Summary
Objective: To compare a locking plate (LP) with pin and tension-band wire (pin/TBW) for fixation
of mid-patellar transverse fractures.
Materials and methods: Cadaveric canine stifle joints from 10 adult mixed breed dogs (23–36 kg) were used.
Mid-patellar transverse osteotomies were randomly stabilized (in pairs) with either
pin/TBW or a prototype LP. Cyclic loads (1 Hz, 500 cycles) at 100% body weight (90°-135°
stifle joint extension), were applied. Survival or failure of constructs was defined
as <2 mm fracture gap distraction at 500 cycles, or ≥ 2 mm fracture gap distraction
at the number of cycles sustained, respectively. Number of cycles at failure and distraction
gap were compared with a paired Student’s t-test, and a survival analysis performed
with a Mantel-Cox test. All constructs that survived cyclic testing were tested in
single cycle load to failure (1.0 mm/sec; 110° stifle joint extension); yield strength
was compared with a Wilcoxon rank sum test. Significance was set at p <0.05.
Results: All 10/10 LP and three out of 10 pin/ TBW fixations survived cyclic testing. Survival
analysis, number of cycles at failure, and distraction gap all were significantly
different between the two groups (p = 0.0011, p = 0.0013, and p <0.0001, respectively).
Construct yield strength was not significantly different (p = 0.1273).
Conclusions: The failure mode with pin/TBW was consistently similar to failures observed clinically.
The LP demonstrated consistent, reliable and stable fixation.
This work was performed at the Biomechanics Orthopedic Research Laboratory, Cummings
School of Veterinary Medicine at Tufts University, North Grafton, MA, USA.
Keywords
Biomechanical testing - orthopaedic implant - fracture gap - canine - patella
