Prototipagem rápida em cirurgia ortopédica de preservação do quadril

Abstract

Periacetabular osteotomy (PAO) surgery is the treatment of choice for developmental dysplasia of the hip (DDH) in symptomatic skeletally mature patients and the results include improving quality of life, modifying the natural history of disease and eventually the preventing development of hip arthrosis. Therefore, it is considered a hip-preserving surgery. However, because PAO is technically challenging, has a long learning curve and is associated with some serious complications, we envision the possibility of applying rapid prototyping (RP) technology, with three-dimensional surgical planning (3D) and printing of customized guides for this surgery. In this study, we present all the steps in the development of an original low-cost Brazilian process to produce plastic guides customized for OPA and evaluated the accuracy and costs of these guides in an experimental study of cadaver bones. Ten hip bones from human cadavers underwent experimental surgery with assistance of a guide produced in ABS plastic by RP, using tomographic images and a 3D planning process. In no case was there a fracture of the guide (mechanical failure) or a violation of the articular surface or of the posterior column of the acetabulum. This proved the guide's effectiveness in guiding surgical cuts while preventing those complications. The average accuracy of the impression, comparing the absolute mean difference between the planned and obtained cutting slots was 0.28mm (standard deviation = 0.024mm; minimum difference =0.01mm and maximum =0.75mm). According to the computer assisted method (comprising optical scanning and linear measures in Cloudcompare software) the accuracy of the guide was 1.57mm in average (sd=2.15) or 97.23% (comparing the difference between the planned and obtained bone cuts). Tridimensional accuracy of the cuts was estimated comparing the inclination of planned and obtained line A (θA angle) and planned and obtained line B (θB angle) which measured 5,49° e 4,64°, respectively. According to the automated comparison between the planned and obtained volumes (using best alignment tool in Cloudcompare software), on average the maximum distance was 7.21 (sd=3.336), the maximum error=0.34 (sd=0.03), the greater maximum distance=12.55 mm and the smaller maximum distance=3.74mm. The average cost of the filament used per guide was BRA$ 2.28 (sd=BRA$ 0.52). In the economic cost model, the estimated average unit cost of a guide considering all the costs of capital, operation and losses in a hospital environment was BRA$=120.85 (minimum=BRA$ 82.57 and maximum BRA$=684.56). We conclude that it is possible to create inexpensive surgical guides for PAO and with good accuracy using the rapid prototyping technology and the method described in this thesis.