THE BIOMECHANICS AND HISTOPATHOLOGY OF CHEMICALLY PROCESSED PATELLAR TENDON ALLOGRAFTS FOR ANTERIOR CRUCIATE LIGAMENT REPLACEMENT

A study was initiated to examine chemically processed patellar tendon allografts in sheep anterior cruciate ligament repairs, both mechanica lly and histologically. One group of animals received frozen, untreate d allografts, one group received frozen grafts that were processed wit h a chloroform-methanol solvent extraction technique, and one group re ceived frozen tendons treated with a permeation-enhanced extraction te chnique. All animals were operated on unilaterally, with the contralat eral knee acting as a normal, intact control. Histologic analysis afte r 2 months of implantation revealed similar enhanced cellular repopula tion in both chemically treated ligament allografts compared with the more hypocellular, untreated grafts. At 6 months the chloroform-methan ol group demonstrated a more aggressive chronic cellular response with numerous thick-walled vessels relative to the untreated and permeatio n-enhanced grafts. Mechanical testing after 6 months of implantation s howed statistically similar anterior drawer resistance in all grafted knees, yet the two chemically extracted grafts had significantly less stiffness than untreated anterior cruciate ligament grafts. Both treat ment groups also tended to be weaker than the untreated allografts. Al l anterior cruciate ligament reconstructions showed excessive anterior drawer laxity and, regardless of treatment, had lower strength and le ss stiffness than normal anterior cruciate ligament tissue at the 6-mo nth period.