Combining Kinematic and Coordination Gait Modifications to Reduce Medial Knee Contact Force During Walking

• Adam Gotlin

• Kirsten Seagers

Medial compartment osteoarthritis is a leading cause of years claimed by disability worldwide. Joint replacements improve the quality of life for individuals with end-stage osteoarthritis; however, less invasive interventions to prevent or delay surgery are desirable. Increased contact forces in the medial compartment of the knee joint are thought to accelerate the progression of osteoarthritis.

Knee adduction moment (KAM) and total tibiofemoral force (TF) are potential correlates to medial contact force (MCF) in the knee joint (Kutzner et al., 2013; Nagura et al., 2006). Shull et al. (2012) showed experimentally that shifting the foot progression angle inward during walking (i.e. toe-in gait) could reduce the first peak in KAM during stance. This is accomplished by shifting foot's center of pressure laterally and altering the ground reaction force vector. Lowering the KAM tends to shift knee contact forces laterally, thus potentially alleviating load on the medial compartment. DeMers et al. (2014) showed that muscle recruitment optimization could be leveraged to lower the second peak of TF. His study reveals the sensitivity of contact forces in the knee to internal muscle forces, particularly for muscles crossing the knee joint. Winby et al. (2009) further describes that medial contact force is 42% external forces factors (i..e ground reaction forces) and 58% internal factors (i.e. muscle activation). Decreasing MCF is the focus of interventions to decelerate progression of medial compartment osteoarthritis.

By building a lower-body musculoskeletal model that combines Rajagopal’s full-body musculoskeletal model and Lerner’s contact model of the knee joint, we will confirm whether toe-in gait reduces medial contact force in the knee (Rajagopal et al., 2012; Lerner et al., 2015).

Does decreasing the foot progression angle (toe-in gait) reduce medial contact loads in the knee?

1. Track gait kinematics from one subject using Motion Analysis MOCAP system on an instrumented Bertec treadmill

2. Compare gait cycles from baseline walking (N = 3 steps) to toe-in gait (N = 3 steps)

   1. Average foot progression angle for walking trials:

      1. Baseline: 6.5°

      2. Toe-in: -5.3°

1. Scale a generic musculoskeletal model to get a subject specific model

   1. Start with a combined model from Apoorva Rajagopal’s full body model and Zach Lerner’s knee contact model

   2. Modify mass in scale tool

   3. Modify tibial joint angles in the model .osim file using patient X-ray image

   4. Adjust marker positions from static trial (one leg is in front of the other)

2. Run Inverse Kinematics

   1. Input: tracker file (<trialname>.trc)

   2. Outputs: coordinates file (<trialname_IK>.sto)

3. Run Inverse Dynamics

   1. Inputs: coordinates file; external forces (<GRFs>.mot)

   2. Outputs: results file (<trialname>_results_ID.sto)

4. Run Static Optimization

   1. Inputs: coordinates file; external forces

   2. Outputs: muscle forces (<trialname>_StaticOptimization_force.sto)

5. Use Analyze Tool to calculate joint reaction forces

   1. Input: muscle forces

   2. Outputs: results file (<trailname>_ReactionLoads.sto)

      1. This will contain joint reaction forces in the compartments of the knee

6. Repeat steps 2-4 for all walking trials

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• Study analyzes 6 total steps for 1 subject

• Muscle forces are estimated using static optimization

  • Joint reaction analysis is very sensitive to muscle forces

• Model limitations

  • Lack of arm swing, trunk motion, ligaments, patch contact, etc.

• Experiments were performed in a laboratory setting on a treadmill