A new scoring system for sesamoid displacement in hallux valgus

J. Widnall, A. Perera, A. Molloy

Introduction: It has been shown that inadequate reduction of the sesamoids can lead to recurrent hallux valgus. It can be difficult however to assess the sesamoid position. We propose a simple method of grading sesamoid position; the sesamoid width ratio. We aim to assess for a difference in ratio between those with and without hallux valgus and subsequent correlation with increased deformity. The new grading system can then be tested for inter-observer reliability.

Methods: 277 (103 normal, 87 preoperative, 87 postoperative) AP weight bearing foot radiographs were analyzed for hallux valgus angle (HVA), intermetatarsal angle (IMA), and both medial and lateral sesamoid width (mm). The sesamoid width ratio (SWR; lateral/medial width) was then calculated. Using statistical methods based upon HVA and IMA grading, three groups of increasing hallux valgus severity, in accordance with SWR, were defined; normal ≥1.30, moderate 1.29 - 0.95 and severe ≤0.94. Sixty images (10 normal, 25 preoperative, 25 postoperative) were then sent on disc to three separate reviewers to assess for inter-observer error.

Results: A statistically significant correlation was shown between the SWR and both HVA and IMA (r = -0.24 and -0.18 respectively, p < 0.05). Once organized into normal, moderate and severe, in accordance with SWR, both the HVA and IMA group means were statistically different (ANOVA p < 0.0001 and p < 0.0002). With regards to inter-observer error, a fair agreement between raters existed when looking at group classification (Fleiss’ kappa 0.33, 0.10 to 0.53 95% CI). The intra-class correlation (ICC), looking at the SWR value, returned a similar result (ICC = 0.35).

Conclusion: The diameter and subsequent ratio of sesamoid width is an easy value to calculate. There is good correlation between the SWR and hallux valgus deformity as defined by HVA or IMA. The sesamoid width ratio exhibits fair inter-observer reliability.