Measuring sesamoid position in hallux valgus: when is the sesamoid axial view necessary?

Measuring tibial sesamoid position is an important component of the preoperative radiographic evaluation of hallux valgus as it helps guide the surgeon in surgical selection. Tibial sesamoid position is typically measured on an anteroposterior (AP) radiograph on a scale from 1 to 7 as described by Hardy and Clapham. Some authors have advocated measuring the position on the sesamoid axial view, noting that the AP and axial views often yield different measurements. There is no consensus as to which view is more helpful in guiding the surgeon's surgical decision. Weightbearing radiographs of 99 feet in patients with a clinical diagnosis of hallux valgus were retrospectively reviewed. Tibial sesamoid position was measured on the AP view using the 7-point scale of Hardy and Clapham. Tibial sesamoid position was also measured on the axial radiograph. Cohen's kappa statistic was used to assess agreement of measurements obtained on the 2 views. There was poor agreement of the AP and axial views, with a kappa of 0.31. In our analysis of the data, it was determined that the lack of agreement was due mainly to X-rays showing tibial sesamoid positions of 4 and 5. A subgroup analysis of all X-rays with tibial sesamoids in positions other than 4 or 5 showed excellent agreement, with a kappa of 0.95. Anteroposterior and sesamoid axial views of feet with hallux valgus show excellent agreement in patients with the tibial sesamoid in positions other than 4 or 5. If the tibial sesamoid has a position of 4 or 5 on the AP, an axial view may be warranted to further understand the extent of deformity.

Diagnostic, Level IV: Case series.