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

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

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.

Development of Proprioception After Shoulder Arthroplasty 609

Fig. 3. The reversed shoulder arthroplasty (REVERSE) group graphically showed an improvement of the AAR at 30° of flexion and 30° of abduction. However, there is a deterioration for the other movements. The total proprioception performance (total)

Movement Mean [°] SD [°] Mean [°] SD [°]

30° of flexion 7.4 4.1 8.2 4.3 0.669 60° of flexion 4.8 2.7 8.4 8.7 0.211 30° of abduction 9.5 5.7 8.5 3.1 0.562 60° of abduction 6.1 4.1 7.8 4.5 0.144 30° of external rotation 5.7 5.4 11.2 10.1 0.065 30° of internal rotation 7.9 5.7 17.6 21.1 **0.039**  Total 6.9 3.4 10.3 5.2 **0.018**  *TSA* total shoulder arthroplasty, *Hemi* hemiarthroplasty, *REVERSE* reversed arthroplasty, *SD* standard

Table 1. Active angle reproduction test (AAR) in all groups (TSA, HEMI and REVERSE)

**Preoperatively Three years** 

**postoperatively** P value

deteriorated by trend from 8.1° [SD 4.8] to 9.9° [SD 1.8].

before operation and three years thereafter

deviation;

3.1] to 8.6° [SD 1.4] (fig. 2), in the HEMI subgroup from 6.1° [SD 2.1] to 12.4° [SD 8.3] (fig. 1) and in the reversed subgroup from 8.1° [SD 4.8] to 9.9° [SD 1.8] (fig. 3).

Although there are different underlying concepts and biomechanics between the TSA, HEMI and REVERSE group, the results were included in a combined analysis to get a general impression of the intervention of implantation of an arthroplasty: in all groups three years after shoulder arthroplasty the total proprioception performance (total) measured by the AAR deteriorated significantly (from 6.9° [SD 3.4] to 10.3° [SD 5.2]; p=0.018) (table 1). The internal rotation deteriorated significantly from 7.9° [SD 5.7] to 17.6° [SD 21.1] (p=0.039) (table 2). The comparison between the controls (NORM) and the three years postoperative values of all arthroplasty groups (TSA, HEMI and REVERSE) reveals a significant worse AAR in the arthroplasty group three years after shoulder arthroplasty (10.3° [SD 5.2] vs. 7.8° [SD 2.3]; p=0.030) (fig. 4).

Fig. 2. The comparison pre- to postoperative values after implantation of a total shoulder arthroplasty (TSA) showed no significant differences between pre- and postoperative AAR. By trend, there is a deterioration of proprioception three years after surgery. The total proprioception performance (total) deteriorated by trend from 7.1° [SD 3.1] to 8.6° [SD 1.4].

3.1] to 8.6° [SD 1.4] (fig. 2), in the HEMI subgroup from 6.1° [SD 2.1] to 12.4° [SD 8.3] (fig. 1)

Although there are different underlying concepts and biomechanics between the TSA, HEMI and REVERSE group, the results were included in a combined analysis to get a general impression of the intervention of implantation of an arthroplasty: in all groups three years after shoulder arthroplasty the total proprioception performance (total) measured by the AAR deteriorated significantly (from 6.9° [SD 3.4] to 10.3° [SD 5.2]; p=0.018) (table 1). The internal rotation deteriorated significantly from 7.9° [SD 5.7] to 17.6° [SD 21.1] (p=0.039) (table 2). The comparison between the controls (NORM) and the three years postoperative values of all arthroplasty groups (TSA, HEMI and REVERSE) reveals a significant worse AAR in the arthroplasty group three years after shoulder arthroplasty (10.3° [SD 5.2] vs. 7.8°

Fig. 2. The comparison pre- to postoperative values after implantation of a total shoulder arthroplasty (TSA) showed no significant differences between pre- and postoperative AAR. By trend, there is a deterioration of proprioception three years after surgery. The total proprioception performance (total) deteriorated by trend from 7.1° [SD 3.1] to 8.6° [SD 1.4].

and in the reversed subgroup from 8.1° [SD 4.8] to 9.9° [SD 1.8] (fig. 3).

[SD 2.3]; p=0.030) (fig. 4).

Fig. 3. The reversed shoulder arthroplasty (REVERSE) group graphically showed an improvement of the AAR at 30° of flexion and 30° of abduction. However, there is a deterioration for the other movements. The total proprioception performance (total) deteriorated by trend from 8.1° [SD 4.8] to 9.9° [SD 1.8].


*TSA* total shoulder arthroplasty, *Hemi* hemiarthroplasty, *REVERSE* reversed arthroplasty, *SD* standard deviation;

Table 1. Active angle reproduction test (AAR) in all groups (TSA, HEMI and REVERSE) before operation and three years thereafter

Development of Proprioception After Shoulder Arthroplasty 611

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

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,

The AAR has been used to assess shoulder proprioception before, for example, in shoulder instability. Pötzl and colleagues examined the proprioceptive capabilities of 14 patients with recurrent anterior shoulder instability preoperatively and at least five years postoperatively using the AAR test [20]. In their series the joint position sense improved significantly in abduction, flexion, and rotation (p<0.05). They concluded that five years after surgical restoration of shoulder instability the joint position sense improved significantly to the same level as normal healthy shoulders. Having these results in mind we have to ask why proprioception measured with a comparable AAR deteriorates after shoulder arthroplasty,

**10. Possible reasons why proprioception deteriorates after shoulder** 

In shoulder arthroplasty, the operative approach for implantation of a TSA and hemiarthroplasty includes the cutting (and subsequent repair) of the subscapularis muscle and usually release of all glenohumeral ligaments. In cuff tear arthropathy the subscapularis is damaged from the beginning or released during surgery in our technique. However, these structures contain afferent and efferent structures important for proprioception. Therefore, concerning the influence on proprioceptive structures, the surgical procedures for shoulder instability and shoulder replacement are distinct. Since the approach in TSA and hemiarthroplasty is identical, a comparison seems to be valid. The different approach and the lack of the rotator cuff in cuff tear arthropathy limits a direct comparison with the other groups. However, the aim of this study was not the comparison of different types of implants that were implanted for different indications. The aim of this study was to assess proprioception changes three years after shoulder arthroplasty within the three groups. What we observed in our study is that nociceptors may also play an important role. During the repeat postoperative measurement, the patients mentioned that they were lacking the information input of pain sensation that they had usually during motion of the arm before

course of three years after shoulder arthroplasty. How can we explain that?

and the muscle strength that is necessary to reassume the position.

**9. Proprioception in shoulder instability** 

whereas it improves after surgery of shoulder instability?

**arthroplasty** 

Fig. 4. The comparison between the controls and the three years postoperative values of all arthroplasty groups (TSA, HEMI and REVERSE) shows significantly better total proprioception performance (total) in the control (NORM) than in the arthroplasty group (10.3° [SD 5.2] vs. 7.8° [SD 2.3]; p=0.030).
