Ultrasound evaluation of the first finger’s sesamoid bones: diagnostic value of sesamoid and subsesamoid indices

Purpose: Our analysis focuses explicitly on applying two sonographic and morphological indexes (sesamoid index and subsesamoid index) to better evaluate post-traumatic consequences to the sesamoids of the first finger. Methods: In 2 years, we enrolled 75 patients, divided into two groups: 60 without any history of trauma and 15 reporting hyperextension trauma of the first finger. We performed clinical and instrumental examinations (sonography and X-ray) on patients with one or more symptoms compatible with sesamoiditis, while an MRI scan was performed only on patients with an acute onset and severe symptomatology. We measured both the short and long-axis diameter (in mm) for each sesamoid as well as the relation between the two parameters (sesamoid index, SI and subsesamoid index, SubI). Results: All 15 patients showed sonographic alterations of the SI above the reference range, while the alterations of SubI varied according to the acuteness and gravity of trauma. In all cases, the X-ray did not show any relevant alterations. MRI scans in patients with acute symptoms confirmed the sonographic findings. Conclusion: Sonography enabled diagnosis of micro-injuries which were invisible to X-Ray and allowed to detect possible damages to the sesamoid complex, providing a qualitative and quantitative evaluations of the post-traumatic alteration of the metacarpophalangeal joint of the 1st finger and is therefore valid, combined with clinical examination and hand X-ray, in the evaluation of sesamoiditis without the need to perform further examinations.