The pes planus foot type and its evolutionary significance: the use of radiographic measurements of the talus and calcaneus in the interpretation of hominin pedal remains

This dissertation explores the relationship between the morphology of the talus and calcaneus, as expressed by certain measurement variables, and the medial arch height in the foot of modern humans. Features seen in fossil hominins pedal remains have been postulated as similar to that found in the pes planus foot type. Since pes planus (flatfoot) can only be identified in a functional, intact, weight-bearing foot, radiographs were used to examine this relationship. However, before radiographic measurements of the talus and calcaneus could be analyzed in the same manner as physical bone, the relationship between measurements taken from a physical bone and its radiographic image had to be identified. Two separate studies using limbs amputated for medical reasons were undertaken to examine this relationship. In the first study selected linear measurements were performed on each skeletonized talus and calcaneus. Corresponding landmarks were identified on the radiographic images and the distances between these points determined. Using the measurements taken from the physical bone, the accuracy of the radiographic measurements was evaluated. Most sagittal and transverse plane measurements were associated (r2 = 0.20 -0.88, p < 0.001). In the second study, selected angular measurements were performed on both bone and radiograph and evaluated in a similar manner. As in the first study, most transverse and sagittal plane measurements were associated (r2 = 0.35 - 0.78, p < 0.001). The results of these two studies indicated that selected linear and angular measurements of the talus and calcaneus taken from radiographic images could be compared quantitatively to the physical bone, demonstrating that they provide useful information concerning both bones. The third study examined the relationship between arch height and talar and calcaneal morphology using a collection of weight-bearing radiographs ordered for medical evaluation. Selected variables derived from the first two studies were employed to examine this relationship. The results of the third study indicated that most angular measures of the calcaneus are associated with arch height to some degree (r2 = 0.17 -0.44). However, angular measurements of the talus and linear measurements of both the talus and calcaneus either did not correlate with arch height or were weakly associated. These results demonstrated that the relationship between the morphologies of these bones and the biomechanics of the modern human foot is complex, requiring further investigation. The three studies presented here suggest that selected measurements of the talus and calcaneus taken from radiographic imaging of weight-bearing radiographs can provide valuable information on the morphologies of the talus and calcaneus in the pes planus foot of modern humans that can be used in the interpretation of hominin pedal remains. From the results of the third study, hypotheses were developed concerning the pes planus foot type: that the shape of the talus does not play a major role in pes planus; variations in the “locking mechanism” of the calcaneocuboid joint may account for variations in arch height in modern humans; variations in the shape of the calcaneus are related to arch height and pes planus. These hypotheses should help stimulate further investigation concerning both the evolution of the bipedal hominin and the analysis of foot type in osteological collections of ancient as well as recent human populations. There is still much work to be done in the understanding of the relationship between the biomechanical function of the human foot and the morphology of the talus and calcaneus.