The Biomechanics and Histopathology of Chemically Processed Patellar Tendon Allografts for Anterior Cruciate Ligament Replacement

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Abstract
A study was initiated to examine chemically processed patellar tendon allografts in sheep anterior cruciate liga ment repairs, both mechanically and histologically. One group of animals received frozen, untreated allografts, one group received frozen grafts that were processed with a chloroform-methanol solvent extraction tech nique, and one group received frozen tendons treated with a permeation-enhanced extraction technique. All animals were operated on unilaterally, with the con tralateral knee acting as a normal, intact control. His tologic analysis after 2 months of implantation revealed similar enhanced cellular repopulation in both chemi cally treated ligament allografts compared with the more hypocellular, untreated grafts. At 6 months the chloroform-methanol group demonstrated a more ag gressive chronic cellular response with numerous thick- walled vessels relative to the untreated and permeation- enhanced grafts. Mechanical testing after 6 months of implantation showed statistically similar anterior drawer resistance in all grafted knees, yet the two chemically extracted grafts had significantly less stiffness than un treated anterior cruciate ligament grafts. Both treatment groups also tended to be weaker than the untreated allografts. All anterior cruciate ligament reconstructions showed excessive anterior drawer laxity and, regard less of treatment, had lower strength and less stiffness than normal anterior cruciate ligament tissue at the 6-month period.