An adjustable spacer instrument, kit of parts and surgical methods of use in a knee arthroplasty procedure are described. The adjustable spacer comprises a first member having a substantially planar upper surface and a second member having a substantially planar lower surface. An angular adjustment mechanism is interposed between the first member and the second member, and is operable to adjust the degree of tilt between the upper surface and the lower surface. A releasable lock is provided which can maintain the degree of tilt. The spacer instrument can be used with the knee in extension or flexion to allow various cuts or re-cuts to be made to the tibia or femur while the ligaments are in balance or to balance the ligaments.
