Pedicle Screw Receiving Sleeve With Self-Aligning Thread Inlet
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Solution Overview
Problem
Existing pedicle screw systems face challenges in ensuring correct positioning of the set screw without additional guidance elements, leading to tilting and potential thread damage, especially in open surgery where visibility is restricted.
Innovation Solution
The internal thread of the receiving sleeve and external thread of the clamping screw feature a widened inlet section, allowing for alignment and correct seating without additional guidance, reducing the risk of tilting and thread damage by forming a ramp-like structure that guides the clamping screw into coaxial alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a set screw is applied to a pedicle screw without additional guidance elements, then the device complexity is reduced, but the positioning precision deteriorates leading to tilting and thread damage
Solution Approach 1:
The internal thread of the receiving sleeve is pre-formed with a widened inlet section that acts as a built-in guide. This preliminary geometric feature ensures that when the clamping screw is inserted, its external thread automatically aligns with the widened inlet, preventing tilting before the screwing action begins. The alignment function is built into the thread geometry itself, eliminating the need for separate guidance elements.
Solution Approach 2:
The widened inlet section of the internal thread acts as an intermediary zone between the free space and the fully engaged thread. This transitional geometric feature serves as a mediator that gradually guides the clamping screw from a potentially misaligned position into proper coaxial alignment with the receiving sleeve, preventing direct engagement that would cause tilting.
2Force
If the set screw is pressed onto the tulip with axial pre-force, then the clamping effectiveness is improved, but the risk of tilting increases due to mismatch between flat upper side and thread geometry
Solution Approach 1:
The widened inlet section is pre-formed in the internal thread geometry to create a self-aligning entry zone. This preliminary geometric feature ensures that when axial pre-force is applied to the clamping screw, the force is applied along the correct coaxial axis from the beginning, preventing the tilting that would otherwise occur due to the mismatch between the flat upper side and thread geometry.
3Ease of operation
If the thread inlet is cut to reduce thickness for easier engagement, then the ease of operation is improved, but the strength of the thread is reduced making it more susceptible to damage from tilting
Solution Approach 1:
The thread geometry is modified locally only at the inlet section where a widened entry zone is created. This local geometric modification facilitates easy engagement and self-alignment without affecting the strength-critical portions of the thread further along its length. The local quality change is confined to the entry zone, preserving the overall thread strength while improving operability.
Solution Approach 2:
The widened inlet section performs the preliminary function of guiding and aligning the clamping screw before the main thread engagement begins. This preliminary alignment action prevents tilting that would otherwise require reduced thread thickness, thereby maintaining full thread strength while achieving easy engagement through the pre-formed geometric guide.
4Manufacturing precision
If additional guidance elements such as guide sleeves are used to prevent tilting, then the positioning precision is improved, but the device complexity and cost increase
Solution Approach 1:
The guidance function is merged with the existing internal thread structure of the receiving sleeve. Instead of adding a separate guide sleeve as an independent component, the guiding geometry is integrated directly into the thread formation process. This merging of functions eliminates additional parts while maintaining the self-aligning capability, thereby reducing device complexity and cost.
Solution Approach 2:
The internal thread of the receiving sleeve serves multiple functions simultaneously: it provides the clamping action through thread engagement and also provides the alignment guidance through its widened inlet section. This multi-functionality eliminates the need for separate guidance elements, as the same structural feature performs both clamping and guiding roles, reducing overall system complexity.
Data Source
Figure 1~2
Figure 3~4
AI summary
The present invention relates to a bone screw (2), in particular pedicle screws with a receiving sleeve (3) that has a sleeve wall (7, 8) which forms a seat for a longitudinal support for the surgical connection of adjacent bone screws (2) and is provided with an internal thread (5), wherein a thread turn (10) of the internal thread (5) has a widened lead-in region (18) on the thread lead-in side.