Early changes in the tensile strength and morphology of primary sutured skin wounds in rats.

The specific aim of this study was to measure the TS of rat skin wounds during the first week following surgical injury. Biomechanical and histological data were collected daily (days 1 to 7 following surgery) from separate groups of Sprague-Dawley rats (N = 12) each with two 3 cm long parallel skin incisions on the back. The wounds were immediately closed by four simple sutures. A control group (N = 15) was used to obtain TS measurements of unwounded skin. TS was measured by applying a ramp load until wound separation and estimated by dividing the yield strength by the wound area. The time course of biomechanical recovery followed a step-plateau pattern with the largest increase in TS observed one day after surgery (0 - 1.60 g/cm(2)). The plateau stage extended from day 1 to 5 (1.60 - 3.88 g/cm(2)). The final step (day 5-7) indicated a period of rapid rise in wound TS (3.88 - 11.57 g/cm(2)). Since even on day 7 the mean TS was only 4% of unwounded skin, the wound had to be protected from tensile loads. Histological analysis confirmed that the early changes in TS (day 1) correlated with the fibrin accumulation of the wound edges followed by a plateau stage caused by the tissue proliferation. The rapid increase in wound TS was characterized by cross-linking the incisions with collagen fibres with escalating organization. We conclude that from a biomechanical perspective, sutures can be removed during the "plateau phase", but the wound must be protected from tensile loads.