A connector for windscreen wiper is disclosed. Such a detector allows a servo circuit to compensate for a reversed-connected read-write head, and thus allows a manufacturer to forego time-consuming and costly testing to determine whether the head is correctly connected to the servo circuit. In the used position, the headrest is held stationary by a toggle linkage, which, within its self-limiting swing zone, acts as a pivoting element between the impact cushion and the pivotal axle. The layer of the patient-specific porous construct substantially replicates the porous structure of the bone layer of the specific patient. The top cover may also be an in situ applied semipermeable membrane.