Morphological and Biochemical Changes in Bone-to-tendon Insertion Site after Achilles Tendon-Bone Graft in Rabbits

Rhee, Seung Koo; Go, Hae Suck; Choi, Jung Keun; Lee, Won Hee; Kim, Young Sik; Kwon, Soon Yong

Abstract

Allografts or autografts of bone-tendon unit has been used widely for ligament or tendon reconstruction of ligament injuries or ligament deficiencies after limb salvage operation to treat malignant bone tumors around joints. While the remodeling process of the ligament or tendon itself after allograft or autograft and the microscopic and biomechanical changes of tendon- bone graft interface have been widely investigated, little is known about the ultrastructural and biochemical changes of the transitional zone in tendon-bone junction. This study was performed to analyze the morphological changes by microscopic (part I), and ultrastructural, and biochemical remodeling of the transitional zone after tendon-bone auto- and allo-grafting (part II). Preliminary, a microscopic studies at bone to tendon insertion site was done as control (part I). And as an experimental work (part II), a total of twenty four rabbits were divided into two group. In 12 animals (allograft group), an Achilles tendon-bone unit was taken with tenotomy 3 cm proximal to calcaneal attachment and osteotomy 5mm distal to the attachment site. This unit was preserved below -70degrees C for 2 weeks and then it was transplanted to another rabbit. In the other 12 animals (autograft group), the Achilles tendon-bone unit was harvested with the same maneuver from one side and transplanted to the other side of the rabbit. After operation, their legs were immobilized with short leg cast for 4 weeks, and then mobilized freely. Four animals in each group were sacrificed at four, eight and sixteen-weeks after transplantation, and their grafted Achilles tendon-bone interfaces were used for analysis of the ultrastrucural and biochemical changes. The following results were obtained. Part I: We conducted an experiment (part I) to investigate the histologic chronologic changes of tendon to bone fixation using the Cole's method and the role of periosteum to the tenodesis. The periosteum around the tenodesis was excised in group I, but it was incised longitudinally and sutured to tendon in group II. As a result, the tendons in the marrow cavity of tibia were firmly fixed by fibrosseous metaplasia in group I at 8 weeks after experiment, but not formed the fibrocartilagenous layer in both groups as a transitional zone of internal stress transmission from tendon to bone in normal tendon, and the group II show the firm connection between sutured periosteum and transferred tendon by external calluses after 3 weeks. These mean the periosteum should be sutured over the inserted tendon to get the early rigid fixation by the induction of external callus around the edges of the tendon to bone insertion. Part II: Histologically in part II experiment, new cartilage cells were observed at postoperative 16 weeks with locally presence of faint tidemark in the autograft group but not in the allograft group. Complete histological remodeling of the transitional zone had not restored both groups.. Ultrastructural analysis revealed no definite differences, but showed time-related restoration of fibers and fibroblasts between both groups except the slightly rapid appearance of parallelism and cross-striation of microfibrils in the autograft group. From biochemical analysis, type I collagen was increased in its concentration, and an early rapid increase of type III collagen and glycosaminoglycan was also observed. In conclusion, these data suggested that type III collagen and glycosaminoglyan are important in stabilization of grafted tendon-bone unit, especially in the transitional zone. The histological and biochemical changes in allograft group were relatively similar to that of autograft group although the allograft group showed the delayed pattern of remodeling. And so the tendon-bone allograft could be used as a good but second substitute followed by autograft.