Biomechanical Analysis of Retrograde Superior Ramus Screw Fixation Constructs

Justin F. Lucas, Milton L. Chip Routt, Jonathan G. Eastman

Research output: Contribution to journalArticlepeer-review

Abstract

OBJECTIVE: To investigate the biomechanical performance of different size and length retrograde superior ramus screws. MATERIALS AND METHODS: A vertical superior ramus fracture was created in osteoporotic composite hemipelvis bone models (Sawbones, Vashon Island, WA). After reduction, 4 fixation groups were created by inserting either a solid 4.5 mm (Depuy Synthes, Paoli, PA) or cannulated 7.0 mm screw (Zimmer, Warsaw, IN) of either 80 mm (short) or 140 mm (long) in length. An intact and an unstabilized osteotomy group were also created. Samples underwent cyclic loading for 5000 cycles with data acquisition at regular intervals. At the end of cyclic loading, load to failure was performed. RESULTS: The displacement after 5000 cycles for 4.5 mm short screws was significantly greater than 4.5 mm long and 7.0 mm short screws. At 5000 cycles, the 4.5-mm short screws had a significantly lower stiffness and lower load to failure than all other screws and were not different from the osteotomy model. CONCLUSIONS: Short 4.5-mm screws demonstrated increased displacement, lower stiffness, and decreased load to failure compared with all other screws. The biomechanical performance of 4.5-mm short screws was no different than unstabilized controls. Longer bicortical screw fixation is suggested when possible. Additional biomechanical and clinical studies are needed to fully understand the significance of these findings.

Original languageEnglish (US)
Pages (from-to)187-191
Number of pages5
JournalJournal of orthopaedic trauma
Volume35
Issue number4
DOIs
StatePublished - Apr 1 2021

ASJC Scopus subject areas

  • Surgery
  • Orthopedics and Sports Medicine

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