Document Type
Thesis
Date of Award
5-31-1987
Degree Name
Master of Science in Biomedical Engineering - (M.S.)
Department
Biomedical Engineering Committee
First Advisor
Michael Pappas
Second Advisor
David S. Kristol
Third Advisor
Clarence W. Mayott
Abstract
The Harrington Distraction Rod is presently attached to the spines of patients who suffer from scoliosis and vertebral fractures. The rod's purpose is to apply a distractive force to the scoliotic curve in an attempt to reduce its severity. In fractures this rod is implanted to reduce the fracture and increase the stability of the spinal column. Harrington distraction rods are also inserted in order to give mechanical support to the spinal column.
Presently the Harrington Distraction Rod, manufactured by Zimmer, is one—quarter inch in diameter and made of 316L cold—worked stainless steel. The proximal end of the rod consists of eleven ratchets which are spaced one—quarter inch apart. The distraction rod is attached to the spinal column by means of single or double 316L cold—worked stainless steel hooks.
The purpose of this study was to optimize the present Harrington Rod design in an attempt to reduce distraction rod-related failures due to rotation of the rod and lower hook dislocation. The design of the lower hook was modified to attach the lower portion of the rod more securely to the spine. The redesign allows the lower hook to sit centrally on the vertebrae, resting on the spinous process. Prototypes were developed and models were built.
The effects of replacing the sharp-angled ratchet system with smooth undulations was also studied. A model of the rod with the smooth undulations was developed and a theoretical stress analysis was performed. This stress analysis, which compares the present ratchet design to the model with smooth undulations, shows improvement in the load carrying capability of the redesigned Harrington rod. Theoretical analysis indicates a reduction of rod-related failure due to rod fracture by fatigue, buckling or yielding.
Recommended Citation
Pisani, Margaret Ann, "Optimization of the design of the Harrington distraction rod and hooks" (1987). Theses. 3301.
https://digitalcommons.njit.edu/theses/3301
