Ossification Centres

The ultrasound appearance of tendons in children is similar to that of adults, except that in children the tendons attach to the hypoechoic cartilage surrounding the ossification centre of the bone rather than the bone itself (Fig. 4.1). Normal tendons ap-... 

The effects of skeletal trauma may be simulated by normal anatomical variations during development, projection artefacts and overlap of adjacent structures. Secondary ossification centres or irregular sites of ossification that appear fragmented are often mistaken for traumatic injury. The mach effect is a physiological form of edge enhancement created when there is an abrupt change from light to dark (radio-opaque to radiolucent) or vice versa at a concave or convex interface of a subject. Its presence at the interface of structures can simulate a fracture line. Similarly, overlap of normal structures such as skin or soft tissue folds can produce an identical appearance (Fig. 7.1). 

Apophysis - Secondary ossification centre characteristically sited at a bony prominence which acts as the insertion site for a tendon. An apophysis is separated from the metaphysis by a physis. When it ossifies it does not contribute to longitudinal growth of the bone and these do not form articular surfaces. They are prone to acute or chronic avul-... 

Accessory ossicle - Small supernumerary bone found at characteristic sites as normal variants. They occur most commonly in the carpus, foot and ankle and vary in size. Typically a round, well corticated separate nodule of ossification adjacent to bone formed by the primary or secondary ossification centre. These may he mistaken for avulsion or chip fractures. Occasionally an accessory ossicle may fuse with the adjacent hone. These ossicles are usually of no clinical significance although they can occasionally cause pain. Some may be the result of previous trauma. 

Fig. 7.1. a Pseudofractures of the epiphyseal ossification centres (arrows). The curved epiphyseal plates of the middle phalanges are superimposed on the secondary ossification centres at their bases producing an effect simulating fractures at the lateral margins, b Overlapping soft tissues of the fingers simulate oblique fractures in a child... 

The ossification centres for the acromion and coracoid processes may be mistaken for fractures. The acromion process may develop in two parts. 

The proximal humeral epiphysis arises from two, sometimes three separate ossification centres (Fig. 7.12). The first ossification centre develops medially at about 2 weeks of age and the second ossification centre develops in the greater tuberosity between 6-12 months of age. When the arm is internally rotated, the first appearing medial ossification centre is rotated into a lateral position and can give the false impression of shoulder joint disruption. The rare third centre occurs in the lesser tuberosity in the third year of life, and when visualised on the axillary shoulder view, may be mistaken for a fracture. This ossification centre fuses with the shaft of the humerus at 6-7 years of age. The radiolucent proximal physis of the humerus is tented and in various oblique positions can be mistaken for a fracture (Fig. 7.13). The normal bicipital groove in the proximal humerus may simulate periosteal new bone formation (Fig. 7.14). 

Fig. 7.9. Large, unfused ossification centre for the coracoid process in an adolescent (arrow)...

Fig. 7.11. Manubrium and sternal ossification centres projected over the ribs taken in oblique projection as part of a skeletal survey in suspected non-accidental injury (arrows)...

Any epiphysis or apophysis may develop from multiple centres and similarly the epiphysis of the distal radius or ulna may arise from two ossification centres appearing deft or bipartite (Fig. 7.21) (Harrison and Keats 1980). Separate ossification centres for the radial or ulna styloid processes may fuse with the main ossification centre or persist unfused as accessory ossicles into adulthood. In late adolescence or early adulthood remnants of the fusing or fused epiphysis can be mistaken for fractures. These include fine sclerotic or lucent lines and residual epiphyseal spurs (Fig. 7.22). 

The carpal bones may appear irregular and fragmented during normal development if they develop from several ossification centres prior to coalescing into one bone mass. The pisiform is the bone most frequently affected and can be easily mistaken for a post-traumatic bony fragment or even a foreign body within the soft tissues of the palm when viewed in lat-... 

Fig. 7.15. Multiple ossification centres in the developing trochlea of the humerus in an adolescent boy (arrow)...

Fig. 7.16. Separate ossification centres for the olecranon in an adolescent boy (arrowheads)...

Fig. 7.17. a Irregular ossification centre for the trochlea is projected over the joint space with rotation (arrow). This also produces simulated dislocation of the ossification centre for the medial epicondyle (arrowhead), normally sited on the AP view (b)... 

Fig. 7.18. Normal position of the ossification centre for the Fig. 7.19. Normal apparent separation ofthe ossification cen-...

Fig. 7.20. Fusion of the ossification centre for the lateral epi- Fig. 7.21. Two separate ossification centres for the distal ul-condyle with the capitellum prior to closure (arrow) nar epiphysis...

Extra and false epiphyseal ossification centres (pseudoepiphyses) may appear in the distal cartilage of the thumb metacarpal and the proximal cartilaginous portion of the index to little finger metacarpals. These differ from true epiphyses because they arise... 

Various secondary ossification centres develop in the pelvis at different ages. Accessory ossification centres may develop at the tip of the ischial spine and the rim of the acetabulum between 14 and 18 years of age (Fig. 7.26). The normal apophyseal centres on the inferior border of the ischium (Fig. 7.27) should not be mistaken for avulsion injuries, although they may be separated by violent hamstring contraction. The fusing ischiopubic synchondroses maybe mistaken for healing fractures, particularly... 

Fig. 7.26. The os acetabuli in a 13-year-old girl (arrow). This is an ossification centre for the acetabular rim...

Fig. 7.25. Accessory ossification centres at the bases of the index and little finger metacarpals (arrows) that can simulate fractures...

The ossification centres for the proximal femur consist of the capital femoral epiphysis, and ossification centres in the greater and lesser trochanters. The capital femoral epiphysis may be cleft or bifid as a normal variant. During development the ossification centres for the greater and lesser trochanters are irregular and often appear separated from the neck and proximal femoral shaft (Fig. 7.30). The distal femoral epiphysis increases rapidly in width between the second and sixth years of life. Irregularity of the lateral and medial margins of the epiphysis is... 

Fig. 7.33. The fabella (arrow) in a 15-year-old boy. There is a secondary ossification centre at the lower pole of the patella...

The tibial tubercle begins to ossify between 7 and 9 years of age, beginning distally, and progressively enlarging proximally and anteriorly while the main tibial ossification centre expands downward towards the tubercle. A section of epiphyseal cartilage usually remains between these two ossification centers until close to physeal maturity (Ogden 1984). The ossification centre for the tibial tubercle... 

Fig. 7.42. Multiple accessory ossification centres related to the medial malleolus in a 12-year-old girl...

Fig. 7.41. Accessory ossification centres related to the malleoli in an 8-year-old. These can be mistaken for fractures...

Accessory ossification centres may occur in the epiphyses of the metatarsals and phalanges of the toes. They are particularly common in the great toes (Fig. 7.50). Incompletely fused metatarsal pseudoepiphyses can be mistaken for fractures. These occur distally in the first metatarsal and proximally in the... 

Fig. 7.47. Multicentric ossification centres for the navicular simulating avascular necrosis. This is a normal developmental variant. If the ossification centres do not fuse a bipartite navicular can be mistaken for a fracture...

Cl is formed from three primary ossification centres, comprising an anterior arch and two neural arches which surround the anterior arch and fuse in the midline by 3 years of age to form the posterior arch. The anterior arch is ossified in only 20% of cases at birth and usually becomes visible as an ossification centre by 1 year of age (Fig. 7.52). The neural arches appear by the fetal week and fuse with the anterior arch by 7 years of age. The presence of... 

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