We studied human anterior cruciate ligament allograft specimens by quantitative electron microscopy to analyze 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 reconstructions were from fresh-frozen allogenic Achilles, tibialis anterior or posterior, or peroneus longus or brevis tendons and had been implanted 3 to 96 months previously. By 12 months after surgery, the anterior cruciate ligament allografts consisted predominantly of small-diameter collagen fibrils (30 to 80 nm), which resulted 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 persisted 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.

Achilles Tendon↗

PubMedDate not supplied

The long-term biomechanical and viscoelastic performance of repairing anterior cruciate ligament after hemitransection injury in a goat model.

To test the healing of the partially torn anterior cruciate ligament, we transected the posterolateral bundle in 11 adult female goats and tested the ligaments at 12, 24, and 52 weeks and 3 years after surgery. As early as 12 weeks after surgery translucent fibrous tissue covered the wound. The differences in anteroposterior laxity between right and left knees measured at 45 degrees and 90 degrees of flexion were not significantly different at each period. Results of Instron testing of the posterolateral bundle revealed the normalized changes in load-relaxation and Young's modulus were not significantly different at each period, but the ultimate tensile strength and stiffness at 3 years were significantly higher than at 12 weeks (P < 0.05) Failure started at the repair site for the 12-week group, but at 24 and 52 weeks the failure occurred throughout the ligament. At 3 years, the specimens failed with bony avulsion, indicating the repaired tissue was not the weakest link of the bone-ligament-bone complex. This study shows that under favorable conditions, partial anterior cruciate ligament injuries are capable of repair. What is more important, the high ultimate tensile strength and stiffness of the 3-year repaired tissue indicate full structural repair of such an artificial transection injury may be possible.

Animals↗