Validation of Feedback Control Approach for an Implantable Limb Lengthening Device

Abstract

Lower limb length discrepancy (LLD), defined by unequal length of paired lower limbs, contributes to lower back pain, osteoarthritis of the hip, and stress fractures [1–3]. The Center for Disease Control and Prevention estimated that there were approximately 700 children born with LLD each year in US [4]. Patients may receive distraction osteogenesis treatment, in which an osteotomy is performed on the shorter limb, and mechanical force is applied to gradually distract the two halves of the bone during the healing process. This stretches the bone callus during healing to achieve desired limb length upon callus consolidation [5]. The current correction devices are external fixators that leave unsightly scars and are prone to infection [6]. While recently developed intramedullary devices address many of the persistent issues with external lengthening devices, size limitations and potential damage to the bone growth plates make them impractical for use in children [7, 8]. The proposed research addresses an unmet need by developing a novel implantable extramedullary device for LLD correction that is targeted for pediatric use. The device will be implantable, submuscular, and fixed to the outside surface of the bone (extramedullary), thus allowing for use in children without concern for injury to the growth plates. The device’s function will be similar to an external fixator; however, it will not require exposed hardware, which increases risk of infection, or muscle penetration from the pins, which causes pain. Additionally, the device incorporates real-time control of the distraction rate, reducing the risk of complications arising from fixed rate distraction such as premature consolidation and non-union of the callus. [9–11]. The investigators of this study have previously designed and constructed a distraction mechanism prototype and test frame [10]. The current study aims to validate the real-time controller of the prototype.