aetiology
Last reviewed 01/2018
The aetiology of clinodactyly is unknown. The common mechanism of deviation involves an abnormality in the growth of the middle phalanx that tilts the alignment of an interphalangeal joint surface - commonly the distal interphalangeal joint - relative to the axis of the digit.
One common aetiology is the formation of a 'delta phalanx' within the middle phalanx. This is also known as a longitudinal bracketed epiphysis or longitudinal epiphyseal bracket. Rather than the normal transverse physis, this longitudinally orientated physis extends around the phalanx in a 'C' shape with the open part facing the ulna. The longitudinal restriction on the non-open side results in unconstrained growth of the opposite side. A wedge-shaped middle phalanx results with deviation of the distal interphalangeal joint articular surface.
Occasionally a similar deformity is due to a fibrous band on the ulna side of the digit acting as an external constricting band.