Hamstring tendon grafts for reconstruction of the anterior cruciate ligament: Biomechanical evaluation of the use of multiple strands and tensioning techniques

Background Our hypothesis that multiple, equally tensioned strands of hamst ring graft used for reconstruction of the anterior cruciate ligament are st ronger and stiffer than ten-millimeter patellar ligament grafts was tested biomechanically with use of tendons from cadavera, Methods: In the first part of the study, we measured the strength and stiff ness of one, two, and four-strand hamstring grafts, from fresh-frozen cadav eric knees, that had been tensioned equally when clamped, In the second par t of the study, we compared four-strand grafts to which tension had been ap plied by hand and then clamped with similar grafts to which tension had bee n applied,vith weights and then clamped. The grafts for the two experiments were obtained from thirty-four paired and ten nnpaired knees. We also stud ied the effects of cooling on the biomechanical properties of grafts by com paring patellar ligament grafts tested at 13 degrees Celsius with those tes ted at room temperature. Results: Two equally tensioned gracilis strands had 185 percent of the stre ngth and 210 percent of the stiffness (1550 +/- 428 newtons and 336 +/- 141 newtons per millimeter, respectively) of one gracilis strand (837 +/- 138 newtons and 160 +/- 44 newtons per millimeter, respectively). Two equally t ensioned semitendinosus strands had 220 percent of the strength and 220 per cent of the stiffness (2330 +/- 452 newtons and 469 +/- 185 newtons per mil limeter, respectively) of one semitendinosus strand (1060 +/- 227 newtons a nd 213 +/- 44 newtons per millimeter, respectively). Four combined strands (two gracilis strands and two semitendinosus strands) that were equally tensioned with weights and clamped had the additive tens ile properties of the individual strands. With the numbers available, four combined strands that were manually tensioned and clamped were not found to be significantly stronger or stiffer than two semitendinosus strands that were equally tensioned with weights (p > 0.07), Conclusions: Four combined strands that were equally tensioned with weights and clamped were stronger and stiffer than all ten-millimeter patellar lig ament grafts that have been described in previous reports. All strands of a hamstring graft must be equally tensioned for the composite to have its op timum biomechanical properties. Clinical Relevance: Because of the well recognized donor-site morbidity ass ociated with the use of patellar ligament grafts for reconstruction of the anterior cruciate ligament, multiple-strand hamstring-tendon grafts have be come an increasingly popular choice. Our data demonstrate that equally tens ioned four-strand hamstring-tendon grafts have initial tensile properties t hat are higher than those reported for ten-millimeter patellar-ligament gra fts; thus, from a biomechanical point of view, they seem to be a reasonable alternative.