4.6 Article

The Impact of ACL Laxity on a Bicondylar Robotic Knee and Implications in Human Joint Biomechanics

Journal

IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING
Volume 67, Issue 10, Pages 2817-2827

Publisher

IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TBME.2020.2971855

Keywords

Knee; Ligaments; Surgery; Legged locomotion; Actuators; Kinematics; Biomechanics; biomechatronics; biomedical engineering; biological system modeling; humanoid robots; legged locomotion

Funding

  1. UK Engineering and Physical Sciences Research Council
  2. UK Medical Research Council
  3. Ossur inc
  4. EPSRC [1790878] Funding Source: UKRI
  5. MRC [UKDRI-7003, MC_PC_16046] Funding Source: UKRI

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Objective: Elucidating the role of structural mechanisms in the knee can improve joint surgeries, rehabilitation, and understanding of biped locomotion. Identification of key features, however, is challenging due to limitations in simulation and in-vivo studies. In particular the coupling of the patello-femoral and tibio-femoral joints with ligaments and its impact on joint mechanics and movement is not understood. We investigate this coupling experimentally through the design and testing of a robotic sagittal plane model. Methods: We constructed a sagittal plane robot comprised of: 1) elastic links representing cruciate ligaments; 2) a bi-condylar joint; 3) a patella; and 4) actuator hamstrings and quadriceps. Stiffness and geometry were derived from anthropometric data. 10 degrees - 110 degrees squatting tests were executed at speeds of 0.1 - 0.25 Hz over a range of anterior cruciate ligament (ACL) slack lengths. Results: Increasing ACL length compromised joint stability, yet did not impact quadriceps mechanical advantage and force required for squat. The trend was consistent through varying condyle contact point and ligament force changes. Conclusion: The geometry of the condyles allows the ratio of quadriceps to patella tendon force to compensate for contact point changes imparted by the removal of the ACL. Thus the system maintains a constant mechanical advantage. Significance: The investigation uncovers critical features of human knee biomechanics. Findings contribute to understanding of knee ligament damage, inform procedures for knee surgery and orthopaedic implant design, and support design of trans-femoral prosthetics and walking robots. Results further demonstrate the utility of robotics as a powerful means of studying human joint biomechanics.

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