Re: Oberg KC. Classification of congenital upper limb anomalies: towards improved communication, diagnosis, and discovery. J Hand Surg Eur. 2019, 44: 4–14

I read with interest this excellent review on the Oberg-Manske-Tonkin (OMT) classification of congenital upper limb anomalies. In the classification, congenital dislocation of the radial head is classified as an error in the radio–ulnar (anteroposterior) axis. I have reviewed the pathogenesis of congenital dislocation of the radial head (Al-Qattan et al., 2016) and identified five different primary insults. Four out of five insults lead to disturbed anteroposterior radio–ulnar growth axis. The fifth pathway of pathogenesis is related to collagen abnormality and not to the anteroposterior axis of development. The annular ligament (which is made of collagen type I) is attached to the margins of the radial notch of the ulna; and it supports the head of the radius in the correct place without having any attachments to the radius. Mutations that lead to collagen type I abnormalities will be associated with congenital dislocation of the radial (and these are reviewed in my paper). One example of these mutations is COL1A1/COL1A2 mutations that cause osteogenesis imperfecta types I to IV, and congenital dislocation of the radial head is a feature of all four types. If abnormal collagen is a primary cause of congenital dislocation of the radial head, the frequency of congenital dislocation of the radial head in these types of osteogenesis imperfecta should be proportionate to the severity of the collagen abnormality, which is mildest in type I followed by type IV, and is relatively severe in type III. The frequencies of congenital dislocation of the radial head in these three types of osteogenesis imperfecta are 2%, 13%, and 22%; respectively (Fassier et al., 2007). I think that congenital dislocation of the radial head is best categorized under two different categories in the OMT classification.