, p = 0.02; r = 0.45, p = 0.01) but not peak torque symmetry (62.9 ± 16.1%) (r = 0.32, p = 0.10; r = 0.34, p = 0.10). Interpretation: Dynamic stiffness and energy absorption are lower in the surgical knee during landing from a jump. Therapeutic interventions that target increasing quadriceps RTD may help optimize dynamic stability and energy absorption during landing.

Original languageEnglish
Pages (from-to)73-81
Number of pages9
StatePublished - Jun 2023

Bibliographical note

Funding Information:
Our hypothesis was partially supported by finding knee stiffness and work symmetry were associated with quadriceps RTD symmetry but were not associated with peak torque symmetry. Since a double limb landing is a bilateral task, the use of limb symmetry indices may provide insight into the relationships knee mechanics has with quadriceps RTD and peak strength. While quadriceps peak torque and RTD are often positively associated, emphasis on training the muscle to contract quickly may allow the quadriceps to better control the external knee flexion moment early in landing. An individual’s ability to contract the quadriceps quickly may be crucial in absorbing energy through the knee extensor mechanism, which could otherwise be imposed on the ACL and other passive structures of the knee [19] . In support of this premise, Huang et al. report an association between RTD symmetry and symmetrical sagittal plane knee mechanics during landing in females after an ACL reconstruction [15] . Further work is needed to evaluate if training to increase quadriceps RTD can increase joint stiffness during a drop vertical landing.

Publisher Copyright:
© 2023


  • Anterior Cruciate Ligament
  • Joint Stiffness
  • Knee Joint
  • Patellar Tendon
  • Quadriceps Rate of Torque Development
  • Rehabilitation

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine


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