Abstract
Background:
Loosening of the glenoid component continues to be the foremost cause of medium and long-term failure of shoulder replacements. The purpose of this study was to evaluate the clinical and radiographic results of a minimally cemented all-polyethylene pegged glenoid component designed for biologic fixation.
Methods:
Forty-four shoulders in forty-one patients with a mean age of sixty-six years underwent total shoulder arthroplasty with a pegged bone-ingrowth glenoid component. Outcome data included the American Shoulder and Elbow Surgeons questionnaire, the Simple Shoulder Test, and visual analog scales. A detailed radiographic analysis was performed by two board-certified musculoskeletal radiologists who were blinded to clinical and patient-reported outcomes. The radiographs were evaluated with regard to the presence of radiolucent lines at the bone-cement interface, implant seating, and the radiodensity between the flanges of the central peg.
Results:
The mean duration of clinical follow-up was four years and the mean duration of radiographic follow-up was three years. Twenty shoulders had perfect seating and radiolucency grades, thirty had increased radiodensity between the flanges of the central peg, and three demonstrated osteolysis. Radiodensity about the uncemented central peg at the time of the latest follow-up was positively associated with perfect seating and radiolucency grades on the initial postoperative radiographs (p = 0.03, Fisher exact test). The Simple Shoulder Test score, the American Shoulder and Elbow Surgeons score, and all visual analog scale scores had improved significantly (p < 0.01) at the time of the latest follow-up.
Conclusions:
Total shoulder arthroplasty with a minimally cemented, all-polyethylene, pegged glenoid implant can yield stable and durable fixation at short to medium-term follow-up (mean, four years).
Level of Evidence:
Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.
Total shoulder arthroplasty has resulted in significant improvement in pain and function when used for the treatment of degenerative conditions of the shoulder. Most authors have reported good-to-excellent outcomes in >90% of shoulders, but glenoid component loosening is the most common cause of medium and long-term failure despite the development and use of contemporary shoulder replacement systems1-3.
In 2006, we retrospectively reviewed all articles pertaining to total shoulder arthroplasty that had been published between 1996 and 2005 and retrieved from the MEDLINE and Ovid databases2. Component loosening accounted for 161 (39%) of the 414 complications reported in thirty-three series involving 2540 unconstrained total shoulder replacements. This represented a 10% increase compared with our review of forty-one series involving 1858 total shoulder replacements reported between 1975 and 1995, despite refinements in the surgical technique, the availability of improved instrumentation, and the introduction of new glenoid designs represented in the 2006 review1-3.
Various glenoid implant designs exist, including cemented all-polyethylene, cemented metal-backed, porous-coated bone-ingrowth, and screw-fixation designs4-12. Early enthusiasm for metal-backed glenoid components has diminished as studies with longer follow-up have revealed osteolysis, clinical loosening, and component failure9-12. Consequently, most of the emphasis at the present time is focused on contemporary cemented all-polyethylene components. Currently, both experimental and clinical evidence has shown that polyethylene glenoid components with pegs in both the superior-inferior and anterior-posterior positions on the glenoid surface (biaxial pegs) demonstrate superior fixation and a decreased rate of early glenoid component loosening compared with keeled implants4-6,13-23. However, persistent concerns regarding loosening of glenoid implants has led to the development of new designs aimed at improving the durability of this component. In July 2002, we began using a novel biaxially pegged, all-polyethylene glenoid component that required minimal cement fixation for the peripheral pegs and allowed for bone ingrowth into the flanges of an uncemented central peg. Although the concept has been validated in a canine model15, data regarding the clinical and radiographic outcomes of this glenoid prosthesis are limited24,25. A previous in vivo study demonstrated that use of a glenoid component with a flanged central peg results in superior mean fixation strength in a weight-bearing canine model at short-term (three and six-month) follow-up15. Additionally, radiographic and histological examination of the pegged components demonstrated fingerlike projections of bone, consistent with osseous integration, between the flanges of the implant15.
The purpose of the present study was (1) to evaluate the radiographic findings in a series of patients; (2) to compare the clinical results to prior published results involving pegged glenoid components; (3) to examine the radiographic findings for evidence of the hypothesized increase in radiodensity about the central flanged peg; and (4) to determine whether the initial postoperative seating and radiolucency scores had an effect on the subsequent radiodensity about the central peg.
