Bone Peg With Offset Threads For Extraction
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Solution Overview
Problem
Existing bone pegs used in stabilizing fractures, particularly in the proximal humerus, face difficulties in removal due to insufficient cancellous bone density and divergent angles, making it challenging to withdraw the peg from the bone and plate without leaving the head submerged.
Innovation Solution
A bone peg with a head portion and shaft portion, featuring synchronized head and shaft threads of equivalent pitch, allowing the shaft threads to maintain contact with the bone after the head threads clear the plate aperture, facilitating easier withdrawal by extending beyond the plate body for grasping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If smooth pegs are driven into the proximal humerus at divergent angles, then subchondral support is provided to compensate for insufficient cancellous material, but the pegs become difficult to withdraw and the head remains submerged within the plate hole
Solution Approach 1:
The peg is segmented into two distinct threaded portions: a head threaded portion for engagement with the bone plate aperture and a shaft threaded portion for engagement with the bone. This segmentation allows each portion to perform its specific function independently, enabling reliable fixation while facilitating easy withdrawal by allowing the head to be accessed and grasped for removal
Solution Approach 2:
The invention introduces an axial dimension to the thread configuration by offsetting the head threaded portion from the shaft threaded portion along the longitudinal axis of the peg. This axial separation allows the head threads to clear the plate aperture during withdrawal while the shaft threads remain engaged with the bone, enabling the head to extend beyond the plate for grasping and removal
2Manufacturing precision
If the head threaded portion and shaft threaded portion advance simultaneously, then synchronized engagement with plate and bone is achieved, but the head threads must clear the plate aperture before shaft threads disengage from bone
Solution Approach 1:
The head threaded portion is designed to advance and clear the plate aperture before the shaft threaded portion disengages from the bone. This preliminary action ensures that the head is positioned to extend beyond the plate for grasping, while the shaft threads maintain engagement with the bone until the final stages of withdrawal, simplifying the removal process
Solution Approach 2:
The invention uses equivalent pitch for both head and shaft threads to maintain synchronized advancement, but introduces an axial offset between the two threaded portions. This parameter change in axial positioning allows the head to clear the plate aperture first, enabling easy withdrawal while maintaining manufacturing simplicity through consistent thread pitch
Data Source
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AI summary
A bone peg (10) configured for cooperation with a threaded aperture (82) on a bone plate (14) for use in stabilizing a fracture of a bone (16) includes a head portion (22) and a shaft portion (24). The head portion has a head threaded portion (30) that incorporates head threads (32) having a first pitch. The shaft portion extends from the head portion to a distal end (22) of the bone peg. The shaft portion includes (i) a shaft threaded portion (50) that incorporates shaft threads (60) having a second pitch, (ii) a first unthreaded portion (52) and (iii) a second unthreaded portion (54). The shaft threaded portion is disposed intermediate the first and second unthreaded portions. The first unthreaded portion axially offsets the head threaded portion from the shaft threaded portion. The pitches allow the threaded portions to advance through the aperture and the bone in a synchronised manner.