Outcomes of Metaphyseal versus Diaphyseal Stems in Conversion Total Hip Arthroplasty after Intramedullary Nailing.

INTRODUCTION: Diaphyseal-engaging stems are conventionally used in conversion total hip arthroplasty (cTHA) after prior intramedullary nailing (IMN) to bypass screw holes and previously instrumented metadiaphyses. However, it remains unclear if cementless metaphyseal or standard cemented stems can also provide satisfactory fixation in this scenario. This study compared the early outcomes of cTHA using three femoral stem designs: metaphyseal cementless, diaphyseal cementless, and standard cemented. METHODS: A retrospective review of 80 patients who underwent cTHA after prior IMN at a single academic center from 2014 to 2024 was conducted. Patients received either a metaphyseal press-fit stem, a standard-length cemented stem, or a diaphyseal-engaging stem. The 90-day complications were recorded, including any reoperation, periprosthetic joint infection (PJI), periprosthetic femoral fracture, or dislocation. An "at-risk" subgroup analysis of stem tips that were within four centimeters proximal of the interlock hole was also conducted. Patients who received metaphyseal stems were younger (56 versus 77 versus 72 years, P < 0.001) and had lower Charlson Comorbidity Index (1.5 versus 4.0 versus 2.2, P = 0.019) scores compared to those who received cemented stems or diaphyseal stems. RESULTS: There were no significant differences in 90-day complication rates observed among the three stem groups (P = 0.10). Notably, no postoperative periprosthetic fractures occurred in any group (P = 1.000). There were no differences in reoperation (P = 0.232), PJI (P = 1.00), or dislocation (P = 0.61) rates between the three groups. The "at-risk" subgroup analysis of 15 patients demonstrated no significant differences among the three groups for any complication and, notably, had no postoperative periprosthetic fractures. CONCLUSION: Metaphyseal-engaging stems and standard cemented stems in cTHA after IMN demonstrated similar outcomes to diaphyseal stems and may be reasonable options in cTHA after IMN in select patients.