A positioning block (10) for use in total knee replacement surgery, permitting five degrees-of-freedom movement relative to a bone element (39) to which it is fixed. The positioning block (10) comprises a mounting member (14) including a fastener receiving mount element (24) by means of which mounting member (14) is removably engaged to the bone element such that the mounting member (14) is selectively rotatable relative to the bone element, about three substantially perpendicular axes of rotation. Fastener receiving mount element (24) slides within a central guide slot (22) disposed within a mounting member body (20) which also forms part of mounting member (14) A guide body portion (12) is engaged with the mounting member (14) such that it is translatable relative there to along a proximal-distal axis (43) and together with the mounting member-body(20) is translatable relative to the fastener receiving mount element(24) along an anterior-posterior axis (47), while being rotationally fixed relative to the mounting member(14) such that the guide body portion(12) and the mounting member(14) rotate together relative to the bone element(39). Computer means identify and display the position of the positioning block(10).Linvention concerne un bloc de positionnement (10) sutilisant en arthroplastie totale du genou, qui permet deffectuer un mouvement à cinq degrés de liberté par rapport à un élément osseux (39) auquel il est fixé. Le bloc de positionnement (10) comprend un élément de fixation (14) rotatif qui sassemble amovible à lélément osseux, de sorte que lélément de fixation (14) peut tourner de manière sélective par rapport à lélément osseux autour de trois axes de rotation sensiblement perpendiculaires. Une partie corps de guidage (12) est mise en contact avec lélément de fixation (14) de façon à pouvoir effectuer un mouvement de translation par rapport à celui-ci le long dun axe proximal-distal (43) et dun axe antérieur-postérieur (47), cette partie étant fixée en
