A hypothetical method for calculation of the access point, direction angle and access angle for percutaneous nephrolithotomy.

Urinary stone disease has an increasing prevalence across the globe, and endoscopic treatment modalities have replaced open surgery. Percutaneous nephrolithotomy (PCNL) is a successful, safe and reliable minimally invasive method in the treatment of renal stones, especially big (≥2 cm) or complex ones. Gaining access is the most critical step of this procedure, which can affect the rest of the operation. Although previously described techniques, eye of the needle and triangulation techniques, are being used for gaining access, urologists (especially novice ones) can still have problems during this step. Some navigation concepts have been developed in order to make the access safer, easier and more successful, however, none of them has been incorporated in daily routine practice till now because of either complicated techniques or requirement of sophisticated equipment. Our hypothesis is that the access point, direction angle and access angle in order to touch a stone during PCNL can be calculated by the data obtained from the computed tomography images with the help of mathematical formulations, namely the theorem of the cosine.