Rebecca J Nesbitt 1 ; Marc T Galloway 2 ; Samuel Harms 2 ; Cynthia Gooch 1 ;

1. Impacts of Stifle Joint Remodeling on Vertical Ground Reaction Forces Following MCL Transection and Medial Meniscectomy INTRODUCTION RESULTS METHODS DISCUSSION Rebecca J Nesbitt1; Marc T Galloway2; Samuel Harms2; Cynthia Gooch1; David L Butler1; Jason T Shearn1 1Biomedical Engineering, University of Cincinnati, Cincinnati, OH, 2 Cincinnati Sports Medicine, Cincinnati, OH • Pre-Op Vertical Ground Reaction Forces (N=13): • Compared to VGRFs during level walking (44.05 ± 3.04 %BW), inclined walking increased average hind limb VGRFs (48.05 ± 2.65 %BW); declined walking decreased average hind limb VGRFs (38.64 ± 2.88 %BW; p<0.001) (Fig 2). • Declined walking significantly decreased peak hind limb VGRFs (56.7 ± 5.03 %BW; p<0.05) compared to level walking (59.60 ± 4.51 %BW) and even more significantly (p<0.001) when compared to inclined walking (61.21 ± 4.512 %BW) (Fig 2). • 12 Weeks Post-Injury (MCL N=4, MM N=4): • MCL injured animals experienced lower VGRFs during single leg stance for all grade conditions and in both injured and uninjured limbs (Fig 3). • MM injured animals experienced less of an effect in declined and level conditions and no effect in the uninjured limb. • VGRFs for both injuries were most significantly impacted in the inclined grade condition, with VGRFs of the injured limb stance phase dropping by an average of 3.6 ± 3.69 %BW (p<0.05). • Current anterior cruciate ligament (ACL) reconstruction techniques remain ineffective in avoiding or delaying onset of osteoarthritis, implicating a failure to completely restore native ACL function [1]. • Functional demands on the ACL remain impossible to measure directly in-vivo. • Our lab has used robotics to measure 3D forces in the ligament by reproducing kinematics of activities of daily living (ADLs) in the sheep model [2]. • Up to 13% of patients sustaining ACL injuries also sustain dual medial meniscus (MM) injuries. Up to 10% sustain dual medial collateral ligament (MCL) injuries [3]. • Left unrepaired, the injuries may alter the ACL’s functional demands, resulting in inadequate ACL reconstruction outcomes for patients with dual injuries. • These structures alter ACL loading in cadaveric studies [4-5]. • Impact on ACL functionality during in vivo ADLs remains unknown. • Changes in ACL functionality due to joint healing and remodeling remains unknown. • This study tracks stifle joint remodeling as indicated by vertical ground reaction forces (VGRFs) during level, inclined, and declined walking in response to surgically imposed MCL transection or medial meniscectomy. 50μm Objective Establish ACL reconstruction design criteria following combined injury to either the MCL or MM aimed at: 1) accelerating patient return to pre-injury activities and 2) slowing or stopping premature joint degeneration • Surgical Procedure • Approved by the University of Cincinnati IACUC • Surgically expose medial aspect of left hind limb • MCL injuries remove 1cm of ligament at joint line (Fig 1A) • MM injuries remove entire MM (Fig 1B) • VGRF Measurement • Thirteen (13) female Suffolk sheep • (2-6 yrs; 100-200 lbs) • Recorded at 1 m/s during level (0˚), inclined (+6˚), and declined (-6˚) walking conditions using an instrumented treadmill (KistlerGaitway) • Two force plates measured fore and hind limbs • Statistical Analysis • Data normalized over a full gait cycle • Welch two sample t-test determined significance Injured Limb Fig. 3. (VGRFs normalized to pre-injury) Compared to pre-op, MCL injuries decrease VGRFs during both single limb stances for all ADLs and surface grades. MM injuries decrease VGRFs during single injured limb stance for inclined grade. Fig. 2. (Pre-Surgery VGRFs) Compared to level, inclined gait increases VGRFs while declined gait decreases VGRFs, especially during single hoof stance. • Surface grade significantly affects average and peak hind limb VGRFs as weight shifts forward in declined and backward in inclined conditions. • VGRF changes in response to MCL and MM injury occur in single limb stance, corresponding to drive phase of gait . • Forelimb VGRFs remain consistent, demonstrating the animal does not offload to the forelimbs during the drive phase of gait (data not shown). • Week 1 VGRFs of the MCL cohort were identical to pre-injury and gradually altered over 12 weeks with differences not observable until week 4 of recovery (data not shown), leading to the hypothesis that changes in the MCL cohort resulted from adaption and remodeling in response to the loss of key structures contributing to the proprioception pathways affecting both injured and intact hind limbs. • Week 1 VGRFs of the MM cohort were severely altered and gradually approached pre-injury levels as the animal healed, leading to the hypothesis that changes in the MM cohort were the result of a physical change in anatomy affecting the biomechanics of the joint. • Future studies quantifying the 3-D forces and torques on the knee and ACL by reproducing measured in vivo motions on a 6-DOF robot will further quantify the clinical and functional significance of knee remodeling following an MCL or MM injury and estimate in vivo load requirements for ACL reconstructions in patients with dual injuries. References 1. Lohmander, Arthritis Rheum, 2004; 2. Herfat, Annals of Biomed Eng, 2012; 3. Majewski, Knee, 2006; 4. Ma, ActaOrthopScand, 2000; 5. Papageorgiou, Am J Sports Med, 2001; 6. Herfat, Biomech Eng, 2011 Acknowledgements Research support provided by NIH grant AR056660. We thank Andrea Lalley, Andrew Breidenbach, Fanny Frauziols, Nathan Kemper, & Alex Dziech for animal training assistance. A Fig. 1A. (MCL Procedure) 1cm section of MCL spanning the joint line. 1B. (MM Procedure) Vacant medial compartment previously containing the MM. B