Passive and Dynamic Stabilizers of First Ray Alignment After TMT-I Fusion: The C1-C2 Intercuneiform Ligament and Peroneus Longus in a Sequential Cadaveric Destabilization Model.

BACKGROUND: Current guidelines recommend first tarsometatarsal joint (TMT-I) fusion in case of symptomatic hallux valgus (HV) with TMT-I instability. Despite successful TMT-I fusion, recurrence rates of 1.7% to 2.9% have been reported suggesting that residual instability of surrounding structures may contribute to recurrent deformity. The aim of this study was to measure the effect of sequential sectioning of the surrounding ligamentous structures in a TMT-I fusion model with and without activation of the peroneus longus tendon.

METHODS: Crossed-screw TMT-I fusion was performed in 6 cadaveric feet, and an optical infrared marker camera system was installed to detect relative movements between the first and second metatarsal head. A transverse force of 10 N and a vertical force in the coronal plane of 15 N were applied on the first metatarsal head and sectioning of the M. abductor hallucis, the dorsal and plantar Lisfranc ligaments, and the medial-middle intercuneiform ligament (C1-C2) were performed. The influence of the peroneus longus tendon (PL) was additionally evaluated.

RESULTS: In the transverse plane, significant changes occurred after sectioning of dorsal and plantar Lisfranc ligaments and predominantly after cutting the medial-middle intercuneiform ligament (C1-C2) without PL force (mean difference: 2.3°, 95% CI: -4.16 to -0.4°, P = .0234). In coronal plane, the overall effect of ligament release was not significant (P = .132); post hoc analysis identified a significant increase in first metatarsal translation only after release of the M. abductor hallucis tendon without PL force (mean difference: 0.9°, 95% CI: -1.68 to -0.09°, P = .033). There was a significant influence of the PL force, especially in transverse plane (P < .001).

CONCLUSION: Sequential sectioning of the M. abductor hallucis, dorsal and plantar tarsometatarsal ligaments, and the medial-middle intercuneiform ligament was associated with progressive first ray instability in this cadaveric model. PL activation provided a significant dynamic stabilizing effect, particularly in the transverse plane, where it compensated for progressive ligamentous insufficiency; in the coronal plane, abductor hallucis release was the primary destabilizing event and PL compensation was significant only under full destabilization.