This study involved a retrospective review of a consecutive series of forty-eight patients (fifty-one shoulders) treated with primary total shoulder replacement for primary or secondary osteoarthritis of the glenohumeral joint between July 2002 and November 2006 by a single surgeon (M.A.W.). All arthroplasties were performed with the Anchor Peg Glenoid component (DePuy, a Johnson & Johnson company, Warsaw, Indiana) that featured a circumferentially fluted, interference-fit central peg designed for osseous integration and three smaller peripheral pegs designed for fixation with a total cement volume of <1 cm3 (Fig. 1). All three peripheral pegs were located 10.3 mm from the center of the implant at the 12 o'clock, 5 o'clock, and 7 o'clock positions to maximize component stability.
This glenoid component was available in a choice of five sizes with a diameter of curvature of 46, 50, 54, 58, or 62 mm. The five corresponding prosthetic humeral heads had a diameter of curvature that was 6 mm less than that of the glenoid component (40 to 56 mm).
Outcome data were collected prospectively according to the standard of care at our institution. Patient self-assessment instruments included the American Shoulder and Elbow Surgeons (ASES) questionnaire, the Simple Shoulder Test (SST)26,27, and visual analog scale (VAS) assessments of shoulder comfort with the arm at rest, shoulder pain with strenuous activity, and overall quality of life. A VAS score of 0 reflected a pain-free or problem-free response and 100 reflected severe pain or a severe problem. Clinical assessments were performed preoperatively and postoperatively by the same clinical research examiner, who was blinded to the radiographic findings and patient-reported outcome data. Active elevation and external rotation (with the arm adducted) at the shoulder were recorded in 5° increments. Internal rotation was recorded as the highest pelvic or vertebral level on the back that the patient could reach with the thumb extended. Analyses of patient-reported and physiological outcome data were performed without any knowledge of patient identity or radiographic results.
Seven patients (seven shoulders) were excluded; six were lost to follow-up and one had died of unrelated causes. The remaining forty-one patients (forty-four shoulders) had a minimum of two years of follow-up and formed the study group. Forty of these patients returned to our institution for examination and radiographs at regular intervals, and a local orthopaedic surgeon sent in the results of a clinical examination and recent radiographs for the other patient. The mean duration of clinical follow-up in the study group was four years (range, two to seven years). The study group included eighteen women and twenty-three men with a mean age of sixty-six years (range, fifty-two to seventy-nine years) at the time of the arthroplasty. Ten of the forty-four shoulders had undergone previous surgical procedures, including rotator cuff repair (nine shoulders), anterior capsulorrhaphy (one), and superior labral repair (one). Eight shoulders had undergone one previous procedure; one shoulder, two procedures; and one shoulder, three procedures. All patients in the study gave full verbal and written consent for operative treatment and participation in this study, and the study was approved by our institutional review board.
Radiographic Analysis
The radiographic evaluation included an axillary lateral radiograph and an anteroposterior radiograph made perpendicular to the plane of the scapula. All radiographs were judged to be of adequate quality for analysis. Anteroposterior radiographs were considered to be adequate if a clear space was visible between the humeral head and the glenoid. Axillary lateral radiographs were deemed adequate if a clear space was visible between the glenoid and the coracoid process anteriorly and between the glenoid and the scapular spine posteriorly. Fluoroscopic imaging was not utilized. The mean duration of radiographic follow-up was three years (range, two to six years).
Glenoid bone loss was evaluated on preoperative radiographs and graded according to the method of Walch et al.28. The postoperative radiographs were analyzed and graded according to (1) the presence of radiolucent lines at the bone-cement interface, (2) the contact or seating of the medial portion of the glenoid prosthesis on the glenoid surface, and (3) the radiodensity about the flanges of the uncemented central peg.
Radiolucency about the pegs and the efficacy of component seating on the host subchondral bone were both evaluated according to the method of Lazarus et al.5. According to this method, radiolucency was graded on a scale from 0 to 5, with a perfect score of 0 indicating no radiolucency. Grades 0 and 1 were classified as “better cementing” and grades 2 and 3 as “worse cementing” (see Appendix and Fig. 2). Glenoid component seating was graded on a scale from A to E, with A indicating perfect seating. Grades A, B, and C were classified as “better seating” and grades D and E as “worse seating”5 (see Appendix and Fig. 3). The method of Lazarus et al. has been reported to have a Cronbach alpha coefficient (reliability) of between 0.75 and 0.85 for pegged and keeled glenoid components. (The Cronbach alpha coefficient is a measure of internal consistency; the maximum possible value of 1.0 is the most desirable, and values above a threshold of 0.8 are conventionally considered to represent good reliability.)
