During the critical period of development of the embryo around 8 weeks, a whole variety of things can go wrong with development of the hand. Some of these are inherited, but many arise with no previous occurrence in the family. With the more complex abnormalities, the advice of an expert in genetics is necessary to answer questions about inheritance.
Some abnormalites are part of a syndrome, which means that there are other abnormalities elsewhere in the body, and if these involve the heart or other major organs it is very important that they are recognized as they may affect decisions about treatment of the hand under general anaesthetic.
Correction of abnormalities needs experience both in the surgical techniques involved, and in all aspects of management of children, bearing in mind emotional and developmental needs, family requirements and pressures, and the vulnerability of growing tissues and structures to interference by surgical operations and the scars they cause.
Because of the complexity of the hand and its development, the abnormalities themselves are correspondingly complex and difficult to classify. The commonest are webbing of the fingers (syndactyly) and extra fingers or thumb (polydactyly). In both these groups the basic aim of treatment is obvious, but technical refinement is needed to obtain a result leaving the hand as near structurally and functionally normal as possible.
The most distressing abnormalites are those involving absence of part or all of the hand. As with all abnormalities, the immediate management of the difficult situation after birth of the baby, or at the time of prenatal diagnosis by ultrasound, is very important, and expert advice and counselling should be available to the family as soon as possible. Parents naturally wish to be given authentic advice about what to expect in the way of treatment, including timing, and often they will need help and support in coming to difficult decisions about choices of possible treatment, especially when surgical reconstruction is contemplated.
The deficiency may be localized and minor, or may involve whole digits, part or all of the hand, or major parts of the whole limb. In many cases even the remaining parts of the limb may be poorly developed, limited in growth, or very abnormal from the start.
Absence of a thumb leaves a functional and cosmetic defect which can be overcome, but as always there is a cost in terms of secondary scarring or structural change. Usually the most appropriate reconstruction is modification of the index finger to form a thumb, a complex operation called pollicization. Careful counselling is needed to allow a confident decision to be made about this operation, particularly because it involves a reduction in the number of fingers to allow construction of the thumb. Provided a full complement of normal fingers is present, the functional and structural improvement justifies the sacrifice, but the need for expertise is clear.
Absence of the thumb may be combined with poor development of the whole side of the forearm (radial hypoplasia or aplasia), and as a result the wrist joint is unstable or non-existent, and the hand turns inwards at the wrist. Future function may be severely affected, and usually requires surgical correction before the thumb is reconstructed. Correction of radial dysplasia is difficult and not always fully successful. Preliminary straightening of the wrist may be necessary, using an external fixation device, an external curved bar attached to pins entering the bone. Once the wrist can be held straight, the muscles are rebalanced and the skin rearranged, an operation called radialization. During later growth there may be some recurrent wrist angulation requiring further surgery. The limb will always be smaller than normal, with diminished functional capacity, and the elbow may also be affected.
When more severe absences of fingers occur, consideration can be given to digital reconstruction by microvascular toe transfer. The indications for this are clearly defined, and when undertaken the objectives of the reconstruction should be equally clear. There should always be a significant functional gain involved, and there should be virtually no likelihood of functional deficit in the foot as a result of removal of the toe for reconstruction. For this reason the big toe is never used, and it is generally accepted by most surgeons doing this work that only the second toe of a normal foot should be used. Following this the foot should be functionally normal, just slightly narrower. If a second toe from each foot is used, this narrowing does not matter, and even if not it is unlikely to be a problem. This is not the place for a detailed analysis of the relative indications, but the features that are taken into account are whether there is one normal hand, how many digits are missing and therefore the proportionate difference that adding one or two functional digits would make, the presence in the remaining part of the hand of all the structures needed to make the new digit work and feel, and of course the wishes and feelings of the parents and often extended family – much careful explanation is needed, without persuasion, and it is helpful if parents can meet previous patients or at least see photographs or videos. Patients in whom this type of reconstruction may be indicated would be treated in collaboration with Professor Simon Kay in Leeds.
A variety of other abnormalities occur and cannot be described in detail here. In all of them the principles of management are the same, detailed analysis of the condition and its likely future effects, counselling and discussion leading to formulation of a plan of treatment designed to improve functional capacity, preserve future growth potential and leave as normal appearance as possible, minimizing scarring. Treatment should be timed so as to avoid unnecessary family separation at critical stages, avoid hospitalisation if possible, and provide the intended functional ability early enough to take full advantage of the young child’s enhanced learning and developmental capacity.