Tension Level During Preconditioning Influences Allogeneic Tendon Properties

Objective: Anterior cruciate ligament(ACL) injury is a common diseaseon clinical.It is a ideal method to apply allograft tendon ACL ofcryopreservation in arthroscope and this method has acquired well effect. Itnot only corresponds to micro-operation, but also avoids the syndrome ofautoallergic material.However, the mechanical properties of allograft tendonsuch as viscoelasticity will cause the laxity of the knee joint, so it is necessaryin the intraoperative allogeneic tendon pretreatment, to reduce the tensioncaused by the loss due to factors such as viscoelasticity, to maintain the kneejoint stability.By exploring influences of different pre-tension level for allogeneictendon on the stiffness, tension, and maximum load, to provide appropriatepre-tension to improve allogeneic tendon biomechanical properties, reducingthe knee relaxation after anterior cruciate ligament reconstruction.Methods: There were48deep-frozen allogeneic tendon grafts providedby the bone tissue of shanxi library.The grafts were pairwised for24tendonswhich were used to measure hole device to measure the diameter of theallograft tendon, about7±0.5mm. The24allograft tendon grafts wererandomly divided into groups as80N,160N,320N group, by pre-tension forcelevels,n=8.The grafts were sutured with No.2nonabsorbable sutures to eachtendon at both ends continuous sutured line weaving around20mm at bothends after rewarming. Then the grafts were wrapped with gauze at both endsand clamped on the biomechanics machine fixture, and the length betweengrips was35mm which measured with a vernier caliper. Each group oftendons in the respective pre-tension level of pre-stretch for10minutes,replicate preconditioning of a graft on a graft board.Each graft was unloadedfor approximately1minute, to represent transfer from the graft board to the knee, and then cyclically loaded25times to represent preconditioning withinthe knee after femoral fixation. During cyclic loading, the grafts wereelongated in displacement due to viscoelastic, so we had to fixed again. Thenwe loaded to approximately80N, on behalf of the initial tension of tibialfixation. The slope of the force versus displacement data from60N to80Nwas calculated to characterize the stiffness at the end of the application ofinitial tension. The actuator was not lowered below the position and themachine automatically records the changes in the tendon tension. Every15minutes to spray saline solution to the graft during the test to maintainhumidity. Half an hour later, the tensile test of allogeneic tendon had tested,read the slope of the corresponding maximum load and calculated thestiffness.Results: The320N group pretreated three sets of maximum stiffnesswas156±4.7N/mm, the160N group was141±4.2N/mm,80N group was113±6.2N/mm. The stiffness of the three groups after preconditioning weresignificant (F=146.27P <0.01). The construct stiffness was larger for the320N preconditioning level than for the80N and160N preconditioning level.The160N and80N group stiffness was significant differences. The320Ngroup pretreated three sets of maximum stiffness was156±4.7N/mm, the160N group was141±4.2N/mm,80N group was113±6.2N/mm. Half anhour later, the stiffness among the three groups were significantly different(F=421.77P <0.01). The320N group stiffness was significant differenceswith the160N group and80N group, the160N group and80N group wassignificant differences. Half an hour later, the320N group was the maximumstiffness,263±7.2N/mm,160N group was250±6.8N/mm,80N group was174±5.5N/mm. Half an hour later the tension among the three groups aredifferent (F=687.68P<0.01). The160N group was significant differencesfrom the320N and80N group. The160N group tension was70.05±0.03Nlarger than80N group and320N group;80N group and320N group tensionwas no significant difference (p>0.05). The maximum load among the threegroups were significant (F=23.411P <0.01),the320N group maximum load have significant difference with80N group and160N group,320Ngroup had the minimum maximum load, was873.7±54.13N;80N groupand160N group maximum load was no significant difference (p>0.05). Thetendons through preconditioning could significantly improve stiffness, but the320N group after pretreatment stiffness and stiffness after half an hour morethan the other two groups. Three groups of allogeneic tendon pretreatmentstiffness were significantly lower than the stiffness at half an hour (p>0.05).Three postoperative tension levels showed a decreasing trend, the biggest dropin five minutes, followed trend was horizontal slow downward. The160Ngroup tension decline the least about12.5%of the initial tension,80N groupand320N group decreased about25%of the initial tension.Conclusion: Increasing the tension applied to allogeneic tendon graftsduring preconditioning can decrease the postoperative loss of tension andstiffness due to viscoelasticity, the increased graft tension and stiffness couldreduce postoperative knee laxity. But more than a certain area would likelytendon maximum load and tension impact, is not conducive to themaintenance of joint stability, and postoperative rehabilitation. Recommended160N preload on allogeneic tendon pretension, be satisfied with the tensionand stiffness, and does not reduce the strength of the tendon.