Good preservation of initial mechanical properties in lipid-extracted,disinfected, freeze-dried sheep patellar tendon grafts

Patellar tendon allografts can be used for anterior cruciate reconstruction to avoid morbidity of autografts on the donor side. Secondary processing of allografts is important for reducing immunological reactions, bacterial contamination and improving storage. We analyzed the effects of processing on the mechanical properties of patellar tendon grafts in 20 sheep. Group I (n= 10) was deep-frozen at -80C. Group II (n=10) was processed by a lipid extraction/freeze-drying method, including iodoacetic acid disinfection. The contralateral tendons, freeze-dried by dehydration in a vacuum at -50C for 3 hours, served as controls. We measured failure stress: group I (53, SD 14 MPa), control (26, SD 15 MPa) (p=0.04); group II (49, SD 13 MPa), control (28, SD 5 MPa) (p=0.08). Failure strain, normalized stiffness, and energy to failure were similar in the groups. Our method of extended processing did not change the properties of the deep-frozen patellar tendons. Therefore in vivo experiments can be used when studying the effects of transplantation on mechanical properties.