The duplicated longitudinal epiphysis or “kissing delta phalanx”: evolution and variation in three different disorders

The delta phalanx, also known as the delta bone, or longitudinal epiphyseal bracket (LEB), has been described in a variety of syndromes and dysplasias. However, the “kissing delta phalanx” is not as well recognized in the literature; it consists of a duplicated longitudinal bracketed epiphysis, or a complex of two adjacent delta bones, with opposing convex portions facing each other. Magnetic resonance imaging of the kissing delta phalanx has not been previously described.

To describe the evolution, variation and associated osseous anomalies of the kissing delta phalanx in three patients with distinct distal limb malformations using both plain films and magnetic resonance imaging.

Patient 1 had Rubinstein-Taybi syndrome and, in addition to a kissing delta phalanx in both feet, had corresponding delta metatarsals (MT1). Patient 2 had Cenani-Lenz syndactyly with distinct variation of the kissing delta phalanx in each hand. He had a disorganized appearance to the phalanges, metacarpal fusions and carpal coalitions. Patient 3 had an isolated oligosyndactyly of the left hand with metacarpal fusions and carpal coalitions. All three patients were followed over time. We describe two types of kissing delta phalanges: separated (without fusion of the corresponding epiphyseal brackets) and nonseparated (with fusion of the corresponding epiphyseal brackets). Both types can be seen in the same patient and are a reflection of the relative degree of segmentation of the two delta bones.

The appearance of this rare osseous abnormality changes with time and can be found in a limited number of uncommon disorders. It can also be found in association with other osseous anomalies of the distal extremities; therefore magnetic resonance imaging early in life can greatly assist in surgical planning. Recognition of the kissing delta phalanx may be an important radiological clue to diagnosis of these rare disorders.