This study describes a unique assessment of primate intrinsic foot joint kinematics based upon bone pin rigid cluster tracking. It challenges the assumption that human evolution resulted in a reduction of midfoot flexibility, which has been identified in other primates as the “midtarsal break.” Rigid cluster pins were inserted into the foot bones of human, chimpanzee, baboon and macaque cadavers. The positions of these bone pins were monitored during a plantarflexion-dorsiflexion movement cycle. Analysis resolved flexion-extension movement patterns and the associated orientation of rotational axes for the talonavicular, calcaneocuboid and lateral cubometatarsal joints. Results show that midfoot flexibility occurs primarily at the talonavicular and cubometatarsal joints. The rotational magnitudes are roughly similar between humans and chimps. There is also a similarity among evaluated primates in the observed rotations of the lateral cubometatarsal joint, but there was much greater rotation observed for the talonavicular joint, which may serve to differentiate monkeys from the hominines. It appears that the capability for a midtarsal break is present within the human foot. A consideration of the joint axes shows that the medial and lateral joints have opposing orientations, which has been associated with a rigid locking mechanism in the human foot. However, the potential for this same mechanism also appears in the chimpanzee foot. These findings demonstrate a functional similarity within the midfoot of the hominines. Therefore, the kinematic capabilities and restrictions for the skeletal linkages of the human foot may not be as unique as has been previously suggested.
Data from the recent U.S. Army Anthropometric Survey provide a unique opportunity to assess long-term changes in body dimensions within the Army population. This report considers secular trends for 22 body dimensions within four racial/cultural groups: Whites, Blacks, Hispanics, and Asian/Pacific Islanders. Individuals were grouped by year of birth into 5 year cohorts, spanning 1911 to 1970. Rates of secular change were calculated by regressing age-adjusted dimensions against birth year cohort. Results showed that almost all dimensions sustained statistically significant linear trends, the few exceptions occurring in Asian/Pacific Islanders. The greatest rates of change occurred in dimensions related to soft tissues rather than skeletal dimensions. This pattern is consistent with recent American cultural emphasis on health and physical fitness. The causes of the observed trends, insofar as they have been identified, are related to cultural processes. This suggests that biological forces play a diminished role in shaping the patterns of secular change. Therefore, it may be more appropriate to study secular change in groups that are culturally, rather than biologically, defined.
Functional Alignment is a new method to determine the orientation of a joint's primary rotational axis and the associated movement. It employs three unique concepts. First, data analyses are based upon assessment of spatial positions and not upon movement in a time sequence. Second, analyses are conducted on derived joint rotation matrices instead of tracked markers. This permits reanalysis of published biomechanical results and, therefore, provides a basis for unifying perspectives among different research efforts. Finally, the independent perspectives of the move and base segments require the analysis to use two unique descriptors of the joint axis orientation. These two mathematically necessary descriptors are also shown to be obtainable without reference to the original marker data. The combination of these approaches provides opportunities for additional comparisons of kinematic joint features that have been heretofore underappreciated.
The lack of unambiguous descriptions in the research literature may mean that clinicians are not always applying treatment options in an appropriate manner. Greater clarity of meaning is required for both basic research and clinical applications.
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