**2. Shoulder proprioception**

In 1906, Charles Scott Sherrington published his work about proprioception [26]. He defined the term proprioception as the awareness of movement derived from muscular, tendon, and articular sources. Since then physiologists and anatomists are searching for specialized nerve endings that transmit data on joint capsule and muscle tension [11, 30]. It is known that joint proprioception plays a considerable role in stabilization of the normal healthy

Development of Proprioception After Shoulder Arthroplasty 605

For the measurement, the patients were prepared with four markers placed on the trunk as recommended by the International Society of Biomechanics [31]. Four markers were placed on each forearm: one at the radial and one at the ulnar styloid process of the wrist and two, connected with a wand, on the ulna close to the elbow joint. One marker was placed laterally on the upper arm and one on the acromion. After a static trial, the patient was asked to perform isolated movements of elbow flexion/ extension, shoulder flexion/ extension and shoulder abduction/ adduction to determine the shoulder joint position and the location of the elbow joint axis. Specifically, in these shoulder calibration trials the sternoclavicular joint was treated as a cardan joint. Technical coordinate systems for the ulna/ forearm, humerus, clavicle, and thorax were not deduced by optimization methods as was done for marker clusters [3]. Instead, they were based directly on marker trajectories, i.e. the direction vectors between them, using cross-products as reviewed by Chiari et al. [4]. The technical coordinate system of the clavicle was based on the four thorax markers and the shoulder marker. This coordinate system was used only for dynamic calibration movements, which were limited to a range of shoulder motion of 0-40° flexion and abduction to assume constant glenohumeral movement and exclude skin motion artefacts. Constraint least squares optimization according to Gamage et al. was then used for joint

The anatomical co-ordinate system for the ulna/ forearm, humerus, and thorax were based on the technical coordinate systems of these segments and on the joint axes and joint centers previously determined. A static trial was used to define the neutral position of the thorax. Angles of flexion and abduction were expressed as projection angles relative to the proximal anatomical coordinate system, while internal/ external rotation was defined according to the globe convention [8]. Elbow flexion was defined as the projected angle to the elbow axis. Custom software written in Java (Sun Mircosystems, USA) was used to calculate each joint

The system and biomechanical model was validated with the manual goniometer and intraclass correlation coefficients of 0.989 for intrasubject variability, 0.996 for intersubject variability, and 0.998 for intertester variability were found [22]. Differences of more than 10°

As described before [12, 16], our study group used an active angle reproduction test to measure proprioception: Test person sat on a chair with the arm hanging in 0° abduction and rotation. They were blindfolded to eliminate visual clues and wore sleeveless shirts. We ensured that the arm did not touch the trunk and, consequently, skin contact was minimized. The arm was moved to the desired position by the examiner with visual control of a manual handheld goniometer. In detail, the positions were 30° and 60° abduction, 30° and 60° flexion, and 30° external (and afterwards 30° internal rotation) in 30° abduction (total six joint positions). In the target position the subjects were told to maintain the position for ten seconds, and then the initial position with the arm hanging was resumed. Afterwards, the subject was asked to move the arm back into the target position and the mean value of the joint position was measured. Standardized instructions were given to all subjects, and a test trial was conducted to acquaint them with each test condition. All tests were randomized for side and movement. Two test trials were performed at each angle, and the mean value was used for further analysis. The total proprioception performance (total)

between the two methods were found for shoulder flexion of more than 160° [22, 23].

centre determination [9].

angle in each trial of the angle-reproduction tasks.

**4.2 Active angle reproduction test** 

shoulder by helping to control muscular action [1]. However, there is little data available about proprioception of the replaced shoulder before and after surgery [6, 12, 16]. Parameters routinely examined in previous studies include pain, satisfaction, range of motion, and strength [5].
