A surgical instrument (20) is described which comprises an alignment guide (50) having a first part (54) including a distal end and a second part (56) having a proximal end. The first part is attached to the second part by a pivot mechanism (60) so that the first part can be tilted relative to the second part. A brace (30) is attached toward the proximal end of the alignment guide for attaching the instrument to a limb of a patient. A component (40) is attached toward the distal end of the alignment guide. The pivot mechanism is configured so that tilting the first part does not substantially change the separation between the component and the brace.
