An adjustable trial prosthesis or prosthetic component provides a surgeon with the capability of efficiently and accurately examining a joint's functioning without having to remove a trial prosthesis insert and replace it with another sterilized insert. The adjustable trial has a first surface that approximates the top surface of the corresponding permanent prosthesis and a second surface that engages a bone. A distance adjustment mechanism can alter the distance between the first and second surfaces. The distance adjustment mechanism can include a screw oriented generally between the two surfaces or other distance adjustment mechanisms such as a fluid filled bladder. The adjustable trial can include force transducers to provide information on forces within the joint. To assist a surgeon with the alignment of portions of the musculo-skeletal system, a line of strong light is provided. The light source can be a laser or other suitable light source which is combined with appropriate optics. A balancing apparatus can be used to assess relative tensions on peri-articular soft tissue structures. The balance has a support that is adapted for rigid attachment directly or indirectly to a bone.