Date of Award

12-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Applied Biomedical Engineering

Department

Applied Biomedical Engineering

First Advisor

Colbrunn, Robb W.

Second Advisor

van den Bogert, Antonie J.

Third Advisor

Erdemir, Ahmet

Abstract

Joint mechanics research relies on joint kinematics and kinetics measurements, represented from relative relationships of local coordinate systems (CS) belonging to bones of the joint. It’s common to define these CSs from anatomical landmarks, which are sensitive to observer variability and often don’t result in CS that best represent the functional motion of the joint. This work is presented in three articles addressing the following aims: 1) to develop a method to objectively define coordinate systems through optimization of unique passive movement paths, 2) to develop an alternative method to objectively define coordinates systems for joints with non-unique passive movement paths, and 3) to validate the methods in vitro.

Article 1 introduces an objective method for calculating functional CS definitions for bones in joints that observe three-cylindrical-joint kinematic chain decomposition methods and applies the method on tibiofemoral joint specimens. This method is driven by low resistance joint motion during loading profiles and not from anatomical landmark selection. Significant improvements in CS reproducibility were observed with functional CS, compared to anatomical. Significant decreases in off-axis motion during passive flexion profiles were also observed with functional CS.

Article 2 establishes benefits in using Functional CS in vitro with human cadaveric tibiofemoral joints and rat stifle joints. Functional CS, compared to anatomical, significantly 1) reduced variation in intra-knee kinematic response, 2) reduced kinematic cross-talk, 3) reduced variation in inter-knee kinematic response, and 4) improved force/torque control performance. Scalability was demonstrated, as benefits extended to rat stifle testing.

Article 3 presents a method for establishing Functional-Aggregate vertebral CS in the spine. Functional motion is only used to optimize CS origins, because passive movement paths are non-unique in the spine. An aggregate of anatomical landmarks from the spinal region is used to define axis orientations instead. The method was applied to a full-spine model and cadaveric lumbar spines. The Functional-Aggregate method significantly reduced average CS variation, resulting in reduced average variation in kinematic response across multiple loading conditions and functional spinal units.

The novel methods presented in this work will reduce variability in reported joint kinematics, allowing for better characterization of joint populations, in musculoskeletal research.

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