Spinal Implant Driving Instrument with Nested Shafts
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Solution Overview
Problem
Conventional spinal implants face challenges in maximizing contact with vertebral body endplates, achieving desired lordosis, and preventing dislocation due to their concave nature and limited bone growth capabilities.
Innovation Solution
A driving instrument with an outer and inner shaft, allowing independent adjustment of a spinal implant's proximal and distal regions, ensuring simultaneous rotation of both shafts to actuate adjustment assemblies, maximizing contact with endplates and maintaining the intervertebral space for bone ingrowth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional prosthetic implants are used, then the implant can be inserted between adjacent vertebrae, but the implant may be dislodged or moved from its desired implantation location due to patient movement before sufficient bone growth occurs
Solution Approach 1:
The spinal implant includes expandable bodies that can dynamically change volume and shape. The implant transitions from a compressed state during insertion to an expanded state after implantation, providing progressive stability as bone growth occurs. This dynamic adaptation resolves the contradiction by allowing the implant to be simple during insertion yet provide maximum stability during the healing period.
Solution Approach 2:
The implant is divided into multiple expandable bodies (proximal and distal) that can be independently actuated. Each body contains internal structures such as pistons, chambers, and expansion elements that segment the overall function. This segmentation allows controlled expansion and adjustment while maintaining overall implant stability, addressing both reliability and complexity concerns.
2Reliability
If conventional prosthetic implants are used, then the implant structure is simple, but it is difficult to obtain enough contact between the implant and the concave vertebral body endplates to create bone growth
Solution Approach 1:
The expandable implant bodies feature curved or domed surfaces that conform to the concave geometry of vertebral endplates. This curvature maximizes surface contact area between the implant and bone, promoting osteointegration and bone growth while maintaining a relatively simple overall implant design.
Solution Approach 2:
The implant's volume and shape parameters can be changed after insertion through expansion mechanisms. This allows the implant to adapt its contact surface area to match the specific geometry of the vertebral endplates, enhancing bone contact and growth capability without requiring a complex pre-configured structure.
3Adaptability or versatility
If conventional prosthetic implants are used, then the implant can be inserted, but achieving the desired lordosis is difficult given the limitation of typical prosthetic implants once they are implanted
Solution Approach 1:
The implant incorporates expandable bodies that can be adjusted post-insertion to change the lordotic angle. By controlling the expansion of proximal and distal bodies independently, the implant can dynamically adapt to achieve the desired spinal curvature, providing versatility without requiring a complex multi-component structure.
Solution Approach 2:
The implant is inserted in a compressed state with preliminary positioning, then expanded to achieve the final lordotic configuration. This preliminary action allows for easier insertion followed by controlled adjustment to the desired angle, balancing adaptability with structural simplicity.
4Reliability
If conventional prosthetic implants are used, then the implant structure is simple, but the intervertebral space cannot be maintained during bone ingrowth
Solution Approach 1:
The expandable implant bodies provide dynamic support that maintains intervertebral space throughout the bone ingrowth process. The implant can be expanded to the optimal height to preserve disc space, and this spacing is maintained as bone grows around the implant structures, ensuring reliable space maintenance without complex external fixation devices.
Data Source
AI summary
A driving instrument for adjusting a spinal implant includes an outer shaft having a distal end configured to actuate a proximal adjustment assembly of a spinal implant, and an inner shaft having a distal end configured to actuate a distal adjustment assembly of the spinal implant. The inner shaft is disposed within the outer shaft, with a proximal end of the inner shaft extending proximally from the outer shaft. The proximal end is configured to be rotated such that rotation of the inner shaft results in simultaneous rotation of the inner and outer shafts, with rotation of the outer shaft ceasing at a first value of resistance associated with the proximal adjustment assembly and rotation of the inner shaft ceasing at a second value of resistance associated with the distal adjustment assembly such that cessation of rotation of the inner shaft is independent from cessation of rotation of the outer shaft.