Pelvic Bone Fixation via Tensioning Cable
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Solution Overview
Problem
Existing pelvic fracture fixation systems, such as sacral bars and cancellous screws, are susceptible to failure due to loss of bone strength, loosening of threaded bolts, and loss of bony purchase, particularly in cases of osteoporosis or rotational and longitudinal movement.
Innovation Solution
A bone fixation device comprising two elongated elements with channels and a tensioning cable, where the elements are inserted through lateral openings in the pelvis and secured with a cable stop and crimp to apply compressive force to the bone, providing stability and adjustable compression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If threaded bolts and cancellous screws are used to maintain compression of the pelvis, then the compression can be maintained initially, but the device is susceptible to failure due to loosening of threaded bolts and loss of bony purchase
Solution Approach 1:
The fixation device is divided into two separate rods (first rod and second rod) that can be independently inserted into the bone, each with its own channel. This segmentation allows for more distributed load bearing and reduces the stress concentration on any single threaded component, thereby improving long-term durability and reducing loosening.
Solution Approach 2:
A tensioning cable is introduced as an intermediary element that runs through the channels of both rods. This cable acts as a mediator to transmit and distribute the compressive force evenly across the fracture site, reducing the reliance on threaded bolts for force transmission and minimizing the risk of bolt loosening and bone purchase loss.
2Force
If sacral bars are inserted through the pelvis with threaded nuts to create compression, then compression can be maintained, but the device is susceptible to failure due to loss of bone strength such as osteoporosis
Solution Approach 1:
The tensioning cable serves as an intermediary that distributes the compressive force along the length of both rods, rather than concentrating it at the threaded nut-bone interface. This distributed force transmission reduces the stress on osteoporotic bone and threaded connections, improving fixation reliability in patients with reduced bone strength.
Solution Approach 2:
By using two separate rods with independent channels, the compressive force is distributed across multiple insertion points and bone surfaces, reducing the load on any single threaded connection and making the system more reliable in osteoporotic conditions.
3Device complexity
If fixed-length fixation devices are used, then the device structure is simplified, but the device cannot accommodate anatomical variations in different patients
Solution Approach 1:
The device incorporates adjustable-length rods that can be customized to match the specific anatomical dimensions of each patient. This dynamic adaptability allows the fixation device to accommodate variations in pelvic anatomy while maintaining a relatively simple overall structure, as the adjustment mechanism is integrated into the rod design itself.
4Duration of action of stationary object
If permanent fixation devices are used to maintain compression, then the compression is maintained continuously, but the device cannot be easily removed once the bone has healed
Solution Approach 1:
The fixation device is designed with reversible or adjustable fixation mechanisms that allow it to transition from a permanently fixed state during healing to a removable state after healing. This dynamic design enables continuous compression to be maintained during the critical healing period while facilitating easy removal once the bone has healed, addressing both requirements.
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
The device enhances stability and compression of the fractured bone, reducing the risk of device failure and allowing for adjustable length to accommodate anatomical variations, while enabling easy removal once the bone has healed.
Implementation Method 1
tension applied at a second end of the tensioning element imparts a compressive force to the first and second elements and, consequently to a bone into which the first and second elements are inserted
Data Source
AI summary
A bone fixation device includes a first element extending from a first head to a first shaft along a first longitudinal axis and having a first channel extending therethrough. The first head rests against a portion of bone adjacent to a first hole through which the first shaft is inserted. A second element includes a second shaft extending along a second longitudinal axis to a second head and having a second channel extending therethrough, the second head resting against a portion of bone adjacent to a second hole through which the second shaft is inserted. The second channel is dimensioned to receive the first shaft therein. A tensioning element is insertable through the first and second channels so that tension applied at a second end thereof imparts a compressive force to the a bone into which the first and second elements are inserted.