Spring ligament insufficiency and hallux valgus as an independent risk factors for first ray instability

Introduction: First ray instability (FRI) arising from failed plantar/interosseous ligaments is strongly associated with planovalgus, leading to synovitis and deformity. Our hypothesis is that proximal spring ligament insufficiency (SLI) drives secondary FRI in the absence of hallux valgus (HV) and may be an independent risk factor.

Methods: Patients with FRI, screened by Klaue's test, were recruited. Patients' normal contralateral feet with previous radiographs were included as controls. First ray dorsal translation was measured with a digital Klauemeter. Spring ligament integrity was assessed using lateral translation distance as an indirect measure of spring ligament strain. Intermetatarsal angle and hallux valgus angle were recorded to classify the severity of HV.

Results: Seventy feet included, 54 had symptomatic FRI and 16 were asymptomatic contralateral feet included as control. Twenty-three feet had moderate/severe HV and 47 had mild/normal HV. Moderate/severe HV was associated with FRI (OR, 10.31; p = 0.029). Forty-five feet with SLI had a strong association with FRI (OR, 100.7; p < 0.0001). SLI without moderate/severe HV was the most prevalent group (31/54), followed by SLI with moderate/severe HV, 29.63% (16/54). Moderate/severe HV without SLI was prevalent in 11.1% (6/54) and 1.85% (1/54) had no SLI or moderate/severe HV. In a multivariate logistic regression analysis model, both SLI and severe/moderate HV were independent predictors of FRI.

Conclusion: This is the first study that links SLI and HV as independent risk factors to FRI. 98.15% of FRI can be attributed to SLI, HV or both. First ray instability may allude to the strong presence of spring ligament insufficiency in the absence of hallux valgus.

Level of evidence: Level III, retrospective cohort study.