Finite Element Analysis of Transhumeral and Transtibial Percutaneous Osseointegrated Endoprosthesis Implantation.
Carolyn E Taylor, Heath B Henninger, Kent N Bachus
PMID 35178528WHAT IT FOUND
Current sizing instructions for osseointegrated implants work for the upper arm but fail for the lower leg.
The tibia requires a larger implant to achieve stability, but this increases fracture risk. A circular implant design is likely unsuitable for transtibial amputation.
Key findings
01The optimal implant size for the tibia is three sizes larger than the manufacturer's instructions, whereas the instructions are accurate for the humerus.
02Increasing the tibial implant size to achieve stability causes a sharp rise in stress, leaving little margin for error before fracture risk increases.
03An elliptical implant design increased stability force without increasing stress in a pilot simulation, suggesting the current circular design is flawed for the tibia.
STILL TO COME
How it was doneWhat they found
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What it does not show
The study used only three cadaveric bones per site, which does not represent the wide variation in bone quality, osteoporosis, or disuse atrophy seen in actual amputees. The computer models overestimated the force required for implantation by about 334 N compared to physical tests, meaning the absolute stability numbers are not perfectly accurate. The study only tested one specific amputation level (40% for tibia, 30% for humerus). Results may differ for shorter or longer residual limbs. The models did not account for the porous coating on the actual implant, which can file away bone during insertion and alter stability.
Declared interests
The authors declared no commercial or financial conflicts of interest. The work was funded by the US Department of Veterans Affairs and the US Army Medical Research and Materiel Command.
The easy way to misread this
Do not interpret this as evidence that osseointegration is unsafe for transtibial amputees in general. The study only shows that the specific circular implant design tested here is poorly suited for the tibia. Other designs or surgical techniques may perform differently.