ACHILLES-TENDON HEALING - A CORRELATION BETWEEN FUNCTIONAL AND MECHANICAL PERFORMANCE IN THE RAT

The pathogenesis and treatment of rupture of the Achilles tendon remai n a source of controversy. This study presents the results of a biomec hanical, functional, and morphological evaluation of a group of rats t hat had division and repair of the Achilles tendon. A total of 46 rats were used: 18 for biomechanical testing, 18 for functional evaluation , and 10 for histology. Morphological examination revealed an early in flammatory response with loose connective tissue formation that was re placed gradually by fibroblasts and a collagenous matrix. The function al evaluation (Achilles functional index [AFI]) was made from measurem ents of the hind pawprints of walking rats. Division and repair of the Achilles tendon produced a significant functional impairment (mean [/-SEM] AFI = -87 +/- 8; p < 0.001), which gradually improved with heal ing time. The load to failure for the repaired tendons consistently im proved with healing time, in a manner similar to the functional recove ry. The average deformation (repair/control) varied considerably and w as not related to healing time. The stiffness of the repaired tendons increased with healing time and was 60% of the corresponding control s ide by day 15. The major finding of this study was a strong correlatio n between the AFI and the failure load of the healing tendon-bone cons tructs (250-300 g group, r = 0.97, p < 0.001; 325-375 g group, r = 0.9 6, p < 0.001).