Stemless shoulder arthroplasty systems with uncemented metaphyseal fixation have been used in Europe for glenohumeral osteoarthritis since 2004. The stemless design has several theoretical advantages compared with the stemmed shoulder arthroplasty systems: restoring patients' anatomy, preserving humeral bone stock, and few complications in component removal if the need for a revision arthroplasty arises. The purpose of the study is to compare the short-term, patient-reported outcome of stemless and stemmed total shoulder arthroplasty.

Glenohumeral joint osteoarthritis is a common cause of shoulder pain, affecting up to one-third of patients older than 60 years. Surgical treatment is indicated for patients with glenohumeral arthritis who continue to experience significant symptoms despite an appropriate course of non-operative management. Shoulder arthroplasty accounts for the third most common joint replacement procedure after the hip and knee arthroplasty. Based on data from the National Patient Registry, The Statistical Department of the Danish National Board of Health, the use of primary shoulder replacement in Denmark increased from 12 replacements per 100,000 inhabitants in 2005 to 19 replacements per 100,000 inhabitants in 2015. Glenohumeral osteoarthritis is now the most common indication for shoulder arthroplasty in Denmark.

Many different shoulder arthroplasty designs are available on the market. The stemless shoulder arthroplasty system with uncemented metaphyseal fixation has been used in Europe for glenohumeral osteoarthritis since 2004. The indications for anatomical stemless TSA are the same as for anatomical stemmed TSA: osteoarthritis, rheumatoid arthritis, and post-traumatic osteoarthritis or osteonecrosis.

The contraindications for anatomical stemless TSA are acute proximal humerus fracture, inadequate metaphyseal bone stock, and rotator cuff insufficiency.

Stemless TSA has several theoretical advantages over stemmed TSA: restoring patients' anatomy (humeral shaft angle, humeral head diameter, and lateralization); preserving humeral bone stock, and few complications in component removal should the need of a revision arthroplasty arise. A recent review of 3,360 anatomical total shoulder arthroplasties found an overall complication rate of 10.3%. Periprosthetic fractures accounted for 6.7% and humeral component loosening for 1.4% of all complications. Complications related to the stemmed humeral component can be divided into intraoperative (malpositioning, false route, periprosthetic fracture) and postoperative (loosening, migration, disassembly, periprosthetic fracture, stem fracture) complications. When a revision is necessary because of infection or periprosthetic fracture, the removal of a well-fixed or cemented humeral component can be challenging and lead to bone damage.

Few outcome studies on stemless TSA are available. A recent review of 11 observational studies (published 2010-2016), incorporating a total of 929 patients, reported comparable short- and midterm functional outcomes between stemmed and stemless shoulder prosthesis. Otherwise, there are few well-conducted and adequately powered clinical studies.

The objective of this study is to increase knowledge about shoulder function after operation with anatomical TSA by comparing the patient-reported outcome after stemmed and stemless anatomical TSA for glenohumeral osteoarthritis.

Inclusion Criteria:

1. Patients aged ≥ 18 years.
2. Patients have been referred to the Orthopedic Department or Zealand University Hospital, Koege or Hvidovre University Hospital for shoulder pain during the study period.
3. Patients have the ability to read trial information in Danish and give informed consent.
4. The diagnosis will be based on plain radiographs (at least two perpendicular views), reduction of joint space, and/or osteophyte formation.
5. Clinical presentation with pain at night and/or daily pain, pain in overhead activity, and consumption of pain medication.

Exclusion Criteria:

1. Previous shoulder surgery that involves the humeral head and/or the glenoid cavity.
2. Patients with alcohol or drug abuse problems that can compromise rehabilitation and follow-up appointments as assessed by the recruiting surgeon at the first visit.
3. Patients unable to understand instructions in Danish, follow the rehabilitation protocol, or answer the questionnaires because of physical or cognitive inabilities as evaluated by the recruiting surgeon at the first visit.
4. Brachial plexus palsy.
5. Patients with previous fractures around the shoulder (clavicle, scapula, and proximal humerus fractures).
6. Patients with MRI scan-verified full thickness total tear of one or more of the rotator cuff tendons.
7. Patients with CT scan-verified glenoid retroversion ≥ 20° that does not allow glenoid component fixation without bone graft or need an augmented glenoid component.

Patients will be blinded to which implant type they are receive. This will be done by not sharing the operation chart files with the patient's online file records; the inserted shoulder prosthesis will be noted by a unique code in operation file, and the radiologist will be asked not to describe the post-operation x-ray controls.

The primary investigator will conduct the blinded statistical analysis supervised by the biostatistician.