Finite element study of the acetabulum in cemented hip arthroplasty investigating retention or removal of the subchondral bone plate.

The importance of the subchondral bone plate of the acetabulum when preparing the pelvis for a cemented acetabular cup during total hip arthroplasty (THA) has been investigated using finite element analysis. The effect of retaining or removing the subchondral bone plate and the use of anchoring holes are compared. Loading was applied via both hip joint contact force and the activity of up to 22 muscles at five stages through the load bearing phase of the gait cycle. Removing the subchondral bone plate leads to decreased stresses in the cancellous bone and slightly increased stresses in the cortical shell superior to the acetabulum. The differences between the two cases are small, nevertheless there are indications that removal of the subchondral bone plate reduces the stresses. Increasing the cement penetration depth leads to a slightly more rigid structure, due to cement penetrating the cancellous bone. Adding anchoring holes moves the position of the highest cancellous bone strains from the bone-cement interface into the cancellous bone. Thus removal of the subchondral bone plate should lead to an increased potential for cement penetration into the cancellous bone which should be beneficial for cup fixation and thus improve long term implant survival.

Warble infestations by Hypoderma tarandi (Diptera; Oestridae) recorded for the first time in West Greenland muskoxen.

In the northern hemisphere, Caribou (Rangifer spp.) populations are known to be infested with the skin-penetrating ectoparasite, Hypoderma tarandi (Diptera; Oestridae). Although regarded as host specific, H. tarandi has been reported from other species, and has become of increasing concern as a zoonosis infecting humans. In February 2012, concurrent with the hunting of muskoxen, we examined carcasses for muscle and tissue parasites, and recorded warble larvae infestations. DNA extracted from samples of larvae was amplified targeting 579 bp of the COI gene, and subsequently sequenced, to be confirmed as H. tarandi. Infestation by oestrid flies has not previously been reported in muskoxen in West Greenland.