Surgeons must balance the infection risk associated with fresh-frozen allograft tissue with the potential biomechanical inferiority of terminally irradiated tissue. The authors of the present study have made strides toward identifying a compromise between sterility and stability. We would suggest to the readers, however, that these are biomechanical results from the laboratory and do not represent patient outcomes. Thus, before the implementation of electron beam (e-beam) sterilization strategies, in vivo animal models should be investigated for biomechanical durability and histologic incorporation.
ACL (anterior cruciate ligament) reconstruction involving allograft tissue has seen marked fluctuation with regard to use, acceptance, and excitement. Initially, allografts seemed to be the answer to reducing perioperative pain, limiting morbidity, and hastening recovery. This early enthusiasm has more recently been tempered by studies reporting significantly higher revision rates for ACL reconstructions performed with allograft compared with autograft tissue. The MOON group determined that use of allograft was a predictor of worse outcomes for the IKDC (International Knee Documentation Committee) questionnaire and KOOS (Knee injury and Osteoarthritis Outcome Score)1 and that the odds of revision were four times higher among those who underwent ACL reconstruction with allograft compared with autograft2. A meta-analysis of 5182 patients reported a threefold increase in the rerupture rate for BTB (bone-patellar tendon-bone) allograft reconstruction (12.7%) compared with BTB autograft (4.4%)3. A Canadian study involving nearly 13,000 ACL reconstructions indicated that allograft use was an independent risk factor for revision within five years4. Another study of 122 military cadets who had undergone ACL reconstruction prior to matriculation demonstrated that those who underwent allograft reconstruction were 7.7 times more likely to undergo subsequent revision5. When reading the above studies, it is important to remember that these were often mixed cohorts with regard to graft fixation and, perhaps more importantly, allograft processing.
The critical question remains: Is the problem the allograft tissue itself or the manner in which it is processed? Although this answer remains elusive, the authors of the present study have made a valiant effort to address this question. It would appear that processing does play a role in graft failure. For example, high-dose gamma irradiation has been demonstrated to have detrimental effects on the biomechanical properties of grafts6-10. In response, some surgeons have traded the biomechanical risk for infection and immunologic risks—turning to fresh-frozen, nonirradiated, allograft tissue. This exodus is supported by several recent clinical outcomes studies. A systematic review, for example, revealed no difference between autograft and non-chemically processed, nonirradiated allograft. Mariscalco et al.11 identified nine prospective or retrospective comparative studies that compared autograft with nonirradiated allograft ACL reconstruction and failed to identify any significant differences between graft types with regard to failure, instrumented laxity, or subjective outcome measures. Another study of a younger population (less than twenty-five years old) retrospectively compared fifty-three patients who underwent BTB autograft with twenty-eight patients who underwent nonprocessed BTB allograft reconstruction and also found no difference with regard to the aforementioned outcome measures12.
Guo et al.13 identified three cases of acute synovitis that they believed were secondary to immunologic rejection among thirty-three patients who underwent fresh-frozen allograft ACL reconstruction. Is there a compromise that could reduce infection and immunogenicity while preserving mechanical properties? Perhaps e-beam irradiation is the solution. In fact, e-beam irradiation was shown previously to more closely preserve graft properties compared with gamma irradiation14. The follow-up study, however, demonstrated adverse biomechanical effects of high-dose e-beam irradiation in an in vivo sheep ACL model15.
Other investigators found that allografts treated with low16,17, moderate18, and even high-dose gamma irradiation16 had comparable biomechanical properties to nonprocessed allograft in the laboratory, but the clinical outcomes in patients have not supported this method for allograft sterilization1-5.
Although the present study uses sound methodology and does a very good job investigating a clinically relevant question, we would caution against the implementation of e-beam sterilization for clinical use, at least until additional animal studies validate these interesting laboratory findings.
1. Spindler KP, Huston LJ, Wright RW, Kaeding CC, Marx RG, Amendola A, Parker RD, Andrish JT, Reinke EK, Harrell FE Jr, Dunn WR; MOON Group. The prognosis and predictors of sports function and activity at minimum 6 years after anterior cruciate ligament reconstruction: a population cohort study. Am J Sports Med. 2011 Feb;39(2):348-59. Epub 2010 Nov 17.
2. Kaeding CC, Aros B, Pedroza A, Pifel E, Amendola A, Andrish JT, Dunn WR, Marx RG, McCarty EC, Parker RD, Wright RW, Spindler KP. Allograft versus autograft anterior cruciate ligament reconstruction: predictors of failure from a MOON prospective longitudinal cohort. Sports Health. 2011 Jan;3(1):73-81.
3. Kraeutler MJ, Bravman JT, McCarty EC. Bone-patellar tendon-bone autograft versus allograft in outcomes of anterior cruciate ligament reconstruction: a meta-analysis of 5182 patients. Am J Sports Med. 2013 Oct;41(10):2439-48. Epub 2013 Apr 12.
