In a “typical” total shoulder arthroplasty, the head (“sphere”) and the glenoid cavity (“socket”) are replaced to mimic the normal anatomy and biomechanics of the glenohumeral joint. In particular, the head of the humerus is replaced by a metal implant made of cobalt, chromium or titanium alloys and mounted (either sealed or cemented) by means of the stem, imitating the anatomical head. The articular surface of the glenoid cavity is replaced by a plastic insert (polyethylene) that mimics the size, shape and anatomy of the normal glenoid cavity. This procedure is indicated for patients with severe osteoarthritis of the shoulder with normal function of their rotator cuff.
The “typical” total shoulder arthroplasty with the polyethylene insert for the glenoid cavity and the prosthesis of chromium/cobalt alloy for the humerus.
Reverse total shoulder arthroplasty is a newer prosthesis using a “non-anatomical” philosophy to replace a joint in those patients suffering from severe osteoarthritis and poor rotator cuff functionality. In addition, this type of prosthesis can be used to replace total arthroplasty after complications, such as loosening or infection or complicated fractures in elderly patients who cannot be treated with osteosynthesis, due to bone defect and poor residual bone quality.
Prostheses by various manufacturers are available according to the surgeon’s preferences. As depicted, the polyethylene is placed on the humerus’ side, while the “metallic sphere” on the glenoid cavity’s side.
HOW DOES THE REVERSE TOTAL SHOULDER ARTHROPLASTY WORK?
Reverse total shoulder arthroplasty was developed in the 1980s in France by Paul Grammont, and while successful in Europe, in the United States it could not be used until it was approved by the FDA in 2004.
In the normal shoulder, the rotator cuff muscles help to hold the humeral head in the glenoid cavity, providing a directional force to the center of the joint. This force compensates for the upward force exerted by the deltoid on the shoulder.
The rotator cuff muscles support shoulder lift and rotation. In patients with rotator cuff’s injury (e.g. mass rupture), the deltoid muscle pulls the head of the humerus upwards and out of the glenoid cavity, making the extremity impossible to lift. This pathological condition can lead to arthritic lesions with specific characteristics (“rotator cuff arthropathy”).
Typical anatomy of the rotator cuff: Subscapularis, supraspinatus, infraspinatus and teres minor. These muscles and their tendons keep the humeral head in the glenoid cavity.
In reversed total arthroplasty, the humeral head (sphere) is replaced with a hollow surface (polyethylene), while the glenoid cavity of the shoulder is replaced with a metallic sphere. This creates a firm grip so that the patient can use the deltoid to raise their hand without the help of the rotator cuff. The prosthesis is fixed in place with screws for the glenoid cavity and cement or with a press-fit for the humerus.
WHY THE “TYPICAL OR CLASSICAL” TOTAL ARTHROPLASTY IS NOT RECOMMENDED FOR SOME PATIENTS?
In some patients, the rotator cuff tendons have undergone massive rupture, which is irreparable mainly due to poor tissue quality or shrinkage and degeneration due to the chronicity of the injury. Often, irreparable damage to the rotator cuff occurs after chronic rupture and failure of surgical repair, or after a fracture or after total shoulder arthroplasty, and should be treated otherwise.
The X-ray depicts the dislocation of the prosthesis (humeral insertion) to the acromion (upwards) due to failure of the rotator cuff’s functionality. The purple dotted line indicates the anticipated center for the humeral head, while the red dotted line indicates the actual position of the humeral head.
A detailed medical history should be obtained after the decision to have surgery followed by an evaluation by a cardiologist and an anesthesiologist. Most often a CT or MRI scan is performed prior to surgery. Lastly, it is important to inform the surgeon about any skin infection, any feeling of shortness of breath or chest pain.
SURGICAL TREATMENT AND HOSPITALIZATION
Depending on each case and the surgeon’s preference, the patient undergoes topical anesthesia (nerve blocking) for further analgesia. The surgery is performed under general anesthesia and usually lasts for two hours, but may last longer if needed. This is especially true when it comes to replacement surgery after total arthroplasty failure (revision). However, the total surgery time is longer if the whole procedure is calculated (from anesthesia to resuscitation).
The patient is then hospitalized for about 2-3 days and is discharged, as the case may be. The recovery time is primarily determined by the surgeon and the physiotherapist. During hospitalization, powerful painkillers are administered intravenously and after hospital discharge orally. Some patients stop using the drug within the first week post-operatively.
Finally, some patients will require blood transfusions intraoperatively or postoperatively as appropriate.
After physiotherapy consultation, the patient begins an intensive physiotherapy program during the first 2 to 6 weeks after surgery. Initially, the patient begins with exercises to restore shoulder range of motion, while strengthening exercises begin after 8 weeks of surgery.
During the rehabilitation period, the patient visits the surgeon to assess the expected progress.
In addition, the patient should be aware that in the first few weeks after surgery he / she will not be able to self-serve and should be properly prepared, informing the family or friendly environment.
Finally, the patient should be monitored by his surgeon on an annual basis or at least every two years.
A large number of patients may have appropriate indications for reverse total shoulder arthroplasty. As mentioned above, the strongest indication is in patients over 70 years with severe osteoarthritis and rotator cuff insufficiency. Rarely, it can be used in younger patients but only as a “rescue” operation and only when there is no other therapeutic option to relieve pain and improve joint function.
Reverse arthroplasty is considered a “rescue” operation for young patients with high expectations and requirements, because of some significant limitations. In all patients, it is recommended not to use the operated limb in high-demanding activities, such as weightlifting, carpentry or contact sports. In general, patients should avoid vigorous activity with this limb, in order to avoid premature wear of the materials. Therefore, activity restriction ensures increased prosthesis longevity. However, activities such as golf seem to be tolerated quite well.
CONTRAINDICATIONS – WHO SHOULD NOT BE SUBMITTED TO REVERSE ARTHROPLASTY
A key prerequisite for a successful reverse total arthroplasty is a functional deltoid muscle. Patients with nerve damage (and especially the axillary nerve) or patients after previous surgery are not good candidates as muscle function is not guaranteed. In addition, patients with severe bone defect of the glenoid cavity are not good candidates for reversible arthroplasty as the bone may not be sufficient for a secure fixation of the glenoid insert (glenoid sphere). These are usually patients who have undergone previous surgery or cases of congenital hypoplasia or deformity of the shoulder.
Finally, patients with active infections are not candidates for any prosthetic replacement surgery. Only months later and after the infection is completely eliminated can the patient undergo arthroplasty.
A limited number of studies have shown that semi-arthroplasty can benefit the elderly patient with arthritis and dysfunctional rotator cuff or patients who have failed arthroplasty procedures. Semi-arthroplasty is intended for patients with low requirements and poor quality of glenoid cavity’s bone and in cases of failure of any other arthroplasty surgery.
The “final” alternative is resection arthroplasty, that is, removal of all inserts of the prosthesis without replacement, allowing the formation of scar tissue. This is a limb “rescue” operation and a solution to an emergency that is considered very rare.