Expandable Hammertoe Implant Fixation
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Solution Overview
Problem
Conventional hammertoe implants, such as those using Kirschner wires and screw implants, suffer from issues like pin tract infections, loss of fixation, migration, and pistoning, which compromise stability and compression across the joint, necessitating a durable and stable implant with minimal pistoning and easy insertion with minimal tissue damage.
Innovation Solution
A bone implant with an elongate shaft and an expandable section that couples to a reverse countersink in a second bone, utilizing a surgical tool with an expandable cutting edge to form the countersink, providing a stable and secure fixation without protruding ends and minimizing tissue damage during insertion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If Kirschner wires are used for hammertoe correction, then the surgery can be performed with simple temporary fixation, but pin tract infections, loss of fixation, migration, and breakage occur
Solution Approach 1:
The implant is divided into two separate units: a first unit with anchoring structures that engages the proximal phalanx, and a second unit with anchoring structures that engages the distal phalanx. These units are connected by a fitting mechanism, allowing each unit to be optimized for its specific function while working together to provide stable fixation without protruding ends.
Solution Approach 2:
The fitting mechanism allows one unit to be inserted into or coupled with the other unit, creating a nested configuration. This nesting approach enables the implant to be inserted through a minimal incision in a collapsed or compact state, then expanded or locked into place within the bone structure, providing stable fixation without requiring protruding external components.
2Reliability
If compression screws are used as implant alternative, then permanent fixation is provided without protruding ends, but pistoning effect occurs where the implant toggles or moves within the bone
Solution Approach 1:
The implant transitions from a static, rigid compression screw design to a dynamic articulated design with two units connected by a fitting. This fitting allows controlled movement and adjustment, enabling the implant to adapt to bone movement while maintaining stable fixation. The articulation reduces pistoning by allowing the implant to flex with physiological movements rather than rigidly resisting them.
Solution Approach 2:
The implant changes its physical state or configuration through the fitting mechanism, which may allow for adjustment of compression force, angular positioning, or relative movement between units. This parameter adjustment capability enables the implant to optimize its fixation stability while accommodating bone healing and physiological movement, reducing the pistoning effect.
3Adaptability or versatility
If articulated or two-unit implants are used, then flexibility to toe movement is provided, but moving parts such as fittings and hinges decrease stability, lifespan, and compression force
Solution Approach 1:
The implant is segmented into two units connected by a fitting, with each unit having anchoring structures that engage different bones. This segmentation provides flexibility for toe movement while distributing mechanical stresses across multiple anchoring points, reducing the burden on the fitting mechanism and improving overall stability and lifespan.
Solution Approach 2:
The anchoring structures on both units are designed to be firmly anchored into the bones before the fitting mechanism comes under full load. This preliminary anchoring action ensures that the majority of stabilizing force comes from the bone-implant interfaces rather than relying solely on the fitting's mechanical strength, thereby improving reliability.
4Reliability
If conventional screw implants are used, then permanent fixation is achieved, but tissue damage occurs during insertion and compression across the joint is insufficient
Solution Approach 1:
The articulated design with a fitting mechanism allows dynamic adjustment of compression force across the joint. The fitting can be designed to progressively increase compression as the bones heal, providing adequate compression force without requiring excessive insertion force that would damage surrounding tissue. The flexibility of the articulation also allows for natural bone movement during healing.
Data Source
AI summary
A bone implant comprising an elongate body having a first end and a second end coupled by a shaft is disclosed. The first portion is configured to couple to a first bone. The second portion comprises a first expandable section comprising at least one expandable feature. The first expandable section is configured to be received within a reverse countersink in a second bone in a collapsed state and to expand within the reverse countersink. The expandable feature couples to a bearing surface of the reverse countersink. A surgical tool comprising a shaft and at least one expandable cutting edge is disclosed. The shaft is sized and configured to be received within a canal formed in a bone. The expandable cutting edge is formed integrally with the shaft. The expandable cutting edge is configured to expand from a collapsed position to an expanded position for forming a reverse countersink.