Effect of Insert Material on Interlocking Screw Stability in Retrograde Femoral Nailing: Ultra-High Molecular Weight Polyethylene Versus Polyetheretherketone

OBJECTIVES: To compare short-term implant complications between 2 iterations of the Retrograde Femoral Nailing System Advanced (DePuy Synthes, Raynham, MA), specifically evaluating interlocking screw backout in constructs using ultra-high molecular weight polyethylene (UHMWPE) versus polyetheretherketone (PEEK) distal inserts. DESIGN: Retrospective chart review. SETTING: Single academic, Level-1 Trauma Center. PATIENT SELECTION CRITERIA: Included were adult patients (age ≥18 years) who underwent retrograde femoral nailing for AO/OTA type 32 or 33 fractures between July 2024 and July 2025 with at least 3-month follow-up. The UHMWPE insert was used until December 2024; the PEEK insert was implemented system-wide beginning January 2025. OUTCOME MEASURES AND COMPARISONS: The primary outcome was rate of distal interlocking screw backout. Secondary outcomes included reoperation, infection, and nonunion. RESULTS: A total of 109 patients (113 fractures) met inclusion criteria: 50 fractures in the UHMWPE group [28 males (61%)] and 63 in the PEEK group [32 males (50%)]. There were no significant differences in sex, body mass index, diabetes, smoking status, or fracture pattern distribution between groups ( P > 0.05). The average age was higher in the PEEK group (63 vs. 48 years; P < 0.001). Screw backout occurred in 3 of 50 fractures (6%) in the UHMWPE group compared with 0 of 63 in the PEEK group ( P = 0.04). Two of the 3 patients with backout in the UHMWPE group required reoperation. There were 2 (4%) nonunions in the UHMWPE group and none in the PEEK group ( P = 0.11). All fractures in the PEEK group went on to union without evidence of screw backout or nonunion. There was one infection in the PEEK group requiring irrigation and debridement. CONCLUSIONS: The use of a PEEK insert in the Retrograde Femoral Nailing System Advanced system was associated with favorable early outcomes, including the absence of interlocking screw backout compared with the original UHMWPE insert. These findings support the effectiveness of the design modification and may guide implant selection in femoral fracture fixation. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.