**4. Measurement of proprioception**

Because proprioception is a complex system that relies on central integration of various afferent and efferent elements, it is difficult to measure proprioceptive performance. Up to now, there is no consensus on how proprioception should be measured because the different components of proprioception are difficult to examine at the same time. For clinical purposes, most authors differentiate between static proprioception and dynamic proprioception [21]. Static proprioception is usually defined as the position sense, what means conscious perception of the orientation of different parts of the body with respect to another. Dynamic proprioception is defined as kinesthesia and the sense of rates of movement [11].

### **4.1 Joint angle analysis with the Heidelberg Upper Extremity Model (HUX)**

In our studies [12, 16], we used the Heidelberg Upper Extremity Model (HUX) to measure joint angles as described before [23]: Therefore a twelve-camera motion analysis system (Vicon 612; Vicon, Lake Forest, USA) working at 120 Hz was used to monitor the patients' movements. The spatial resolution of the system was approximately 1 mm. The underlying model consisted of seven segments: thorax, clavicles, upper arms, and forearms. The sternoclavicular joint and the glenohumeral joint were treated as a ball-and-socket joint, whereas the elbow was treated as a hinge joint. Translational degrees of freedom were not considered in any of these joints.

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

By reason that the shoulder joint is balanced and centered by the rotator cuff and the glenohumeral ligaments, it can be postulated that proprioception plays an important role in the postoperative outcome and rehabilitation. However, to date there are only three studies analyzing proprioception after shoulder replacement [6, 12, 16]. Two of these studies [6, 12] have a short follow-up period, in both cases six months. Cuomo et al. [6] performed a passive and guided angle-reproduction test in 20 patients with shoulder osteoarthritis before and six months after total shoulder arthroplasty (TSA) with only one degree of freedom at a time and reported improvement of proprioception [6]. Kasten et al. [12] found out, six months after shoulder arthroplasty, proprioception remained unchanged or deteriorated, as assessed by an active and unlimited angle-reproduction test with 3D motion analysis [12]. It was assumed that this finding was most likely attributable to the relatively short rehabilitation period of six months. Therefore, the purpose of the third study by Maier et al. [16] was to examine the patients from the study described by Kasten et al. [12, 14] again three years postoperatively to find out whether proprioception changes after a longer rehabilitation period of three years. In the present study, the same active and unlimited angle-reproduction test with 3D motion analysis was used as described before [12]. The present study firstly describes the results of proprioception development in a cohort of

different shoulder arthroplasties, including patients with reverse prosthesis.

**4.1 Joint angle analysis with the Heidelberg Upper Extremity Model (HUX)** 

Because proprioception is a complex system that relies on central integration of various afferent and efferent elements, it is difficult to measure proprioceptive performance. Up to now, there is no consensus on how proprioception should be measured because the different components of proprioception are difficult to examine at the same time. For clinical purposes, most authors differentiate between static proprioception and dynamic proprioception [21]. Static proprioception is usually defined as the position sense, what means conscious perception of the orientation of different parts of the body with respect to another. Dynamic proprioception is defined as kinesthesia and the sense of rates of

In our studies [12, 16], we used the Heidelberg Upper Extremity Model (HUX) to measure joint angles as described before [23]: Therefore a twelve-camera motion analysis system (Vicon 612; Vicon, Lake Forest, USA) working at 120 Hz was used to monitor the patients' movements. The spatial resolution of the system was approximately 1 mm. The underlying model consisted of seven segments: thorax, clavicles, upper arms, and forearms. The sternoclavicular joint and the glenohumeral joint were treated as a ball-and-socket joint, whereas the elbow was treated as a hinge joint. Translational degrees of freedom were not

motion, and strength [5].

**3. Proprioception after shoulder arthroplasty** 

**4. Measurement of proprioception** 

movement [11].

considered in any of these joints.

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 centre determination [9].

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 angle in each trial of the angle-reproduction tasks.

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

### **4.2 Active angle reproduction test**

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)

Development of Proprioception After Shoulder Arthroplasty 607

Shapiro-Wilk test, and the homogeneity of variance was assessed using the Levene test. The angle between the long axis of the humerus and the trunk position was determined. Differences in shoulder joint angles between target and reproducted position were compared between the pre- and postoperative examination with a Wilcoxon-test for the groups TSA, HEMI, and REVERSE. Afterwards as a second outcome measure differences

The hemioarthroplasty (HEMI) subgroup revealed significant lower AAR at 30° of external rotation before surgery with 3.1° [SD 3.5] as compared to three years after surgery 12.8° [SD 10.7]; (p=0.031) (fig. 1). By trend, in the TSA subgroup the AAR deteriorated from 7.1° [SD

among these groups and the controls were examined by a Mann-Whitney *U* test.

**7. Results of proprioception measurement three years after shoulder** 

Fig. 1. The hemioarthroplasty (HEMI) group showed significant lower AAR at 30° of external rotation three years after surgery (3.1° [SD 3.5] vs. 12.8° [SD 10.7]; (p=0.031)). Otherwise there were no significances between pre- and postoperative AAR, although the total proprioception performance (total) almost reached significance (p=0.063). Graphically,

there is a deterioration in all movements.

**arthroplasty** 

was defined as the mean value of all single measurements (six joint positions) to have one quality to compare proprioceptive ability.
