Session: 06-09-01: Musculoskeletal and Sports Biomechanics

Paper Number: 148077

148077 - Novel Robotic Testing System Design to Investigate the Isolated Effects of Knee Bracing in Injured Cadaveric Knees 

INTRODUCTION: Prophylactic knee braces aim to prevent ligamentous injury by providing additional stability to the knee in response to external loading. However, braces migrate (i.e., proximal-distal brace motion with respect to clamps) approximately 0.3-25.0mm during activities due to interactions with the skin and muscle which has implications for cadaveric studies investigating their mechanistic effects utilizing robotic testing systems. Thus, the objective of the current study was to determine the utility of a novel robotic testing system set up (i.e., custom femoral and tibia clamps) that allows brace migration to quantify the effects of bracing on knee kinematics in response to external loading. Major design criteria included: 1) New clamp design maintains the working range of the universal force moment sensor (UFS), 2) brace migration in response to external loads is between 0.0 and 25.0mm, and 3) kinematics in response to a 10Nm valgus torque are within literature values and decrease with brace application in medial collateral ligament deficient (MCLD) knees.

METHODS: The femoral and tibial clamps were fixed to the lower and upper end plate of the robotic manipulator, respectively, and the forces and moments generated by the clamp were measured and compared to the original clamp. The working range for the UFS is 660N in the x-y directions, 1980N in the z direction, and 60Nm for torques about all axes. To address design criteria two and three, one cadaveric knee was utilized in four states: 1) Intact, 2) Intact Simulated Brace, 3) MCLD, and 4) MCLD Simulated Brace. For braced conditions, the brace was attached to each clamp on the medial and lateral sides of the knee using 4 ball bearing carriages and guide rails allowing proximal-distal brace migration with respect to the clamps. Migration was quantified as the distance each carriage moved at 30°, 60°, and 90° of flexion in respect to full extension using a dial caliper (negative=distal, positive=proximal migration) during an externally applied 10Nm valgus torque. Simultaneously, kinematics was collected at each flexion angle. The loading condition was chosen based on the function of the MCL and clinical application of braces.

RESULTS: Forces and moments generated by the clamps ranged between -2.4-32.5N and -0.1-0.3Nm, which were within 3.8N and 0.1Nm of the original clamp. Brace migration in Intact and MCLD Simulated Brace states ranged from -0.3-7.6mm (range 7.9mm) and -9.9-0.4mm (range 10.3mm) in response to a 10Nm valgus torque, respectively. Minimal differences in valgus rotation were observed for Intact and Intact Simulated Brace states across all flexion angles. However, more apparent differences in valgus rotation were observed between MCLD and MCLD Simulated Brace states, where bracing reduced valgus rotations by 0.1-3.7° throughout flexion (Figure 1). Valgus rotations throughout flexion ranged from 2.1-4.2°, 2.2-3.9°, 4.3-11.7°, and 0.6-9.6° for the Intact, Intact Simulated Brace, MCLD, and MCLD Simulated Brace states, respectively.  

CONCLUSION: The major finding was that the novel robotic testing system setup was capable of simulating brace function and produced reasonable kinematics in response to a 10Nm valgus torque. Specifically, the first design criterion was accepted since the forces and moments generated by the clamp were well within the working range of the UFS and almost identical to the original clamp. The second design criterion was also accepted as the magnitude of brace migration was within the absolute values reported in the literature (0.3-25.0mm vs. 7.9 and 10.3mm). Furthermore, Intact and MCLD knees have been shown to have valgus rotations ranging from 2.0-5.0° and 8.0-12.0° in response to valgus torques, respectively. Thus, the kinematics observed in the current study are reasonable given they are within the reported ranges. With brace application, one would expect valgus rotations to decrease in MCLD knees due to the additional stiffness provided by the brace, which was also observed, resulting in the third design criterion being accepted. Therefore, the novel robotic testing system setup can effectively investigate the simulated effects of bracing on joint function in cadaveric knees.

Presenting Author: Luke Mattar University of Pittsburgh

Presenting Author Biography: I am a Post-Doctoral Associate working in the Orthopaedic Robotics Laboratory in the Department of Orthopaedic Surgery at the University of Pittsburgh. My research interests include joint biomechanics, injury biomechanics, sports biomechanics, and the effects of non-operative and operative treatment for musculoskeletal pathologies. My Pre-Doctoral work investigated the effects of non-operative treatment in individuals with rotator cuff tears and quantified changes in in-vivo kinematics, patient reported outcomes, and tear propagation longitudinally following exercise therapy. My current work focuses on the effects of knee bracing on joint function in native and injured cadaveric knees using a 6 Degree of Freedom robotic testing system.

Authors:

Luke Mattar University of Pittsburgh
Tianyu Chen University of Pittsburgh
Jumpei Inoue University of Pittsburgh
Gal Peretz University of Pittsburgh
Martin Fagerström Chalmers University of Technology
Volker Musahl University of Pittsburgh
Richard Debski University of Pittsburgh