A partial endoprosthesis device for preserving the motion of a vertebral joint for implant into a spinal segment comprising two adjacent vertebrae (10',10"), wherein at least one of said two adjacent vertebrae is a cervical vertebra, said adjacent vertebrae (10',10") comprising a lower vertebra having a couple of upper articular processes with respective upper articular facets and an upper vertebra (10") having a couple of lower articular processes (2") with respective lower articular facets (3"), each upper articular facet of said lower vertebra articulated with a corresponding lower articular facet (3") of said upper vertebra (10"), said device comprising: - an elongated articular portion extending along a longitudinal axis between a first end and a second end axially opposite to each other, said articular portion having a first face and a second face opposite to said first face, wherein said first face comprises a central protrusion along said longitudinal axis having a height, with respect to said face, set between 0.5 mm and 3 mm, preferably between 1.5 and 2.5 mm, and having a surface made of an osteointegrable material; wherein said first face has a plurality of primary stabilization elements, - a shoulder portion adjacent to said first end and arranged at an angle with respect to said articular portion opposite to said second face; - said articular portion has a thickness (s 1,s 2) increasing from said first end going towards said second end, characterized in that - said second face has a surface roughness Ra lower than 0.2 μm, - said primary stabilization elements are elongated and flexible elements, and - said primary stabilization elements extend laterally with respect to said protrusion, between an own first connection end for connecting with said protrusion and an own free end, and form an acute angle (β) with the direction of said longitudinal axis of said articular portion, said acute angle oriented towards said first end of said articular portion. - an elongated articular portion extending along a longitudinal axis between a first end and a second end axially opposite to each other, said articular portion having a first face and a second face opposite to said first face, wherein said first face comprises a central protrusion along said longitudinal axis having a height, with respect to said face, set between 0.5 mm and 3 mm, preferably between 1.5 and 2.5 mm, and having a surface made of an osteointegrable material; wherein said first face has a plurality of primary stabilization elements, - a shoulder portion adjacent to said first end and arranged at an angle with respect to said articular portion opposite to said second face; - said articular portion has a thickness (s 1,s 2) increasing from said first end going towards said second end, - said second face has a surface roughness Ra lower than 0.2 μm, - said primary stabilization elements are elongated and flexible elements, and - said primary stabilization elements extend laterally with respect to said protrusion, between an own first connection end for connecting with said protrusion and an own free end, and form an acute angle (β) with the direction of said longitudinal axis of said articular portion, said acute angle oriented towards said first end of said articular portion.