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| At birth, the following primary ossification centers are generally present: the phalanges, metatarsals, calcaneus, and talus. The cuboid may or may not be present at birth; however, it usually is present by six months of age. The cuneiform bones will be the next to appear, in the following order: lateral, medial, and intermediate. The cuboid and lateral cuneiform primary ossification centers are visible in this 9 month old male. There are no secondary ossification centers yet visible. |
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| Several secondary ossification centers (or, epiphyses) are now apparent: the bases of all proximal phalanges, the first through fourth toe distal phalanges, the first metatarsal base, the second metatarsal head, and the distal tibia and fibula (compare to the 9 month old above). Occasionally, ossification centers may appear multipartite, such as you see at the first metatarsal base. Also, note the irregularity of the second and third metatarsal bases; this is also a normal developmental variation. Though you cannot see the remaining lesser tarsal bones, they are still anatomically present but as cartilage. |
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It is quite normal for the tarsal bones to have multiple centers of ossification. Especially note the multiple ossification centers for the medial cuneiform and navicular bones. Eventually, these multiple centers coalesce and form one primary ossification center in the adult. (The rare bipartite medial cuneiform and navicular bones would obviously be the exceptions.) Also in this patient, note the significant irregularity along the bases of the second and third metatarsals bilaterally. In fact, there appear to be secondary ossification centers at the bases of these metatarsals where they are not normally found. Again, this irregularity along the bases as well as the appearance of the secondary ossification centers in the opposite end of the bone does not necessarily represent pathology, but represents a variation of normal. |
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(Unfortunately, there was movement of the patient resulting in some blurring of the images. There also were fingerprints all over the originals!) The film to the left shows a bipartite ossification center for the calcaneus. There is a large ossification center for the body, and a second, smaller ossification center for the anterior process. |
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| Above are two films of the same patient's opposite foot; the right film was taken one year later. Notice coalescence of the two calcaneal ossification centers in the latter image. |
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It is quite common for secondary ossification centers (epiphyses and apophyses) to form from multiple centers of ossification. In this example, there are two ossification centers for the first metatarsal base as well as the third metatarsal head. All tarsal bones are now visible, and the middle phalangeal secondary ossification centers are visible, and there is variant irregularity of the third and fourth metatarsal bases. Primary and secondary ossification centers generally should be symmetrical in appearance bilaterally, but variations in development between the two feet frequently occur. Another normal developmental feature is the small bone hypertrophy along the lateral aspect of the first metatarsal head. |
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The first metatarsal epiphysis is normally found proximally, at the base. Occasionally, a cleft my be seen in the first metatarsal head that simulates an additional distal epiphysis. This distal "epiphysis" has been coined a pseudoepiphysis. There are discrepancies in the literature as to whether this is simply a variant finding or whether it truly represents a secondary ossification center. In a younger patient, it may actually appear totally separate from the first metatarsal distal metaphysis. |
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Another variant of normal development is the bipartite hallux proximal phalanx basal epiphysis. This finding is unilateral in this particular patient. It may be mistaken for fracture. If there is a history of trauma to this area, serial, monthly radiographs over several months may be necessary to determine whether or not it is indeed a fracture or variation of normal. The bipartite hallux proximal phalangeal basal epiphysis is not uncommon, and may or may not be bilateral. |
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Clefts are commonly seen along the margins of the hallux proximal phalangeal heads. They are usually seen along one side, either medial or lateral but generally laterally, as is seen in this patient. They are considered to simply represent developmental variations. Eventually, these clefts will fuse to the remainder of the bone. |
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Occasionally, the middle phalangeal ossification centers, both primary and secondary, can be quite irregular in appearance. The epiphyses may appear cone-shaped, such as in the second digit. Also, one might see clefts along the medial and lateral margins of the heads of the middle phalanges, such as in the third digit. |
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There are two forms of epiphyses, pressure epiphyses and traction epiphyses. Pressure epiphyses are found at the ends of long bones, such as the metatarsals and phalanges. Traction epiphyses, however, are found in areas where there are tendon insertions that exert pull of the secondary ossification centers. These later traction epiphyses are termed apophyses. Ossification of the apophyses begins somewhere around 8 to 12 years of age depending on sex and variability within sexes. It will begin as a very subtle ossification just along the lateral aspect of the fifth metatarsal base. It appears to be ossifying from multiple centers in example A. The apophysis gradually appears crescent-shaped, as in film B (a 12 year old male). Continued ossification of an apophysis and closure of the physis can be seen in the film C (a 14 year old male). Note the enlargement and elongation towards the proximal end of the bone. The junction between the apophysis and base appears very irregular, mixed with sclerosis and lucency, which are normal findings during physeal closure. (Note that the axis of the apophysis is longitudinal, i.e., anterior-to-posterior in direction. This is important because fractures of the base or tuberosity will either be transverse or oblique in nature.) The apophysis will eventually form the tuberosity. |
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Initial ossification of the calcaneal apophysis begins posteriorly and inferiorly (A). The ossification center will eventually extend inferiorly, from the tuberosity, all the way superior to the bursal projection. The calcaneal apophysis frequently develops from multiple ossification centers, as in A, B & D. In fact, the adjacent metaphysis of the calcaneus can be quite irregular and jagged in appearance, sometimes simulating the appearance of a saber saw (A & B). Please note that the calcaneal apophysis is sclerotic (or, more dense) relative to the calcaneal body. These findings are normal!!! In C, note continued ossification of the calcaneal apophysis. Its entire superior extent has not yet ossified adjacent to the bursal projection. Again, note the sclerotic density of the apophysis relative to the body. As the calcaneal apophysis continues to ossify, its appearance may simulate a fracture if multipartite. However, this example (D) represents multiple ossification centers that have not yet fused to one another. Obviously, if the posterior heel is painful and/or there is a history of trauma to this region, fracture would have to ruled out, either by bone scintigraphy, MRI, or the assessment of monthly serial radiographic studies. |
© Copyright 1998, Robert A. Christman, D.P.M.
These articles and figures may not be published, reposted, or redistributed without permission from Dr. Christman.
This page was updated May 5, 1998.