Stemless Hemiarthroplasty of the Shoulder Using the SMR® System: Summary of Six-Year Experience and Surgical Technique.

PURPOSE OF THE STUDY In the last number of years, the anatomic hemiarthoplasty has gradually been pushed out of clinical practice by modern reverse shoulder arthroplasty (RSA) designs. This is due to the clear excellent functional results of RSAs in a wide spectrum of indication criteria. Nevertheless, RSAs have several possible complications that cannot occur in an anatomic hemiarthroplasty. In anatomic hemiarthoplasty, the importance of correct indication criteria and observing correct operative technique including soft tissue reconstruction is much more important than in RSA. Furthermore, there is a clear recent trend of increased use of humeral components fixed only in the proximal metaphyseal cancellous bone. Our aim was to summarise our six-year experience with the SMR® Stemless (LimaCorporate, Italy) system which is one of the most modern ones. MATERIAL AND METHODS Twenty cases of SMR® Stemless anatomic shoulder hemiarthroplasty performed between 2016 and 2021 were included in the study. All patients were followed up prospectively. The function was evaluated preoperatively and at the last follow-up. We evaluated the range of active elevation, classic Constant Score (CS) and pain level according to the visual analogue scale (VAS). Statistical evaluation was performed by using basic statistical methods and the statistical significance of the results was assessed with a paired t-test. Level of statistical significance was set at p= 0.01. RESULTS The mean follow-up in our cohort was 3.01 years (range 0.32-5.69, Median 2.82, SD 1.56) All cases were indicated for surgery due to primary osteoarthritis with a limitation of movement and pain. The mean postoperative CS was 85.7 (range 70-96, Median 86, SD 6.83). The mean active elevation postoperatively was 143° (range 100-170°, Median 150°, SD 20.76). Mean postoperative pain according to VAS was 1.05 (range 0-4, Median 1, SD 1.02). The mean preoperative elevation was 60.5° (range 30-100°, Median 65°, SD 18.83). After surgery the mean elevation increased to 143° (range 100-170°, Median 150°, SD 20.76). Statistical evaluation showed a statistically significant increase in the CS (41.7 preoperatively to 85.7 postoperatively), range of active elevation (60.5° preoperatively to 143° postoperatively) and a statistically significant decrease in pain (VAS 6.95 preoperatively to 1.05 postoperatively). We observed no cases of failure or loosening of the implant. A statistically significant increase in post-operative range of motion was demonstrated. DISCUSSION Most modern shoulder arthroplasty designs now include implants allowing for proximal humerus metaphyseal fixation in hemiarthroplasty and even RSA designs. The advantage of metaphyseal fixation without the use of a longer stem is clear. Notably, treatment of periprosthetic humeral fractures is simpler, extraction of the implant for any reason is easier and the preoperative anatomic position of the humeral head can be respected. As with any anatomic shoulder arthroplasty, the functional result is dependent on correct indication criteria, precise surgical technique, correct humeral head position and soft tissue reconstruction - primarily the rotator cuff. CONCLUSIONS Between 2016 and 2021, we performed 20 SMR® stemless shoulder hemiarthroplasties for primary osteoarthritis. The mean follow up was 3 years. The shoulder function improved significantly post-operatively in all patients. There were no cases of implant loosening or failure. Radiographic evaluation showed no implant loosening or change in implant position in the humeral metaphysis. Key words: shoulder joint replacement, reverse shoulder arthroplasty, SMR, stemless, total shoulder arthroplasty, shoulder hemiarthroplasty, EPOCA, wear.