Background: Minimally invasive cancellous bone biopsy is a common medical procedure in which a needle is used to extract a piece of cancellous bone for examination. Unfortunately, this procedure is not always successful, as sometimes the biopsy can slip partially or completely, necessitating a new biopsy. The occurrence of these errors is not well documented, but the main causes are believed to be an inadequate grip on the biopsy by the current golden standard or improper use of the additional instrument of the golden standard. This study aimed to design a novel mechanism for use in a biopsy needle, with the goal of combating the causes of the errors by providing an integrated design that guarantees the extraction of a biopsy.
Methods: The design process was explored by plotting the potential variations onto a design tree. This resulted in four distinct concepts. Criteria were established to evaluate the concepts. The Cam-follower concept was chosen as the final design. This mechanism was then constructed into a functioning prototype. This prototype was tested in a visual experiment and in a material experiment using gelatin and artificial bone tissue phantoms.
Results: The cam-follower mechanism was able to close off 89% of the end of the needle prototype. It was successful in extracting complete biopsies from the gelatin tissue phantom. The analysis of the softest bone was challenging due to the lengthwise compression of the biopsies. The needle prototype had difficulty penetrating the medium hard artificial bone and broke beyond use during these tests. The needle prototype was not put through its paces on the most difficult artificial bone type prepared for the experiment because of the harm it had sustained.
Discussion and conclusion: The Cam-follower mechanism is an integrated instrument that is intended to improve the efficacy of minimally invasive bone biopsy instruments. The current needle prototype was able to extract biopsies of higher quality and size from the gelatin tissue phantom compared to the golden standard. However, it failed to extract a viable biopsy from the artificial bone tissue phantoms, meaning that the design did not meet its goal. It is possible that the tissue phantoms used in this study did not accurately replicate real bone tissue, which could have impacted the results. Additionally, the main focus of the design was on the mechanism when the bone was already penetrated, so any issues that arose during penetration were not addressed before the material test. It is recommended to further refine the design with these results in mind. Small changes, such as incorporating elements from the golden standard like the tapered end and the sharpened cutting edge of the outer needle, could have a positive effect and enable the cam-follower to guarantee extraction of a biopsy, which would open the door to a clinical application.