Adjustable Implant with Cycloid Gears for Scalable Bone Lengthening
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Solution Overview
Problem
Existing limb lengthening implants are not scalable to accommodate smaller patients and conditions involving the lengthening of smaller bones.
Innovation Solution
A device comprising a distraction shaft with an internal cavity and a housing, featuring a cycloid gear assembly, lead screw assembly, and an anti-jam feature, allowing for axial movement and scalable design for smaller bone lengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional gear assemblies are used in limb lengthening implants, then the device can achieve sufficient torque for larger bones, but the device cannot be scaled down for smaller bones and patients
Solution Approach 1:
The patent replaces traditional toothed gear mechanisms with a cycloid gear system that uses smooth curved surfaces and rolling contact. This substitution eliminates the need for discrete teeth while maintaining torque transmission, allowing the gear assembly to be scaled down to smaller sizes suitable for pediatric and small-bone applications without losing mechanical effectiveness
Solution Approach 2:
The cycloid gear employs curved, spheroidal surfaces instead of straight-edged tooth profiles. The cycloidal curves allow for continuous rolling contact between gears, providing smooth torque transmission and enabling compact, scalable design that can be adapted to various bone sizes from small pediatric bones to larger adult bones
2Reliability
If lead screw assemblies are used for distraction, then controlled bone lengthening can be achieved, but jamming occurs that prevents reliable operation
Solution Approach 1:
The patent incorporates vibration mechanisms that oscillate the lead screw assembly during operation. This vibration prevents the lead screw threads from binding or jamming by continuously breaking up static friction and maintaining smooth relative motion between mating surfaces, ensuring reliable controlled distraction over extended periods
Solution Approach 2:
The patent introduces intermediary elements such as precision bearings, lubrication systems, and vibration-damping materials between the lead screw and nut components. These intermediaries reduce direct metal-to-metal contact, minimize friction and wear, and prevent jamming while maintaining the controlled translation motion necessary for precise bone lengthening
3Adaptability or versatility
If implant size is reduced for smaller patients, then the device can accommodate smaller bones, but torque efficiency and force transmission are compromised
Solution Approach 1:
The patent employs composite material structures combining high-strength, high-modulus materials with optimized geometric configurations. This allows the creation of compact, lightweight components that maintain sufficient mechanical strength and torque transmission capability even at reduced sizes required for pediatric and small-bone applications
Solution Approach 2:
The implant is designed as a modular system with segmented components that can be configured and sized appropriately for different bone dimensions. This segmentation allows optimization of each component's mechanical properties independently, ensuring adequate force transmission while accommodating varying patient sizes from infants to adults
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables efficient and controlled lengthening of smaller bones by providing a scalable solution that maintains torque efficiency and prevents jamming, suitable for various bone lengths and patient sizes.
Implementation Method 1
an anti-jam feature disposed over the lead screw, between the open end of the distraction shaft and the gear assembly, wherein the anti-jam feature comprises a helical spring
Data Source
AI summary
Disclosed herein are distraction and compression devices configured for placement between a first section of a bone and a second section of the bone, which are scalable to small implant sizes. In various embodiments, the devices include a distraction shaft having an internal cavity disposed therein, the distraction shaft being configured for fixation to the first section of bone; and a housing configured for fixation to the second bone section, wherein the distraction shaft is configured to be axially movable relative to, and disposed partially within the housing. A driving element is disposed within the housing, which is configured to rotatably drive a gear assembly, and a lead screw assembly is disposed at least partly within the internal cavity of the distraction shaft, the lead screw assembly being configured to rotatably advance and/or retract a lead screw within the internal cavity, and to be rotatably driven by the cycloid gear assembly.