A Novel Minimally-Invasive Implantable Limb Deformity Correction Device
Thousands of children are born in the United States annually with limb deformities and leg length inequalities. Others suffer injuries or infections affecting future growth, leaving them with similar limb deformities. Current tools used to treat these deformities are limited and often require prolonged use of external fixation limb deformity correction devices (LDCDs) with transcutaneous pins that cause pain, unsightly scars, and commonly infections. Implantable lengthening LDCDs exist, but can neither correct angular deformity nor be used in children due to growth plate injury concerns. The purpose of this initiative was to design, fabricate, and evaluate the kinematics of a prototype LDCD which addresses these concerns. The prototype permits lengthening and two angular degrees of freedom for limb deformity correction. This implantable design is extramedullary, enabling use in children. In order to design a sophisticated control system for the device the kinematics of the system must be fully understood. Furthermore a kinematic model must be created which is capable of predicting the location of the device end effector based on motor data. This model will be used in conjunction with implanted 6 DOF force/torque sensors to develop a biomechanics model of the device interacting with the bone and surrounding tissue. Using this information an observer model will be created that will set the distraction and contraction rate of the device, minimize localized muscle strain (which leads to patient pain), and provide real time feedback of callus health.
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