Foot & Ankle International - September 2020 - 1150

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affects the tibiotalar joint.14 This is supported by a biomechanical study that demonstrated that a large spring ligament tear led
to decreased static stability of the ankle joint.14 Previous anatomic studies have demonstrated that the superomedial spring
ligament blends with the superficial deltoid ligament, forming
a larger medial ligament complex, the tibiocalcaneonavicular
ligament (TCNL), which provides medial peritalar stability to
the talonavicular, subtalar, and tibiotalar joints.3,5 The importance of restoring peritalar stability in surgical treatment for
advanced stages of AAFD has been suggested.4,11,18 Previous
biomechanical studies have demonstrated that reconstruction
of the tibionavicular ligament resulted in improved talonavicular and hindfoot valgus deformity compared with anatomic
spring ligament reconstruction.1 The reconstructed tibionavicular ligament is anatomically identical to the tibionavicular
limb of the TCNL. Given the above findings, TCNL allograft
reconstruction in patients with advanced AAFD with medial
peritalar instability was proposed and a promising clinical outcome was reported.2,9
The purpose of our study was to (1) investigate the kinematic effect of spring ligament tear in the development of peritalar instability in a cadaveric flatfoot model, (2) investigate
the kinematic effects of the deltoid-spring ligament (TCNL)
reconstruction in an advanced-stage flatfoot model with medial
peritalar insufficiency, and (3) compare the combined deltoidspring ligament (TCNL) reconstruction with independent anatomic spring or anatomic deltoid ligament reconstructions.
This study focused on investigation of static restraint, specifically the TCNL, in maintaining peritalar stability. The role of
dynamic stabilizers, such as the posterior tibialis tendon (PTT)
or flexor digitorum longus (FDL) transfer, was not included.
We hypothesized that (1) increased spring ligament tear size
(0, 1, and 2 cm) would result in increased talonavicular joint
abduction (axial), talar plantarflexion (sagittal), and increased
valgus alignment of the subtalar and tibiotalar joints (coronal),
and (2) the combined deltoid-spring ligament (TCNL) reconstruction would be more effective in restoring peritalar kinematics compared with anatomic spring or anatomic deltoid
ligament reconstruction alone.

Methods
Ten fresh-frozen cadaveric foot specimens, all female, with a
mean age of 52.3 (range, 31-64) years were used for this
study. We ordered lower leg specimens without gross deformity and no history of injury or surgery. Visual inspection
was performed to confirm appropriately maintained medial
arch with absence of malalignment of the heel. The specimens were cut 20 cm proximal from the ankle joint. The skin,
superficial soft tissue, muscles, and tendons of the ankle and
foot were removed while taking care to preserve the static
stabilizers throughout. The fibula was secured to the tibia
using a single cortical screw to provide a stable mortise that
could withstand cyclic high axial loads.1,16 The proximal tibia

Foot & Ankle International 41(9)
was secured in epoxy bonding cement (Bondo/3M, Atlanta,
GA). The Achilles tendon was isolated and preserved for
loading to simulate the midstance phase of the gait. To simplify the experimental model, we did not load other flexor or
extensor tendons.1,16 Reflective markers were then placed on
the distal tibia, posterior talus, talar neck, calcaneal tuberosity, navicular, and first metatarsal to allow for a multiplecamera capture system (Prime 13, OptiTrack; NaturalPoint,
Inc., Corvallis, OR) to conduct multiplane joint motion analysis (Figure 1). Placement of at least 2 reflective markers on
each bone allowed assessment of orientation of the talus and
first metatarsal in the axial and sagittal planes using a custom-written computer code using MATLAB software
(MathWorks, Natick, MA). Similarly, relative changes of
tibio-talar-calcaneal orientation in the coronal plane were
assessed. Specifically, we measured the talo-first metatarsal
(T-1MT) angle in the axial and sagittal planes, the talonavicular abduction angle in the axial plane, and the tibiotalar and
subtalar joint alignment in the coronal plane (Figure 2).

Flatfoot Model
A flatfoot model was created similar to previous studies.1,16
The foot was first preconditioned using a cyclic axial load of
1150 N under an electromagnetic loading frame with a 10-kN
load cell (Instron ElectroPuls 10000, Norwood, MA, USA)
with a 350-N load applied to the Achilles tendon for a groundreaction force of 800 N. Once preconditioning was complete,
we sequentially created 3 different stages (mild, moderate,
and severe) of flatfoot in the order of severity. The purpose of
making different stages of the flatfoot model was to track
kinematic changes at different points in creating an advanced
flatfoot model and was irrelevant from the Johnson-Strom
clinical classification. To create the mild flatfoot, medial and
inferior talonavicular interosseous ligaments of the talonavicular joint were incised without extending the sectioning proximally: 0-cm spring ligament tear. An 800-N ground-reaction
force was applied for 200 cycles. The T-1MT abduction angle
was measured in the axial plane to gauge the degree of flatfoot
achieved.1,16 In 1 study, mild to moderate flatfoot was defined
as an axial T-1MT abduction angle of 5 to 15 degrees.1 Given
the above, the severity of the flatfoot was considered mild
when the axial T-1MT abduction angle reached 5 to 10
degrees. If 5 to 10 degrees of forefoot abduction was not
reached, additional cycles were applied until the goal abduction angle was achieved.1,16 The moderate flatfoot was created
by further sectioning the spring ligament by 1 cm proximally
along the superomedial part of the spring ligament. A surgical
ruler was utilized to mark the length of sectioning. The foot
was cycled under the same conditions until the axial T-1MT
abduction had achieved 10 to 14 degrees. To make the severe
flatfoot, the spring ligament was sectioned for another 1 cm
(total, 2-cm tear) in the same trajectory, followed by cyclic
loading until the axial T-1MT abduction angle was greater
Foot & Ankle International - September 2020

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