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The incidence of early radiolucencies about a pegged glenoid component using cement pressurization
The incidence of early radiolucencies about a pegged glenoid component using cement pressurization Shane Barwood, MD, Kevin J. Setter, MD, Theodore A. Blaine, MD, and Louis U. Bigliani, MD, New York, NY
Glenoid component loosening is the most common early mode of failure of total shoulder arthroplasty (TSA) We hypothesised that the use of a pegged glenoid component with a modern glenoid reaming system and an instrumented cement pressurization technique would achieve a low prevalence of early radiolucent lines. Of 81 patients having TSA with a cemented, all polyethylene, 3-peg glenoid component for primary glenohumeral osteoarthritis, 69 had high quality radiographs available for analysis. All preoperative and initial postoperative radiographs were reviewed and graded in a blinded manner using previously established criteria. When the radiolucency grade of cement fixation was converted to a numeric scale of 0 (no radiolucency) to 5 (grossly loose), the mean cementing score was 0.14 + 0.06. Of the 69 shoulders, 62 (90%) had no radiolucencies. These techniques to improve glenoid fixation resulted in a low incidence of early radiolucencies about the glenoid component in patients having TSA for primary glenohumeral osteoarthritis. (J Shoulder Elbow Surg 2008;17:703708.)
Glenoid component loosening is the most common
mode of failure of total shoulder arthroplasty (TSA).1 While the relationship of glenoid loosening to early radiolucencies is still unclear,5,8,10,14,16,18 the prevention of any radiolucency 24 about the glenoid component remains an important surgical goal. Early radiolucencies were initially described by Neer in 1982, 14 and despite modern prosthetic design and surgical technique, they are still common. The reported incidence ranges from 30 to 90%.1-3,13-16,18 This variability has been attributed to differences in
From the Department of Orthopaedic Surgery, Columbia University, New York. Reprint requests: Theodore A. Blaine, MD, Associate Professor, Brown Alpert Medical School, 2 Dudley Street, Providence, RI 02806 (E-mail: [email protected], tblaine@ universityorthopedics.com ). Copyright ª 2008 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2008/$34.00 doi:10.1016/j.jse.2008.01.147
radiographic techniques,9 grading, and reporting methods,6,7 and has contributed to the uncertainty regarding the relationship to loosening. Early radiolucencies at the cement-bone interface have been traditionally related to cementing technique14 and, more recently, to thermal necrosis as well.4 Early radiolucencies at the subchondral bone-component interface are related to incomplete glenoid component seating.13 Despite many reports of early glenoid radiolucencies, most are of keeled components, and many of the reports used free hand burring of the glenoid bone. Modern glenoid components now use specifically designed reamers, and some use multiple pegs rather than a keel with instrumented cement pressurizing techniques in an attempt to improve fixation. In a review of 328 TSA, Lazarus et al reported that the incidence of early radiolucencies was still 94%, despite specific reamers and the use of a pegged glenoid component.13 These pegged components were inserted without instrumented cement pressurization techniques. Recently, Klepps et al reported a significantly decreased incidence of early radiolucent lines at the cement-bone (fixation) interface using instrumented cement pressurization techniques.12 They also concluded that the subgroup of pegged components had a lower incidence of radiolucent lines than keeled components; however, they did not evaluate the subchondral bone component (seating) interface. We hypothesised that the use of a pegged glenoid component with a modern glenoid reaming system and the use of an instrumented cement pressurization technique would achieve a low incidence of early radiolucent lines at both the bone-cement (fixation) interface and the subchondral bone-component (seating) interface, compared to results from the literature. The system we used is also designed to match the glenoid component size to the available glenoid bone stock accurately. We hypothesised that this design would enable accurate component seating, even in the presence of posterior glenoid wear. MATERIALS AND METHODS Eighty-one patients with primary osteoarthritis were evaluated for this study. In all cases, a cemented, all polyethylene, 3-peg glenoid component was used. All preoperative
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Figure 1 Instrumented cement pressurizing device. The cement impactor (left) and sponge (right) are displayed separately. They are combined and used to push the cement under pressure into the glenoid peg holes.
