Improved Methods for Measuring Achilles Tendon Moment Arm Prospectively Applied to Total Ankle Arthroplasty Patients

The plantarflexion moment arm of the Achilles tendon (ATma) is critical to healthy locomotion. However, there is no consensus on the best method for measuring ATma. The first study of this dissertation outlines a novel method for quantifying ATma during dynamic tasks, using motion capture to define a functional axis of ankle rotation and ultrasound imaging to locate the Achilles tendon in vivo. The second study compares two methods for computing the axis of ankle rotation – using either a fixed functional axis or instantaneous helical axes. In plantarflexion and neutral, the fixed axis was the most appropriate choice, and provided estimates of ATma commensurate with previously reported values. The second half of this dissertation applies this novel method to total ankle arthroplasty (TAA). Study 3 found that the reduction in pain observed following TAA was associated with increased walking velocity and performance on locomotor tasks. However, improvements in pain did not fully explain improvements in locomotor function, which led to Study 4, where we investigated whether TAA altered ATma. The results indicated that approximately 37% of the change in ATma following TAA was attributable to a change in talar positioning. Further work is needed to determine any muscle adaptations to TAA, and to investigate whether a relationship exists between changes in ATma and changes in locomotor function following TAA.

Year	Entry
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2013	Gerus P, Sartori M, Besier TF, Fregly BJ, Delp SL, Banks SA, Pandy MG, D'Lima DD, Lloyd DG. Subject-specific knee joint geometry improves predictions of medial tibiofemoral contact forces. J Biomech. November 15, 2013;46(16):2778-2786.
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Year

Entry

1990

Winter DA, Patla AE, Frank JS, Walt SE. Biomechanical walking pattern changes in the fit and healthy elderly. Phys Therap. June 1990;70(6):340-347.

1994

Kitaoka HB, Alexander IJ, Adelaar RS, Nunley JA, Myerson MS, Sanders M. Clinical rating systems for the ankle-hindfoot, midfoot, hallux, and lesser toes. Foot Ankle Int. July 1994;15(7):349-353.

2008

Lawrence RC, Felson DT, Helmick CG, Arnold LM, Choi H, Deyo RA, Gabriel S, Hirsch R, Hochberg MC, Hunder GG, Jordan JM, Katz JN, Kremers HM, Wolfe F; National Arthritis Data Workgroup. Estimates of the prevalence of arthritis and other rheumatic conditions in the United States: part II. Arthritis Rheum. January 2008;58(1):26-35.

2013

Gerus P, Sartori M, Besier TF, Fregly BJ, Delp SL, Banks SA, Pandy MG, D'Lima DD, Lloyd DG. Subject-specific knee joint geometry improves predictions of medial tibiofemoral contact forces. J Biomech. November 15, 2013;46(16):2778-2786.

2000

Stacoff A, Reinschmidt C, Nigg BM, van den Bogert AJ, Lundberg A, Denoth J, Stüssi E. Effects of foot orthoses on skeletal motion during running. Clin Biomech (Bristol, Avon). January 2000;15(1):54-64.