An anti-backout stylus comprising a stylus and a locking stylus holder. The locking stylus holder engages the stylus at a series of discrete positions during insertion of the stylus into the holder. The locking stylus holder prevents inadvertent backing out of the stylus by preventing the stylus from being withdrawn to a previous one of the discrete positions. The locking stylus holder can preferably be selectively disengaged from the stylus to allow for selective withdrawal of the stylus. Each engagement of one of the discrete positions by the locking stylus holder preferably indicates a femoral size. The discrete positions are preferably defined by detents formed on the stylus and a stop member on the locking stylus holder. The locking stylus holder can be provided on an anterior rough cut guide, with the anterior rough cut guide preferably mountable on an intramedullary rod.