and initial postoperative radiographs were reviewed and graded in a blinded manner by 2 reviewers. Neither reviewer was an operating surgeon for any case. Each radiograph was numbered and randomized. Each radiograph was graded 4 times with each of the 2 scales; 2 reviewers read each radiograph twice. Ethical approval was obtained from our institutional review board. The surgical technique for glenoid component insertion was the same in all cases. No patient was excluded because of inadequate bone stock. Glenoid preparation was completed after humeral preparation. As the glenoid component was size matched to both the humeral ‘‘articular’’ size and glenoid bone ‘‘backside’’ size, the required humeral articular size was recorded initially. The glenoid vault was then cleared of labrum and soft tissue and the amount of host bone available for component seating assessed. This identified the appropriate backside size for the glenoid component. Native glenoid version was maintained. If excessive posterior glenoid bone erosion was noted, differential anterior reaming was performed to recreate the native glenoid version and avoid excessive retroversion. A glenoid component was then chosen with the matched articular and backside sizes. If a standard, single-sized glenoid component was not suitable, a ‘‘dual sized’’ component was used. These glenoid components have different sizes of their ‘‘articular’’ and ‘‘backside’’ surfaces to enable proper congruency with the humeral head and maintain proper component seating on available glenoid bone. Alignment guides were used to create a central hole for glenoid reaming, and the glenoid was concentrically reamed. Superior and inferior peg holes were then created with the provided drill and guide. If significant posterior wear was noted prior to reaming, this was addressed with differential anterior glenoid reaming and the glenoid bone resized. After reaming, the glenoid was washed with pulsatile lavage and the peg holes packed with thrombin soaked sponges and dried to ensure a clean bony bed. Cement was introduced into the peg holes only with a 60cc syringe and a pressurizer sponge used to improve cement interdigitation into the cancellous bone (Figure 1). The process of
Figure 2 Illustration depicting the grading system to assess radiolucencies at the cement-bone interface (fixation) of pegged glenoid components. Grade finding: 0, no radiolucency; 1, incomplete radiolucency around 1 or 2 pegs; 2, complete radiolucency (£2 mm wide) around 1 peg only, with or without incomplete radiolucency around one other peg; 3, complete radiolucency (£2 mm wide) around 2 or more pegs; 4, complete radiolucency (>2 mm wide) around 2 or more pegs; 5, gross loosening. (Reprinted with permission from Lazarus MD, Jensen KL, Southworth C, Matsen FA III. The radiographic evaluation of keeled and pegged glenoid component insertion. J Bone Joint Surg Am 2002;84-A:1174-82.)
cementing and pressurization was repeated 4 times, ensuring no cement was applied to the articular surface of the bone. No cement was applied to the component prior to insertion. The component was then inserted, impacted to ensure complete seating, and excess cement removed. The humeral component was then inserted. Preoperative axillary lateral radiographs were used to grade glenoid morphology using the system of Walch,17 and this was confirmed intraoperatively. A subgroup with posterior glenoid wear was defined as those with Walch type B1, B2, and C glenoid morphology, and a concentric wear group was defined as all other groups (Walch type A1, A2). Complete postoperative radiographs, including anteroposterior (AP), axillary lateral (AL), and scapular lateral (SL), were performed either prior to hospital discharge or at the first postoperative visit. Radiographs were then analyzed for sufficient quality for review based on the criteria of Lazarus.13 Of the 81 radiographs reviewed, 69 were considered acceptable for inclusion in this study. Postoperative radiographs were reviewed for radiolucencies at the bonecement interface to assess cement fixation at the pegs. The subchondral bone-component interface was reviewed to
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Figure 3 Illustration depicting the grading system used to assess radiolucencies at the component- subchondral bone interface (seating). Although the figure shows a keeled component, we believe the system can be used for pegged components as the fixation method is not relevant to the component-subchondral bone interface. Grade finding: A, complete component seating; B, < 25% incomplete contact, single radiograph; C, 25-50% incomplete contact, single radiograph; D, <50% incomplete contact, both radiographs; E, > 50% incomplete contact, single radiograph. (Reprinted with permission from Lazarus MD, Jensen KL, Southworth C, Matsen FA III. The radiographic evaluation of keeled and pegged glenoid omponent insertion. J Bone Joint Surg Am. 2002;84-A:1174-82.)
assess glenoid component seating. The quality of component fixation (Table I, Figure 2) and seating (Table II, Figure 3) were assessed by the criteria of Lazarus for pegged components.13 As these criteria were initially developed for a glenoid component with 4 pegs, we modified the criteria by combining the 2 middle pegs into our single central peg. Of the 69 radiographs reviewed, 22 were associated with posterior glenoid wear and allocated to the posterior wear subgroup. The cement fixation grade and seating grade of each glenoid component was assessed 4 times. Each grading was converted to a numeric score (0-5) for fixation and (0-4) for seating, from which the mean score for fixation and a mean score for seating of each component were calculated. This was designated as the shoulders’ final scores. The final scores were used to calculate the study group mean scores of fixation and seating.
