Evaluation of the 1st metatarso-sesamoid joint using standing CT - The Stanmore classification.

BACKGROUND: Little is understood about the role that relative sesamoid displacement and chondral wear have on outcome after hallux valgus (HV) surgery. All existing methods to evaluate relative sesamoid displacement have limitations and furthermore, there have been no radiographic studies evaluating metatarso-sesamoid joint wear. Standing CT scan circumvents many of the existing problems in evaluation of relative sesamoid displacement, and also enables the first radiographic study assessing metatarso-sesamoid joint wear.

METHODS: Fifty feet (in 43 patients) with symptomatic HV (Group A) were compared with a control group of 50 feet (50 patients) (Group B). All images were standardised to enable reproducible measurements. The hallux valgus angle, Intermetatarsal angle, sesamoid rotation angle, sesamoid position and metatarso-sesamoid joint space were measured in all patients.

RESULTS: The intra and inter-observer reliability correlation showed that the standing CT assessment of sesamoid position (1.000), rotation (0.991) and metatarso-sesamoid joint space (0.960) were highly reproducible. There was a highly significant difference (p<0.0001) in sesamoid position, sesamoid rotation and metatarso-sesamoid joint space between Group A and Group B.

CONCLUSIONS: Standing CT has been shown to be a reproducible and accurate method of assessing the relative sesamoid displacement and metatarso-sesamoid joint space narrowing. The results have been used to propose a novel standing CT based classification of hallucal sesamoids, considering the degree of displacement and wear. This classification may ultimately facilitate research to provide new insight into the effect relative sesamoid displacement and chondral wear have on outcomes from hallux valgus surgery.