The mechanical behavior of locking compression plates compared with dynamic compression plates in a cadaver radius model.
OBJECTIVE
The purpose of this cadaveric study was to compare the mechanical behavior of a locked compression plate, which uses threaded screw heads to create a fixed angle construct, with a dynamic compression plate construct in a cadaver radius model.


METHODS
Mechanical study with cyclic testing and high-speed optical motion analysis.


METHODS
Biomechanics laboratory at an academic institution.


METHODS
Eighteen pairs of fresh-frozen human cadaver radii were divided into 3 groups of 6 to be tested as a group in each of the following force applications: anteroposterior (AP) bending, mediolateral bending, or torsion.


METHODS
Each bone was osteotomized leaving a 5-mm fracture gap and then fixed with a plate. For each pair, 1 radius received a standard plate (limited-contact dynamic compression plates; LC-DCP), the contralateral radius was fixed with a locking compression plate (LCP), and specimens underwent cyclic loading. Normalized stiffness, average energy absorbed, and Newton-cycles to failure were calculated. In addition, a 3-dimensional, high-speed, infrared motion analysis system was used to evaluate motion at the fracture site.


METHODS
Construct stiffness, fracture site motion, cycles to failure, and energy absorption. Repeated measures ANOVA were used to detect differences between groups with time.


RESULTS
In the torsion group, LCP specimens failed at 60% greater Newton-cycles than the LC-DCP (1473 vs. 918; P < 0.05). In the AP group, the LC-DCP absorbed significantly greater energy during 10,000 cycles compared with the LCP group (P < 0.05). The 2 constructs demonstrated different biomechanical behavior with time. As cycling progressed in the LC-DCP specimens under torsion testing, stiffness (measured at the actuator at the bone ends) did not change significantly; however, fracture motion (measured at the fracture surfaces) decreased significantly (P = 0.04). The LCP specimens did not display similar behavior.


CONCLUSIONS
Our findings indicated that LCP constructs may demonstrate subtle mechanical superiority compared with the LC-DCP. The LCP specimens had less energy absorption in the AP group and survived longer in the torsion group. Discordance of motion between measurement regions was observed only in the LC-DCP torsion group, and may have been caused by plate-bone slippage or bone-screw subcatastrophic failure. However, many other compared parameters were found to be similar, and the clinical significance of the few differences found between constructs mandates further investigation.
Gardner
Michael J
MJ
Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021, USA. gardnerm@hss.edu
Brophy
Robert H
RH
Campbell
Deirdre
D
Mahajan
Amit
A
Wright
Timothy M
TM
Helfet
David L
DL
Lorich
Dean G
DG
D001696:Biomechanical Phenomena / Q000379:methods; D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D019245:Compressive Strength; D004548:Elasticity; D019544:Equipment Failure Analysis; D006801:Humans; D066298:In Vitro Techniques; D011474:Prosthesis Design; D011885:Radius Fractures / Q000503:physiopathology* / Q000601:surgery*; D013314:Stress, Mechanical