Migration Characteristics of a Proximally Coated Collarless Femoral Stem: A Prospective 2-Year Radiostereometric Analysis Study

BACKGROUND: Collared femoral stems have been considered to reduce the risk of early subsidence over collarless stems. However, with advances in material technology, new surface treatments have been introduced into cementless stem design to enhance primary fixation and long-term stability. This study aims to analyze the early migration behaviors of a proximally coated collarless femoral stem and cementless acetabular component and compare the outcomes with commercially available cementless stems and acetabular cups. METHODS: A total of 24 patients (25 hips) undergoing total hip arthroplasty were recruited and followed up for 2 years. All patients received a Masterloc femoral stem (Medacta International SA, Castel San Pietro, Switzerland) and an Mpact acetabular component (Medacta International SA, Castel San Pietro, Switzerland) with tantalum beads embedded during the operation. Radiographs for radiostereometric analysis were taken immediately postsurgery, 6-months, 1-year, and 2-years postoperatively. RESULTS: The median condition number for this study was 59. The median stem subsidence was −0.08 mm (−2.47 to 0.40) at 2 years. The median cup subsidence was −0.03 mm (−0.38 to 0.57) at 2 years. The migration of the Masterloc stem was less than that of other cementless collarless, as well as collared stems, as reported in literature. CONCLUSIONS: This study has demonstrated the high stability and fixation provided with the use of a collarless cementless stem. The subsidence seen in both this cementless femoral stem and acetabular cup at 2 years postoperative was below the range reported in literature for cementless collarless and collared stems.