Introduction: Aseptic loosening of the intramedullary stem in massive segmental bone tumour implants is problematic. We have shown that osteointegration of extracortical bone to a grooved hydroxyapatite (HA) coated collar located adjacent to the transection site reduced implant failure but integration occurred in only 70% of patients. Reduced loosening may be due to stress transfer at the osteointegrated shoulder of the implant, thereby improving stresses along the intramedullary stem. Selective laser sintering (SLS) can produce novel titanium porous components with varying pore sizes and degrees of structural stiffness. The complete porous structure can be electrochemically coated with hydroxyapatite (ECHA), whereas line of sight plasma spraying only coats the outer surface. We aimed to investigate two novel porous collar designs manufactured using SLS augmented with ECHA. We hypothesised that ECHA coated SLS manufactured collars of a large and small pore design, would enhance osteointegration in an in vivo ovine model compared to the current plasma sprayed HA coated grooved design. Finite element analysis (FEA) techniques were used to investigate the effect of different levels of osteointegration at the shoulder and we hypothesised that stresses adjacent to the intramedullary stem are reduced with increasing osteointegration within the collar.