TENDONS ATTACHED TO PROSTHESES BY TENDON BONE BLOCK FIXATION - AN EXPERIMENTAL-STUDY IN DOGS

To develop a method of tendon attachment to a metallic endoprosthesis, we evaluated fixation strength, clinical function of the tendon, and morphological changes in an experimental model. The canine supraspinat us tendon was removed from the greater tubercle of the humerus and att ached to a titanium prosthesis. In 12 animals, the bone block underlyi ng the tendon insertion was preserved and attached in one limb; the so ft part of the tendon was attached directly to the prosthesis in the c ontralateral limb. Fixation strength was evaluated after 16 weeks of i n vivo implantation (12 specimens) and compared with the in vitro fixa tion strength (12 specimens) and with intact normal controls (six spec imens from cadavera). Function of the tendon in vivo was evaluated by force-plate analysis (at 3-week intervals). All specimens were evaluat ed histologically. Sixteen weeks after surgery, the tendon-bone block attachment was significantly stronger (mean, 16%) than the direct tend on attachment and not significantly different from the normal control, and the direct tendon attachment was significantly weaker (mean, 68%) than the normal control. There was significantly more weight-bearing on the limbs with a tendon-bone block attachment than on the limbs wit h a direct tendon attachment at bath 3 and 6 weeks postoperatively. Bo th front legs showed increased weight-bearing with time, but the diffe rences were not statistically significant. Anchorage by tissue ingrowt h to the titanium prosthesis was found consistently - there was bone i ngrowth in the tendon-bone block attachments and fibrous tissue ingrow th in the direct tendon attachments. When a bane block was preserved, the strength and stiffness were comparable with those of a normal tend on insertion. This mechanical linkage was capable of transmitting musc le forces to the prosthesis and consequently to the limb.