Arthroskopie

Juergen Hoher, Masataka Sakane, Tracy M. Vogrin, John D. Withrow, Freddie H. Fu, Savio L-Y. Woo


The purpose of this study was to determine the viscoplastic deformation in a quadrupled semiteninosus graft construct using a titanium button/tape and screw post/suture fixation technique in response to cyclic loading. Eight quadrupled grafts for replacement of the anterior cruciate ligament (ACL) were prepared from human cadaveric semitendinosus tendons. For fixation, a polyester tape attached to a titanium button and four #2 nonresorbable sutures attached to each of the four tendon ends tied around a post screw were used. The graft contrsuct was mounted on an INSTRON testing machine, withthe titanium button and the post screw rigidly fixed at a constant distance of 120 mm. Cyclic creep tests (with 100 cycles each) were preformed (A) between 20 and 100 N and (B) between 20 and 150 N (Fig 1). The test sequence was A1-A2-B1-B2-A3 with a rest period of 1 h between single tests for graft recovery. The length of the graft construct after each rest period was used to determine the permanent elongation. Relative length changes along the graft construct (proximal, central, distal) were determined using a video tracking device. Finally, a load-to failure test was performed. Under all test conditions the maximum elongation of the graft construct increased from the first to the 100th cycle, ranging from 1.0 mm to 3.1 mm. While these so-called creep patterns were almost identical in A1 and A2, elongations under A3 were 3-4 mm higher than under A1 and A2, probbaly as a result of higher loads at B1 and B2. The permanent elongation of the graft constructs after completion of the test series revealed that about 97% of this deformation occurred within the fixation materials and interfaces (distal and proximal section) and only about 3% within the tendon tissue (central section). The load-to-failure test revealed an ultimate load of 416 + 36 N and a stiffness of 32.4 + 1.3 N/mm. All constructs failed at the polyester tape. Our results indicate that repetitive cyclic loading at relatively low loads can result in substantial, permanent elongation of a quadrupled semitendinosus graft constructwith endobutton/tape and suture/post screw fixation method. Similar loads may be experienced bythe graft construct during early postoperative activities and be a cause of gradual failure before graft incorporation is complete. We conclude that aggressive postoperative rehabilitation be applied with caution when using this graft construct. Better fixation materials and/or techniques should be developed to improve biomechanical behavior of the graft construct.