In vitro comparison of tension and stiffness between hamstring tendon and patella tendon grafts

Following anterior cruciate ligament reconstruction, grafts relax and warm from the temperature of the operating room to body temperature. The current study compared graft tension and stiffness between patella tendon and hamstring tendon grafts. Six quadruple strand hamstring tendon grafts and six patella tendon grafts were preconditioned and loaded to 105 N while at 20°C. Graft tension and stiffness were measured after 15 min, after an additional 4 h, and after increasing the temperature to 34°C. A two-way repeated-measures analysis of variance and a post hoc test were used to compare the measurements between the two types of graft and identify significant (p < 0.05) changes for each type of graft. Tension was significantly larger for the patella tendon grafts, although the stiffness values were not significantly different (p > 0.8). For both types of graft, tension and stiffness decreased significantly with time and the temperature increase. The lowest tension and stiffness measurements were 50±11 N and 129±35 N/mm, respectively, for the patella tendon grafts, compared to 18±5 N and 115±11 N/mm, respectively, for the hamstring tendon grafts. Both types of graft lose tension to relaxation and a temperature increase, but the tension loss is larger for hamstring tendon grafts.