An orthopedic surgical instrument includes a keel punch, an adapter, and a guide tower. The adapter includes an elongate body and a radial locking pin. The guide tower includes a sidewall that defines a passageway configured to receive the keel punch and the adapter. The guide tower also includes one or more L-shaped slots in the sidewall. The adapter and the keel punch lock with each other when the adapter is rotated in a first direction and unlock when the adapter is rotated in a second direction. The locking pin and the L-shaped slot lock with each other when the adapter is rotated in the second direction and unlock when the adapter is rotated in the first direction. Hence, when the adapter is rotated in the second direction for disengaging from the keel punch the locking pin simultaneously engages the L-shaped slot and locks the guide tower to the adapter.