Introduction: The spring ligament (SL) is increasingly recognised as the major structure that fails in acquired adult flatfoot deformity (AAFD). This is the first study that demonstrates integrity of repair of the SL.
Patients and methods: Six pairs of fresh frozen cadavers were setup in a standardised fashion with ankle in plantargrade (mean age 59 years, BMI 25). A 25N lateral force was applied to the medial metatarsal head using an algometer. Lateral displacement of the foot was measured with SL intact, sectioned, following FibreWire® repair, then Arthrex InternalBrace (IB) reconstruction, then with selective sectioning of each limb of the IB reconstruction.
Results: In 12 specimens, overall lateral translation with SL intact was 21mm±4.9. This increased to 39.2mm±10.9 (p<0.05) with SL sectioning, no significant improvement to 34.2mm±9.5 with repair (p=0.159), before significantly returning to baseline 16.55mm±5.1 (p<0.001) with the IB. Augmenting with FDL did not influence lateral translation (p=0.586).
Conclusion: Restoration of SL integrity is fundamental to prevent flatfoot. This study shows traditional repair models fail to provide sufficient resistance to planovalgus. Using an augmented device such as the IB provides optimal resistance to lateral translation and hence planovalgus, particularly the plantar limb of the augmentation.
Keywords: Acquired adult flatfoot deformity; Augmentation; Pes planus; Reconstruction; Spring ligament; Tibialis posterior.
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