Chemically processed patellar tendon allografts for ovine anterior cruciate ligament reconstruction

A study was initiated to mechanically and histologically examine chemically processed patellar tendon allografts in sheep anterior cruciate ligament (ACL) repairs. One group of animals received frozen grafts that were processed with a chloroform/methanol solvent extraction technique, and a third sheep group received frozen tendons treated with a permeation enhanced extraction technique. Histologic analysis after two months of implantation revealed similar enhanced cellular repopulation in both chemically treated ACL allografts compared to the more hypocellular untreated grafts. Mechanical testing after six months of implantation showed statistically similar anterior drawer resistance among all grafted knees, yet the two chemically extracted grafts had lower strength and stiffness on average than untreated ACL grafts. Greater mean anterior drawer displacements were found in all grafted knees when paired with the contralateral unoperated right knees, although this trend was found significant only in the two chemical treatment groups. All allografts regardless of treatment had lower strength and stiffness than normal ACL tissue at the six-month time period.