Assessment of the Size of the Surgical Site in Minimally Invasive Hip Surgery.

Minimally invasive approaches to the hip are beneficial to the patient, but reduce the space available for manipulation by the surgeon. Determining the available working space is important for the development of surgical instruments, to track movements during surgery, as well as to classify the invasiveness of the procedure. We evaluate three measurement methods to assess the volume of eight surgical sites in a cadaver study. The cavities were filled with an alginate cast to determine its dimensions. Second, the depth, height, and width of the surgical site were measured with a ruler and the volume was calculated. Last, the surface registration method was used to reconstruct the site. We found that the mold filling method provides accurate results in determining the volume of a surgical site. The manual method using a ruler showed excellent reliability, but the calculations tended to overestimate the volume of the surgical site. In contrast, surface reconstruction tended to underestimate the volume of a surgical site, but the results closer resembled the ones derived from the mold filling method. We presented a new method to assess the size of the surgical site intraoperatively in minimally invasive hip surgery. The manual method is reliable, but not as accurate as the surface reconstruction, while the mold filling method cannot be used in an intraoperative setup. Although surface reconstruction showed deficits regarding reliability, due to the lack of direct contact to the patient, it remains an appealing technique to measure the surgical site.