The radiographic appearance of the bone adjacent to the periphery of the flanges of the central peg and the radiodensity between the flanges of the central peg were graded on a scale from 1 to 3. Bone in contact with the periphery of the flanges of the central peg accompanied by increased radiodensity between the flanges on the latest postoperative radiograph was considered the optimal outcome and resulted in a grade of 3. Bone in contact with the periphery of the flanges but no increase in radiodensity between the flanges resulted in a grade of 2, and osteolysis about the central flanges resulted in a grade of 1. As this is the first use of this grading scale, its reliability is unknown.
Shoulders with “perfect” component seating (grade A) and no radiolucency (grade 0) on the initial postoperative radiographs were also compared with the remaining shoulders to determine whether seating and radiolucency had an effect on the radiodensity about the central peg at the time of the latest follow-up.
The radiographs were evaluated by two board-certified musculoskeletal radiologists who were familiar with the grading systems and who were blinded to clinical and patient-reported outcomes. As a precaution to ensure patient confidentiality, all identifying data on the radiographs were obscured and the sets of patient radiographs were arranged in a random order and numbered from 1 to 44. The evaluators were provided with tables that summarized the grading scales for radiolucency and component seating as well as illustrations that depicted the grading scales. Each individual set of patient radiographs was rated twice by each evaluator, and these four grades were averaged to yield a final score. (To average a set of four letter grades for radiolucency or bone quality, the grades were converted to numeric values, averaged, rounded to the nearest whole number, and converted back to a letter grade.)
Surgical Technique
The total shoulder arthroplasty technique used in this series, including humeral and glenoid exposure and preparation, has been previously described in detail29. Humeral version was determined by assessing the posterosuperior articular surface of the humeral head and then resecting the humeral head in a plane just inside the rotator cuff insertion to the level of the greater tuberosity. Humeral head size and glenohumeral offset were selected to best match the normal three-dimensional proximal humeral geometry.
A power reamer was used to create a concentric glenoid articular surface for seating of the glenoid component and also to correct any excessive glenoid retroversion (as determined by the surgeon's best judgment). Orientation of the reamer was facilitated by palpating the lateral extent of the subscapularis fossa at a point midway between the superior and lateral borders of the scapula. A line connecting this point to the center of the glenoid face represented the normalized center line of the glenoid29. Orienting the reamer to the normalized glenoid center line enabled the surgeon to improve pathologic glenoid version. Next, drill guides were used to precisely bore the central fixation hole and the smaller peripheral fixation holes. Each hole was palpated to its full depth with a probe and checked by direct visualization to determine whether it penetrated the glenoid vault cortex. The quality of the glenoid bone preparation was checked by inserting a trial glenoid component and verifying that it did not rock even when an eccentric load was applied to its rim. After irrigation with pulsatile lavage to remove blood from the glenoid fixation holes, these holes were reexamined; no communication between fixation holes was observed in any patient. To achieve hemostasis, topical thrombin (GenTrac, Middleton, Wisconsin) was sprayed into each of the peripheral fixation holes and SURGICEL (Ethicon, Somerville, New Jersey) was then inserted; the SURGICEL was subsequently removed at the time of cementing. Cementing of the three peripheral holes was accomplished with a total of <1 cm3 of polymethylmethacrylate. Care was taken to avoid the central peg hole, the cement was introduced into the peripheral peg holes without use of a syringe (since the additional pressurization created by a syringe would have increased the risk of cement extravasation into the central peg hole), and the central peg hole was suctioned prior to placement of the glenoid component to ensure that no cement was present in the hole. Prior to insertion of the glenoid prosthesis, finely morselized bone graft obtained during the terminal phase of glenoid reaming was placed between the flanges of the central peg to facilitate osseous integration (Fig. 4). The humeral component was implanted in a mean of 25° of retroversion without cement. Morselized cancellous bone graft from the humeral head was used for adjunctive compaction bone-grafting of the humeral prosthesis in seventeen shoulders30.
Statistical Analysis
Changes between the preoperative assessment and the latest postoperative assessment were evaluated with use of the paired t test (for continuous variables) or the Fisher exact test (for categorical variables, including ordinal outcomes).
Source of Funding
There was no outside funding source for this study.
