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Our study employed a simulated weightbearing flatfoot
model with a focus on assessing kinematic changes associated with a large spring ligament tear and subsequent combined deltoid and spring ligament reconstruction. Several
clinical and biomechanical studies have evaluated reconstruction of either the spring ligament or the deltoid ligament alone.1,3,7,9,10,16,20 Reconstruction of the spring
ligament with a peroneus longus allograft was suggested to
restore hindfoot alignment not corrected with a bony procedure alone.20 A few authors reported favorable clinical and
radiographic outcomes of deltoid ligament reconstruction
using auto- or allograft in patients with stage IV AAFD.7,9
Haddad et al10 reported a promising biomechanical result of
superficial and deep deltoid ligament reconstruction in a
cadaveric foot. Previous authors reconstructed either the
spring ligament or deltoid ligament only, whereas our
TCNL reconstruction method aims to simultaneously
reconstruct both the deltoid and spring ligaments in an
effort to improve medial peritalar stability.
The concept of peritalar instability has increasingly
gained interest.2,4,7,11,14,18 Colin et al4 described a case series
of 4 patients with unstable valgus ankle deformities and
stage IV AAFD. The authors noted progressive instability
of the hindfoot and severe flattening of the arch after performing isolated tibiotalar fusion to correct an unstable
ankle. Similarly, several studies reported development of
valgus tibiotalar tilt following hindfoot arthrodesis.8,12,15
Together, these studies support the notion that the expansive
medial ligamentous complex contributes to both hindfoot
and ankle stability and suggests the need for additional soft
tissue reconstruction to provide peritalar stability, especially in patients who may have residual valgus deformity
or inadequate talonavicular joint reduction after osseous
correction performed for AAFD reconstruction.2
In our analysis of the reconstruction techniques, the combined deltoid-spring ligament (TCNL) reconstruction was the
only reconstruction method that significantly corrected both
the subtalar and tibiotalar valgus alignment of the severe flatfoot model. When evaluating the lateral T-1MT angle, both
the isolated spring ligament and combined deltoid-spring ligament reconstructions corrected the sagittal alignment. The
isolated deltoid reconstruction was unable to correct to the
lateral T-1MT angle. This suggests that the combined deltoidspring ligament reconstruction technique provided more
effective restoration of stability to all 3 peritalar joints as it
crosses the talonavicular, subtalar, and tibiotalar joints. We
suggest TCNL reconstruction in (1) stage IIB AAFD with a
high propensity for further progression of deformity after
osseous correction is performed, such as a large spring ligament tear (>1.5 cm) with residual valgus alignment or inadequate talonavicular reduction as determined intraoperatively,
or (2) stage IV AAFD.2 We feel that these patients will benefit
from augmentation of medial stability to maintain surgical
correction and limit further progression of residual deformity.2

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Since the proposed TCNL reconstruction technique does not
effectively reconstruct tibiotalar ligament, we are considering
modifying the technique to add reconstruction of the deep deltoid ligament in stage IV AAFD.
One of the strengths of our study is the use of a 3-dimensional motion capture system that allowed for accurate measurement of kinematic changes. However, there were
limitations inherent to the flatfoot model. We modified a previously developed cadaveric flatfoot model by combining
ligament sectioning and cyclic axial loading until a desired
deformity was achieved.1,16 Although the ligament sectioning
was consistent for all specimens, the number of cyclic loads
required to achieve a desired deformity differed for each specimen due to variation in baseline stiffness. We were not able to
differentially quantify the contribution of ligament sectioning
versus cyclic loads in the development of flatfoot. Simulated
weightbearing was limited to loading only the Achilles tendon
to simplify the model. Since other tendons were not loaded,
contributions from dynamic stabilizers, especially the PTT,
were not considered in our analysis. We acknowledge the lack
of bony realignment and FDL transfer procedures that typically accompany soft tissue procedures. Stabilization of the
syndesmosis by placing a screw across the fibula and tibia
may have unnaturally constrained the mortise and restricted
the tibiotalar joint valgus tilt measured under load. The graft
tensioning for each reconstruction method may have been
inconsistent. We modeled a tensioning technique previously
described and placed the foot in the "position of reduction" to
ensure the graft was firmly and consistently tensioned in all
cases.1 Though there was no quantification of the force to tension the graft, we felt this represented a more realistic scenario
comparable to surgical situations. Additionally, ligament
creep associated with successive reconstructions and loadings
may have affected the final tension and kinematic outcomes.
To mitigate this, we adjusted the reconstructed ligament tension by rewrapping fiber suture in screw posts to achieve the
consistent position of reduction and randomized the order of
the reconstruction methods.

Conclusion
As AAFD progresses due to a compromised medial peritalar stability, the subtalar and tibiotalar joints develop valgus deformities. Prior anatomical studies have identified an
expansive medial ligamentous complex, the TCNL, as one
of the most consistent structures. Our study suggests that
reconstruction of TCNL, rather than isolated deltoid or
spring ligament reconstruction, may provide improved peritalar stability in advanced flatfoot deformity.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with
respect to the research, authorship, and/or publication of this article. ICMJE forms for all authors are available online.
Foot & Ankle International - September 2020

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