Quantification and localisation of damage in rat muscles after controlled loading; a new approach to study the aetiology of pressure sores.

To obtain more insight in the aetiology of deep pressure sores, an animal model was developed to relate controlled external loading to local muscle damage. The tibialis anterior muscle (TA) and overlying skin of a rat were compressed between indentor and tibia. Loads of 10, 70 and 250kPa at skin surface were applied for 2 or 6h. During half of the 10 and 250kPa experiments interstitial fluid pressure (IFP) in the TA was measured. The TAs were excised 24h after load application. Both amount and location of damage were assessed by histological examination using a semi-automated image-processing program. In six of eleven loaded muscles damage was found. The damage was located from superficial to deep muscle tissue in a zone never exceeding the diameter of the indentor. The IFP measurements interfered with the occurrence of damage; application of 10 and 70kPa loads only caused damage when combined with IFP measurements, whereas IFP measurements increased damage at 250kPa loads. The results showed that the developed animal model can be used to provoke local damage by applying a controlled load and that the amount and location of damage can be assessed using the newly developed techniques.