Statistical analysis The influence of preoperative glenoid morphology on component seating was assessed using the 2-tailed Fisher’s exact test, with significance set at the P < .05 level. With
22 patients in the posterior wear group and 47 patients in the concentric wear group, there is greater than 80% power (a level 0.05) to detect a 34% difference in the ‘‘better’’ shoulder seating grades, if that percentage is at least 90% in the concentric wear group. The intraobserver and interobserver reliability of each grading system was calculated with the Pearson product-moment correlation coefficient.
RESULTS A summary of results, including preoperative glenoid wear pattern, is given in Table III. Nineteen shoulders had a dual sized glenoid component inserted and 22 shoulders had significant preoperative posterior glenoid wear (Walch type B2).17 When the radiolucency grade of cement fixation was converted to a numeric scale of 0 (no radiolucency) to 5 (grossly loose), the mean cementing score was 0.14 + 0.06. Of the 69 shoulders, 62 (90%) had no radiolucencies, 4 had grade 1, and 3 had grade 2 (Table III). No shoulder was considered more than grade 2.
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Table I Grading scale for radiolucencies about pegged glenoid components grade 0 No radiolucency 1 Incomplete radiolucency around one or two pegs 2 Complete radiolucency (£2 mm wide) around one peg only, with or without incomplete radiolucency around one other peg 3 Complete radiolucency (£2 mm wide) around two or more pegs 4 Complete radiolucency (>2 mm wide) around two or more pegs 5 Gross loosening
Table II Grading scale for completeness of glenoid component seating grade Findings
Figure 4 Initial postoperative axillary lateral radiograph. Solid arrow indicates the position at the posterior glenoid rim of residual cement between component and subchondral bone. Solid line ‘‘A’’ is the proportion of unsupported glenoid component which is less than 10%.
Figure 5 Initial anterioposterior radiograph of the same patient as seen in figure 8. Solid arrow ‘‘A’’ points to a thin line of cement passing along the entire length of the glenoid component. Although this is classified as grade E seating (>50% incomplete contact, single radiograph), we believe that when the axillary lateral radiograph is considered (see Figure 4), the amount of component seating is more accurately represented as grade B (< 25% incomplete contact, single radiograph).
When the radiolucency grade of component seating was converted to a numeric scale of 0 (complete seating) to 4 (> 50% incomplete contact, single radiograph), the mean component seating score was 0.62 + 0.13. Forty-four shoulders had grade A (complete)
A Complete component seating B <25% incomplete contact, single radiograph C 25-50% incomplete contact, single radiograph D <50% incomplete contact, both radiographs E >50% incomplete contact, single radiograph
seating (64%), 15 had grade B, 6 had grade C, none had grade D, and 4 had grade E (Table III). Twenty-one of 22 shoulders (96%) with preoperative posterior wear glenoid morphology (Walch type B2)17 had adequate grade A, B, or C seating, and the other was considered inadequate grade E seating. Forty-four of the 47 shoulders (94%) with preoperative concentric wear glenoid morphology had adequate grade A, B, or C seating, and the remaining 3 were considered inadequate grade E seating. The dual size glenoid component was used in 9 of 22 shoulders with posterior wear (41%), compared to 10 of the 47 with concentric wear (21%). The radiographic ratings for radiolucencies of cement fixation were similar for interobserver and intraobserver reliability (0.86 and 0.83, respectively). The observers mean scores agreed to within 1 grade of each other at all times. The radiographic interpretation of component seating was also similar for interobserver and intraobserver reliability (0.89 and 0.90, respectively). The observers mean scores agreed to within 1 grade of each other 90% of the time. DISCUSSION The combined techniques of glenoid reaming, a size matched glenoid component, pegged glenoid fixation, and instrumented cement pressurization results in a low incidence of early radiolucencies about the glenoid component in TSA for glenohumeral osteoarthritis. Although the relationship between this lower incidence and long-term glenoid loosening is uncertain, these results compare favorably to others in which early radiolucencies have been assessed.