Clinical Findings
The mean SST score (and standard deviation) improved from 3.0 ± 1.9 preoperatively to 9.1 ± 3.2 at the time of the latest follow-up (p < 0.01), and the ASES score improved from 34.1 ± 15 to 84.5 ± 16.9 (p < 0.01). All mean VAS results also improved significantly (p < 0.01). Comfort with the arm at rest improved from a mean of 62.0 ± 20.3 preoperatively to 10.0 ± 13.0 at the time of the latest follow-up, pain with strenuous activity improved from 82.0 ± 14.1 to 18.1 ± 22.5, and overall quality of life improved from 35.3 ± 26.1 to 5.3 ± 8.2.
All shoulder motion measures improved significantly (p < 0.01). Forward flexion improved from a mean of 5.1° ± 25.6° preoperatively to 147.0° ± 22.8° at the time of the latest follow-up, and external rotation improved from 9.4° ± 12.8° to 44.0° ± 10.6°. Preoperatively, the highest level that could be reached in internal rotation was the hip in fifteen shoulders, the buttocks in thirteen, and L5 in seven. At the time of the latest follow-up, the mean improvement was 5.5 sacral and vertebral levels.
Radiographic Analysis
The Cronbach alpha coefficient of the four individual radiographic scores derived from each patient's initial postoperative radiographs was 0.64 for radiolucency and 0.44 for seating. (The radiodensity about the central peg was not evaluated at this time point.) The reliability at the time of the latest follow-up was higher, with a Cronbach alpha coefficient of 0.91 for radiolucency, 0.90 for seating, and 0.88 for radiodensity about the flanges of the central peg.
Preoperatively, the glenoid morphology was graded as Walch A1 in twenty shoulders, A2 in four, B1 in seven, and B2 in thirteen. The initial postoperative radiographs for thirty-two (73%) of the forty-four shoulders indicated both a perfect seating grade and a perfect radiolucency grade. Three other shoulders had a perfect radiolucency grade and a seating grade of B, and nine had a perfect seating grade and a radiolucency grade of 1. At a mean radiographic follow-up of three years (range, two to six years), twenty shoulders had both a perfect seating grade and a perfect radiolucency grade. One shoulder had a radiolucency grade of 5 and a seating grade of E after a traumatic anterior shoulder dislocation. Altogether, thirty-eight shoulders had both a “better” seating grade and a “better” radiolucency grade as defined by Lazarus et al.5. At the time of the latest follow-up, thirty shoulders had bone adjacent to the peripheral aspect of the central peg flanges and increased radiodensity between the flanges of the central peg (grade 3), eleven had bone up to the flanges but no increased radiodensity between the flanges (grade 2), and three had osteolysis (grade 1) (Figs. 5-A through 5-D). Sixty-five percent (thirteen) of the twenty subjects with Walch A1 glenoid morphology had perfect seating and radiolucency grades (no radiolucency and complete seating) at the time of the latest follow-up, compared with only 29% (seven) of the twenty-four subjects with morphology worse than A1 (p = 0.03, Fisher exact test).
Shoulders with perfect seating (grade A) and optimal radiodensity about the central peg (grade 3) were also compared with the remaining shoulders to determine whether initial seating and radiolucency on the initial postoperative radiographs had an effect on the radiodensity between the flanges of the central peg at the time of the latest follow-up. For this comparison, radiodensity about the central peg at the time of the latest follow-up was classified as either increased bone density or similar or decreased bone density compared with that on the initial postoperative radiographs. Increased radiodensity about the central peg at the time of the latest follow-up was positively associated with perfect seating and radiolucency grades on the initial postoperative radiographs (p = 0.03).
Complications and Revisions
One shoulder had glenohumeral instability after an abduction/external rotation injury at five weeks following the arthroplasty. Management included subscapularis repair and removal of a loose glenoid component with bone-grafting of the glenoid vault. The pain and instability resolved. At the time of the latest follow-up, four years postoperatively, the patient was satisfied with the outcome of the surgery and had no major limitations.
Glenoid loosening is a substantial concern and one of the most common causes of failure of total shoulder arthroplasty. The etiology of component loosening is multifactorial and is associated with the implant design and materials, the method of fixation, the surgical technique, and patient factors such as bone loss and bone quality1-5,13,15,16,18,22,23.
