Quantifying wear depth in hip prostheses using a 3D optical scanner

Abstract

The visualization of wear depth in hip prostheses can assist the evaluation of new bearing materials and implant designs. The goal of this study was to develop an accurate, fast, and economical methodology to generate colorimetric maps of wear depth in hip implants using a structured light 3D optical scanning system. The accuracy and precision of this novel technique were determined using reference blocks with known wear depths. This technique was then used to measure the in vitro wear of a hip resurfacing device for canines that incorporates a highly cross-linked polyethylene liner. The 3D optical scanner had an average accuracy of 2.1 µm and an average precision of 1.4 µm, which corresponded to errors less than 10% when measuring wear depths of 20 µm or greater. The scanner was able to repeatedly generate 3D colorimetric maps of wear depth in highly cross-linked polyethylene liners in 20 min or less. These colorimetric maps identified localized regions with 3-fold greater wear than the average wear depth, and revealed liners with asymmetric wear patterns. For the first time, this study has validated the use of 3D optical scanning to quantify in vitro surface wear in a hip replacement device.

Guidelines for Accurate Multi-Temporal Model Registration of 3D Scanned Objects

“…Therefore, registration was optimized when using the entire object geometry to obtain the mapping function. However, when morphological differences do exist between the reference and target 3D model (e.g., mechanical wear), mapping functions obtained from an unaltered subset of the 3D model (i.e., registration block) can have significantly lower target registration errors compared to selecting the entire object geometry [ 10 ].…”

“…The 3D optical scanning system consisted of a rotary table, projector (HDI Advance R3 projector with 16 mm lenses), and two high-resolution cameras (LMI Technologies, Delta, Canada; 2.8 megapixels) ( Figure 2 ). The scanning system used FlexScan3D software (LMI Technologies, Delta, Canada; v3.3.21.8), and the system was calibrated using a calibration card consisting of a 6 × 4.5 cm grid of 5 × 5 mm black and white squares [ 10 ]. The procedure to generate and register 3D models with the scanning system can be split into two steps: data acquisition and post-processing.…”

“…The 3D scanner was used to generate two identical 3D models to serve as the reference and target following the experimental method ( Figure 3 ). All scanning was performed in a dark room, with the only light source coming from the projector [ 10 , 19 ]. This setting was used to minimize the presence of ambient light that could impact scanning quality.…”

“…In post-processing, all 12 scans were combined into a 3D model by automatically fine aligning each scan based on common geometry within the commercial scanning software [ 10 , 19 ]. This was carried out to generate 3D models for the reference and target conditions.…”

“…In recent decades, there have been rapid advancements in the field of three-dimensional (3D) scanning, with applications in product inspection, reverse engineering, medical research, archeology, and construction of urban environment scenes [ 1 , 2 , 3 , 4 , 5 , 6 ]. Data collected from 3D scanners are used to generate 3D model reconstructions of an object of interest that can be used to evaluate geometric or dimensional object quality [ 4 , 7 ] and to quantify morphological changes [ 8 ], including mechanical wear in biomaterials [ 9 , 10 , 11 ]. Such quantification requires the registration of two separate 3D models.…”