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Table III Individual results of glenoid type,(17), fixation grade,(11) seating grade,(11) and type of glenoid component used Glenoid Type
Total
Fixation Grade
Number
A1
32
0 1 2 3
29/32 3/32 0/32 0/32
A2
7
0 1 2 3
6 1 0 0
B1
8
0 1 2 3
7 0 1 0
B2
22
0 1 2 3
20 0 2 0
Seating Grade A B C D E A B C D E A B C D E A B C D E
Number 18 8 3 0 3 5 1 1 0 0 5 2 1 0 0 16 4 1 0 1
Component Std¼ 26 Dual¼ 6
Std¼ 4 Dual¼ 3
Std¼ 7 Dual¼ 1
Std¼ 13 Dual¼ 9
Dual, dual radius glenoid component; Std, standard size component.
Initial radiolucencies at the cement-bone interface may weaken component fixation. Radiolucencies at the subchondral bone-component interface imply incomplete component seating, which has been shown to increase rocking forces at the component edge.6 The relative importance of radiolucencies at the subchondral bone-component interface compared to the cement-bone interface is not known; however, we consider limiting the prevalence of both important. The low incidence of radiolucencies related to fixation at the cement-bone interface in this study is likely multifactorial. Component design appears important. Pegged fixation appears to have reduced radiolucencies compared to keeled designs.12,13 We feel that this may be due to several factors, including the precise fit between the pegs and bone holes. The cylindrical size of the bone holes allows more effective cement pressurization with the precise fit of the pressurizing instrument combined with a pressurizer sponge. As less bone is removed and less cement used, the heat generated by the cement is reduced and may limit surrounding thermal necrosis.4 We reported a greater prevalence of radiolucencies associated with incomplete component seating (25/69) than with cement fixation (7/69). There were 4 components with grade E seating (> 50% incomplete contact, as seen on a single radiograph). The implication from the grading system is that these grade E components are inadequately seated and, therefore, more likely to fail. However, despite these 4 components fulfilling the radiographic criteria for grade E, we felt they were all were clinically stable,
actually had greater than 90% bone contact, and, therefore, a similar prognosis to components with grade B seating (<25% incomplete contact, single radiograph). This disagreement with the rating system arose because Lazarus defines ‘‘a component that was backed by an intervening layer of cement was deemed as unsupported,’’ according to a single AP radiograph. While we agree with this principle, difficulties arise using the classification system when a small amount of cement remains on the posterior rim of the glenoid (Figure 4). We consider the component in Figure 4 well seated with at least 90% component-bone seating; however, this cement rim appears as a long cement line along the component-bone interface on the AP radiograph and may appear often to pass the entire length of the component (Figure 5). We considered that this AP appearance was, therefore, classified as >50% incomplete contact based on this single radiograph; however, the axillary lateral radiograph findings of > 90% complete seating with a small posterior rim of cement are not accounted for. We suggest that the classification system be modified to account for both the AP and the axillary radiograph appearances in all grades. There was no difference in seating grades for the subgroup with preoperative posterior glenoid wear. We attribute this to the ability of the component to be accurately sized to the available glenoid bone stock in all cases using, when required, the dual size glenoid. The main limitations of our study include the use of plain radiographs. The accuracy of plain radiographs has been questioned when interpreting radiolucencies
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about a glenoid component9,11 An analysis using fluoroscopy or computerized tomography would be a more accurate method of assessing component fixation and seating. Plain radiography is still the most common imagining method used to review TSA components. The axillary lateral radiograph is difficult to standardize; however, we feel that it is important to use these to obtain imaging in two planes. The amount of cement used for pegged components is less than for traditional keeled components, and is potentially more difficult to assess on radiographs. The use of high quality radiographs in this study should minimize these issues. A second limitation of this study is that it does not determine the relative importance of each individual technique or design described to improve glenoid fixation but reports on their combined results. The relative importance of the glenoid reaming, instrumented cementing technique, pegged design, dual radius design, or other factors cannot be ascertained from this study. Early radiolucencies about a glenoid component are a common finding in TSA. This study demonstrates that the use of surgical techniques to improve glenoid fixation (glenoid reaming, instrumented cement pressurization, and a size-matched polyethylene pegged glenoid) leads to a low incidence of early radiolucencies. The long-term effect of reduced early radiolucencies in these patients remains to be determined.
REFERENCES
1. Barrett WP, Franklin JL, Jackins SE, Wyss CR, Matsen FA III. Total shoulder arthroplasty. J Bone Joint Surg Am 1987;69:865-72. 2. Bell SN, Gschwend N. Clinical experience with total arthroplasty and hemiarthroplasty of the shoulder using the Neer prosthesis. Int Orthop 1986;10:217-22. 3. Brems JJ. The glenoid component in total shoulder arthroplasty. J Shoulder Elbow Surg 1993;2:47-54.
