Abstract
Migration of an implanted prosthesis due to aseptic loosening is difficult to detect without regular imaging. In this paper, a low-cost, non-radiographic, robust diagnostic technique is presented, which can detect the migration of the humeral component of an elbow prosthesis. The system consists of a single magnet single sensor configuration and migration data are based on the variation in the magnetic field. The magnetic sensor was enclosed in titanium alloy and a magnet was embedded at a reference point in the humeral bone enclosed in ultra-high molecular weight polyethylene (UHMWPE). A layer of bone cement was then placed between the enclosed magnet and sensor. An algorithm linked with a Savitzky- Golay (SG) filter was developed that could decouple, convert, and filter the magnetic field signal to provide both the linear and angular displacement. The system was also designed to eliminate the cross talk and non-linearity effect of the magnet. The highest resolution the sensor achieved was 0.3 mm with a detectable linear migration range of 0.3 mm to 4 mm in the x/y axis and between 8-20 mm in the z-axis (along the humeral canal). The detectable rotational range was 0.5 to 3.0 degrees in the x/y axis. The repeatability of the calibrated sensor was analysed and showed a standard deviation of 0.05 mm over 150 cycles. The resolution was dependent upon the operating conditions and sensor positioning. There was no interference from the titanium alloy, bone cement nor the UHMWPE. This sensor system offers an alternative non-radiographic option for measuring migration of implanted prostheses.
Highlights
Aseptic loosening of the elbow prosthesis is considered to be the key contributor in the failure of total elbow arthroplasty (TEA) [1]–[5]
MAGNETIC FIELD DISTRIBUTION Figure 7 shows the contour plot of the magnetic field density of the magnet (Br andBz) in the z-r plane
To avoid multiple results when determining r and z from the magnetic field, it was determined that the movement of the magnet in the r plane should not exceed the specified regions as showed in the plots and all the movement should be restricted between these regions
Summary
Aseptic loosening of the elbow prosthesis is considered to be the key contributor in the failure of total elbow arthroplasty (TEA) [1]–[5]. A study investigating TEA from the Finnish nationwide joint registry publication shows that 47 % of revision surgeries are carried out because of aseptic loosening [6]. The 10-year survival rates of total knee (TKA) and hip arthroplasties (THA) are reported at 90 % and 95 % respectively [5], [11], [12] with the survival rate of TEA being 79.2 % [5]. Detection of loosening is key to identifying early bone loss and the ‘‘silent failure’’ often seen in TEA as well as reducing the clinical burden and financial implications.
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