Alternative glenoid resurfacing and management of glenoid deficiency

Issue: December 2004

ByAndrew Green, MD

Andrew Green, MD,
is chief of Shoulder and Elbow Surgery, Brown Medical School, Rhode Island Hospital, Providence.

Treatment of the glenoid in primary and revision shoulder arthroplasty remains challenging. From a technical standpoint, achieving adequate exposure and recreating normal anatomic parameters may be difficult. Although advanced glenohumeral arthritis is usually treated with total shoulder arthroplasty, alternative glenoid resurfacing options can be considered in some clinical situations. These include cases of young patients in whom there is concern about the longevity of a prosthetic glenoid component, patients with primary glenoid deficiency of either congenital or pathologic origin and patients with failed prosthetic glenoid implants. When considering alternative glenoid resurfacing and glenoid bone grafting, a surgeon should understand the background and principles of normal glenohumeral anatomy and kinematics and consider the rationale for the various surgical options.

Background and principles

When the hyalin articular cartilage surfaces of the humeral head and/or the glenoid are damaged, the smooth fluid motion can be compromised. The articular surface of the glenoid is approximately 25% to 30% of the surface area of the humeral head. Although the actual bony surface is relatively flat, the articular surface and labrum at the periphery increase the depth of the glenoid socket such that in a normal shoulder the humeral head and glenoid are concentric. The basic principles of glenoid resurfacing are to recreate normal glenoid architecture and glenohumeral relationships. A number of parameters including the contact area and conformity or mismatch of the glenohumeral joint, glenoid version, the glenoid center line, shape and size of the glenoid, and glenoid surface material must be considered.

Glenohumeral mismatch

Glenohumeral mismatch has been studied in vitro. Prosthetic glenohumeral radial mismatch of approximately 4 mm produces active translations similar to pre-arthroplasty in cadaver shoulders.¹ Additionally, humeral head translation during active joint positioning after prosthetic arthroplasty correlates with component conformity.² Glenohumeral mismatch in shoulder replacement provides the translation that is present in a normal shoulder. In addition, mismatch may serve to decrease edge loading of the glenoid replacement and may affect or improve glenoid longevity.

Glenoid version

Normal glenoid version has been shown to vary from approximately -8º to -2º. Retroversion is often increased in patients with glenohumeral osteoarthritis as some degree of posterior glenoid wear typically occurs in these patients. This is also a common finding in patients with capsulorraphy arthropathy. Glenoid version has traditionally been assessed with axillary lateral radiographs. Nyffeler and colleagues³ found that plain radiographs may overestimate the degree of posterior glenoid wear. Advanced imaging with computed tomography (CT) scan or magnetic resonance imaging is the best method for the assessing glenoid anatomy.

Glenoid center line

The glenoid center line is the line through the center of the glenoid that is perpendicular to the plane that is determined by a line extending from the anterior to the posterior edge of the glenoid rim (Figure). In a normal shoulder, this line passes through the center of rotation of the humeral head. Restablishing this relationship is critical to the restoration of glenohumeral stability and kinematics.

Figure

Calculation of the balance stability angle.

Adapted from Matsen F, Lippitt S. Shoulder Surgery: Principles and Procedures. Philadelphia:
Elsevier; 2004:499.

Balance stability angle

The balance stability angle is the angle determined by the glenoid center line and the line that extends from the humeral head center to the edge of the glenoid (Figure). When this angle is large there is greater glenohumeral stability. Similarly, when the glenoid is smaller due to deficiency or secondary to reaming, there is less stability and the resultant force required to dislocate the humeral head is less. This effect of glenoid size on glenohumeral stability is especially pertinent in the anterior and posterior directions. Thus, there may be a limit to the extent of medialization of the glenoid that can be accepted when reaming to correct for eccentric glenoid wear.

Glenoid offset

Glenoid offset refers to the distance from the base of the coracoid to the articular surface of the humeral head. Little variability of this anatomic parameter exists. The thickness of a prosthetic glenoid component can substantially influence the lateral humeral offset (ie, thicker or metal backed glenoids). Lateral humeral offset can affect deltoid and rotator cuff function.