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4. Churchill RS, Boorman RS, Fehringer EV, Matsen FA III. Glenoid cementing may generate sufficient heat to endanger the surrounding bone. Clin Orthop Relat Res 2004;419:76-9. 5. Cofield RH. Total shoulder arthroplasty with the Neer prosthesis. J Bone Joint Surg Am 1984;66:899-906. 6. Collins D, Tencer A, Sidles J, Matsen F III. Edge displacement and deformation of glenoid components in response to eccentric loading. The effect of preparation of the glenoid bone. J Bone Joint Surg Am 1992;74:501-7. 7. Franklin JL, Barrett WP, Jackins SE, Matsen FA III. Glenoid loosening in total shoulder arthroplasty. Association with rotator cuff deficiency. J Arthroplasty 1988;3:39-46. 8. Godeneche A, Boileau P, Favard L, et al. Prosthetic replacement in the treatment of osteoarthritis of the shoulder: early results of 268 cases. J Shoulder Elbow Surg 2002;11:11-8. 9. Havig MT, Kumar A, Carpenter W, Seiler JG III. Assessment of radiolucent lines about the glenoid. An in vitro radiographic study. J Bone Joint Surg Am 1997;79:428-32. 10. Hawkins RJ, Bell RH, Jallay B. Total shoulder arthroplasty. Clin Orthop 1989;242:188-94. 11. Kelleher IM, Cofield RH, Becker DA, Beabout JW. Fluoroscopically positioned radiographs of total shoulder arthroplasty. J Shoulder Elbow Surg 1992;1:306-11. 12. Klepps S, Chiang AS, Miller S, Jiang CY, Hazrati Y, Flatow EL. Incidence of early radiolucent glenoid lines in patients having total shoulder replacements. Clin Orthop Relat Res 2005;435: 118-25. 13. Lazarus MD, Jensen KL, Southworth C, Matsen FA III. The radiographic evaluation of keeled and pegged glenoid component insertion. J Bone Joint Surg Am 2002;84-A:1174-82. 14. Neer CS II, Watson KC, Stanton FJ. Recent experiences in total shoulder arthroplasty. J Bone Joint Surg 1982;64A:319-37. 15. Norris BL, Lachiewicz PF. Modern cement technique and the survivorship of total shoulder arthroplasty. Clin Orthop 1996;328: 76-85. 16. Torchia ME, Cofield RH, Settergen CR. Total shoulder arthroplasty with the Neer prosthesis: long-term results. J Shoulder Elbow Surg 1997;6:495-505. 17. Walch G, Badet R, Boulahia A, Khoury A. Morphological study of the glenoid in primary glenohumeral osteoarthritis. J Arthroplasty 1999;14:756-60. 18. Wallace AL, Phillips RL, MacDougal GA, Walsh WR, Sonnabend DH. Resurfacing of the glenoid in total shoulder arthroplasty. A comparison, at a mean of five years, of prostheses inserted with and without cement. J Bone Joint Surg Am 1999; 81:510-8.
Glenoid component loosening is the most common early mode of failure of total shoulder arthroplasty (TSA) We hypothesised that the use of a pegged glenoid component with a modern glenoid reaming system and an instrumented cement pressurization technique would achieve a low prevalence of early radiolucent lines. Of 81 patients having TSA with a cemented, all polyethylene, 3-peg glenoid component for primary glenohumeral osteoarthritis, 69 had high quality radiographs available for analysis. All preoperative and initial postoperative radiographs were reviewed and graded in a blinded manner using previously established criteria. When the radiolucency grade of cement fixation was converted to a numeric scale of 0 (no radiolucency) to 5 (grossly loose), the mean cementing score was 0.14 + 0.06. Of the 69 shoulders, 62 (90%) had no radiolucencies. These techniques to improve glenoid fixation resulted in a low incidence of early radiolucencies about the glenoid component in patients having TSA for primary glenohumeral osteoarthritis. (J Shoulder Elbow Surg 2008;17:703708.)
