In-vitro correlation between tension and length change in an anterior cruciate ligament substitute

The length change and tension patterns from multiple insertion locations of an anterior cruciate ligament substitute were studied in 10 cadaver knees. Length change was measured with a spring-loaded isometer of low stiffness, and tension was measured with a piezoelectric load cell. In both instances a thin Kevlar test ligament was positioned in five different femoral and two different tibial ligament insertion locations, that were all located within the normal attachments of the anterior cruciate ligament. Differences were found regarding length changes and tension patterns from a simulated active extension between the central, posterior, and anterior femoral locations. All locations showed larger length change and tension values in extension than in flexion. The anterior femoral ligament insertion location showed length change and tension patterns with increasing values in flexion compared to the other femoral locations. The anterior tibial ligament insertion location showed smaller excursions of both length and tension, than did the central one, but the patterns of the curves were similar. A statistically significant correlation was found between length change and tension patterns throughout a 130-0 /dg range of motion. A statistically significant correlation was also found between the maximum length and tension values. No fixed relationship was found between the magnitude of the length and tension values, when different intervals of the range of motion were studied.