Background: Malposition of the sesamoids relative to the first metatarsal head may relate to intersesamoid crista underdevelopment or erosion. Using 3-dimensional models created from weightbearing CT (WBCT) scans, the current work examined crista volume and its relationship to first metatarsal pronation and sesamoid station. Methods: Thirty-eight hallux valgus (HV) patients and 10 normal subjects underwent weightbearing or simulated WBCT imaging. The crista was outlined by the inferior articular surface, and a line was drawn to connect the lowest point of each sulcus on either side of the intersesamoidal crista throughout the length of the crista. The volume was calculated. Sesamoid station and first metatarsal pronation were calculated from the 3D reconstructions. The mean crista volumes between HV and normal patients were statistically compared, as were the crista volume and pronation angle between sesamoid stations. Results: The mean crista volume in HV patients was 80.10 ± 35 mm3 and in normal subjects was 150.64 ± 24 mm3, which differed significantly between the 2 groups ( P < .001). Mean crista volumes were found to be statistically significantly different between the sesamoid stations ( P < .001) with decreasing crista volumes significantly and strongly correlated with increasing sesamoid station ( r = −0.80, P < .001). There was no difference in the mean pronation angle between the 4 sesamoid stations ( P = .37). The pronation angle was not associated with crista volume ( P = .52). Conclusion: HV patients have lower mean crista volume than normal patients. Crista volume is correlated with sesamoid station. Pronation of the first metatarsal was not associated with crista volume. Clinical Relevance: Crista volume may offer an additional determinant for the severity of hallux valgus.

Category: Bunion Introduction/Purpose: The progression of hallux valgus (HV) deformities results in dislocation of the sesamoids from their position (station) under the plantar surface of the distal first metatarsal. With this dislocation, the crista separating the two sesamoids erodes as the contact of the medial sesamoid with the crista applies pressure with weightbearing. Recently, three dimensional (3D) reconstructions of the metatarsals and first phalanx have demonstrated a means to find a consistently quantify first metatarsal pronation. These same reconstructions can also produce a reliable technique to compute the volumes of the bones involved. The purpose of the current investigation is to examine the relationship of the volume of the crista to pronation and to sesamoid station. Methods: Eleven HV patients and five normal subjects with weightbearing or weightbearing equivalent CT (WBCT) imaging were randomly selected from the senior author’s patients. Pronation was quantified on WBCT scans using 3D reconstructions as described by Campbell et al. (FAI 2018). Crista volume was determined using a line drawn to connect the nadir of each sulcus on either side of the intersesamoidal crista in each slice of the WBCT image (Figure 1). Sesamoid station was also quantified on WBCT scans using the established four point categorization. A linear regression was performed to determine if the volume of the crista was associated with the pronation angle. The sesamoid station was simplified into two categories - mild medial sesamoid subluxation (less than 50% of the medial sesamoid was lateral to the nadir of the crista) and severe medial sesamoid subluxation - and crista volume between these two groups was compared using a t-test. Results: The regression of crista volume against first metatarsal pronation angle did not show statistical significance (P=0.94, r2=0.03). The mean crista volume in the mild medial sesamoid subluxation group was 156(+-47, range 72 - 231)mm3. The mean crista volume in severe medial sesamoid subluxation was 95 (SD 39, range 35 - 160) mm3. The t-test using simplified sesamoid station to compare crista volumes found that the mean crista volume in the mild medial sesamoid subluxation group was statistically significantly greater the than the mean crista volume in the severe sesamoid subluxation group (P=0.01). Conclusion: In HV, it has been hypothesized that the medial sesamoid erodes the crista resulting in arthritis. This is often overlooked as a source of pain in these patients. Our study found that pronation of the first metatarsal was not correlated with crista volume suggesting that pronation does not affect erosion of the crista. Instead, our results are the first to demonstrate that medial sesamoid subluxation as determined from sesamoid station results in erosion of the crista. This supports the hypothesis that sesamoid subluxation, arthritis, and crista erosion are important components of the HV deformity.