Glenoid component loosening is the most common
mode of failure of total shoulder arthroplasty (TSA).1 While the relationship of glenoid loosening to early radiolucencies is still unclear,5,8,10,14,16,18 the prevention of any radiolucency 24 about the glenoid component remains an important surgical goal. Early radiolucencies were initially described by Neer in 1982, 14 and despite modern prosthetic design and surgical technique, they are still common. The reported incidence ranges from 30 to 90%.1-3,13-16,18 This variability has been attributed to differences in
From the Department of Orthopaedic Surgery, Columbia University, New York. Reprint requests: Theodore A. Blaine, MD, Associate Professor, Brown Alpert Medical School, 2 Dudley Street, Providence, RI 02806 (E-mail: [email protected], tblaine@ universityorthopedics.com ). Copyright ª 2008 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2008/$34.00 doi:10.1016/j.jse.2008.01.147
radiographic techniques,9 grading, and reporting methods,6,7 and has contributed to the uncertainty regarding the relationship to loosening. Early radiolucencies at the cement-bone interface have been traditionally related to cementing technique14 and, more recently, to thermal necrosis as well.4 Early radiolucencies at the subchondral bone-component interface are related to incomplete glenoid component seating.13 Despite many reports of early glenoid radiolucencies, most are of keeled components, and many of the reports used free hand burring of the glenoid bone. Modern glenoid components now use specifically designed reamers, and some use multiple pegs rather than a keel with instrumented cement pressurizing techniques in an attempt to improve fixation. In a review of 328 TSA, Lazarus et al reported that the incidence of early radiolucencies was still 94%, despite specific reamers and the use of a pegged glenoid component.13 These pegged components were inserted without instrumented cement pressurization techniques. Recently, Klepps et al reported a significantly decreased incidence of early radiolucent lines at the cement-bone (fixation) interface using instrumented cement pressurization techniques.12 They also concluded that the subgroup of pegged components had a lower incidence of radiolucent lines than keeled components; however, they did not evaluate the subchondral bone component (seating) interface. We hypothesised that the use of a pegged glenoid component with a modern glenoid reaming system and the use of an instrumented cement pressurization technique would achieve a low incidence of early radiolucent lines at both the bone-cement (fixation) interface and the subchondral bone-component (seating) interface, compared to results from the literature. The system we used is also designed to match the glenoid component size to the available glenoid bone stock accurately. We hypothesised that this design would enable accurate component seating, even in the presence of posterior glenoid wear. MATERIALS AND METHODS Eighty-one patients with primary osteoarthritis were evaluated for this study. In all cases, a cemented, all polyethylene, 3-peg glenoid component was used. All preoperative
703
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Figure 1 Instrumented cement pressurizing device. The cement impactor (left) and sponge (right) are displayed separately. They are combined and used to push the cement under pressure into the glenoid peg holes.
and initial postoperative radiographs were reviewed and graded in a blinded manner by 2 reviewers. Neither reviewer was an operating surgeon for any case. Each radiograph was numbered and randomized. Each radiograph was graded 4 times with each of the 2 scales; 2 reviewers read each radiograph twice. Ethical approval was obtained from our institutional review board. The surgical technique for glenoid component insertion was the same in all cases. No patient was excluded because of inadequate bone stock. Glenoid preparation was completed after humeral preparation. As the glenoid component was size matched to both the humeral ‘‘articular’’ size and glenoid bone ‘‘backside’’ size, the required humeral articular size was recorded initially. The glenoid vault was then cleared of labrum and soft tissue and the amount of host bone available for component seating assessed. This identified the appropriate backside size for the glenoid component. Native glenoid version was maintained. If excessive posterior glenoid bone erosion was noted, differential anterior reaming was performed to recreate the native glenoid version and avoid excessive retroversion. A glenoid component was then chosen with the matched articular and backside sizes. If a standard, single-sized glenoid component was not suitable, a ‘‘dual sized’’ component was used. These glenoid components have different sizes of their ‘‘articular’’ and ‘‘backside’’ surfaces to enable proper congruency with the humeral head and maintain proper component seating on available glenoid bone. Alignment guides were used to create a central hole for glenoid reaming, and the glenoid was concentrically reamed. Superior and inferior peg holes were then created with the provided drill and guide. If significant posterior wear was noted prior to reaming, this was addressed with differential anterior glenoid reaming and the glenoid bone resized. After reaming, the glenoid was washed with pulsatile lavage and the peg holes packed with thrombin soaked sponges and dried to ensure a clean bony bed. Cement was introduced into the peg holes only with a 60cc syringe and a pressurizer sponge used to improve cement interdigitation into the cancellous bone (Figure 1). The process of
Figure 2 Illustration depicting the grading system to assess radiolucencies at the cement-bone interface (fixation) of pegged glenoid components. Grade finding: 0, no radiolucency; 1, incomplete radiolucency around 1 or 2 pegs; 2, complete radiolucency (£2 mm wide) around 1 peg only, with or without incomplete radiolucency around one other peg; 3, complete radiolucency (£2 mm wide) around 2 or more pegs; 4, complete radiolucency (>2 mm wide) around 2 or more pegs; 5, gross loosening. (Reprinted with permission from Lazarus MD, Jensen KL, Southworth C, Matsen FA III. The radiographic evaluation of keeled and pegged glenoid component insertion. J Bone Joint Surg Am 2002;84-A:1174-82.)