4. Wasserstein D, Khoshbin A, Dwyer T, Chahal J, Gandhi R, Mahomed N, Ogilvie-Harris D. Risk factors for recurrent anterior cruciate ligament reconstruction: a population study in Ontario, Canada, with 5-year follow-up. Am J Sports Med. 2013 Sep;41(9):2099-107. Epub 2013 Jul 15.
5. Pallis M, Svoboda SJ, Cameron KL, Owens BD. Survival comparison of allograft and autograft anterior cruciate ligament reconstruction at the United States Military Academy. Am J Sports Med. 2012 Jun;40(6):1242-6. Epub 2012 Apr 24.
6. Gibbons MJ, Butler DL, Grood ES, Bylski-Austrow DI, Levy MS, Noyes FR. Effects of gamma irradiation on the initial mechanical and material properties of goat bone-patellar tendon-bone allografts. J Orthop Res. 1991 Mar;9(2):209-18.
7. Sun K, Tian S, Zhang J, Xia C, Zhang C, Yu T. Anterior cruciate ligament reconstruction with BPTB autograft, irradiated versus non-irradiated allograft: a prospective randomized clinical study. Knee Surg Sports Traumatol Arthrosc. 2009 May;17(5):464-74. Epub 2009 Jan 13.
8. Schwartz HE, Matava MJ, Proch FS, Butler CA, Ratcliffe A, Levy M, Butler DL. The effect of gamma irradiation on anterior cruciate ligament allograft biomechanical and biochemical properties in the caprine model at time zero and at 6 months after surgery. Am J Sports Med. 2006 Nov;34(11):1747-55. Epub 2006 May 30.
9. Salehpour A, Butler DL, Proch FS, Schwartz HE, Feder SM, Doxey CM, Ratcliffe A. Dose-dependent response of gamma irradiation on mechanical properties and related biochemical composition of goat bone-patellar tendon-bone allografts. J Orthop Res. 1995 Nov;13(6):898-906.
10. Fideler BM, Vangsness CT Jr, Lu B, Orlando C, Moore T. Gamma irradiation: effects on biomechanical properties of human bone-patellar tendon-bone allografts. Am J Sports Med. 1995 Sep-Oct;23(5):643-6.
11. Mariscalco MW, Magnussen RA, Mehta D, Hewett TE, Flanigan DC, Kaeding CC. Autograft versus nonirradiated allograft tissue for anterior cruciate ligament reconstruction: a systematic review. Am J Sports Med. 2014 Feb;42(2):492-9. Epub 2013 Aug 8.
12. Barber FA, Cowden CH 3rd, Sanders EJ. Revision rates after anterior cruciate ligament reconstruction using bone-patellar tendon-bone allograft or autograft in a population 25 years old and younger. Arthroscopy. 2014 Apr;30(4):483-91.
13. Guo L, Yang L, Duan XJ, He R, Chen GX, Wang FY, Zhang Y. Anterior cruciate ligament reconstruction with bone-patellar tendon-bone graft: comparison of autograft, fresh-frozen allograft, and γ-irradiated allograft. Arthroscopy. 2012 Feb;28(2):211-7.
14. Hoburg AT, Keshlaf S, Schmidt T, Smith M, Gohs U, Perka C, Pruss A, Scheffler S. Effect of electron beam irradiation on biomechanical properties of patellar tendon allografts in anterior cruciate ligament reconstruction. Am J Sports Med. 2010 Jun;38(6):1134-40. Epub 2010 Apr 1.
15. Schmidt T, Hoburg A, Broziat C, Smith MD, Gohs U, Pruss A, Scheffler S. Sterilization with electron beam irradiation influences the biomechanical properties and the early remodeling of tendon allografts for reconstruction of the anterior cruciate ligament (ACL). Cell Tissue Bank. 2012 Aug;13(3):387-400. Epub 2012 Feb 5.
16. Grieb TA, Forng RY, Bogdansky S, Ronholdt C, Parks B, Drohan WN, Burgess WH, Lin J. High-dose gamma irradiation for soft tissue allografts: high margin of safety with biomechanical integrity. J Orthop Res. 2006 May;24(5):1011-8.
17. Yanke AB, Bell R, Lee A, Kang RW, Mather RC 3rd, Shewman EF, Wang VM, Bach BR Jr. The biomechanical effects of 1.0 to 1.2 Mrad of γ irradiation on human bone-patellar tendon-bone allografts. Am J Sports Med. 2013 Apr;41(4):835-40. Epub 2013 Feb 6.
18. Balsly CR, Cotter AT, Williams LA, Gaskins BD, Moore MA, Wolfinbarger L Jr. Effect of low dose and moderate dose gamma irradiation on the mechanical properties of bone and soft tissue allografts. Cell Tissue Bank. 2008 Dec;9(4):289-98. Epub 2008 Apr 23.