**8. Discussion of our findings with the literature**

To our knowledge there are only three studies analyzing proprioception after shoulder arthroplasty [6, 12, 16]. Two are short-term studies with a six months follow-up [12, 16] and one is a middle-term follow up study [16]: Cuomo et al. [6] performed a prospective analysis of 20 consecutive patients with unilateral advanced glenohumeral arthritis who underwent total shoulder arthroplasty (TSA). Shoulder proprioception testing for passive position sense and detection of motion was performed one week before surgery and six months after TSA. Six months after TSA, position sense and the sensitivity of detection of motion were significantly improved (p<0.05) and did not differ significantly from the contralateral shoulder or the controls. Cuomo concluded that in patients with advanced glenohumeral arthritis after TSA there was a marked improvement in proprioception.

In our study group, Kasten et al. [12] assessed proprioception six months after shoulder arthroplasty by an *active* and unguided angle-reproduction test with 3D motion analysis. In contrast to Cuomo we found out that six months after surgery proprioception remained unchanged or deteriorated. Due to the fact that this is completely the different result as

Fig. 4. The comparison between the controls and the three years postoperative values of all

proprioception performance (total) in the control (NORM) than in the arthroplasty group

To our knowledge there are only three studies analyzing proprioception after shoulder arthroplasty [6, 12, 16]. Two are short-term studies with a six months follow-up [12, 16] and one is a middle-term follow up study [16]: Cuomo et al. [6] performed a prospective analysis of 20 consecutive patients with unilateral advanced glenohumeral arthritis who underwent total shoulder arthroplasty (TSA). Shoulder proprioception testing for passive position sense and detection of motion was performed one week before surgery and six months after TSA. Six months after TSA, position sense and the sensitivity of detection of motion were significantly improved (p<0.05) and did not differ significantly from the contralateral shoulder or the controls. Cuomo concluded that in patients with advanced glenohumeral

In our study group, Kasten et al. [12] assessed proprioception six months after shoulder arthroplasty by an *active* and unguided angle-reproduction test with 3D motion analysis. In contrast to Cuomo we found out that six months after surgery proprioception remained unchanged or deteriorated. Due to the fact that this is completely the different result as

arthroplasty groups (TSA, HEMI and REVERSE) shows significantly better total

arthritis after TSA there was a marked improvement in proprioception.

(10.3° [SD 5.2] vs. 7.8° [SD 2.3]; p=0.030).

**8. Discussion of our findings with the literature** 

Cuomo et. al., it was concluded, that this is either due to the different measurement methods (active versus passive) or the relatively short rehabilitation period of six months. Maybe an improvement would also be found in the mid-term follow-up. That's why we investigated the same patients three years after shoulder arthroplasty by the same active angle reproduction test to measure the development of proprioception [16]. The middl-term follow-up showed no improvement but rather a deterioration of proprioception over the course of three years after shoulder arthroplasty. How can we explain that?

Cuomo et al. used a hydraulic machine that passively moved the arm. The patient had to indicate when he or she noted movement ("detection of motion") and, in a separate approach, when he or she passively reassumed a joint position that was previously defined ("passive position sense"). Cuomo and colleagues thus measured two entities of proprioception separately. The outcome of the AAR test, used in our setting, can be influenced by some elements: The test person has to actively move the arm and is therefore not limited regarding the direction of movement. Consequently, a more comprehensive concept of proprioception is tested, comprising the elements of position sense, motion sense, and the muscle strength that is necessary to reassume the position.
