Semi-constrained Screw Assembly for Spinal Plate Stability
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Solution Overview
Problem
Conventional spinal plate assemblies face issues with bone screws backing out due to torsional and bending motions, leading to patient discomfort and potential separation of the spinal plate from vertebrae.
Innovation Solution
A semi-constrained screw assembly with a removable screw head and screw shank, featuring threaded segments with slits, allows for poly-axial movement and secure locking to the bone plate, preventing screw backout by engaging a lip on the plate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bone screws are used in spinal plate assemblies, then the spinal plate can be attached to vertebrae, but the screws tend to back out or withdraw from the bone due to normal torsional and bending motions
Solution Approach 1:
The screw assembly is divided into separate components: a screw head with threaded segments and slits, and a screw shank. This segmentation allows the threaded segments to engage with the bone plate while the slits permit controlled movement, preventing backout while maintaining attachment stability.
Solution Approach 2:
The screw assembly incorporates dynamic elements through the slits in the threaded segments, which allow the screw to move poly-axially relative to the bone plate during normal spinal motion. This dynamic capability prevents the screw from backing out while still maintaining secure attachment.
2Reliability
If bone screws are secured firmly to prevent backout, then fixation stability improves, but the screws may separate from the spinal plate or cause patient discomfort
Solution Approach 1:
The screw assembly changes the geometric parameters of the threaded segments by incorporating slits that allow controlled movement. This parameter modification enables the screw to adapt to normal spinal motions without causing discomfort, while still maintaining firm fixation stability.
3Strength
If the screw head is rigidly locked to the bone plate, then attachment strength increases, but the screw cannot accommodate normal torsional and bending motions of the spine
Solution Approach 1:
The screw assembly separates the locking function (threaded segments engaging the bone plate) from the movement function (slits allowing poly-axial motion). This segmentation enables the screw to maintain strong attachment while accommodating normal spinal motions through controlled movement of the screw shank relative to the bone plate.
Data Source
AI summary
A semi-constrained screw and a cervical plate assembly that engages to a cervical area of the human vertebrae system are disclosed. The semi-constrained screw and cervical plate assembly includes a cervical plate and one or more semi-constrained bone screws. Each semi-constrained bone screw includes an elongated shank, which is mechanically and releasably coupled to a head portion. The head portion includes one or more threaded segments which define one or more slits therebetween. As the semi-constrained bone screw is driven through the screw opening in the cervical plate and into the bone, the head portion allows poly-axial movement of the shank relative to the head portion.