An instrument for use in resecting a portion of a greater tubercle of a humerus in shoulder arthroplasty includes a guide support having a first end which can be coupled to the humerus. The guide support extends laterally and over the greater tubercle. The instrument also includes a cutting guide movably coupled to the guide support. The cutting guide including curved frame for abutting the humerus. The guide support extends at an angle between about 30° and about 60° from the longitudinal axis which is defined by the humerus.
