Fibular Hemimelia (FH) is either a partial absence or total absence of the fibular. It is also known as a congenital long bone longitudinal deficiency of the fibular. It is the most common long bone longitudinal deficiency.
Reports from some medical papers quote an incidence of FH between 1:50,000 and 1:135,000. However, recent anecdotal evidence suggest USA incidence is between 1:20,000 and 1:33,000, with UK incidence being around 1:50,000. Usually only one leg is affected, with the right fibula affected more often than the left. Males are 50% more likely to be affected than females.
There is a wide variation in how legs are affected by FH – ranging from mild to severe. A leg affected by FH will look shorter than an unaffected leg. In moderate to severe forms the tibia may be bowed (anteromedial bowing) – a skin dimple can be seen at the top of the bowed tibia. Fibular hemimelia is often associated with other lower limb anomalies: Parts of the femur may be small in shape (hypoplastic) or the whole bone may be noticeably short (e.g. in Proximal Femoral Focal Deficiency).
Soft tissues can also be affected by FH, including muscles and ligaments that attach to the fibula which help to stabilize the knee joint, in particular the anterior cruciate ligament. The combination of abnormal musculature and a small shaped femur will make the knee unstable (hypermobile) and there may be a ‘knock-knee’ (valgus) deformity.
If the bottom section of the fibula is absent, the ankle may also be affected. There is often fusion of the bones in the hind foot and/or mid foot (tarsal coalition). The foot may be pointing downwards and outwards (equinovalgus), often in a fixed position – this is known as a clubfoot. The foot may be small in size and the outer toes may be missing.
The sketch below shows a baby with FH – the left leg has a bowed tibia (with overlying skin dimple), a clubfoot and the outer toes are missing.
Treatment is largely dependant upon how much fibula is still remaining and how the rest of the leg has been affected by FH. Doctors may use one of a number of classifications to decide how a leg has been affected by fibular hemimelia – the Birch et al classification, the Catagni classification, the Achterman & Kalamchi’s classification or the Lett’s classification. These classifications help doctors to advise parents about which treatments are available. [Read more…]