Foot & Ankle International - July 2018 - 838

838

Foot & Ankle International 39(7)
parameters for cyclic loading. Half of the ultimate tensile
load of the weakest configuration was used as the upper limit
for cyclic loading. Each specimen was placed on an MTS
uniaxial load frame and pretensioned to 10 N. The plantar
plate-suture construct was then cyclically loaded from 10 N
to the upper limit determined in the pilot phase at 0.25 Hz
using a half-sinusoidal waveform as described by Ma et al.22
Displacement (millimeters) was measured over time.

Load-to-Failure Testing
Following cyclic load testing, each specimen was loaded to
failure under a displacement control at a rate of 1 mm/sec.
Displacement (millimeters) was again measured over time.
The ultimate tensile load (maximum load before failure in
Newtons), stiffness (load over displacement in Newtons/
millimeter), and mode of failure (suture breakage or pullout) was determined from the load-displacement curves.
Data were recorded at a rate of 100 Hz.

Statistical Methods

Figure 1. Representative image of experimental design. The
MTS Load Cell is located above the platform, the specimen is
potted in polymethyl methacrylate and secured to the base, and
the suture construct is placed between the plantar plate and
load cell.

of the plantar plate by a single surgeon in each specimen
for biomechanical testing (Figure 3).

Biomechanical Testing
Following experimental repairs, samples were mounted and
biomechanical testing was performed on a Materials Testing
System 858 Mini Bionix (MTS) with a Honeywell 100 lbf
load cell secured to the crosshead. The testing platform was
controlled using Test Star II software (MTS). Tested variables
included number of cycles required to reach 2 mm of suture
displacement, ultimate tensile load (Newtons), and displacement of suture at time of failure (millimeters). Load (Newtons)
versus displacement (millimeters) was recorded to determine
the ultimate tensile load and stiffness (Newton/millimeter).

Cyclic Load Testing
Cyclic load testing was performed to evaluate the biomechanical properties of each configuration under repetitive
load conditions. Preliminary analysis on pilot lesser toes
were used for initial power analysis and to determine the load

Power Analysis. The second, third, and fourth toes of three
additional specimens were used to conduct load-to-failure
testing without cyclic loading for a preliminary power analysis. Specimens were once again sorted into 3 equal groups,
such that each suture configuration was assigned to a different lesser toe in each group and each stitch was placed 2
mm proximal to the distal aspect of the plantar plate. Based
on the results, only 3 specimens would be required to detect
a statistically significant difference with 80% power and
P = .05. Ultimately, 9 specimens were chosen to test each
suture configuration on multiple samples of each type lesser
toe (ie, second, third, and fourth toes).
Statistical Analysis. Measurement outcomes of the tested
variables comparing the luggage-tag, horizontal mattress,
and modified Mason-Allen constructs were completed with
a 1-way analysis of variance model to evaluated for statistical significance when comparing the number of cycles
required to reach 2 mm of suture displacement, ultimate
tensile load or load to failure, displacement of suture at time
of failure, and stiffness. Post hoc t testing with Bonferroni
correction for multiple comparisons was performed if
appropriate. All reported P values are 2-tailed, with an α
level of .05 detecting significant differences (SPSS Statistics version 23.0, IBM, Armonk, NY).

Results
Results are summarized in Table 2. Each specimen was
placed through cyclic loading to determine the number of
cycles before each construct produced 2 mm of

Table of Contents for the Digital Edition of Foot & Ankle International - July 2018