Shoulder arthroplasty marked by changes

Due to its complexity and other factors, the procedure should be limited to shoulder surgery centers.

Issue: Issue 3 2003

ByHans Jürgen Refior, MD

Hans Jurgen Refior, MD --- Hans Jürgen Refior, MD

Today, orthopaedic surgeons perform total shoulder arthroplasty in high frequency. According to manufacturers’ reports, the greatest number of shoulder prostheses is sold in the United States; however, a high number of shoulder prostheses are implanted each year in Europe, especially in France. The number of such operations is increasing in Germany.

Convincing scientific results as well as promising clinical outcomes following shoulder arthroplasty helped to overcome surgeons’ reluctance about this kind of surgery. In Germany, Zippl and Engelbrecht started performing shoulder arthroplasty about the same time Neer did in the United States. Even if the basic science associated with the biomechanics of shoulder arthroplasty has a long history in Germany, it has only been within the last few years that the frequency of shoulder arthroplasty has risen in Germany.

Early temptations to replace both the humeral head and glenoid surface resulted in loosening of the glenoid implant. As a result, surgeons preferred hemiarthroplasty to total shoulder arthroplasty. But clinical results following shoulder hemiarthroplasty were insufficient initially. At the beginning of the 1990s, orthopaedic surgeons were advised to use shoulder prostheses only in patients with extended and painful loss of function of the shoulder.

Wrong indications, low numbers of patients, lack of good surgical technique among single surgeons and insufficient implant design prevented widespread acceptance of shoulder arthroplasty in Germany.

Attitudes changed

Following intensification of shoulder arthroplasty in the United States and France, surgeons’ attitude toward shoulder arthroplasty also changed positively in Germany. Improved clinical outcomes fostered a growing interest in shoulder replacement. Based on the success of the Neer II prosthesis, a number of manufacturers replaced monoblock prostheses with modular prostheses. These modular prostheses are now recognized as second-generation implants.

A decade ago, modular shoulder prostheses became standard implants in the United States. Even today (eg, Norris and Ianotti, 2002), the second-generation modular prostheses are still in common use, as reported at this year’s American Academy of Orthopaedic Surgeons meeting in New Orleans.

Although there is broad agreement in Europe and United States concerning indications for shoulder arthroplasty, French surgeons tried to improve the established modular concept based on anatomic studies. As a result of this endeavor, orthopaedic surgeons Walch and Boileau improved the design and individual adaptation of the modular standard shoulder implant and helped introduce a third-generation humeral head prosthesis. Various medial and posterior offsets and different degrees of inclination, along with the adaptable size of the humeral head and possibility of retroversion, characterize these prostheses.

This threefold modular concept of Walch and Boileau is fully adaptable to the individual anatomic situation. Ultimately, the original center of rotation, physiologic kinematics and stability of the joint are recovered. At the same time, increased tension of the rotator cuff can be prevented.

A number of clinical studies verified the positive impressions given by Walch and Boileau. More and more manufacturers developed new implants regarding the aforementioned features. In the German-speaking countries, Gerber, Hertel, Habermeyer and Resch recently introduced new refinements in shoulder prostheses.

There is no reason why, until recently, surgeons in the United States predominantly used modular shoulder prostheses. Two working groups in the United States are promoting further development of anatomical-adapted

It seems that these new developments are attracting more attention in the United States.

It must also be mentioned that there are developments and modifications of shoulder prostheses facilitating advanced fracture treatment by correct positioning of the stem and an improved adaptation of the fractured tubercula. These kinds of prostheses increasingly replace the second-generation modular stem prostheses.

Prosthesis options

A broad variance of shoulder prostheses is offered for special pathologic conditions of the shoulder in Europe. In addition to the bipolar prosthesis (Duohead prosthesis) and the inverse shoulder arthroplasty developed by Grammont in 1986, there are the cup prostheses from Copeland and others.

The first two mentioned prostheses are commonly used for the treatment of rotator cuff tears and defect arthropathies. In contrast, the cup prosthesis is widely used to treat simple omarthritis, necrosis of the humeral head and rheumatoid arthritis cases.

Only recently have orthopaedists been able to solve the problem of a force-coupled total shoulder arthroplasty with the replacement. The implant is exposed to concentric and eccentric forces induced by both compression forces and shear forces. In addition, the anatomic preconditions for stable fixation of the glenoid implant are insufficient. Due to these reasons, implant developers must carefully regard the design and fixation of the glenoid.

Clinical studies of total shoulder replacement with conform glenoid replacement demonstrated that there arises a decreased range of motion and an increase in polyethylene debris, especially for asymmetric loading of the glenoid edge. In this context, the so-called “rocking-horse phenomenon” leads to implant loosening.

Newer glenoid components

Newer glenoid components are characterized by nontraditional design, allowing glenohumeral translation, reduced polyethylene debris and the avoidance of the aforementioned phenomenon. However, there is the disadvantage that the contact stress is increased leading to increased debris. Finally, a number of clinical researchers note decreased joint stability with the newer glenoid components.

Matsen has made demands for a suitable preparation in order to achieve optimal congruency of the bony glenoid and the implant to avoid loosening. Surgeons fix the glenoid implant using cement. Even if the Neer system of triangular keeled design is common, the replacement with pegged glenoid, which is also in clinical use, seems to be superior.

In reality, various factors influence clinical results. The damage of the glenoid bone stock during preparation, the technique of cementing and the direct influence of polymerizing cement must be considered in the development of radiolucent lines and loosening of the glenoid.

However, cementless implants are not in widespread clinical use. The pathomechanical influences of stable fixation on a metal-polyethylene combination negatively impact the clinical outcome.

Unresolved matters

There are a number of problems not yet solved in shoulder arthroplasty. However, patients regularly gain an increased quality of life following these operations.

Orthopaedic surgeons can only attain good, permanent results if the indication is critically and competently considered, if the implant is carefully selected based on shoulder pathology and the surgeon is experienced. Considering all of these facts, it is reasonable to assert that these patients should only be treated in shoulder surgery centers.

For your information:
Hans Jürgen Refior, MD, is chairman of the department of orthopaedics at the University of Munich. He is chairman of the Orthopaedics Today Editorial Advisory Board for 2002.