This paper presents a cadaveric validation of a novel planning and navigation system for peri-acetabular osteotomy (PAO). In total 8 computer assisted PAO procedures was performed on 4 cadavers (each cadaver has two hip joints). By comparing the pre-operatiely planned situation and the intra-operatively achieved situation, an average error of 0.65°, 0.56° and 0.91° was found respectively along three motion components: External Rotation/Internal Rotation, Abduction/Adduction and Extension/Flexion.
PAO planning module. The aim of this module is to allow the virutal simulation of the reorientation procedure using the surface models generated from the model generation module. It starts with a fully automatic detection of the acetabular rim, which allows for computing important information quantifying the acetabular orientation such as coverage, extrusion index, lateral centre-edge (LCE) angle, version and inclination. This module provides a graphical user interface allowing the surgeon to conduct a virtual osteoomy and to further reorient the acetabular fragment until an optimal realignment is achieved.
Intra-operative navigation module. Based on an optoelectronical tracking technique, this module aims for providing intra-operative visual feedback during acetabular fragment reorientation until the pre-operatively planned orientation is achieved.
In order to validate this newly developed planning and navigation system for PAO, a cadaveric study was conducted. In total 8 computer assisted PAO procedures was performed on 4 cadavers (each cadaver has two hip joints). Preoperative planning was conducted with the PAO planning module. Subsequently the intra-operative navigation module was used to track acetabular and pelvic fragments, supporting and guiding the surgeon during the osteotomies around the acetabulum. After separation of the acetabular fragment from the pelvis, the navigation system then guided the surgeon during the reorientation of the acetabulum until the pre-operative plan was achieved. Acetabular reorientation measured by the version and inclination Angle can be planned preoperatively and subsequently realized intraoperatively without significant difference. In order to assess the error difference between the preoperatively planned and the intra-operatively achieved acetabular orientation, we compared the decomposed rotation components derived from the acetabular fragment reorientation between the planned and intra-operative situations because the instant version and inclination Angle correspond a specific decomposed rotation components of acetabular fragment. 3
As shown in Fig.2, the decomposed rotation components of the acetabular fragment between the pre-operatively planned situation and the intra-operatively achieved situation were compared. According to Table 1, 8 groups of acetabular reorientation data were obtained. It can be seen that the average errors along three motion components (External Rotation/Internal Rotation, Abduction/Adduction and Extension/Flexion ) are 0.65°, 0.56° and 0.91°, respectively, which are accurate enough for PAO surgical intervention. The maximal error is from the 4th cadaver with the biggest registration error. It was found that the 4th cadaver has prosthesis implanted, which made it difficult to segment high quality model from its CT data. This is why mean error of the 4th cadaver is slightly worse than those of the rest of cadavers. Cadaver1 Cadaver2 Cadaver3 Cadaver4 left hip right hip left hip right hip left hip right hip left hip right hip
In this paper, we present a cadaveric validation of a comprehensive planning and navigation system for PAO. Our experimental results demonstrate the accuracy of this newly developed system. A clinical trial is planned to further validate the effacicy of the developed system for PAO interventions. Our experimental results demonstrated that there is no significant difference between the pre-operatively planned and final intra-operative acetabular orientation, measured by decomposed rotation angles. We concluded that preoperative planning and subsequent conduction of acetabular reorientaion in PAO is technically feasible and is associated with good accuracy in the experimental cadaveric setup. 5