Emphasis is currently focused on contemporary cemented all-polyethylene components, but uncertainty remains regarding whether a keeled or a pegged design provides the most durable fixation. The cumulative data from several studies suggest that keeled glenoid components are more likely to develop radiolucent lines and to shift in position compared with pegged glenoid components4,5,13,14,16-18,31. In a large multicenter study of 328 total shoulder replacements, Lazarus et al. reported a clear trend toward superior technical outcomes for biaxially pegged components compared with keeled components5. These authors provided several plausible explanations for this finding: (1) the fixed geometry of the pegged component, resulting in a more precise fit to host bone; (2) the precision of the instrumentation used with the pegged component; and (3) the smaller volume of cement used with the pegged component, resulting in the generation of less heat and a lower risk of necrosis of adjacent bone.
In contrast to the reports that favored pegged glenoid components for total shoulder arthroplasty, Throckmorton et al. reported no difference in outcome between keeled and pegged glenoid components7. At a mean follow-up of forty-six months, neither the number of components with radiolucency nor the number deemed at risk of loosening differed significantly between the fifty patients with a polyethylene keeled component and the fifty with a uniaxially pegged glenoid component. One plausible explanation for these radiographic results involves the uniaxial (in-line) design of the three pegs in the glenoid component used in the study. It is conceivable that uniaxially pegged components function similar to keeled components, a possibility that is supported by finite-element studies of biaxially pegged glenoid components that have shown that pegs anterior and posterior to the meridian of the implant improve resistance to eccentric loads13,19,21. It is also conceivable that the stability of the uniaxially pegged implant was compromised by the implantation techniques, which included curetting and undermining the subchondral glenoid bone after the peg holes had been created.
The present study evaluated a glenoid component with both minimally cemented peripheral pegs and a central peg with flanges designed to permit bone ingrowth. To our knowledge, only two reports have described both clinical and radiographic results of this glenoid component despite its estimated use in over 33,000 shoulder arthroplasties worldwide32. Churchill et al. reviewed twenty total shoulder arthroplasties at a minimum follow-up of five years and reported bone growth between the flanges of the central peg in fifteen of the glenoid components24. In 2011, Arnold et al. evaluated thirty-five total shoulder arthroplasties at a mean follow-up of forty-three months with use of thin-cut (0.625-mm) computed tomography25. The presence of bone between the flanges of the central peg of the glenoid component was demonstrated in thirty-two of the thirty-five shoulders.
Although the methodology used for radiographic evaluation in the present study differed somewhat from those of Churchill et al.24 and Arnold et al.25, our data corroborated theirs. In the present study, thirty (68%) of the forty-four shoulders had increased radiodensity between the flanges of the central peg, which we interpreted as bone ingrowth (osseous integration); this is similar to the findings reported by Churchill et al.24 and Arnold et al.25. Furthermore, our findings demonstrated a positive association between better radiolucency scores on the initial postoperative radiographs and higher radiodensity scores at the time of the latest follow-up, which supports the findings of both of these studies24,25. Additionally, the present study demonstrated a positive association between perfect seating scores on the initial postoperative radiographs and increased radiodensity between the flanges of the central peg at the time of the latest follow-up. It is reasonable to postulate that good implant seating, the absence of radiolucency, and increased radiodensity between the flanges of the central peg may all contribute to the longer-term success of the glenoid component.
The limitations of the present study include (1) the absence of histological data to confirm the radiographic findings; (2) the possibility that the results may not be replicable with other pegged glenoid designs; (3) the poor reliability of the initial radiographic findings; (4) the possibility that the patients, who were from a referral-based practice at a single institution, may not be representative of other patient populations; (5) the absence of long-term follow-up; (6) the shortcomings inherent in a case series; (7) the lack of correlation between clinical and radiographic outcomes; and (8) performance of the surgery by a single surgeon who had considerable expertise with shoulder arthroplasty, again resulting in the possibility that the results may not be generalizable. The strengths of the study include (1) the collection of validated outcome data; (2) performance of the clinical measurements by a single, blinded observer; (3) blinding of the radiographic examiners to the patient-reported outcome scores and the clinical findings; and (4) the consecutive (nonselected) series of patients with a single diagnosis and surgical procedure.
In conclusion, the early and intermediate-term results of this glenoid design are very encouraging and are comparable with those reported in the literature for glenoid implants with multiple pegs that were all cemented. Longer-term follow-up will determine whether better radiolucency scores, improved glenoid seating, and increased radiodensity about the central peg will be associated with improved patient-reported outcome measures and with the durability of the glenoid implant in total shoulder arthroplasty.
Tables showing the grading scales for radiolucency and completeness of seating are available with the online version of this article as a data supplement at jbjs.org.
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Anchor Peg Glenoid unit sales data from DePuy Orthopaedics, Inc. and DePuy International, Ltd. 2011.
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