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Surgical approach: Hemiarthroplasty vs. total arthroplasty
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A surgeon must decide between a hemiarthroplasty or a total shoulder arthroplasty when performing shoulder replacement surgery. Currently, surgeons debate the indications for and results of total shoulder replacement vs. hemiarthroplasty. A surgeon decides which procedure to use based on the extent of damage to the shoulder.
Hemiarthroplasty
Hemiarthroplasty was popularized by Charles Neer, MD,1 and represented a significant advance in shoulder arthroplasty. Hemiarthroplasty is a technically easier and faster procedure than total shoulder arthroplasty, and a surgeon is not concerned with glenoid loosening.
As part of a multicenter study in France, my colleagues and I assessed more than 600 patients with primary osteoarthritis. Patients undergoing hemiarthroplasties were compared with patients undergoing total shoulder arthroplasties. Results showed highly significant improvements over preoperative values in every parameter evaluated for both groups of shoulders. Results of this study showed that pain levels, activity and mobility were better for patients who underwent total shoulder arthroplasty. Patients who underwent total shoulder arthroplasties achieved significantly better objective results than patients who underwent hemiarthroplasties at follow-up, including mean constant scores. Good or excellent results were reported in 86% of hemiarthroplasties and 94% of total shoulder arthroplasties.
Hemiarthroplasties resulted in a higher incidence of radiolucent lines around the humeral component and humeral implant migration. In patients undergoing total shoulder arthroplasties, 56% had a radiolucent line around the glenoid component. Also, my colleagues and I looked at patients’ active mobility postoperatively. Patients who underwent total shoulder arthroplasty had better elevation by approximately 15º and better external rotation by approximately 10º. Overall, patients were satisfied in both categories; however, those who underwent total shoulder arthroplasty had a significantly higher percentage of good and excellent results than those having hemiarthroplasty.
In a study by Levine and colleagues,2 researchers demonstrated that the results of hemiarthroplasty are not as good with nonconcentric glenoid morphology. Specifically, patients with concentric glenoid wear had 86% satisfactory outcomes compared to 63% in patients with nonconcentric wear.
Hertel and colleagues3 reported on glenoid erosion after hemiarthroplasty. They identified that multiple factors contribute to glenoid erosion. Researchers also discovered that glenoid erosion may occur early (within the first postoperative year). Glenoid erosion is typically painful and can necessitate a revision for glenoid resurfacing.
Biological resurfacing
Hemiarthroplasty can be combined with biological resurfacing of the glenoid as an alternative to total shoulder replacement. Biological resurfacing involves the use of fascia lata or meniscal allograft instead of a glenoid component. Meniscal allografts resurface an eburnated glenoid surface without concerns of loosening of a glenoid component.
In a study by Burkhead and Hutton,4 promising early results were reported. They concluded that biological resurfacing of the glenoid appears to improve the results of hemiarthroplasty and may be the procedure of choice for young patients with end-stage glenohumeral arthritis.
Glenoid component
Several glenoid component designs are available — convex-back keel, flat-back keel, peg and metal-back. Investigations studying the advantages of the peg vs. the keel designs are being performed. Biomechanical studies support peg designs, whereas clinical studies are divided. Also debated is the use of convex-back components vs. flat-back components. Biomechanical studies support convex-back, with the advantage of resisting shear forces. Other studies have shown that the convex-back design has lower radiolucencies than the flat-back designs on immediate postoperative and at two-year postoperative radiographs.5
A study by Boileau and colleagues testing metal-back designs has yielded excellent early results.6 However, at a minimum of three-years’ follow-up, the results clearly showed that the survival rate of cementless, metal-backed glenoid components is inferior to cemented all-polyethylene components. Although the incidence of radiolucency at the glenoid-cement interface with all-polyethylene components is high and remains a concern, the high rate of loosening, because of the absence of ingrowth and the accelerated polyethylene wear, has led most surgeons to abandon the use of metal-backed glenoids.
