Surface blood flow and histology of human anterior cruciate ligament allografts

We measured surface blood flow in 53 anterior cruciate ligaments (ACLs) reconstructed with allogeneic tendon grafts using laser Doppler flowmetry and examined their histology through biopsy specimens procured during second-look arthroscopy to investigate the fate of ACL allografts on a long-term basis. The age of the grafts, i.e., time from the reconstruction to the second-look arthroscopy, ranged from 6 to 89 months. Six-month grafts showed significantly higher blood flow than the other older ones from 12 to 89 months, which showed a blood flow level equivalent to normal control ACLs. Histological studies revealed that ACL allografts remodeled with time, and that they reached stability by 18 months postimplantation. These results confirmed the concepts of age-dependent remodeling of allografts and their longevity in the human knee joint.