Hydroxyapatite-Coated Compaction Short Stem Represents a Characteristic Pattern of Peri-Prosthetic Bone Remodelling After Total Hip Arthroplasty

Purpose: We aimed to investigate the differences in peri-prosthetic bone remodelling between the full hydroxyapatite (HA)-collared compaction short stem and the short tapered-wedge stem. Methods: : This retrospective cohort study enrolled 159 consecutive patients (159 joints) undergoing total hip arthroplasty (THA) using the full HA compaction short (n=64) and short tapered-wedge (n=95) stems. Body mass index (BMI), peri-prosthetic bone mineral density (BMD), and clinical factors, including the Japanese Orthopaedic Association score and the University of California Los Angeles (UCLA) activity score, were assessed and compared. Results: : Both groups showed similar peri-prosthetic BMD changes. Peri-prosthetic BMD was almost maintained in the distal femur and Gruen zone 6 with both type of stems, but significant BMD loss was found in zones 1 and 7 in both groups and in zone 2 of the full HA compaction stem group. Significant positive correlations were found between the proximal femoral BMD changes and the UCLA score in the tapered-wedge stem group but not between BMD changes and clinical factors in the full HA compaction stem group. Femoral bone shape affected the peri-prosthetic BMD changes in the tapered-wedge stem but not in the full HA compaction group. The stem collar of the full HA compaction stem did not affect peri-prosthetic BMD, but unique bone remodelling in the calcar region was observed in 27.6% cases. Conclusion: Peri-prosthetic bone remodelling remained unaffected by clinical and radiographic factors after THA with the new short full HA compaction stem. Therefore, the new stem may be useful in a variety of cases.