Does Stem Design for Conversion Total Hip Arthroplasty From Previous Short Intramedullary Nail Predispose to Fracture?

Introduction: Conversion to total hip arthroplasty (THA) from prior short intramedullary nail (IMN) is an increasingly common procedure. Currently, there are no studies investigating if distal interlock screws serve as stress risers contributing to perioperative fractures, or whether primary stems can be used in previously reamed and fractured femurs. We hypothesized that conversion would be successful regardless of stem design.

Methods: Nineteen patients who underwent short IMN to THA conversion were retrospectively identified from 2013 to 2022, with a mean 13 months between the procedures. Patient demographics, as well as intra- and postoperative variables, including stem design, length of stay, fractures, unplanned readmissions, and revisions, were collected. Mean follow-up was 13 months.

Results: A diaphyseal-engaging revision stem was used in 13 cases, with metaphyseal press-fit stems and cemented stems each used in 3 cases. Two patients (one diaphyseal stem, one cemented stem) sustained intraoperative greater trochanteric fractures. No postoperative fractures were found. Four emergency department visits (21%) and one unplanned readmission (5%) were reported within 30 days, with 1 emergency department visit (5%) and two readmissions (11%) within 90 days. Stratified by stem type, we observed no notable difference in length of stay or procedure length.

Discussion: This is the first study to investigate conversion to THA from short IMN. Overall, there were two intraoperative fractures, but no distal fractures or revisions. Although the distal interlock screw was commonly bypassed with a revision-type diaphyseal stem, this was not universal. Further research is needed to determine if primary arthroplasty stem designs can be used in this setting.

Level of evidence: Level III Treatment Study.