Locking screw-plate interface stability in carbon-fibre reinforced
polyetheretherketone proximal humerus plates
David J. Hak
Vivek B. S. Chadayammuri
Received: 19 June 2017 /Accepted: 26 June 2017 /Published online: 13 July 2017
SICOT aisbl 2017
Purpose Carbon-fibre reinforced polyetheretherketone
(CFR-PEEK) plates have recently been introduced for
proximal humerus fracture treatment. The purpose of
this study was to compare the locking screw-plate inter-
face stability in CFR-PEEK versus stainless steel (SS)
proximal humerus plates.
Methods Locking screw mechanical stability was evaluated
independently in proximal and shaft plate holes. Stiffness
and load to failure were tested for three conditions: (1) on-
axis locking screw insertion in CFR-PEEK versus SS plates,
(2) on-axis locking screw insertion, removal, and reinsertion
in CFR-PEEK plates, and (3) 10-degree off-axis locking
screw insertion in CFR-PEEK plates. Cantilever bending at
a rate of 1 mm/minute was produced by an Instron machine
and load-displacement data recorded.
Results Shaft locking screw load to failure was significantly
greater in CFR-PEEK plates compared to SS plates
(746.4 ± 89.7 N versus 596.5 ± 32.6 N, p < 0.001). The
stiffness and load to failure of shaft locking screws was sig-
nificantly decreased when inserted 10 degrees off-axis com-
pared to on-axis in CFR-PEEK plates (p < 0.001). Stiffness
and load to failure did not vary significantly following screw
reinsertion in CFR-PEEK plates.
Conclusion The mechanical stability of locking screws in
CFR-PEEK plates is comparable or superior to locking screws
in SS plates.
Keywords Proximal humerus fracture
Carbon-fibre-reinforced polyetheretherketone (CFR-PEEK)
plates have recently been introduced for fracture treatment
. CFR-PEEK is a composite biomaterial composed of car-
bon fiber sheets embedded in a polyetheretherketone matrix.
Compared with metal plates, CFR-PEEK plates have several
beneficial features. The elastic modulus of CFR-PEEK is clos-
er to that of cortical bone, and its increased flexibility may
improve fracture healing. CFR-PEEK implants have a high
load carrying capacity and an ability to withstand prolonged
fatigue strain . CFR-PEEK plates are radiolucent, allowing
improved assessment of fracture reduction and fracture
healing that can sometimes be obscured by metal implants.
In addition there is a marked reduction in artifact with both
computed tomography and magnetic resonance imaging .
Two clinical studies examining the use of CFR-PEEK
plates in the treatment of proximal humerus fractures have
reported satisfactory clinical outcomes [4, 5]. Despite the on-
going clinical use of CFR-PEEK plates, there have not been
any biomechanical studies that have investigated the stability
of the locking screw-plate interface in these implants. There
are various locking screw mechanisms among different man-
ufacturers of CFR-PEEK plates. In some, the locking screw
threads cut through the softer CFR-PEEK, essentially tapping
their own threads, while in others the cone threads of the screw
match threads machined in the plate holes.
* David J. Hak
Department of Orthopedic Surgery, Denver Health Medical Center /
University of Colorado, Denver, CO, USA
Department of Orthopaedic Surgery, University of Colorado School
of Medicine, Aurora, CO, USA
University of Colorado School of Medicine, Aurora, CO, USA
International Orthopaedics (SICOT) (2017) 41:1735–1739