Characterizing and Simulating Needle Insertion Forces for Percutaneous Renal Access

Background: Percutaneous needle access is a critical step of performing percutaneous nephrolithotomy. Development of a synthetic model that accurately represents the forces encountered while gaining percutaneous renal access, allows for high ease of use and prevention of negative skill transfer. The objectives of this study were to define the needle insertion forces used during percutaneous renal access and to develop a multilayer synthetic physical simulator model based on human tissue data that is compatible with the SimPORTAL fluoro-less C-arm trainer (CAT) camera system. Materials and Methods: Needle insertion data were collected using in situ fresh human cadaveric tissue within 72 hours of death. Ultrasound guidance was used to place percutaneous reference needles into the kidney, and axial force vs displacement data was collected using a custom-built force measurement device. A novel multilayer model that includes several types of synthetic materials for simulation of distinct tissue layers was developed based on the human tissue reference data. The multilayer prototype model and an existing single material model were subsequently tested using the same needle insertion protocol and the results were compared with human tissue data. Results: Average maximum forces for needle puncture into skin ranged from 2.75 to 2.80 N for human tissue and from 4.53 to 4.19 N for simulated human tissue. The overall slope for all force vs displacement data was 0.35 to 0.59 N/cm for human tissue. The overall slope was comparatively lower for the multilayer model (0.17 N/cm) and was highest in the existing single material model (5.08-9.79 N/cm). Conclusions: We have defined the forces for percutaneous renal access using fresh human cadaveric tissue and designed a multilayer synthetic simulator model that can be utilized for training percutaneous needle access to the renal collecting system using the CAT camera system.