Comparison of 2 Mattresses for the Prevention of Bedsores by Measuring Skin Pressure in the Sacral Area

Inclusion Criteria: * The patient must have given his/her informed and signed consent * The patient must be insured or beneficiary of a health insurance plan * The patient spends more than 12 hours in bed and verticalisation is possible * The patient has a stable medical condition (no complication in the last 10 days) and no visible pressure ulcers * The patient is at risk for pressure ulcers as assessed by a score ≤ 15 on the Braden Scale * The patient weighs less than 120 kg Exclusion Criteria: * The patient is in an exclusion period determined by a previous study * The patient is under judicial protection, under tutorship or curatorship * The patient refuses to sign the consent * It is impossible to correctly inform the patient * The subject has a contra-indication for a strictly supine position * The patient has a knee flexion deformity \> 10 ° * The patient is in a state of agitation or refuses to cooperate * The patient's weight is greater than 120 Kg * The length of stay is less than one month