About Class VII Symbrachydactyly
A short, plain-language note for anyone who clicked through from Olivér’s story. Written by his dad, not a doctor — sources at the bottom.
The short version
Symbrachydactyly (sim-brak-ee-DAK-tih-lee) is a congenital limb difference where part of an upper limb — the hand, the wrist, or the forearm — is shorter or missing. There are often small, soft “nubbins” of skin or fingertip-like tissue at the end. It happens around the 4–6th week of pregnancy and is already complete by the time a parent knows they’re expecting.
It is not caused by anything the pregnant parent did or didn’t do, it is not progressive, and it is usually not inherited — the recurrence risk for the next pregnancy is no higher than the general population’s.
Olivér’s case
Olivér’s right arm ends a little way below the elbow, with a soft tapered stump and small rudimentary nubbins. There is no hand, no wrist, no metacarpals. His left arm is unaffected and his right shoulder, elbow and biceps work normally — he can lift, push, hug, and stabilise objects against his body. He is, as the marketing page says, essentially one-handed; he is not in any pain and he is not behind on any developmental milestone we’ve been told to watch for.
The classification (Yamauchi & Tanabu)
In 1990, Yamauchi and Tanabu proposed a seven-type classification of symbrachydactyly based on which bones are present on x-ray. Each type describes a more proximal level of bone absence than the last. Olivér’s presentation is Class VII — the most distal level of the classification, where the forearm itself is partially absent.
- Triphalangia All bones present; some phalanges are short. Often near-normal hand function.
- Biphalangia One or more phalanges missing in one or more digits.
- Monophalangia Affected digits contain only one phalanx.
- Aphalangia Soft “nubbins” without any phalangeal bones inside them.
- Ametacarpia Thumb, digits and one or more metacarpal bones absent.
- Acarpia Digits, thumb and one or more carpal (wrist) bones absent.
- Forearm-amputation type — Olivér’s class The distal portion of the forearm is absent; small rudimentary nubbins sit on the amputation stump. The hand and wrist are not present.
A note on other classifications
Most medical literature uses the older Blauth & Gekeler four-type system: short-finger, cleft, monodactylous, and peromelic. The wider Oberg-Manske-Tonkin (OMT) framework groups symbrachydactyly under “failure of formation of the proximal-distal axis.” Yamauchi’s seven-type version is the one used by community organisations like the Lucky Fin Project, where we first heard Olivér’s diagnosis described in plain language.
Cause, treatment, what to expect
The current best guess for the underlying mechanism is a brief interruption of blood supply to the developing limb in early pregnancy. The condition is not associated with most syndromes, although it can co-occur with Poland syndrome.
Treatment is unhurried and individual. Many children do extraordinarily well with no intervention at all. Some types are candidates for microvascular toe-to-hand transfers; many families choose adaptive prosthetics for sport or play; many do not. Limb-different children almost universally find their own way of doing things long before adults catch up.
Where to read more
- Lucky Fin Project — community for limb-different kids and their families. Where the seven-class language is used in plain English.
- Symbrachydactyly — PMC review (NIH) — the medical paper this page leans on.
- Wikipedia — Symbrachydactyly — a more general overview.
- Symbrachydactyly — Diagnosis, Function, and Treatment (PubMed)
If anything on this page is wrong or out of date, please tell us — hello@olitrack.app.