Bipartite medial cuneiform: new frequencies from skeletal collections and a meta-analysis of previous cases.

Bipartition of the medial cuneiform is a malsegmentation defect of the foot characterized by separation of the normal cuneiform into dorsal and plantar segments. In many cases, these segments are held together by means of a cartilaginous or fibrocartilaginous bridge, resulting in a deep, lytic-like pit in dry bone reminiscent of those seen in cases of non-osseous tarsal coalition. Partial bipartition, where separation of the two segments is incomplete, may also occur. Though originally documented over 250 years ago, relatively little is known about the bipartite medial cuneiform. The purpose of this paper is to present thirteen new cases (ten complete, three partial) from Egypt, England, South Africa, Denmark, and the United States, and to analyze all known cases to investigate patterns in sex, laterality, frequency, and associated anomalies. Results suggest that bipartite medial cuneiforms are significantly more prevalent in males. Bipartite medial cuneiforms are also frequently bilateral, perhaps indicating a strong genetic component. Identification of this condition in multiple individuals from a cemetery could, therefore, suggest a familial relationship. Frequencies of this variant are consistently less than 1% in most large samples, and significant frequency differences among samples from around the world are rare. Several other minor congenital variations have been noted in individuals with bipartition of the medial cuneiform. However, additional systematic research is needed to elucidate further the prevalence of associated variants.

Os acromiale: population differences and their etiological significance.

The os acromiale is an accessory bone resulting from failure of the acromial apophysis to fuse to the scapula. It is a relatively frequent defect affecting 4-18% of most large skeletal series. The etiology of os acromiale is poorly understood, and two competing hypotheses have been proposed: (1) that the accessory bone represents a genetic defect, and (2) that it results from mechanical stress on the developing acromion. In order to assess the evidence for these two hypotheses, os acromiale frequencies from a South African cadaver sample (n = 494) were compared to frequencies from a medieval Danish archaeological sample (n = 532). The South African frequency (18.2%) was significantly higher than the medieval Danish frequency (7.7%, p < 0.0001). These results mirror those of another study comparing African- and Euro-Americans, and tend to support the genetic hypothesis. However, a left side bias (72%) was also found among the South Africans (p = 0.013), lending some support to the mechanical stress hypothesis. Sex and age biases were also examined but were not found. In order to further test the mechanical hypothesis, the medieval Danes were divided into groups of higher and lower socioeconomic status based upon cemetery type. Lower status individuals were presumed to have engaged in strenuous labor activities more often and at a younger age than higher status individuals. However, comparison of these two groups failed to demonstrate a significant frequency difference (p = 0.105). Based on the results of this study, it is suggested that a third etiology combining a genetic predisposition for os acromiale with mechanical stress as the proximate cause should also be considered.

Pedal symphalangism in modern American and Japanese skeletons.

Pedal symphalangism is a surprisingly common heritable trait of the human foot. In individuals exhibiting the trait, the joint between the intermediate and distal phalanges of one or more lateral toes never develops, resulting in toes with two phalanges rather than three. This study was undertaken to explore variation in the frequency of pedal symphalangism among groups with widely different geographic ancestry, and to consider the applicability of this trait to skeletal biological distance studies. A total of 460 Euro-American, 191 African-American and 99 Japanese skeletons were examined for presence of pedal symphalangism. The American individuals date to the first half of the 20th c, while the Japanese individuals date to the late 19th and early 20th c. Although the country of ancestry is unknown for most of the American individuals, the Euro-Americans appear to be largely northern European, with roots in Germany, Ireland and Scandinavia, while the African-Americans are primarily descendants of slaves with roots in west African countries such as Nigeria, Benin, Togo, Ghana and Sierra Leone. Frequencies of fifth toe pedal symphalangism were calculated and compared among all three samples and found to be significantly higher in modern Japanese (83.7%) than in either Euro-Americans (46.4%) or African-Americans (44.0%). The Euro- and African-American frequencies were statistically indistinguishable for symphalangism of the fifth toe. In the fourth toe, however, the opposite result was found. The African-American frequency (7.9%) was significantly higher than the Euro-American frequency (2.6%), while no difference was found between the African-Americans and Japanese (11.7%). Since fourth toe pedal symphalangism has never been observed in the absence of fifth toe involvement, some of the same genes are clearly involved in producing the trait in both toes. However, differences in the pattern of fourth and fifth toe expression among the three groups identified in this study suggest that additional genetic or developmental factors may play a role in expression of pedal symphalangism in each of the toes.

Articular surface defects in the third metatarsal and third cuneiform: nonosseous tarsal coalition.

Frequencies of articular surface defects on the third metatarsal and third cuneiform, seen as pits of varying sizes on the plantar one third of the tarsometatarsal articular face, were investigated in skeletal populations from North America and Japan, as well as in gibbon, orangutan, chimpanzee, and gorilla skeletons. The apes did not exhibit the defects, although the number of observed specimens of each type was small. The newly presented human frequencies corresponded well with those from other published sources. The defects appeared both unilaterally and bilaterally, with no apparent sex or side biases. Statistical tests between the various populations found that, in general, geographically close populations had more similar frequencies of the defect. Possible etiologies for the defect were investigated, including biomechanical influences, degenerative arthritis, infection, trauma, and a developmental condition known as tarsal coalition, which proved to be the best explanation. Tarsal coalition results from the failure of a joint space to form properly during fetal growth. It can occur between any two adjacent bones of the foot. Several clinically important coalitions, whose presence interferes with normal walking, are known. However, coalition between the third metatarsal and third cuneiform has not been reported in the clinical literature, suggesting that the defect causes little or no foot dysfunction. Tarsal coalition is thought to have a strong genetic component, suggesting that the pit defect may be useful as a skeletal nonmetric trait, as others have stated.

Os intermetatarseum: a heritable accessory bone of the human foot.

The os intermetatarseum is a relatively common accessory bone of the human foot located at the tarsometatarsal border between the first and second metatarsals. It can occur as an independent ossicle or as an osseous spur projecting from the proximal ends of the first two metatarsals, or the distal end of the first cuneiform. To determine the frequency of this congenital defect in native North American groups and East Asians from Japan, the skeletons of 846 Native Americans and 125 modern Japanese and Ainu were examined for the presence of the os intermetatarseum. The North American skeletons are from archaeological sites in various parts of Canada and the United States, including the Arctic coast, the Subarctic, the Aleutian Islands, the Northern Plains, the Illinois River area, and the Southwest. Overall frequencies ranged from no occurrence among the Arctic samples to 8% of individuals from Pecos Pueblo. Second metatarsal spurs occurred in particularly high frequencies among American Indians, whereas the East Asians were only found to have os intermetatarseums associated with the first cuneiform. Because pedigrees have shown the os intermetatarseum to be an inherited defect, its high frequency among some Native Americans may be due, in part, to a higher degree of genetic relatedness among the individuals in the North American samples than among the relatively modern East Asians.