Rationale

Charles Neer, MD,^4,5 first developed an unconstrained humeral head replacement for reconstruction of displaced proximal humerus fractures. These implants were subsequently used to treat glenohumeral arthritis with humeral head replacement. Later, a cemented polyethylene glenoid component was developed to resurface arthritic glenoids in order to provide a better fulcrum for humeral head rotation and rotator cuff function. More recent modular total shoulder designs allow a surgeon to independently size the stem, prosthetic head and glenoid. Total shoulder arthroplasty has outcomes that are comparable to that reported for total hip and knee arthroplasty.

The most common cause of failure of total shoulder replacement is glenoid loosening. Concerns about glenoid implant durability and longevity exist. Glenoid replacement is a technically demanding procedure with a longer operative time than in hemiarthroplasty. This has discouraged some surgeons from routinely performing glenoid replacement. In addition, a high rate of glenoid loosening has been noted in patients with rotator cuff deficiencies, including patients with rheumatoid arthritis and in those with cuff tear arthropathy due to the eccentric forces placed on the superior glenoid rim. Generally, glenoid replacement is contraindicated in these patients.

A number of options in glenoid arthroplasty exist. When the articular surface is intact, such as in patients with early stages of avascular necrosis, the native glenoid should be preserved. In some patients with primary glenohumeral osteoarthritis, posttraumatic arthritis and rheumatioid arthritis, damaged cartilage can be left untreated. Concentric reaming of the glenoid without prosthetic replacement, biologic soft tissue resurfacing and prosthetic replacement are also options.

The typical candidates for alternative glenoid resurfacing are young, active patients with advanced glenohumeral arthritis. Other candidates include patients who have inadequate bone for primary prosthetic glenoid replacement and those undergoing revision arthroplasty. Younger patients who perform higher demand activities should be considered for alternative resurfacing. Several studies have suggested that the outcome of humeral head replacement for glenohumeral osteoarthritis is not as good as the outcome or result of total shoulder replacement. Therefore, another consideration is whether the patient is willing to accept a result that may not be as good in order to avoid the issue of glenoid failure in the future. There are supporters of total shoulder arthroplasty and humeral head replacement with alternative resurfacing. Parsons and colleagues⁶ found that progressive glenoid wear occurs after humeral head replacement. This study suggests that glenoid cartilage erosion can be expected after humeral head replacement in young, active individuals, and that such wear may adversely affect function or necessitate conversion to total shoulder arthroplasty. Similarly, most comparative studies note that even at short and medium term follow-up there is a considerable incidence of conversion to total shoulder replacement.

Outcomes of Reverse Shoulder Replacement

Douglas W. Jackson, MD: Shoulder replacement relieves pain and restores active range of motion in most patients. What do you tell patients who have had a reverse prosthesis about pain and function? What can they expect after surgery?

T. Bradley Edwards, MD: I tell my patients experiencing cuff tear arthropathy that they should regain overhead function after surgery. For patients undergoing revision surgery or patients with a fracture or an irreconstructible proximal humerus, I tell them that if I can restore them to 90º of active elevation, then the surgery will have been a success. I tell my patients that surgery will not provide them with a normal shoulder because external rotation is not restored. It is important that surgeons do not mislead patients to believe that surgery is a perfect solution.

Drew Miller, MD: For patients with rotator cuff tear arthropathy, I tell them that they can expect excellent pain relief. Regarding functional improvement, I tell patients that they should be able to elevate their arm to at least 90º. Because functional improvement is not as predictable as pain relief, it is important to explain to patients that they need to consider pain relief and function separately.

Jackson: Do you have data on success with revision surgery and on failures of the primary shoulder arthroplasty? How long do you tell patients that they can expect their prosthetic replacement to last?

Edwards: Generally, I quote older data that demonstrate that the glenoid is the complication with primary arthroplasty. There is an 85% chance that the initial implants will be intact and functioning in 15 years. It is rare to perform revision surgery after 15 years. Pain relief is the principal achievement with revision arthroplasty. As far as overhead function, patients are functioning so poorly to begin with that any restored function will be an improvement.

Tom R. Norris, MD: A greater tuberosity avulsion after humeral head replacement for a fracture at six months is not mobilizable or reconstructible by standard techniques. Once greater tuberosity has retracted, a massive rotator cuff tear emulates. The Food and Drug Administration approval of the reverse prosthesis gives surgeons the option of revising shoulders.

