A new clamping technique for biomechanical testing of tendons in small animals. aprobst@uni-muenster.de

When biomechanical properties of tendons are studied, the technique of clamping the tendons in the testing machine presents a methodological challenge, especially when murine tendons are examined. These short tendons tend to rupture at the transition line to the fixation, leading to false interpretations. Therefore a new clamping technique for investigation of healthy murine Achilles tendons (n = 50) was developed, in which the intramuscular tendon fibers were fixed between two paper strips and the calcaneus was wedged into a conical slot in a wooden block and then mounted in the testing machine (n = 20). This technique was compared with the conventional clamping technique that fixes both ends of the tendon by clamps (n = 15) and an earlier described method that used glue or plastic cement for the fixation of the intramuscular tendon fibers and calcaneus in the testing machine (n = 15). When tested by the new clamping technique, 17 tendons ruptured intratendinously at a mean tensile force of 8.4 +/- 1.1 N. Three Achilles tendons (17%) tore at the site of paper fixation and had to be excluded from investigation. Data from 73% of the measurements fixed by gluing had to be excluded because slippage of the proximal tendon fibers and contamination of the tendon with glue occurred. All the conventionally clamped tendons ruptured at the site of fixation at a mean tensile force of 6.1 +/- 2.3 N (p < .05). This was 30% lower than with the new clamping technique. Thus, the newly developed clamping technique enables investigators to obtain more valid biomechanical studies of the murine Achilles tendon.