A hinge mechanism 10 to lift the rear edge of a bonnet 11 of a motor vehicle comprises an upper leaf 13 connected to the bonnet 11, a lower leaf 12 connected to the body structure of the vehicle and a middle leaf 14 connected to the upper leaf 13 and the lower leaf 12. The middle leaf 14 is connected to the upper leaf 13 by means of a stud 16 and a slot 17 connection so as to limit movement of the bonnet from a normal position to a deployed position under an upward force exerted by a lift actuator. The stud 16 and slot 17 connection is provided with a resiliently deformable element 30 arranged at the end of the slot for dissipating impact energy of the stud 16 against the slot 17 during the upward force.