Intramedullary Rod Instrument with Centralizer and Angular Adjustment
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Solution Overview
Problem
Intramedullary rods used in knee arthroplasty procedures face challenges due to variability in the intramedullary canal's width, direction, and straightness, making it difficult to correctly position cutting guides or blocks, and existing angular adjustment mechanisms are cumbersome and hard to use.
Innovation Solution
A short intramedullary rod with a centraliser mechanism that self-centers within the canal and an angular adjustment mechanism with a rotatable collar system providing multiple angles and clear indicia for easy selection, allowing for precise angular adjustments and improved usability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a long intramedullary rod is used to engage the intramedullary canal, then the rod becomes self-locating, but the positioning of components attached to the rod becomes compromised due to variability in canal width, direction and straightness
Solution Approach 1:
The rod is divided into two functional segments: a long distal portion that provides self-location within the canal, and a short proximal portion that extends beyond the canal to support cutting guides and blocks. This segmentation allows each portion to fulfill its specific function optimally.
Solution Approach 2:
A centraliser mechanism acts as an intermediary component between the rod and the cutting guide/block. This mechanism includes a body with a centralising portion that engages the rod and a guide/block supporting portion that holds the cutting tools, thereby mediating the positioning relationship between the self-locating rod and the precision-required cutting components.
2Adaptability or versatility
If an angular adjustment mechanism with a pivot mechanism is used to change the angle of the rod, then angular orientation can be adjusted, but the mechanism becomes difficult to use in practice due to small operating levers and limited space for scale display
Solution Approach 1:
The angular adjustment mechanism is repositioned from the distal end of the rod to the proximal end, where there is ample space for operator access and scale display. This dimensional relocation transforms the adjustment mechanism from a cramped, hard-to-use configuration to an open, easily accessible one.
Solution Approach 2:
The angular adjustment function is replicated at the proximal end through a separate adjustment mechanism that mirrors the angular adjustment capability but provides it in a more accessible location with adequate space for operation and reading.
3Ease of operation
If the intramedullary rod is made short to improve positioning, then the rod can be more easily positioned relative to the bone, but the rod loses its self-locating capability in the intramedullary canal
Solution Approach 1:
The rod is segmented into a long distal portion (at least 20cm) that provides self-location and a short proximal portion that enables easy positioning and component attachment. This segmentation resolves the contradiction by assigning different length requirements to different functional zones.
Solution Approach 2:
The centraliser mechanism serves as an intermediary that bridges the gap between the short rod and the requirement for reliable canal engagement. It provides the missing self-centralisation function while allowing the rod to remain short for ease of positioning.
Data Source
AI summary
A femoral instrument for use in the intramedullary canal is described and includes an intramedullary rod having a tip at a free end. A body is attached to the intramedullary rod and has a face with a bone abutting portion. A centralizer mechanism is located within the rod and is operable to deploy and retract a plurality of members to engage and disengage an inner surface of the intramedullary canal. The length of the intramedullary rod from the tip to the face of the body is less than 30 cm. The instrument can also include an angular adjustment mechanism. The angular adjustment mechanism can have a plurality of formations and can be rotated about the longitudinal axis of the intramedullary rod to present at least a one of the formations to abut a portion of the body to define the relative angle between the body and the intramedullary rod.