We read with interest the letter to the editor regarding our case report about a nonsyndromic unilateral syndactyly of the hand. The author concludes, based on his clinical experience and unpublished data, that this syndactyly is not novel and may be classified as syndactyly type IX.

To the best of our knowledge, the published literature defines syndactyly type IX as a distinctive combination of clinical features that includes “osseous synostosis of third and fourth metacarpals” [1]. However, this is not the case in our patient, who presented with fusion of the second and third proximal phalanx. Thus, different fingers (second and third vs. third and fourth) and different bones (phalanges vs. metacarpals) are involved when comparing our case and the published definition of syndactyly type IX. Therefore, we cannot classify our case as syndactyly type IX according to the published classification system.

Classification of our case as syndactyly type IX would require an adaptation of the current classification, which seems plausible but awaits publication. As stated in our original report, we conclude that the classification of syndactylies is still evolving with the need for adaptation to new variants.