PSI - Issue 2_A

1254 M. Karanika et al. / Procedia Structural Integrity 2 (2016) 1252–1259 M. Karanika, D. Georgiou, S. Darmanis, Α . Papadogoulas, E.D. Pasiou, S.K. Kourkoulis / Structural Integrity Procedia 00 (2016) 000 – 000 3

The short survey of previous paragraphs clearly indicates that the problem is still open and the conclusions drawn are not always towards the same direction. As already mentioned this could be attributed to improper laboratory simulation of the actual loading and supporting conditions, the different displacement measuring techniques used and the lack of any standardization. Moreover the number of tests per fixation technique is limited (usually two to five specimens are used), for obvious reasons, resulting inevitably to difficulties in the statistical correlation of the results. In the present study the problem is addressed by taking advantage of the three dimensional Digital Image Cor relation (3D-DIC) technique (in conjunction with traditional clip gauges) for the determination of displacements. The object is two-folded: To assess the applicability and efficiency of 3D-DIC when it is used in experiments with fractured and fixated pelvises and to comparatively assess the efficiency of some widely used fixation techniques. 2. The experimental protocol 2.1. The specimens and the experimental set-up For the needs of the study about thirty cadaveric semi-pelvises were used with considerable degree of osteoporosis. The semi-pelvises were artificially fractured. Every effort was paid for the fractures of all pelvises to be identical to each other. All fractures were of the “B2 T -type ” according to Letournel and Judet (1993). Five of the specimens were used during a preliminary protocol which permitted optimum spatial arrangement of the constituent elements of the experimental set-up (loading frame, cameras and white light sources of the 3D-DIC system), design of a proper system for supporting the specimens and applying the load, and finally calibration of a number of experimental parameters, like for example the loading rate, the sampling rate, the data acquisition and storage constants etc. The remaining twenty five pelvises were classified in five groups of five specimens each. The fractured pelvises of each group were fixated following five different techniques as it is shown in Table 1. Some characteristic specimens are shown in Fig.2. After fixation the specimens were painted white and then using a black spray a random pattern of black dots was created on their surface (as it is shown in Fig.3a) to assist application of 3D-DIC. Using a suitable adhesive two pairs of knife edges were attached on either side of the fourth fracture (at the outer surface of the anterior column, Fig.3b). A semi-spherical implant made of material simulating the properties of articular cartilage mounted in the acetabulum assisted uniform distribution of the load. Then the specimen was attached to the loading frame. Table 1: The five specimen groups used in the present study, classified according to the fixation system used in each group. Fixating system Specimens’ Class Anterior column Posterior column I Plate Plate II Plate Screw III Locking Plate Screw IV Plate Locking Plate V Plate (Stoppa) Locking Plate

Fig. 2. Typical fractured semi-pelvises used in the experimental protocol, fixated according to various techniques.