Publication Date

12-2019

Date of Final Oral Examination (Defense)

9-2-2019

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Mechanical Engineering

Department

Mechanical and Biomechanical Engineering

Major Advisor

Clare K. Fitzpatrick, Ph.D.

Advisor

Trevor Lujan, Ph.D.

Advisor

Gunes Uzer, Ph.D.

Abstract

Crouch gait a progressively degrading gait deviation associated with the neurological disorder cerebral palsy. If left untreated it can lead to anterior knee pain and a loss of ambulation. At present there exists no agreed upon metric for determining the surgical procedures used to treat crouch gait and there is insufficient means to analytically compare the results of different procedures. The aims of this thesis work were to create a pipeline to transform a patient’s gait analysis data into a finite element model, develop a model of sufficient complexity to evaluate a range of outcomes by which to judge the efficacy of a surgical procedure, analyze the change between pre- and post-operative models and the changes between models with different surgical procedures, and to quantify the impact of varying different surgical parameters.

A generic lower limb rigid body musculoskeletal model was developed and used in conjunction with patient-specific static and dynamic motion capture to create scaling factors and joint kinematics, respectively. The musculoskeletal model was scaled and converted into a finite element model. This lower torso model was integrated with a detailed finite element model of the knee joint including patella, femur and tibia heads, associated articular cartilage, patellofemoral ligaments, patellar tendon, and quadriceps tendons. This type of combined finite element model was created for each patient, pre- and post-operatively, for a series of patient’s treated for crouch gait at Children’s Hospital Colorado. Each model was modified to replicate the surgical procedure(s) that each individual patient underwent. Comparison between pre- and post-operative models show significant improvement in tibiofemoral flexion-extension and patellar articular cartilage stress in post-operative models.

In order to assess the effect of surgical parameters on muscle efficiency, the finite element model was modified such that tibiofemoral flexion-extension was controlled by adaptive muscle forces calculated using a proportional-integral feedback control system. The feedback system adjusted quadriceps and hamstrings forces to try and meet a target flexion profile. A feedback control model was created for three patients; subsequently, each model was modified to run multiple simulations with modified surgical procedures and parameters. The models were modified to include distal femoral extension osteotomy procedures of 0º, 15º, or 30º, or patella tendon advancement procedures with 0 cm, 1 cm, or 2 cm shortening. The muscle forces needed to reach the target kinematics were compared. Further simulations are required to identify clear links between surgical decisions and patient-specific parameters, but the developed model shows promise for future studies both for crouch gait and other musculoskeletal pathologies.

DOI

10.18122/td/1626/boisestate

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