Crista Volume Measured from 3D Reconstructions Shows a Relationship to Sesamoid Station

CATEGORY: Bunion INTRODUCTION/PURPOSE: The hallux valgus (HV) deformity results in progressive subluxation of the sesamoids from their position (station) under the plantar surface of the first metatarsal head. This subluxation may result in erosion of the crista that separates the sesamoid grooves due to contact with the tibial sesamoid during weightbearing. While previous work using weightbearing CT (WBCT) scans has suggested that tibial sesamoid position is associated with degenerative change of the sesamoid metatarsal joint (Katsui FAI), no studies have quantified the relationship between sesamoid metatarsal degenerative changes and sesamoid subluxation. The purpose of the current investigation is to examine the relationship of the volume of the crista to first metatarsal pronation and sesamoid station, using three-dimensional models of patients' deformities created from WBCT scans. METHODS: Thirty-nine HV patients and nine normal subjects underwent weightbearing or simulated weightbearing CT (WBCT) imaging. Crista volume was determined using a line drawn to connect the nadir of each sulcus on either side of the intersesamoidal crista for the length of the crista (Figure 1). The Mann-Whitney U test was used to compare mean crista volume between HV and normal patients. WBCT scans were used to establish sesamoid position using a four-stage scale (Kim FAI 2015) and quantify first metatarsal pronation using 3D reconstructions as previously described (Campbell FAI 2018). Single-factor analysis of variance (ANOVA) tests were used to compared the crista volume and pronation angle between the four sesamoid stations. A linear regression was performed to determine whether crista volume was associated with the pronation angle. Spearman's rank coefficient (r) was used to test the relationship of the sesamoid station against the crista volume and pronation angle. RESULTS: The mean crista volume in HV patients was 80.10 mm(3) +- 35 mm(3) and in normal subjects was 150.64 mm(3) +- 24 mm(3), which differed significantly between the two groups (P<0.001). Mean crista volumes were found to be statistically significantly different between the sesamoid stations (P<0.001) with decreasing crista volumes significantly and strongly correlated with increasing sesamoid station (r = -0.80, P<0.001). The mean standard deviation values of the crista volume by sesamoid station were 154.4 mm(3) +- 18.7 mm3 for station zero, 98.19 mm3 +- 26.9 mm(3) for station one, 78.45 mm(3) +- 30.1 mm(3) for station two, and 44.77 mm(3) +- 13.5 mm(3) for station three. There was no difference in the mean pronation angle between the four sesamoid stations (P=0.37). Additionally, no statistically significant relationship was found between sesamoid station and pronation angle. The pronation angle was not associated with crista volume (P=0.52). CONCLUSION: Our study found that HV patients have significantly lower mean crista volumes compared to normal patients. Crista volume was strongly correlated with sesamoid subluxation/station, suggesting that tibial sesamoid subluxation results in erosion of the crista. In contrast, the pronation deformity was not associated with crista volume demonstrating that the degenerative changes of the sesamoid metatarsal are not related to the rotational deformity of the first metatarsal. This supports the hypothesis that tibial sesamoid subluxation may result in osteoarthritis of the sesamoid metatarsal joint and may be an overlooked source of pain in HV.