Effects of pretwist on biomechanical properties of canine patellar tendon

The purpose of this study was to measure the effect produced on canine patellar tendon of a 90 degree pretwist on the following mechanical properties: failure stress, failure strain, average elastic modulus, and strain energy density. Forty adult mongrel dog cadavers, killed for other studies, were used. Paired patellar tendons were isolated with patellar and tibial bone and the central 4.0-4.6 mm of tendon used for testing. Specimens were elongated to failure using a Materials Testing System (MTS). Only those paired specimens both failing in substance were analyzed. Eight paired specimens were analyzed, both with 0 degree twist, for right-left reproducibility. Thirty-two paired specimens were randomly assigned to four groups: right 0 degree/left 90 degree clockwise pretwist; right 0 degree/left 90 degree counterclockwise; left 0 degree/right 90 degree clockwise; left 0 degree/right 90 degree counterclockwise. No statistically significant differences were present between the paired untwisted specimens in any mechanical property. In the pretwisted specimens, there were statistically significant differences between the group left/clockwise and right/counterclockwise and the group left/counterclockwise and right/clockwise with respect to the mechanical properties failure stress, average elastic modulus, and strain energy density. No statistically significant differences were observed between the two groups for failure strain. For the canine patella-patellar tendon-tibia complex (PPTTC), the mechanical properties failure stress, average elastic modulus, and strain energy density are sensitive to both side (left/right) of PPTTC and direction (clockwise/counterclockwise) of pretwist. Pretwist of patellar tendon grafts in anterior cruciate ligament reconstruction may produce significant changes in their mechanical properties that vary with the direction of twist.