Biomechanical analyzes on effects of change of initial tension on the mechanical properties of the frozen anterior cruciate ligament in the dog.

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1. We developed helical cryoprobe in which liquid nitrogen was circulated to perform in situ freezing of the canine anterior cruciate ligament (ACL). To know the ability of the cryoprobe we froze the ACLs of 12 adult dogs. After freezing, the ligaments were investigated with microscope and cell culture to detect living cell. No living cell was found in the frozen ACL.It was proved that the in situ freezing killed all fibroblasts of the ACL.2. The ACLs of the 20 mature beagle dogs were frozen in situ with the specially designed helical cryoprobe. After all fibroblasts died, the ACLs were thawed out with physiological saline. The tibial insertion of each ACL was made free from the tibia with a cylindrical bone block by penetrating a hollow reamer. The dogs were divided in two groups. At the first group, the bone block was reduced anatomically (physiological tension group : P group). At the second group, an initial tension of 20 N was applied on the ACL by pulling the bone block to the di … More stal direction with a tensiometer, resulting in distal translocation of the tibial insertion (high tension group : H group). Then, the each bone block was firmly fixed with an interference screw. The differences of the in situ frozen ACLs between the P and the H groups were investigated about the changes of mechanical properties and ultrastructure.3. There were no significant differences in the mechanical properties between the P and the H groups at 6 weeks after surgery. On the other hand, the tensile strength, maximum load and the tangent modulus in the H group were significantly lower than those in the P group at 12 weeks (p<.05). No significant differences could be found in thecross sectional area and in the strain at failure.4. The ACLs of four dogs were analyzed ultrastructurally. At 6 weeks after surgery, fibroblasts entered into the superficial substance of the in situ frozen ACL in the P group, although inflammatory cells entered into the intersubstancial space in the H group. At 12 weeks, the fibroblasts were found at all the substance of the ACL in the P group, although the degenerative change of the substance was found in the H group. Less