Shoulder Arthroplasty

The latter have to be congruent and provide low friction conditions between them to allow for unimpeded range of motion, yet at the same time, along with the soft tissues surrounding the joint, which have to be respected during closure, provide stability to the prosthetic joint. There are essentially three variants of shoulder arthroplasty:  the hemiarthroplasty (HA), where only the articular surface of the humeral head is replaced with a prosthetic one, the anatomic total shoulder arthroplasty (TSA), where both the glenoid and the humeral head articular surfaces are replaced with prostheses of similar curvature, and, finally, the reverse shoulder arthroplasty (RSA), where both articular surfaces are replaced with reverse curvature prostheses.  

The choice between the aforementioned prosthesis types depends mostly on the biologic age of the patient, the condition of the rotator cuff muscles and the integrity of their tendons as well as the precise indication for shoulder arthroplasty. Anatomic shoulder arthroplasty is generally indicated for primary and secondary forms of shoulder osteoarthritis provided there is sufficient glenoid bone stock, the rotator cuff and the deltoid muscles are intact and functional, the brachial plexus (the major nerve plexus supplying the upper limb) is fully functional, and there is no superior migration of the humeral head indicating the presence of rotator cuff arthropathy and no evidence of active infection. Shoulder hemiarthroplasty, on the other hand, is indicated in cases of primary arthritis where the rotator cuff is deficient, or the glenoid bone stock is inadequate, or in younger patients and active laborers, due to the increases risk of glenoid component loosening in these age groups. It is also indicated in select patients with rotator cuff arthropathy, in osteonecrosis of the humeral head without glenoid involvement, and in some three-part, most four-part and almost all head-splitting proximal humeral fractures in patients younger than 65 – 70 years old. Finally, the reverse prothesis is indicated in older patients with rotator cuff arthropathy, in shoulder osteoarthritis with a concomitant, irreparable rotator cuff tear, in three or four – part and head-splitting proximal humerus fractures in patients older than 70 years or when severe osteopenia is present, in rheumatoid arthritis of the shoulder provided there is sufficient glenoid bone stock, and, finally, after a failed hemiarthroplasty or anatomic shoulder arthroplasty. Of note, for a reverse shoulder arthroplasty to be successful, it is imperative that the deltoid muscle is intact and functional. 

Shoulder arthroplasty is most commonly performed under general anesthesia with the occasional addition of regional nerve blocks (interscalene or supraclavicular) for postoperative pain management. In select cases, however, where the procedure is strongly indicated although the patient may not be fit for general anesthetic, regional anesthesia techniques can be implemented to perform the surgery. During the operation, the patient is placed in a reclined seated (beach-chair) position and the surgical field is appropriately sterilized and draped. All three variants of shoulder arthroplasty have been classically performed through the deltopectoral approach with an incision beginning below the acromion and extending distally, parallel to and lateral to the axillary fold, following the crease between the deltoid and the pectoralis major muscle. The joint is accessed by detaching the insertion of the subscapularis muscle and opening the underlying joint capsule or, in cases of fractures, by following the fracture fragments and the attached rotator cuff tendons to the joint.  However, there is the alternative of the anterosuperior approach, whereby the joint is entered by detaching the anterior edge of the deltoid muscle and, thus, preserving the subscapularis and the rest of the anterior structures. In any case, the next step is to perform a cut (osteotomy) at the level of the anatomical neck of the humerus, unless this has already been created by the fracture itself. If a hemiarthroplasty is to be performed, then only the humerus needs to be prepared to receive a, cementless or cemented, prosthesis comprised of a stem and a prosthetic head. For the anatomic and the reverse prostheses, however, the glenoid surface must also be prepared to receive, respectively, either a cemented, all polyethylene, concave prosthesis or a cementless baseplate supported by a central peg and additional screws upon which is fixed a convex glenosphere. The humeral prosthesis in the anatomic variant is similar to that of the hemiarthroplasty, whereas in the reverse variant it is comprised of humeral stem and a concave surface on top to articulate with the glenosphere. Following prosthesis placement, non-absorbable sutures are used to repair the previously disrupted subscapularis tendon insertion or to affix the tendon-bearing fracture fragments to the humerus and the humeral stem in fracture cases. The rest of the closure is performed in a standard, layered fashion, usually without the need of a drain, while a bulky, soft dressing is applied in the end. Finally, the arm placed in a shoulder immobilizer before the patient leaves the operating theater.  

The major limiting factors of postoperative rehabilitation after shoulder arthroplasty are the presence of a fracture, which would invariably require six to eight weeks of protected passive mobilization until it heals, and a repair of the subscapularis tendon, which may have been detached as part of the surgical approach and would thus require active internal rotation and passive external rotation of the shoulder to be avoided for six weeks. Pushing out of a chair while seated is expressly prohibited during the first six weeks postoperatively. In any other case, a sling is used for comfort for three weeks at which time it is usually discontinued. After the initial period of immobilization, during which only mild scapula mobilization exercises are permitted along with elbow, forearm and hand-wrist exercises, active-assisted and passive shoulder motion is begun. After adequate healing of soft tissues and bony fragments is achieved, more rigorous active motion of the shoulder as well as progressive strengthening exercises are initiated. Patients should expect to regain full use of their arm for activities of daily living at approximately two to three months, while heavy laborers may expect to return to work at four to six months postoperatively. 

As far as complications are concerned, these can be categorized, firstly, to universal, applying to all three types of shoulder arthroplasty, which may include infection, deep venous thrombosis, injury to nearby nerves and blood vessels, joint stiffness and reduced motion, aseptic loosening of the humeral component, failure of the subscapularis repair with subsequent anterior dislocation/instability, malunion or non-union of the tuberosities and periprosthetic fracture (intraoperative or postoperative). Secondly, there are complications specific to each type of arthroplasty, i.e. glenoid component loosening for TSA, glenoid loosening, scapular notching or insufficiency fractures of the acromion for RSA and anterosuperior escape for HA. Though the list may seem long, most of these complications are considered uncommon, while multiple measures are taken to avoid their occurrence or ensure their timely diagnosis and management at every step of the procedure and the follow-up period.  

To summarize, shoulder arthroplasty is a surgical technique which can be applied for the treatment of various shoulder pathologies ranging from fractures to advanced rotator cuff insufficiency and shoulder arthritis. Depending on the indication, it can take the form of a shoulder hemiarthroplasty, an anatomic total arthroplasty or a reverse total arthroplasty. Its success is also largely dependent on the indication for which it is performed, which is why patient selection plays an important role in optimizing long-term outcomes. That being said, shoulder arthroplasty can reliably provide pain relief and improve daily function in a variety of patients.