Measuring instrument for use in orthopaedic surgery

A measuring instrument for use during an orthopaedic surgical procedure in determining the appropriate sizes of femoral and tibial implant components, the measuring instrument comprising a measurement structure, a reference structure and a mask;

• the measurement structure having a longitudinal axis, a set of indicia defining a thickness scale and a sizing indicium separate from the indicia defining the thickness scale;
• the reference structure having a medial limb with an end, a lateral limb with an end and a bridge connecting the end of the medial limb and the end of the lateral limb, the bridge having a hole through which a portion of the measurement structure extends and that allows for relative sliding movement between the measurement structure and the reference structure along the longitudinal axis of the measurement structure;
• at least one of the medial limb and the lateral limb including a set of indicia defining a sizing scale;
• the mask including a wall portion having a window;
• wherein the mask is mountable in a plurality of selective positions on the reference structure with the wall portion of the mask covering at least a portion of the thickness scale on the measurement structure and the window positioned so that one indicia on the thickness scale on the measurement structure is exposed and visible in the window while other indicia on the thickness scale on the measurement structure are covered by the wall portion of the mask.