Topography, Structure and Function of the Patella and the Patelloid in Marsupials

Abstract

The patella is a sesamoid bone that is found in most mammals and is regularly located in the insertion tendon of the quadriceps femoris muscle. Up to now, only a little has been known about the topography, structure and function of the patella in marsupials. Therefore the stifles of 61 marsupials of 30 different species were studied by radiography, necropsy and light microscopy. It was found that only the family of bandicoots (Peramelidae) possessed a typical patella. The other species revealed a patelloid consisting of fibrocartilage. The structure of the patelloid revealed common characteristic features in the following families of marsupials: (1) Dasyuridae, Phalangeridae. Pseudocheriidae, and Potoroidae; (2) Burramyidae; (3) Phascolarctidae, Vombatidae, and Dendrolagus; and (4) Superfamily Macropodoidea (except Dendrolagus and Potoroidae). Our results imply that the degree of differentiation in the fibrocartilage of the patelloid was strongly correlated to the mechanical forces acting on the patelloid which are a result of the specific kind of locomotion and the way of life. Generally the bony patella does not belong to the phylogenetic programme of the marsupials--with the exception of the bandicoots which are very closely related to the subclass of placental mammals (Eutheria).

Evolution of the patellar sesamoid bone in mammals

“…As documented in the pioneering study of sesamoids in Marsupialia by Reese et al (2001), an ossified patella seems to be absent in the great majority of extant marsupial species, both from Australia and the Americas (Flores, 2009; Herzmark, 1938; Holladay et al, 1990; Reese et al, 2001; Rose, 2006; Rowe, 1988), including the sole surviving North American marsupial, the opossum Didelphis virginiana (Figs. 4E and 4F).…”

“…the parafibula, lateral sesamoid or “sesamoid bone of Vesalli”; Fig. 1), as well as a fibrocartilaginous “patelloid”, which may to some degree serve the mechanical function of a bony patella (Reese et al, 2001). However, the mechanics of a fibrous or bony patella remain essentially unstudied (to our knowledge) in non-placental mammals, so this is simply speculation.…”

“…However, the mechanics of a fibrous or bony patella remain essentially unstudied (to our knowledge) in non-placental mammals, so this is simply speculation. Studies have claimed some association between reduction of the patella in many marsupials and locomotor style or ecology (Holladay et al, 1990; Reese et al, 2001), but these deserve testing with more detailed sampling across phylogeny and ontogeny.…”

“…The suprapatella is described as proximal to the patella, occasionally with a fat pad interposed between it and the ossified patella (Fig. 1), whilst the patelloid is described as occupying the same approximate region that a bony patella would (though absence of a patella makes this difficult to objectively assess) (Bland & Ashhurst, 1997; Jungers, Jouffroy & Stern, 1980; Ralphs, Benjamin & Thornett, 1991; Ralphs et al, 1998; Ralphs, Tyers & Benjamin, 1992; Reese et al, 2001; Walji & Fasana, 1983). It is not clear whether the fibrous patelloid in some marsupials (and perhaps some bats Smith, Holladay & Smith, 1995) is homologous to the suprapatella, equivalent to an evolutionarily reduced patella or an independently occurring structure.…”

Hind limb myology of the southern brown bandicoot (Isoodon obesulus) and greater bilby (Macrotis lagotis) (Marsupialia : Peramelemorphia)

“…Secondly, peramelemorphs are unusual among marsupials in that they possess an ossified patella. Typically only a cartilaginous patelloid is present in marsupials (Szalay 1994;Reese, Pfuderer et al 2001), although there are exceptions (Notoryctes; (Warburton 2006). Thirdly, the fibula does not articulate with the femur at the knee, as it does in almost all other marsupials, and consequently there is no femoro--fibular disc (Barnett and Napier 1953).…”