Fig 3. M5 and first phalange of digit 4 delta bone ossification stages.

Stage -1 –Not present. Stage 0 –Very small oval shape undefined delta shape. Stage 1 –Axial surface starts to be linear consistent with delta shape. Stage 2 –one flat surface. Areas or slight irregular perimetral surface typically on the proximal side with a degree of adjacent mineralization which can oppose the epiphyseal surface but not necessarily show definitive osseous bridge formation. Bone density is clearly reduced in peripheral new bone in comparison to the primary ossification center. Stage 3 –Increased mineralization of adjacent proximal cartilaginous surface, consolidation may not be present. Stage 4 –Area increases in consolidation and mineralization, slightly less dense than the body of the delta bone. A defined hyper mineralized physeal plate line is present. The abaxial aspect can show the initiation of the new straight lateral border rather than horseshoe shape. Stage 5 –Density of secondary ossification center is similar to primary bone and initial mineralization present on distal surface with the proximal side showing defined straight lateral border rather than horseshoe shape. Individual variation may result in non-linear borders therefore emphasis should be placed on the secondary ossification centers on the proximal and distal surfaces. Stage 6 –Smooth proximal surface with matching density to the primary ossification center, distal surface still shows some incongruent mineralization. Physeal line is still visible denoted by dotted line. Stage 7 –Smooth proximal surface with complete consolidation of the secondary ossification center on both sides and dissolution of the physeal line. Stage 8 –Degenerative changes present.