Interlocking plate compared with conventional pin fixation for undisplaced femoral neck fractures: a randomized controlled trial with radiostereometric analysis

Aims: In undisplaced femoral neck fractures, fixation failure remains a concern. In vitro studies suggest that interlocking plates increase torsional stability. However, whether this leads to clinically relevant improvement in fixation stability in vivo remains unclear. Accordingly, we tested whether interlocking plate fixation provides increased in vivo fixation stability over 52 weeks in undisplaced femoral neck fractures. Methods: Having been recruited from the Emergency Departments of two hospitals between May 2016 and January 2019, patients were randomized to Hansson pin fixation (n = 12) or Hansson Pinloc plate fixation (n = 13). Postoperative fracture motion was quantified using radiostereometric analysis (RSA) at baseline and at four, 12, 26, and 52 weeks. Clinical outcomes (Harris Hip Score, EuroQol five-dimension (EQ-5D) questionnaire, Timed Up and Go test, and pain and satisfaction using the Numeric Rating Scale) were assessed at the same timepoints. Data were analyzed using linear mixed model to account for missing RSA points. Results: A total of 17 patients completed the 52-week follow-up. The Pinloc group showed a smaller mean total rotation than the pin group, with a mean difference of -7.77° (95% CI -13.27° to -2.28°; p = 0.006) at 52 weeks. The groups diverged significantly in torsional stability at 12 weeks, with a larger between-group difference during follow-up. No between-group differences were observed in total translation or clinical outcomes. Five patients required reoperation: three in the Pinloc group and two in the pin group. Avascular necrosis occurred in three patients. Sub-trochanteric fractures occurred in two patients, both in the Pinloc group. Conclusion: Interlocking plate fixation resulted in increased torsional stability compared with pin fixation during healing of undisplaced femoral neck fractures, consistent with previous in vitro studies. The clinical implications of this finding remain uncertain.