A comparative study of trabecular structure of the patellofemoral joint: Evolutionary and biomechanical perspectives

Abstract

The knee joint in primates is important in facilitating a variety of locomotor behaviours. The patellofemoral joint (PFJ), which encompasses the distal femur and patella, has been relatively understudied from an evolutionary and biomechanical standpoint. The lack of detailed information limits our understanding of joint loading and associated kinematics. Trabecular bone is an ideal material for study as it is highly responsive to mechanical loading associated with different postural and locomotor behaviours. This thesis sought to pursue the question, ‘How do different activities, different locomotor kinematics, and different taxa manifest variation in the internal structure of this joint?’. To do this, trabecular structures in the distal femur and patella were explored using an inter- and intra- specific perspective. Trabecular parameters quantified in this study were bone volume fraction (BV/TV), trabecular thickness (Tb.Th), trabecular spacing (Tb.Sp), connectivity density (Conn.D) and degree of anisotropy (DA). All analyses were conducted on high-resolution MicroCT scans where eight volumes of interest (VOI) of the distal femur and nine VOIs in the patella were quantified. Inter-specific analyses were conducted on extant primates (Homo, Pan and Papio) and Plio-Pleistocene hominins from South Africa (Australopithecus sediba, Australopithecus africanus, and Homo sp./Paranthropus robustus). To explore intra-specific variation within a single species, two human samples (Later Stone Age foragers and contemporary Post-Industrial South Africans) were analysed to determine the effects of activity levels and knee joint pathology (osteoarthritis) on trabecular bone structure. The findings of this study show that there were significant differences in trabecular structure among extant primates and Plio-Pleistocene hominins that indicate unique loading across the PFJ, likely as a result of kinematically different bipedalism and a broader locomotor repertoire than seen in living humans today. This study also showed that significant differences in trabecular structure occur among some extant primate species and that these are likely linked to differences in knee joint loading arising from species-specific knee structure and positional/locomotor behaviours. Within Homo specifically, results showed that trabecular structure in the distal femur and patella differed between groups that demonstrated different activity levels and varying degrees of pathological osteoarthritis. Together, these results show that trabecular structure in the PFJ reflects complex loading and that further interspecific and intraspecific studies are necessary to improve our understanding of structural integrity in the primate knee.