Paediatric musculoskeletal radiology

Congenital anomalies

 

There are many congenital anomalies possible in the skeleton. Any bone can be malformed. In the hand alone there are a large number of anomalies some of which are associated with other malformations and some which are not. Defects of bones in the extremities can be transverse or longitudinal. Longitudinal defects have also been called hemimelia

implying absence of half of a limb. Longitudinal defects is a better term, since often only a small longitudinal portion may be missing. The defects can also be terminal such as absence of fingers or of the hand or intercalary meaning in the middle part of a limb such as phocomelia. A good example of a longitudinal defect is radial hypoplasia or absence. The spectrum of involvement may range from absence of the radius and the first and second metacarpals to where only the thumb may be absent or hypoplastic. The radial defects are associated with many other anomalies or syndromes. Radial defects are associated with an increased incidence of congenital heart disease, vertebral anomalies, imperforate anus, esophageal atresia, renal anomalies, and many others. Ulnar effects are less commonly associated with other anomalies.
In the hand or foot there maybe failure of differentiation of parts such as syndactyly which is fusion of adjacent digits or symphalangism which is fusion of parts of the same digits or tarsal and carpal coalition. Duplications ranging from polydactyly to double limb or dicheiria may occur. Other abnormalities include overgrowth conditions such as megalodactyly, circular constrictions (Streeter bands), and contractures. Deviation of the digits are called clinodactyly when they are in the plane of the hand and camptodactyly when they are perpendicular to it.

Syndactyly

Syndactyly is fusion of adjacent digits. It may be osseus or cutaneous. It may also be seen in otherwise normal individuals. Some forms of syndactyly are familial. A number of syndromes are associated with syndactyly. An example is the Apert syndrome where there is also coronal suture synostosis, facial abnormalities as well as a mitten-like hand and a sock-like foot with osseous and cutaneous syndactyly (Fig. 32).

Polydactyly

Polydactyly is an abnormality of the hand or foot in which there are extra digits or extra portions of digits such as phalanges or metacarpals. If the extra digits are on the radial side of the hand or medialone of the foot the polydactyly is called preaxial. When they are on the ulnar side of the hand or lateral part of the foot they are called postaxial. Polydactyly may be seen as an isolated finding, either sporadic or familial. Postaxial polydactyly of the hand is a common normal variant particularly in individuals of African origin in whom it is inherited as autosomal

a

b

Figure 32. Apert Syndrome. This is a syndrome of coronal suture synostosis associated with a milten-like hand and sock-like foot. a) Hand. There is cutaneous syndactyly and osseous syndactyly of the distal phalanges. There is fusion of the proximal and middle phalanges (symphalangism). The thumb is broad, laterally deviated, and has a triangular proximal phalanx. b) Foot. Cutaneous syndactyly is present. There is partial duplication of the first metatarsal and there is an extra proximal phalanx (polydactyly). The great toe is short and wide.

dominant. It is also seen in a variety of congenital malformation syndromes and sometimes in association with syndactyly.

Proximal focal femoral deficiency

There is a congenital shortening of the femur often with associated coxa vara (Fig. 33). It is also sometimes associated with hypoplasia of the fibula or part of the tibia. The purpose of imaging in these cases is to determine whether the femoral head is well formed, whether it articulates with the acetabulum and whether it is continuous with the femoral shaft. The best approach to evaluation of this abnormality is with MRI which allows the clear delineation of the anatomy (Fig. 33 b). Gradient echo imaging is optimal for this evaluation as the cartilaginous portion of the bones is thus best seen.

 

a

b

Figure 33. Proximal focal femoral deficiency (PFFD). a) The left femur is short and there is a large gap between the proximal left femoral epiphysis and the remainder of the femur. The upper end of the left femoral shaft lies above the femoral head and is smaller than the right. b) MR with gradient echo sequence. The cartilage is white, the bone is black. There is continuity between the femoral head and shaft by the still unossified cartilaginous femoral neck. The greater trochanter is also still composed of cartilage.

Tarsal coalition

Tarsal coalition is one of the causes of pain in the foot in older children. It may present as a spastic flat foot. The most common isolated foot coalitions are the calcaneonavicular and the talocalcaneal. The calcaneonavicular coalition is very easily seen on oblique views of the foot (Fig. 34 a). Talocalcaneal coalitions are more difficult to identify on plain film as one has to obtain an image with the axis of the x-ray beam exactly through the talocalcaneal joint which is often difficult. A much easier method for detecting talocalcaneal coalition is to use coronal CT (Fig. 34 b). The fusion of the middle facet of the calcaneus with the talus is usually clearly delineated in this projection. Often in children the coalitions are not complete, but one sees narrowing and irregularity of the affected joints. This narrowing has the same significance as an osseous coalition and may

 

a

b

Figure 34.Tarsal coalition. a) Calcaneonavicular coalition in a 12-year-old boy who had pain in the foot on walking. There is an irregular space between the calcaneus and talus without complete bony fusion. In unaffected children these bones are further apart. This fusion is often incomplete in children and is best seen in this oblique view of the foot. b) CT of talocalcaneal coalition in a 7-year-old boy. There is an irregular joint at the middle facet. This type of coalition is difficult to detect with radiography and is best visualized with CT. The images were obtained with the child's foot in a tennis shoe which facilitates immobilizing the foot.

need to be treated surgically. A plain film sign of coalition in the lateral view is a beak on the superior distal portion of the talus. If the coalition involves the more distal tarsals this almost invariably indicates association with a congenital malformation syndrome. The talocalcaneal and calcaneonavicular coalitions may be isolated or syndrome associated.

 

Andrew K. Poznanski