Nested Compression Screw Assembly for Orthopedic Fracture Fixation
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Solution Overview
Problem
Current orthopedic fixation devices face challenges such as compression screw breakage, difficulty in removal, and increased lateral prominence of lag screws, which can lead to tissue irritation and reoperation, especially in treating intertrochanteric hip fractures.
Innovation Solution
The orthopedic fixation device incorporates a partially threaded compression screw that nests with a lag screw, allowing for a larger diameter without increasing the IM nail or lag screw size, and a telescopic lag screw assembly that slides relative to the IM nail to maintain fracture compression and prevent soft tissue irritation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the compression screw diameter is increased to prevent breakage, then the strength and reliability of the compression screw is improved, but the size of the IM nail and lag screw must be increased correspondingly
Solution Approach 1:
The compression screw is nested within the lag screw, with the compression screw positioned inside the lag screw's threaded portion. This nesting arrangement allows the compression screw to have a larger effective diameter and strength without increasing the overall size of the IM nail, as the compression screw utilizes the space already defined by the lag screw's thread structure.
Solution Approach 2:
The invention transitions from a single-dimensional screw structure to a two-dimensional nested configuration where the compression screw operates within the radial and axial space of the lag screw. This dimensional reorganization allows independent optimization of compression screw strength without proportionally increasing IM nail dimensions.
2Object-affected harmful factors
If the lag screw is fixed to the IM nail to prevent sliding, then the lateral prominence is reduced, but the ability to allow fracture sliding for healing is lost
Solution Approach 1:
The lag screw is segmented into a fixed proximal portion (within the IM nail) and a movable distal portion (engaging the fracture). The proximal portion remains constrained within the IM nail to minimize lateral prominence, while the distal portion can slide relative to the fracture fragments to accommodate healing movements. This segmentation allows simultaneous achievement of both reduced prominence and maintained adaptability.
Solution Approach 2:
The lag screw assembly transitions from a static fixed structure to a dynamic system where the distal portion can move relative to both the IM nail and fracture fragments. This dynamic capability allows the screw to adapt during the healing process while maintaining a low-profile configuration within the IM nail.
3Ease of operation
If the compression screw is fully threaded to engage the lag screw rack, then the nesting mechanism works properly, but the risk of compression screw breakage increases
Solution Approach 1:
The compression screw uses partial threading rather than full threading along its entire length. The threaded portion is sufficient to engage the lag screw rack and provide the necessary nesting mechanism function, while the unthreaded portions reduce stress concentration and the risk of breakage. This partial action approach provides adequate functional engagement without the excessive material removal that would weaken the screw.
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
This design enhances the strength of the compression screw, facilitates easier removal, and reduces the risk of breakage, while minimizing soft tissue irritation and promoting effective fracture healing.
Implementation Method 1
The compression screw 30 includes an enlarged lateral head 32, a medial end 34, and an externally threaded segment 36 extending from the lateral head 32 to the medial end 34. In use, the threaded segment 36 of the compression screw 30 passes through the opening formed in the body of the IM nail 10 and engages a rack 28 (FIG. 1C) disposed on a side of the lag screw 20.
Implementation Method 2
the compression screw 30 is a fully threaded screw which engages a rack 28 on the lag screw 20 to act as a worm gear. Thus arranged, the compression screw 30 is nested (e.g., meshes) with the lag screw 20.
Implementation Method 3
The outer sleeve 232 may include a plurality of teeth 276 arranged and configured to engage the threads 260 formed on the compression screw 250.
Data Source
AI summary
An orthopedic fixation device (e.g., an intramedullary (“IM”) nail or bone plate) including a lag screw and a compression screw, the compression screw being nested with the lag screw. In accordance with one or more features of the present disclosure, the compression screw may include a partially non-threaded medial segment, an enlarged diameter, and/or a cannulated bore. In addition, and/or alternatively, the lag screw may be provided as an integrated assembly including a lag screw and an outer sleeve to enable the lag screw to telescope or slide relative to the outer sleeve and IM nail.