Prosthetic mismatch
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Prosthetic mismatch is the difference of the radius of curvature between the glenoid component and the humeral head component (Figure). Prosthetic mismatch can be categorized into two systems — a conforming system and a nonconforming system. A conforming system has no mismatch. The glenoid component has the same radius curvature as the humeral component, resulting in a stable construct with minimal concern for prosthetic instability. A conforming system also minimizes wear because there is no translation occurring between the humeral head and the glenoid component. However, native shoulders and prosthetic shoulders have a phenomenon known as obligate translation, in which the head shifts on the glenoid. As this occurs with a conforming system, rim loading of the glenoid can also occur. When rim loading occurs, increased stresses at the glenoid bone and glenoid component interface also occur and may result in radiolucent lines, as well as prosthetic loosening.
Conversely, a nonconforming system has mismatch in which the glenoid has a greater radius of curvature than the humeral component. This allows for obligate translation and minimizes the rim loading and the stresses at the interface between the bone and the prosthesis. However, this may increase polyethylene wear and decrease prosthetic stability.
In a study of more than 300 patients divided into groups, my colleagues and I found that there was a linear relationship between radiolucent line scores and mismatch.7 Based on this retrospective study, the ideal mismatch may be in excess of 5.5 mm. For reducing radiolucent lines and potential loosening, more mismatch is preferred. This study was unable to provide upper limits of preferred mismatch.
Implantation techniques
Glenoid exposure is critical in glenoid implantation. Without good exposure, a surgeon cannot put the component in the proper position and correct deformities. Surgeons perform a standardized subscapularis release and an inferior capsule release of the glenoid. Generally, my colleagues and I carry this release to the six o’clock position. However, in tighter shoulders, it is necessary to extend the release more posteriorly. Neuromuscular paralysis is also helpful.
Another issue to consider is how to position the glenoid. It is important to correct the existing deformity. If the radiographs are good, then a surgeon can perform surgery without any further studies. However, my colleagues and I tend to use a preoperative computed tomography scan to better delineate the deformity that must be corrected. A concept of glenoid preparation is bone compaction instead of bone removal. A keel slot the same size as the prosthetic keel is created, giving a surgeon a primary press-fit fixation during cement curing.
Summary
Total shoulder arthroplasty results in better outcomes than hemiarthroplasty in most patients with primary osteoarthritis. My colleagues and I use total shoulder arthroplasty in nearly all patients with primary osteoarthritis, most patients with rheumatoid arthritis in provided they have a sufficient rotator cuff, in patients with fracture sequelae and instability arthropathy and in patients with late-stage osteonecrosis. Hemiarthroplasty is performed on patients with early-stage osteonecrosis with no glenoid involvement, in patients with severe glenoid deficiency and in patients with massive rotator cuff tear. Although hemiarthroplasty and biological resurfacing are viable options for patients with glenohumeral arthritis, continued advances in glenoid component design and glenoid preparation techniques will minimize the risk of glenoid component loosening.
References
- Neer C. Articular replacement for the humeral head. J Bone Joint Surg Am. 1955;37:215-228.
- Levine WN, Djurasovic M, Glasson JM, et al. Hemiarthroplasty for glenohumeral osteoarthritis: Results correlated to degree of glenoid wear. J Shoulder Elbow Surg. 1997;6:449-454.
- Hertel R, Lehmann O. Glenohumeral joint. Anatomical aspects and implications for prosthesis design. Orthopade. 200l;30:363-369.
- Burkhead WZ Jr, Hutton KS. Biologic resurfacing of the glenoid with hemiarthroplasty of the shoulder. J Shoulder Elbow Surg. 1995;4:263-270.
- Szabo I, Buscayrest F, Edwards TB, et al. Radiographic comparison of flat back and convex back glenoid components in total shoulder arthroplasty. (under review).
- Boileau P, Avidor C, Krishnan SG, et al. Cemented polyethylene versus uncemented metal-backed glenoid components in total shoulder arthroplasty: A prospective, double-blind, randomized study. J Shoulder Elbow Surg. 2002;11:351-359.
- Walch G, Edwards TB, Boulahia A, Boileau P, Mole D, Adeleine P. The influence of glenohumeral prosthetic mismatch on glenoid radiolucent lines: Results of a multicenter study. J Bone Joint Surg Am. 2002;84:2186-2191.