cementing and pressurization was repeated 4 times, ensuring no cement was applied to the articular surface of the bone. No cement was applied to the component prior to insertion. The component was then inserted, impacted to ensure complete seating, and excess cement removed. The humeral component was then inserted. Preoperative axillary lateral radiographs were used to grade glenoid morphology using the system of Walch,17 and this was confirmed intraoperatively. A subgroup with posterior glenoid wear was defined as those with Walch type B1, B2, and C glenoid morphology, and a concentric wear group was defined as all other groups (Walch type A1, A2). Complete postoperative radiographs, including anteroposterior (AP), axillary lateral (AL), and scapular lateral (SL), were performed either prior to hospital discharge or at the first postoperative visit. Radiographs were then analyzed for sufficient quality for review based on the criteria of Lazarus.13 Of the 81 radiographs reviewed, 69 were considered acceptable for inclusion in this study. Postoperative radiographs were reviewed for radiolucencies at the bonecement interface to assess cement fixation at the pegs. The subchondral bone-component interface was reviewed to
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Figure 3 Illustration depicting the grading system used to assess radiolucencies at the component- subchondral bone interface (seating). Although the figure shows a keeled component, we believe the system can be used for pegged components as the fixation method is not relevant to the component-subchondral bone interface. Grade finding: A, complete component seating; B, < 25% incomplete contact, single radiograph; C, 25-50% incomplete contact, single radiograph; D, <50% incomplete contact, both radiographs; E, > 50% incomplete contact, single radiograph. (Reprinted with permission from Lazarus MD, Jensen KL, Southworth C, Matsen FA III. The radiographic evaluation of keeled and pegged glenoid omponent insertion. J Bone Joint Surg Am. 2002;84-A:1174-82.)
assess glenoid component seating. The quality of component fixation (Table I, Figure 2) and seating (Table II, Figure 3) were assessed by the criteria of Lazarus for pegged components.13 As these criteria were initially developed for a glenoid component with 4 pegs, we modified the criteria by combining the 2 middle pegs into our single central peg. Of the 69 radiographs reviewed, 22 were associated with posterior glenoid wear and allocated to the posterior wear subgroup. The cement fixation grade and seating grade of each glenoid component was assessed 4 times. Each grading was converted to a numeric score (0-5) for fixation and (0-4) for seating, from which the mean score for fixation and a mean score for seating of each component were calculated. This was designated as the shoulders’ final scores. The final scores were used to calculate the study group mean scores of fixation and seating.
Statistical analysis The influence of preoperative glenoid morphology on component seating was assessed using the 2-tailed Fisher’s exact test, with significance set at the P < .05 level. With
22 patients in the posterior wear group and 47 patients in the concentric wear group, there is greater than 80% power (a level 0.05) to detect a 34% difference in the ‘‘better’’ shoulder seating grades, if that percentage is at least 90% in the concentric wear group. The intraobserver and interobserver reliability of each grading system was calculated with the Pearson product-moment correlation coefficient.
RESULTS A summary of results, including preoperative glenoid wear pattern, is given in Table III. Nineteen shoulders had a dual sized glenoid component inserted and 22 shoulders had significant preoperative posterior glenoid wear (Walch type B2).17 When the radiolucency grade of cement fixation was converted to a numeric scale of 0 (no radiolucency) to 5 (grossly loose), the mean cementing score was 0.14 + 0.06. Of the 69 shoulders, 62 (90%) had no radiolucencies, 4 had grade 1, and 3 had grade 2 (Table III). No shoulder was considered more than grade 2.
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Table I Grading scale for radiolucencies about pegged glenoid components grade 0 No radiolucency 1 Incomplete radiolucency around one or two pegs 2 Complete radiolucency (£2 mm wide) around one peg only, with or without incomplete radiolucency around one other peg 3 Complete radiolucency (£2 mm wide) around two or more pegs 4 Complete radiolucency (>2 mm wide) around two or more pegs 5 Gross loosening
Table II Grading scale for completeness of glenoid component seating grade Findings
Figure 4 Initial postoperative axillary lateral radiograph. Solid arrow indicates the position at the posterior glenoid rim of residual cement between component and subchondral bone. Solid line ‘‘A’’ is the proportion of unsupported glenoid component which is less than 10%.
