As much as I try to write for the non- physician, there are still medical terms throughout my blog posts. So, in an effort to simplify the terms and explain some basic concepts in the field of congenital hand, I will provide a dictionary of sorts. I hope this helps simplify the terms and ideas.
Polydactyly means extra digit. Polydactyly can be preaxial or radial sided (thumb sided) or postaxial (or ulnar sided, pinky sided) polydactyly. The most common type is postaxial polydactyly. There are a few rare types including central polydactyly (middle of hand) and mirror hand (3 or 4 extra digits on the thumb side).
Syndactyly means joined digits. Most commonly there is only skin connecting the 2 fingers. However, sometimes bone can connect the fingers. Rarely, more than 2 digits are involved in syndactyly. The long and ring fingers are most commonly joined.
Longitudinal Deficiency means limited development on one side of the arm or forearm. The most common type of longitudinal deficiency is radial sided (thumb sided) which may affect the radius bone, the muscles of the forearm and the thumb. Less common is ulnar longitudinal deficiency which affects the pinky side of the forearm and may affect finger development as well.
Radial and ulnar longitudinal deficiency can affect the hand alone or the hand and forearm. Cleft hand has been also called central deficiency as it typically affects the middle digits of the hand (as well as the thumb web space). Cleft hand does not affect the forearm.
Amniotic constriction band has been called more than 30 different terms in the medical literature. Other common terms for this condition (which causes bands, syndactyly, and amputations) in amniotic band syndrome or constriction band syndrome. (although it is not a syndrome) This category is by far the most common diagnosis given by pediatricians but is often inaccurate.
Symbrachydactyly is a tough term because it literally means short, webbed fingers but it is a term used for a broader range of conditions. This includes children with absent fingers with nubbins and some kids with an absent hand or forearm. This diagnosis can be difficult to distinguish from transverse deficiency or congenital amputation.
While I have previously written about causes for less than five fingers, it may be worth repeating. There are five common causes for less than five fingers: radial deficiency, ulnar deficiency, cleft hand, amniotic constriction band, and symbrachydactyly.
Camptodactyly means bent finger, specifically a finger in which the first joint (the PIP joint) does not straighten fully. It can be present at birth, it can be associated with arthrogryposis, or it can present in the early teenage years. Clinodactyly is most commonly seen in the small finger with deviation of the finger towards the ring finger. The other fingers and the thumb can also be affected.
Charles A. Goldfarb, MD
My Bio at Washington University