Abstract
In humans, bipartite scaphoid still does not differentiate clearly from traumatic non-union of the scaphoid. To aid diagnosis, we sought to analyze the main geometrical similarities among bipartite scaphoids from primate species with fused and unfused scaphoid centrales. Four human embryos, four cases of adult humans with bipartite scaphoid, twelve adult specimens of other extant anthropoid primates, and two Neandertal scaphoid specimens were included in this study. Three-dimensional polygon models of the scaphoid and os centrale were generated from CT scan, micro-CT scan, or histological sections. A 3D comparative study of the morphological and morphometrical parameters was performed using the MSC Patran software. The os centrale was smaller than the scaphoid in all specimens and its shape was elongated in the anteroposterior scaphoid direction. The position of the os centrale centroid compared to the scaphoid using direction vectors had a strong orientation along the proximodistal axis in all species. The main morphological feature of bipartite scaphoid was the continuity of the scaphoid from its proximal pole to its tubercule along the anteroposterior axis. In all specimens, if the os centrale was removed, the scaphoid still appeared normal and whole. The bipartite scaphoid in adult humans shares geometrical analogies with monkeys and orangutans, human embryos, and Neandertals. Morphological and morphometrical features identified in this study are useful to differentiate bipartite scaphoid from scaphoid pseudarthrosis. All other criteria suggested in the past lead to misdiagnosis.
Highlights
From the first tetrapods to the appearance of Homo sapiens [1], a disappearance of centrale bones of the carpal segment is observed
The os centrale was smaller than the scaphoid in all specimens (p < 0.01)
Identification of the bipartite scaphoid is important for management and treatment because it is radically different from scaphoid fracture or pseudarthrosis [33]
Summary
From the first tetrapods to the appearance of Homo sapiens [1], a disappearance of centrale bones of the carpal segment is observed. Only the African apes and humans exhibit fusion of the os centrale to the scaphoid and this represents a shared-derived morphological feature. The fusion of these bones is among the clearest morphological synapomorphies of African apes and hominins [3,4]. In African apes, fusion in utero or very early in post-natal ontogeny occurs in almost all individuals (>95%), whereas in Asian apes, fusion only rarely occurs (7%), usually in adulthood [5]. Neandertals represent an extinct group of archaic humans who lived in Eurasia until about 40,000 years ago [6], and the frequency of a distinct os centrale portion of the scaphoid bone was estimated at 42.9%
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