Measurements of the posterior acetabular surface and design of a new anatomical locking plate for acetabular fractures

Objective To design a new type of anatomical locking plate which fits better the shape of posterior acetabular surface in Chinese population and presets reasonable directions of locking screws according to the measurements of the posterior acetabular surface in three dimensional (3D) reconstruction models of normal Chinese acetabulum.Methods Included in this study were CT scan data of the normal pelvis of 171 patients,100 males and 71 females with a mean of age 45.9 years (range,from 18 to 60 years).The imaging data at the.dicom format were imported into the Materiaise' s interactive medical image control system (Mimics,version 10.0) for 3D reconstruction and editing before they were saved as the STL files.Next the STL files were imported into the IMAGEWARE software (Imageware V12.1,US EDS Corporation) to set up standard points and surface of the posterior acetabular surfac e.Based on the database,we designed a new type of anatomical locking plate which could fit the shape of bone surface and preset directions of lock screws.Finally,the data were entered into a computerized numerical control digital milling machine to manufacture a real plate and screws.Results The mean acetabular diameters were 57.6 ± 2.9 mm and 52.6 ± 2.6 mm and the mean widths of the posterior acetabular wall were 40.7 ± 2.9 mm and 38.4 ± 2.4 mm for men and women,respectively,with significant differences between men and women (P ＜ 0.05).After one-tenth of the diameter (d) of the acetabulum (d/10) was chosen as the measurement unit of the new coordinate system,the mean widths of the acetabular wall were 7.10 ±0.52 d/10 and 7.16 ±0.47 d/10 for men and women,respectively,with no significant difference between men and women (P ＞ 0.05).The IMAGEWARE software showed that the anatomic shape of our self-designed new type of locking plate was in complete agreement of that of the posterior acetabular surface.The mean deviation of the plate from the bone surface was 3.2 ± 1.0 mm.The locking directions of screws preset completely avoided the acetabulum.Conclusion The new type of anatomical locking plate we designed provides a new choice for the treatment of acetabular fractures,because it perfectly fits the anatomic shape of the posterior acetabular wall and presets reasonable directions of the locking screws to ensure better stability and safety of the fixation. Key words: Acetabulum;  Models, anatomic;  Bone plates;  Computer-aided design