LOAD AFFECTS REMODELING OF TRANSPLANTED, AUTOGENOUS BONE-PATELLAR TENDON-BONE SEGMENTS IN A RABBIT MODEL

The question of whether or not load affects the remodeling of a transp lanted autogenous free graft was addressed by removal of the patella-p atellar tendon-tibial tubercle complex from the right knees of 15 New Zealand White rabbits. The tubercle was split, and the tendon was divi ded with each half trimmed to an equal width. The autograft complex wa s transplanted into a subcutaneous tunnel on the back of the rabbit. C ontrolled cyclic loads were applied via transcutaneous sutures to half of the graft, while the other half remained unloaded. The mechanical stiffness and strength and the cell density of loaded and unloaded hal ves of the autograft were measured in nine animals at 3 weeks and in s ix animals at 6 weeks. Five autografts from four additional rabbits se rved as unimplanted controls. An analysis of variance showed that the loaded portions of the autografts had a significantly higher failure s trength (mean of 90%) and were significantly stiffer (mean of 62%) tha n the unloaded halves at 3 and 6 weeks. Failure strength was significa ntly greater (mean of 90%) at 3 weeks than at 6 weeks. The autografts were less stiff and had a lower failure strength than the unimplanted controls, with the greatest difference occurring in the unloaded segme nts at 6 weeks. Histology revealed that both loaded and unloaded segme nts demonstrated an increase in cellularity at 6 weeks compared with 3 weeks. This report introduces a model for the study of the effect of load on soft-tissue grafts and demonstrates that loading affects the r emodeling process of a transferred autograft.