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Purpose：Thetechnique of margin convergence has beenapplied to rotator cuff repair to enhance the security of fixation by decreasing the mechanical strain at the margins of the tear．The purposes of this study were to evaluate the effect of margin convergence on rotator cuff repair strengthand to determine which method was mechanically superior.
Method：18 Kangaroo shoulders were divided into threegroups(n=6)．A full thickness tendon defect was created in thesupraspinatus tendon at humeral insertion with asize of 1.0-1.5 cm,thereby simulating amassive rotator cufftear in human shoulder．Three different techniques were employed forrotator cuff repair：Miteksuture anchor alone(Group 1)，margin convergencealone(Group 2)，margin convergence plus Mitek suture anchor (Group 3)．Combined loads were applied in each specimen first with cyclic loadingat a rate of 33mm/sec between 10 and 180N with 2 seconds interval at loading extremes．After cyclic loading was complete the construct．Was loaded to failure at a rate of 5 mm/min．ANOVA and LSD multiple comparisons of the means were applied for testing(significant level,p<0.05).
Results：Cyclic load test showed progressive gap formation in each repaired specimenwith increasing cydcs．Group lreached 50％ failure(5-mm gap formation)at an average of 34 cycles,Group 2 at 75 cycles and Group 3 at 65 cycles．There were significant difference between Groups 1 and 2 (P≤0.001),and Groups 1 and 3(P≤0.001)．After 100 loading cydes，the size of gap formation was onaverage 5.8mm；6.1 mm and 4.7 mm in in Groups 1，2 and 3 respectively．There wasa significant difference between Groupsl and 3(P≤0.015) specimens eventually reached their ultimate failure(10 mill gap formation with or without any suture,tendon or anchor rupture)．Ultimate failure occurred at 374 13N for Group 1，415 37N for Group 2 and 464 63N for Group 3.Group 1 demonstrated failure due to2 sutures breakage at the anchor,2 tendon breakages，and 2 musde-tendon junction failures．In Group 2，one failure with knot loose,others failure occurred atmusde-tendon junction with progressive gap formation to 10 mm at the ultimate loading．In Group 3,three of 6 specimens underwenttendon failure，2 muscle tears and one suture failure at the anchor．
Conclusions：The rotator cuff repairs with the techniques of margin convergenceor margin convergenceplus suture anchor had much superior mechanical strength in gap formation and ultimate failure load．However,the progressive gap formation after cuffrepair seemed always presence if only the existing of any cyclic loads，which may facili tate clinically understanding the phenomena of retear or residual defect after rotator cuff repair．