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 (H), 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 (H), 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 . <EOS>