No difference for changes in BMD between two different cementless hip stem designs 2 years after THA

Abstract

This study evaluates how 2 different total hip arthroplasty (THA) stems compares regarding adaptive bone remodelling. The stems are both proximally porous coated, aiming for proximal fixation, but with different dispersal of the coating. They are also differently designed regarding the distal tip of the stem. We aimed to investigate if there is a difference in periprosthetic adaptive bone remodelling between two different designs. From February 2016 to September 2017, we randomised 62 patients, 1:1 (mean age = 64 years, Female/Male = 28/34), scheduled for an uncemented THA to receive either an EBM or a BM THA stem. We performed dual-energy x-ray absorptiometry (DEXA) scans within a week after surgery and at 3, 6, 12 and 24 months with measurements of bone mineral density (BMD) in the 7 Gruen zones (region of interest (ROI) 1-7). Additionally, Oxford Hip Score and Harris Hip Score were collected at 6, 12 and 24 months. We found a decrease in BMD between the postoperative and the 24-months values in all ROIs for both stems. The greatest decrease over time was seen for both groups in the ROI1 (BM = - 8.4%, p = 0.044, and EBM = - 6.5%, p = 0.001) and ROI7 (BM = - 7%, p = 0.005, and EBM = - 8.6%, p < 0.0005). We found a tendency in ROI2-4 of a higher degree of bone loss in the EBM group. However, this difference only continued beyond 6 months in ROI4 (24 months: BM = - 1.2% and EBM = - 2.8%, p = 0.001). The stems show similar adaptive bone remodelling and are clinically performing well.

Figure 1

The stems. The Echo Bi-Metric stem (EBM) to the left and the Bi-Metric stem (BM) to the right.

Figure 2

Regions of interest (ROIs) of the periprosthetic BMD measurements.

Figure 3

Flowchart.