Repair and reconstruction of the anterior cruciate ligament by the "Sandwich technique". A comparative microangiographic and histological study in the rabbit.

The effect of complete ensheathment of the repaired or reconstructed anterior cruciate ligament (ACL) in the infrapatellar fat pad was studied in a rabbit model. Four to 16 weeks after repair of a transected ACL or insertion of an autologous tendon graft these tissues were evaluated by histology and microangiography. Following ACL repair a high incidence of ligament atrophy was evident in both the ensheathed (43%) and the non-ensheathed control (54%) group. In functional ligaments a similar sequence of remodelling events was evident in both the ensheathed and the non-ensheathed group: infiltration of the transected area by mesenchymal cells, maturation of these cells to fibroblasts, and increasing organization of newly formed collagen fibres. An initial hypervascular reaction was followed by a decrease in the number and an increase in the longitudinal orientation of blood vessels. Despite a similar sequence of remodelling events, however, this process was considerably accelerated in repaired ligaments ensheathed with infrapatellar fat pad compared with non-ensheathed controls. At 16 weeks only the ensheathed repaired ACL resembled the normal ACL morphologically, even though it was still hypercellular. The tendon autograft followed a similar course from an initially avascular and acellular tissue towards a structure similar to the normal ACL. In the ensheathed ligaments and tendon grafts vascular and cellular ingrowth as well as subsequent maturation were again accelerated. This effect may be attributable to improved revascularization and cell repopulation, as well as protection from synovial fluid by the surrounding fat pad.(ABSTRACT TRUNCATED AT 250 WORDS)