Development of a Large Animal Model of Non-Weight-Bearing

Decreased weight-bearing (WB) is commonly recommended to treat lower limb bone and joint disorders. The availability of a large animal model of decreased or non-weight-bearing (NWB) would be invaluable to study its effects on bone and joint healing. We report here the development of a piglet model of NWB following the induction of ischemic osteonecrosis of the femoral head. The purpose of this study was to assess the feasibility, effectiveness, and complications of various methods to induce decreased or NWB on a hind limb of piglets. The methods used to decrease WB on a hind limb evolved from an Ehmer sling to patellar and/or Achilles tenotomies to below and above knee amputations (AKAs). The Ehmer sling (n=2) was not tolerated by the piglets and tenotomies (n=3) were ineffective in decreasing WB after 4 weeks. A below knee amputation-induced NWB in 4 out of 7 animals but the 3 remaining animals were found to weight bear on the residual limb which developed a pressure sore, and were later converted to an AKA. AKA induced NWB in all animals (n=8). At 8 weeks, a significantly decreased femoral head deformity was observed in the AKA amputation group (n=8) compared with the WB control group (n=8) indicating the protective effect of NWB (P<0.001). A bony overgrowth was observed at the end of the residual bone in all amputated animals. In conclusion, AKA method consistently induced NWB in immature pigs.