A patella drill guide and trial instrument (14) has a posterior trial bearing surface (52) which is configured to articulate with a condylar surface of a prosthetic femoral component (154), and which has a curved peak surface that defines the posterior-most surface of the patella drill guide and trial instrument. An opposite anterior surface (62) has a centre spike (66) and a number of peripheral spikes (68, 70) extending outwardly therefrom. A superior/inferior imaginary line (72) bisects the anterior surface in the superior/inferior direction, such that the centre of the centre spike is located on the superior/inferior imaginary line, and the centre spike is longer than the peripheral spikes. Drill guide holes extend through the patella drill guide and trial instrument from the posterior trial bearing surface to the anterior surface.
