The effect of strand configuration on the tensile properties of quadrupled tendon grafts

PURPOSE: To compare selected biomechanical properties of 4 different quadrupled tendon graft preparations applicable for anterior cruciate ligament reconstruction. TYPE OF STUDY: Biomechanical investigation in a cadaver model. METHODS: Graft strands were arranged in parallel, braided, bolo-plait, and twist configurations. Elongation of the graft was monitored during loading with an infrared optical measurement system, which measured the 3-dimensional position of twelve spherical reflective markers mounted within the camera field. Permanent elongation, stiffness, and ultimate strength of each graft configuration were determined. RESULTS: Permanent graft strain after the first incremental loading cycle was 7.2% in braid, 6.6% in twist, 6.5% in bolo-plait, and 3.3% in parallel constructs (P <.0001). Permanent graft strain after a second incremental loading cycle was 1.2% in bolo-plait, 1.1% in braid, 0.7% in twist, and 0.7% in parallel preparations (P =.0012). Braid and bolo-plait grafts were less stiff than twist or parallel grafts (P <.0001). Differences in failure load were not significant (P =.171). CONCLUSIONS: Variation in graft configuration from the conventional, parallel strand pattern lead to increased viscoelasticity and permanent elongation of grafts with repetitive loading. This deficit is expected to cause increased laxity of the reconstructed knee.