Crista Volume Measured from 3D Reconstructions of Weightbearing CT Scans Shows a Relationship to Sesamoid Station

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. 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. 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). 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, which suggests 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. These results are the first to demonstrate that medial sesamoid subluxation as determined by sesamoid station results in erosion of the crista.