Date of Award
Master of Science (MS)
Summers, Joshua D
Anker, Jeffery N
In the USA over 28 million musculoskeletal injuries are treated annually, including 2 million fracture fixation surgeries (about 0.5% of the population). Treatment of large osseous defects use allografts which have failure rates of up to 25%, and complication rates as high as 30-60%. Fracture fixation usually involves mechanical fixation with rods, plates and/or screws which repair slowly and are susceptible to infection. Implant infection and loosening are serious concerns, but can currently only be measured through expensive instrumented implants, biopsy culture, or radiographs. However, none of these directly quantify implant loading and stability. There is therefore a need for a simple, cost effective way to quantify implant loading and stability in patients. The purpose of this study is to develop an optically-based strain measuring orthopaedic screw prototype to quantify strain variation in the implant in-vivo after surgery and monitor the load sharing between the bone and the implant. The screw developed as part of this thesis incorporates a spectral ruler into the screw head, and is based on the Moire effect which indicates strain. The prototype underwent mechanical testing (cyclic loads ranging from 500 N - 2000 N) to closely resemble in-vivo conditions in order to verify the repeatability and reproducibility of the screw to operate as a measurement system. The screw system developed was able to quantify clinically-relevant bone healing strains in the range of 10-3000 ustrains, corresponding to 0.2 -100 um change in length for a 5 mm gauge length spectral ruler. A 1500 N load resulted in 68.64% color change of a 100 micron spectral ruler with the screw able to measure load fluctuations as small as 2.17 N. It exhibited good repeatability and reproducibility but also possessed some amount of hysteresis due to the mechanism of the screw. The work presented in this research also gives a brief background on the evolution of screw prototypes leading to the development of the orthopaedic screw. The findings in this research show encouraging results which will help develop a unique portable tool for physicians to quantify bone healing, implant loosening and/or infection in vivo rather than relying on less quantitative assessments based on pain and radiography. Future research will involve the development of next generation prototypes for orthopaedic screws. It will also look more closely into bending in orthopedic screws and use of luminescent spectral rulers through layers of tissue.
Ravikumar, Nakul, "DEVELOPMENT AND VALIDATION OF AN OPTICALLY-BASED STRAIN MEASURING ORTHOPAEDIC SCREW FOR FRACTURE FIXATION IMPLANTS" (2015). All Theses. 2206.