Alternatives for resurfacing

Alternative glenoid resurfacing involves humeral head replacement with non-prosthetic glenoid resurfacing. The goal of alternative resurfacing is to improve upon the results of isolated humeral head replacement. Levine and colleagues⁷ found that the early outcome of humeral head replacement is better when the humeral head and glenoid are concentric. In a later study, they found that the results of humeral head replacement deteriorate with longer follow-up regardless of whether the humeral head is concentric. A variety of alternatives to prosthetic glenoid resurfacing have been advocated. Biologic resurfacing with soft tissues can be performed with the capsule, fascia lata, Achilles tendon or meniscal cartilage allograft. Burkhead and colleagues⁸reported on six patients who were treated with humeral head replacement and biologic resurfacing of the glenoid with fascia lata or anterior capsule. At two years’ follow-up, five patients had excellent results and one patient had a satisfactory result. Concentric glenoid reaming without resurfacing has been recently advocated as an alternative to total shoulder arthroplasty.⁹ This procedure restores glenohumeral congruity re-establishing the normal glenohumeral relationships. This is the “ream and run” procedure.

Glenoid deficiency

Although glenoid deficiency is seldom severe enough to affect the treatment of the glenoid when performing prosthetic shoulder arthroplasty, it can pose a considerable challenge in occasional cases. Generally, glenoid wear and deficiency are specific to the etiology of the glenohumeral arthritis and the clinical situation. Glenohumeral osteoarthritis is the most common cause of clinically significant glenoid wear. Typically in glenohumeral osteoarthritis there is some degree of posterior glenoid wear. In some patients, glenoid wear or deficiency is extensive enough to affect glenohumeral stability and necessitates modifications in technique. The options for treating glenoid deficiency include attempting to restore glenoid concavity and version with reaming or bone grafting, or accepting the abnormal glenoid anatomy.

Surgeons must determine whether sufficient glenoid bone to allow for prosthetic glenoid replacement or a stable glenohumeral articulation is present. In rare cases, such as glenoid hypoplasia, or severe glenoid erosion due to rheumatoid arthritis or failed glenoid prosthetic, glenoid replacement is impossible. In these cases humeral head replacement alone can often provide adequate pain relief and functional restoration. However, in other instances, glenoid bone grafting may facilitate the restoration of normal glenohumeral anatomy and possibly improve the functional outcome. Glenoid bone grafting is reserved for defects that are too large to correct with reaming. Posterior wear is the most common form of eccentric pattern. The goal is to restore glenoid version to re-establish glenohumeral stability. For evaluation, a computed tomography scan is the most helpful imaging study. In rare cases a 3-D CT reconstruction is helpful. Various techniques exist for bone grafting of glenoid defects. A wedge of bone graft can be harvested from the resected humeral head. Alternatively a step-cut graft, which is a more stable construct but may remove some of the native glenoid, can be used. Autografts are the best option as they are more likely to heal and remain viable than allografts. The results of glenoid replacement with glenoid bone grafting have not been equivalent to glenoid replacement alone.

In many cases glenoid reaming with partial restoration of glenoid version may be performed to avoid grafting. Some degree of retroversion and a smaller glenoid are often accepted with this technique. Nevertheless, this may be preferable to glenoid bone grafting. Chronic glenohumeral dislocation is an uncommon problem that can present with substantial glenoid deficiency. Chronic anterior dislocation is associated with anterior glenoid deficiency. The glenoid can be reconstructed with an anterior graft from the humeral head, iliac crest or allograft calcaneal block with the attached Achilles tendon.

After failure of a prosthetic glenoid there is usually a large glenoid bone defect. In most cases the glenoid cannot be revised with a new prosthetic component. Revision with humeral head replacement alone is often the only alternative. It is important to restore humeral offset to maximize the deltoid and rotator cuff function, with either bone grafting of the glenoid or modifying the humeral head.

Summary

The primary goal of shoulder replacement is pain relief and functional restoration. Generally, total shoulder replacement is thought to provide better pain relief than humeral head replacement. However, there are clinical circumstances in which alternatives to total shoulder replacement are indicated. Alternatives for glenoid resurfacing are indicated in limited and specific circumstances. The long-term risk of glenoid component loosening with total shoulder replacement must be weighed against the potentially inferior outcome of humeral head replacement. Currently, the data to accurately compare these variables do not exist.

References

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