Regional Measurements of Surface Deviation Volume in Worn Polyethylene Joint Replacement Components

Abstract

Total joint replacements can be subject to the loss of polyethylene material due to wear, leading to osteolysis and decreased implant longevity. Micro-computed tomography (micro-CT) techniques have recently been developed to calculate 3D surface deviations in worn implant components. We describe a micro-CT technique to measure the volume of the surface deviations (volume of wear plus creep) within a specific region or compartment, and report its repeatability and reproducibility. Six worn polyethylene tibial inserts were scanned using a laboratory micro-CT scanner and subsequently reconstructed at 50 μm voxel spacing. A previously developed custom software application was used to quantify the 3D surface deviations between the worn tibial inserts and an unworn reference geometry. Three observers (two trained and one expert) used new custom software to manually outline the localized regions of surface deviation (three times for each of the worn inserts) and calculate the volume of the deviations. The overall intraobserver variability in the surface deviation volumes was 3.6% medially and 1.1% laterally. The overall interobserver variability was 4.8% medially and 1.7% laterally. Placement of points in outlining the region of deviation contributed the greatest variability to the measurements. Repeatability and reproducibility of the volume measurements are similar to measurements of total (nonregional) wear volume including a previous micro-CT technique (10%), fluid displacement (4.8%), and radiographic measurements (15.7%). The principles of this technique can likely be used to measure regional wear and creep volume in knee and hip joint replacement components from wear simulator, pin-on-disk, and retrieval studies.

Computed Tomography Techniques Help Understand Wear Patterns in Retrieved Total Knee Arthroplasty

“…The method was based on the peer reviewed [10,22,34] concept that differences in thickness between medial and lateral compartments could be considered a good estimator of magnitude of polyethylene deformation. However, whilst in previous studies the thinnest points were identified by using a calliper, our micro-CT based method provided more accurate and precise measurement [18][19], with high resolution (45 µm). Additionally, it showed a near perfect intra-and inter-observer variability (ICC = 0.98 to 0.99, in both the cases).…”

“…This approach has been already adopted in previous studies [10,22]: compartment thickness was measured with callipers and considered a good estimator of the magnitude of wear. However, our method is based on micro-CT technology, which has been shown to be highly accurate [18][19]. Moreover, our method provided a high resolution (45m).…”

“…Although previous papers [10,16] have used visual inspection and demonstrated that it can give an acceptable estimation about the quality of the damage, it may not be accurate enough to quantify the amount of wear [17]. Recently, the utility of alternative techniques, such as micro-CT scanning has been demonstrated [18,19].…”

Quantification ofin vivoimplant wear in total knee replacement from dynamic single plane radiography

“…In addition, three other tibial inserts were also milled based on the CAD model (without any wear patterns), to be used as unworn controls for determining the accuracy and precision of the milling procedure. Both the unworn and worn milled tibial inserts were subsequently scanned with micro-CT for deviation analysis, as in previously described studies (Teeter et al 2010, Teeter et al 2011. Deviation maps were generated, to quantify the wear volume (against the milled unworn tibial inserts) in the case of the milled worn tibial inserts, and to measure the manufacturing error (against the original CAD model) in the case of the unworn tibial inserts.…”

Nondestructive microimaging during preclinical pin-on-plate testing of novel materials for arthroplasty

“…The software then reported the maximum deviation in each ROI, corresponding to the maximum depth of wear and creep. In a separate validated software application, 24 the wear patch was again outlined as an ROI by an observer, and the wear volume was calculated by integrating the surface curve of the wear patch to obtain the volume beneath the curve that had been worn.…”