OBJECTIVETo study the effects of continuous passive motion on the tendon-bone healing of the semi-tendinous tendon autograft used for anterior cruciate ligament (ACL) reconstruction in rabbits.

METHODSIn 12 healthy 8-month-old male rabbits, an ACL reconstruction was performed by using double semi-tendinous tendon autograft. Postoperatively these animals were treated by either continuous passive motion (CPM) or cage activity. Specimens of the grafts were collected at 6, 12, 24 weeks postoperatively. Histological change in the tendon-bone healing was studied by haematoxylin-eosin and toluidine blue.

RESULTSThere was more new fiber tissue in the anterior half of the interface. Osteoclasts were most numerous at the tunnel aperture and in the anterior half of the interface. Cartilage in the tendon-bone interface was localized to the posterior aspect of tunnels, the area where compressive stress would be predicted. CPM group developed a denser connective tissue with less vascularity and cellularity. The bone tunnel had more areas with ingrowing denser connective tissue compared with cage activity specimens. With the growth of Sharpery's fibers and fibrocartilage into the interface, a direct ligament insertion was found. In the CPM specimens, the interface tissue was more mature and the direct insertion was broader and more structured.

CONCLUSIONSCompressive stress promotes chondroid formation, and the tension promotes fiber formation. Tendon-bone healing may be optimized by CPM after tendon transplantation into a bone tunnel.