Medial Epicondyle Fusion

Like many other primates, humans ossify the appendicular skeletal joints in sequence from elbow, hip, ankle, knee, wrist, to shoulder (Schultz, 1956), although great apes and humans delay the start of this fusion sequence until puberty or after (Figure 9.2 in Smith, 1993). We can place Nariokotome firmly past puberty and into adolescence by evidence that the process of elbow joint ossification had begun (Fig. 10.3), uniting some of the four elements of the distal humerus epiphysis, and by evidence that his shoulders had broadened (see below).

He is also kept to the younger side of adolescence by the lack of fusion of the remaining major long bone epiphyses. In the human elbow, individual centers of ossification of the trochlea, capitulum and lateral epicondyle fuse together at about age 12 in boys; fusion of the whole composite distal epiphysis to the humeral shaft starts about age 12.5; final fusion of the fourth element, the medial epicondyle, lags until approximately age 15 (all ages for boys, see Scheuer and Black, 2000). For Nariokotome, Walker and Leakey (1993) note that the medial (trochlear) half of the distal

Medial Clavicle Fusion

Fig. 10.3 Anterior (left) and posterior (right) views of the right distal humerus of KNM-WT 15000. The trochlea, capitulum and lateral epicondylar centers were fused together at the time of death. This composite distal humeral epiphysis had also fused with the shaft along the full length of the trochlea anteriorly (but incompletely posteriorly).

The medial epicondylar epiphysis was lost and therefore unfused at the time of death. A fracture, seen most easily in the anterior view (left image), runs obliquely across the trochlea indicating those portions of the lateral trochlea and capitulum found separately but fused together. The total preserved bi-epicondylar width is 52.0 mm (Walker and Leakey, 1993).

Fig. 10.3 Anterior (left) and posterior (right) views of the right distal humerus of KNM-WT 15000. The trochlea, capitulum and lateral epicondylar centers were fused together at the time of death. This composite distal humeral epiphysis had also fused with the shaft along the full length of the trochlea anteriorly (but incompletely posteriorly).

The medial epicondylar epiphysis was lost and therefore unfused at the time of death. A fracture, seen most easily in the anterior view (left image), runs obliquely across the trochlea indicating those portions of the lateral trochlea and capitulum found separately but fused together. The total preserved bi-epicondylar width is 52.0 mm (Walker and Leakey, 1993).

humeral epiphysis was fused to the shaft anteriorly but not posteriorly or laterally (the capitulum was fractured off with a portion of the trochlea and found separately). Thus, fusion of the three centers to the shaft had begun and the (missing) medial epicondyle, the fourth element of the growing distal humeral complex, had not fused. The state of his elbow thus places Nariokotome (in human calibration) at >12.5 but <15, but nearer the lower limit because, as Scheuer and Black (2000) note, once the elements of the epiphysis coalesce, the composite epiphysis will not long remain separate from the shaft. Lastly, Ruff and Walker (1993) cite Flecker (1932/1933) and Modi (1957; as cited in Krogman, 1962) who gave a median age or mode of about 13-14 years for the start of fusion of the whole distal humeral epiphysis. Thus, in all, 13 or 13.5 years seems to be a good compromise estimate of skeletal age in this individual using a modern human schedule.

Although most studies of bone age are from the Northern Hemisphere, some data can be found for African children. Agossou-Voyeme et al. (2005) document hand-wrist ossification by age among black children from Benin. Benin boys were generally delayed in hand bone development by 1-2.5 years compared to European, North American, and Asian boys; carpal bone maturation was even more delayed, by 3.5-3.8 years. Authors commented that upper socio-economic levels in Benin resembled average children in British studies, suggesting a nutritional effect. Thus, the Benin study suggests that a strictly African standard for elbow ossification would find Nariokotome's bone age advanced to beyond 13 years, unless comparison was restricted to only the topmost socioeconomic level.

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