INTRAOPERATIVE GRAFT TENSIONING ALTERS VISCOELASTIC BUT NOT FAILURE BEHAVIORS OF RABBIT MEDIAL COLLATERAL LIGAMENT AUTOGRAFTS

The effects of three different degrees of intraoperative graft tension ing on measures of ex vivo laxity, viscoelastic behaviour, and structu ral and material failure of isolated healing medial collateral ligamen t autografts were investigated in a rabbit model. The grafts were orth otopically replaced at one of three different loads (too tight, anatom ic, or too loose) and were mechanically evaluated after 0; 12, 24, and 48 weeks of healing. Laxity of the ligament was influenced by intraop erative graft tensioning at time zero. However, after 12 weeks of heal ing, values for laxity were indistinguishable among the experimental g roups. Cyclic load relaxation, a measure of viscoelastic behaviour, wa s significantly influenced by intraoperative graft tensioning, and thi s effect persisted even after 48 weeks of healing. Grafts placed under excessive tension relaxed one-third less than grafts placed under abn ormally low in situ tension. The relevance of these differences remain s to be determined. Intraoperative tensioning had no significant influ ence on characteristics of structural or material failure of the graft during the first year of healing. These results suggest that, in this model, control of graft tension at the time of placement and fixation does not improve the failure characteristics of the medial collateral ligament. The structural strength of the grafts collectively improved to nearly normal values after 48 weeks; however, material recovery wa s less complete. Failure loads averaged 89% of control values, whereas failure stress averaged only 52% after 45 weeks of healing.