Anterior cruciate ligament reconstruction using cryopreserved irradiated bone‐ACL‐bone‐allograft transplants

Bone‐ACL‐bone allograft transplantation has been investigated as a potential solution to reconstruction of the anterior cruciate ligament (ACL). To minimize disease transmission (e.g. the acquired immuno deficiency syndrome), bony and collagenous tissues should be sterilized. Recent animal studies indicate that gamma irradiation and ethylene oxide sterilization result in diminished histological and biomechanical properties. The purpose of the present study was biomechanical and histological determination of the fate of deep‐frozen gamma‐irradiated (2.5 Mrad) canine bone‐ACL‐bone allografts witb argon gas protection. Particular attention was paid to collagenous and neuroanatomical morphology 3,6 and 12 months after implantation, by comparison to a non‐irradiated control group. Sixty skeletally mature foxhounds were operated on in this study, divided up in two groups of 30 dogs each. In group A animals the ACL was replaced by a deep‐frozen (−80°C) bone‐ACL‐bone LAD‐augmented allograft subjected to 2.5 Mrad gamma irradiation with argon gas protection. The animals in group B received an LAD‐augmented ACL‐allograft transplant without gamma irradiation. All knees from both groups were evaluated 3, 6 and 12 months after implantation in regard to biomechanical properties, collagen morphology and routine histology (haematoxylin and eosin stain, polarization microscopy), neuroanatomical morphology (silver and gold chloride stain) and microvasculature (modified Spalteholz technique). The irradiated ACL allografts withstood a maximum load that was 63.8% (718.3N) of the maximum load of normal ACLs after 12 months. By contrast, the non‐irradiated allografts failed at 69.1% (780.1 N) of the maximum load of normal control ACLs. The allografts appeared to be developing well‐orientated collagen fibres as demonstrated by polarized light microscopy and haematoxylin‐eosin staining. Silver stain technique was additionally employed to demonstrate the presence of Golgilike mechanoreceptors and free nerve endings within the allografts. As in the normal ACL, these neurogenic structures were most commonly found near the surface of the allografts and at the two bony attachments. Modified Spalteholtz microangiographic technique demonstrated similar vascularity to normal ACL in the non‐irradiated allograft group after 12 months, compared to slight hypervascularization in the irradiated groups. This study showed that irradiated ACL allografts have the potential to attain the main biomechanical and histological properties of the normal ACL.