Cranio-caudal differences in granulation tissue formation: an experimental study in the rat

This study examined potential regional differences in the deposition of granulation tissue in cellulose sponges placed in the dorsum of rats. Four cellulose sponge implants, 10 x 10 x 5 mm in size, two in cranial and two in caudal positions, were used to induce granulation tissue formation in the back of the rat. A cranio-caudal difference in connective tissue formation was assessed from 1 to 24 weeks after implantation. Granulation tissue ingrowth, measured histomorphometrically, was enhanced at 2 weeks and the surrounding capsule was thinner from 1 to 3 weeks in implants located in the cranial part of the back. In the cranial position, the number of fibroblasts, assessed semiquantitatively, was higher and the ratio of inflammatory cells to fibroblasts lower at 2-3 weeks. Also, the ratio of hydroxyproline content to total nitrogen content was higher after the first week in cranial specimens. Thus, a distinct cranio-caudal difference in the proliferative phase was observed. These results show the obvious practical considerations underlying the need for randomization or comparison between implants from exactly corresponding cranio-caudal locations.