Collagen Fibril Populations in Human Anterior Cruciate Ligament Allografts

Abstract

We studied human anterior cruciate ligament allograft specimens by quantitative electron microscopy to ana lyze their collagen fibril populations. The specimens were procured at the time of second-look arthroscopy from the superficial region of the midzone of the anterior cruciate ligament grafts after synovial clearage. The grafts used for the anterior cruciate ligament recon structions were from fresh-frozen allogenic Achilles, tibialis anterior or posterior, or peroneus longus or bre vis tendons and had been implanted 3 to 96 months previously. By 12 months after surgery, the anterior cru ciate ligament allografts consisted predominantly of small-diameter collagen fibrils (30 to 80 nm), which re sulted in a unimodal pattern in the collagen fibril profile. The number of large-diameter fibrils (90 to 140 nm) within the allogenic tendon grafts had decreased. This predominance of small-diameter collagen fibrils per sisted in almost all specimens older than 12 months. The anterior cruciate ligament allografts had collagen fibril profiles that did not resemble normal tendon grafts or normal anterior cruciate ligaments, even several years after surgery.