What is the underlying mechanism for the failure mode observed in the proximal femoral locking compression plate? A biomechanical study

Kerstin Schneider, Jong-Keon Oh, Ivan Zderic, Karl Stoffel, R. Geoff Richards, Stefan Wolf, Boyko Gueorguiev, Sean E. Nork

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

Purpose Recently, several cases of clinical failure have been reported for the Proximal Femoral Locking Compression Plate (PF-LCP). The current study was designed to explore biomechanically the underlying mechanism and to determine whether the observed failure was due to technical error on insertion or to implant design. Methods A foam block model simulating an unstable intertrochanteric fracture was created for 3 study groups with 6 specimens each. Group C was correctly instrumented according to the manufacturer's guidelines. In Group P and Group A, the first or second proximal screw was placed with a posterior or anterior off-axis orientation by 2°measured in the transversal plane, respectively. Each construct was cyclically tested until failure using a test setup and protocol simulating complex axial and torsional loading. Radiographs were taken prior to and after the tests. Force, number of cycles to failure and failure mode were compared. Results A screw deviation of 2°from the nominal axis led to significantly earlier construct failure in Group P and Group A in comparison to Group C. The failure mode was characterised by loosening of the off-axis screw due to disengagement with the plate, resulting in loss of construct stiffness and varus collapse of the fracture. Conclusions In our biomechanical test setup, the clinical failure modes observed with the PF-LCP were reproducible. A screw deviation of 2°from the nominal axis consistently led to the failure. This highlights how crucial is the accurate placement of locking screws in the proximal femur.

Original languageEnglish
Pages (from-to)1483-1490
Number of pages8
JournalInjury
Volume46
Issue number8
DOIs
Publication statusPublished - 2015 Aug 1

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Keywords

  • Angular stable plate fixation
  • Biomechanical study
  • Failure mode
  • Proximal femoral locking compression plate
  • Screw loosening
  • Unstable trochanteric fracture

ASJC Scopus subject areas

  • Emergency Medicine
  • Orthopedics and Sports Medicine

Cite this

What is the underlying mechanism for the failure mode observed in the proximal femoral locking compression plate? A biomechanical study. / Schneider, Kerstin; Oh, Jong-Keon; Zderic, Ivan; Stoffel, Karl; Richards, R. Geoff; Wolf, Stefan; Gueorguiev, Boyko; Nork, Sean E.

In: Injury, Vol. 46, No. 8, 01.08.2015, p. 1483-1490.

Research output: Contribution to journalArticle

Schneider, Kerstin ; Oh, Jong-Keon ; Zderic, Ivan ; Stoffel, Karl ; Richards, R. Geoff ; Wolf, Stefan ; Gueorguiev, Boyko ; Nork, Sean E. / What is the underlying mechanism for the failure mode observed in the proximal femoral locking compression plate? A biomechanical study. In: Injury. 2015 ; Vol. 46, No. 8. pp. 1483-1490.
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AB - Purpose Recently, several cases of clinical failure have been reported for the Proximal Femoral Locking Compression Plate (PF-LCP). The current study was designed to explore biomechanically the underlying mechanism and to determine whether the observed failure was due to technical error on insertion or to implant design. Methods A foam block model simulating an unstable intertrochanteric fracture was created for 3 study groups with 6 specimens each. Group C was correctly instrumented according to the manufacturer's guidelines. In Group P and Group A, the first or second proximal screw was placed with a posterior or anterior off-axis orientation by 2°measured in the transversal plane, respectively. Each construct was cyclically tested until failure using a test setup and protocol simulating complex axial and torsional loading. Radiographs were taken prior to and after the tests. Force, number of cycles to failure and failure mode were compared. Results A screw deviation of 2°from the nominal axis led to significantly earlier construct failure in Group P and Group A in comparison to Group C. The failure mode was characterised by loosening of the off-axis screw due to disengagement with the plate, resulting in loss of construct stiffness and varus collapse of the fracture. Conclusions In our biomechanical test setup, the clinical failure modes observed with the PF-LCP were reproducible. A screw deviation of 2°from the nominal axis consistently led to the failure. This highlights how crucial is the accurate placement of locking screws in the proximal femur.

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