MRI findings in Kirner deformity: normal insertion of the flexor digitorum profundus tendon without soft-tissue enhancement.

Kirner deformity is characterized by volar and radial incurvature of the distal phalanx of the 5th finger. A proposed causative mechanism includes abnormal distal insertion of the flexor digitorum profundus tendon along the volar surface of the distal phalanx of the 5th finger. A chronic inflammatory process or altered vascularisation of the soft tissues has also been suggested as the underlying causative mechanism based on MRI findings. We present a teenage boy with Kirner deformity, along with supplementary imaging of his father who also has the deformity, to illustrate MRI findings that dispute the above hypotheses. MRI in both son and father show normal insertion of the deep flexor tendon and no signs of inflammation.