Relationship Between Displacement and Degenerative Changes of the Sesamoids in Hallux Valgus.

BACKGROUND: Although the tangential sesamoid view is used to visualize the sesamoid position relative to the first metatarsal head, correctly evaluating patients with severe varus of the first metatarsal is difficult. Computed tomography (CT) can be helpful due to its cross-sectional images in any plane. The purposes of this study were to evaluate the alignment of the tibial sesamoid and investigate the relationship between malalignment and degenerative change in the sesamoid metatarsal joint (SMJ) using simulated weight-bearing CT imaging in patients with hallux valgus.

METHODS: In total, 269 feet from 142 patients with hallux valgus were included. The mean age was 63.7 years (range, 33-87 years). An anteroposterior weight-bearing radiograph was assessed for sesamoid position into 3 grades: grade 1, the tibial sesamoid was medial to the axis of the first metatarsal; grade 2, the tibial sesamoid was located below the first metatarsal axis; and grade 3, the tibial sesamoid was lateral to the first metatarsal axis. The hallux valgus and intermetatarsal angles (HVA and IMA, respectively) were measured. The lateral shift of the tibial sesamoid relative to the first metatarsal was classified into 3 grades on simulated weight-bearing CT classification: grade 1, tibial sesamoid was entirely medial to the intersesamoid ridge; grade 2, tibial sesamoid was subluxated laterally but located below the intersesamoid ridge; and grade 3, tibial sesamoid was located entirely lateral to the intersesamoid ridge. The differences of HVA and IMA in each grade were confirmed by using 1-way analysis of variance with Bonferroni post hoc corrections. Furthermore, multiple linear regression analysis was used to predict the degenerative change in the SMJ for age, sex, sesamoid position determined by CT or plain radiography, HVA, and IMA. The χ2 test was used for descriptive statistics to analyze the agreement between radiography or CT classifications of sesamoid position against degenerative change in the SMJ.

RESULTS: Based on the radiographic classification of the tibial sesamoid position, 7 feet were classified as grade 1, 72 were grade 2, and 190 were grade 3, respectively. Based on the CT classification, 34 feet were classified as grade 1, 116 were grade 2, and 119 were grade 3. Degenerative change in SMJ progressed according to the sesamoid shift relative to the first metatarsal using either radiography or CT. In radiography, statistically significant differences were found except for the difference in HVA between grades 1 and 2. In addition, statistically significant differences were found between HVA and IMA, along with the grades in CT.In multiple linear regression, degenerative change was correlated with age and sesamoid position in CT and radiographic classifications.

CONCLUSION: Our study showed that lateral shift of the tibial sesamoid increased in association with progression of the hallux valgus deformity. Furthermore, increasing lateral shift of the tibial sesamoid was associated with worsening degenerative change within the SMJ.

LEVEL OF EVIDENCE: Level III, retrospective comparative study.