328 The Effects of Donor Age and Strain Rate on the Biomechanical Properties of Bone-Patellar Tendon-Bone Allografts Field T. Blevins, MD, Aaron T. Hecker, MS, Gregory T. Bigler, MD, Arthur L. Boland, MD, and Wilson C. Hayes,* PhD From the Orthopaedic Biomechanics Laboratory, Charles A. Dana Research Institute, Beth Israel Hospital, and Harvard Medical School, Boston, Massachusetts ABSTRACT Over 50% of all knee injuries involve partial or com- plete tear of the anterior cruciate ligament. Surgical reconstruction of this ligament using an isometrically placed bone-patellar tendon-bone autograft is the cur- rent technique of choice; however, harvest of patellar tendon as a free graft can lead to increased morbidity. To address this issue, allogenic patellar tendon grafts have been introduced as alternatives to autogenic graft material. The purpose of this study was to exam- ine effects of age and strain rate on tensile strength, modulus, and failure mode of bone-patellar tendon- bone allografts from a typical population of tissue do- nors. Eighty-two, fresh-frozen, bone-patellar tendon- bone allografts were harvested from 25 different donors, aged 17 to 54. Paired grafts from individual patellar tendons were assigned randomly to tensile testing at either 10% or 100% elongation per second. Tensile strength, modulus, and failure mode were not significantly different for tests conducted at these 2 strain rates. Correlations between tensile strength and age were not significant for tests conducted at either strain rate. Specimens tested at a strain rate of 100% per second exhibited weak but significant negative correlation between modulus and age, with modulus decreasing 25% over the age range examined. Surgical stabilization is generally indicated in the young, athletically active patient with an unstable, ACL-deficient knee.9, 12,17,19,32 Over the past 25 years, many surgical re- pairs and reconstructions have been used for this purpose. Primary repairs of midsubstance tears have largely led to unsatisfactory results because of the limited healing po- tential of the ACLy,14,17,22 The role of primary healing when the ligament is torn close to its femoral attachment is currently under investigation (R. J. Steadman, personal communication, 1991). Extraarticular reconstructions are no longer favored, largely because of the difficulty in ob- taining isometric graft placement. 12, 17,18 Intraarticular re- constructions using pes tendons, or the central third of the patellar tendon, have proved to be the most successful typ~s.5,17,32 Reconstruction of the ACL using an isometrically placed bone-patellar tendon-bone autograft is the current stand- ard with which other methods of stabilization are judged.5,17 This procedure is reliable and reproducible, and has given 66% to 94% good-to-excellent results in long-term follow-up studies. 1,8,9,18,23,32 Although infrequent, morbid- ity is associated with the use of patellar tendon autografts. Reported complications include patellar tendinitis,l patel- lofemoral pain,1,18,23,26 patella fracture,21 and arthrofibro- sis.1 Synthetic and biodegradable ligaments avoid related donor site morbidity but have exhibited problems with bio- mechanical integrity as well as with fatigue failure, par- ticulate synovitis, and bone resorption. 15,17,27,31 Allografts have the advantage of avoiding donor site morbidity, and they have been used successfully in ACL reconstruc- tions. 4,16,30 Allografts are especially applicable for multiple ligament injuries and for revision cases in which a patellar tendon autograft has been harvested previously. Although the issue of disease transmission is of concern, the risk appears to be minimal.&dquo; There is little agreement on the fate and strength of an allograft after it is placed into the knee. Some investi- gators have suggested that revascularization and healing in allografts proceed at the same rates as in autografts and that their tensile strengths are comparable. 3-5,23,33,41 Others34,3’ have advised against the use of allografts because of their evoked immune response, decreased * Address correspondence and reprint requests to: Wilson C. Hayes, PhD, Orthopaedic Biomechanics Laboratory, Beth Israel Hospital, 330 Brookline Avenue, Boston, MA 02215. No author or related institution has received any financial benefit from re- search in this study.