Figure 5 Initial anterioposterior radiograph of the same patient as seen in figure 8. Solid arrow ‘‘A’’ points to a thin line of cement passing along the entire length of the glenoid component. Although this is classified as grade E seating (>50% incomplete contact, single radiograph), we believe that when the axillary lateral radiograph is considered (see Figure 4), the amount of component seating is more accurately represented as grade B (< 25% incomplete contact, single radiograph).
When the radiolucency grade of component seating was converted to a numeric scale of 0 (complete seating) to 4 (> 50% incomplete contact, single radiograph), the mean component seating score was 0.62 + 0.13. Forty-four shoulders had grade A (complete)
A Complete component seating B <25% incomplete contact, single radiograph C 25-50% incomplete contact, single radiograph D <50% incomplete contact, both radiographs E >50% incomplete contact, single radiograph
seating (64%), 15 had grade B, 6 had grade C, none had grade D, and 4 had grade E (Table III). Twenty-one of 22 shoulders (96%) with preoperative posterior wear glenoid morphology (Walch type B2)17 had adequate grade A, B, or C seating, and the other was considered inadequate grade E seating. Forty-four of the 47 shoulders (94%) with preoperative concentric wear glenoid morphology had adequate grade A, B, or C seating, and the remaining 3 were considered inadequate grade E seating. The dual size glenoid component was used in 9 of 22 shoulders with posterior wear (41%), compared to 10 of the 47 with concentric wear (21%). The radiographic ratings for radiolucencies of cement fixation were similar for interobserver and intraobserver reliability (0.86 and 0.83, respectively). The observers mean scores agreed to within 1 grade of each other at all times. The radiographic interpretation of component seating was also similar for interobserver and intraobserver reliability (0.89 and 0.90, respectively). The observers mean scores agreed to within 1 grade of each other 90% of the time. DISCUSSION The combined techniques of glenoid reaming, a size matched glenoid component, pegged glenoid fixation, and instrumented cement pressurization results in a low incidence of early radiolucencies about the glenoid component in TSA for glenohumeral osteoarthritis. Although the relationship between this lower incidence and long-term glenoid loosening is uncertain, these results compare favorably to others in which early radiolucencies have been assessed.
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Table III Individual results of glenoid type,(17), fixation grade,(11) seating grade,(11) and type of glenoid component used Glenoid Type
Total
Fixation Grade
Number
A1
32
0 1 2 3
29/32 3/32 0/32 0/32
A2
7
0 1 2 3
6 1 0 0
B1
8
0 1 2 3
7 0 1 0
B2
22
0 1 2 3
20 0 2 0
Seating Grade A B C D E A B C D E A B C D E A B C D E
Number 18 8 3 0 3 5 1 1 0 0 5 2 1 0 0 16 4 1 0 1
Component Std¼ 26 Dual¼ 6
Std¼ 4 Dual¼ 3
Std¼ 7 Dual¼ 1
Std¼ 13 Dual¼ 9
Dual, dual radius glenoid component; Std, standard size component.
Initial radiolucencies at the cement-bone interface may weaken component fixation. Radiolucencies at the subchondral bone-component interface imply incomplete component seating, which has been shown to increase rocking forces at the component edge.6 The relative importance of radiolucencies at the subchondral bone-component interface compared to the cement-bone interface is not known; however, we consider limiting the prevalence of both important. The low incidence of radiolucencies related to fixation at the cement-bone interface in this study is likely multifactorial. Component design appears important. Pegged fixation appears to have reduced radiolucencies compared to keeled designs.12,13 We feel that this may be due to several factors, including the precise fit between the pegs and bone holes. The cylindrical size of the bone holes allows more effective cement pressurization with the precise fit of the pressurizing instrument combined with a pressurizer sponge. As less bone is removed and less cement used, the heat generated by the cement is reduced and may limit surrounding thermal necrosis.4 We reported a greater prevalence of radiolucencies associated with incomplete component seating (25/69) than with cement fixation (7/69). There were 4 components with grade E seating (> 50% incomplete contact, as seen on a single radiograph). The implication from the grading system is that these grade E components are inadequately seated and, therefore, more likely to fail. However, despite these 4 components fulfilling the radiographic criteria for grade E, we felt they were all were clinically stable,
actually had greater than 90% bone contact, and, therefore, a similar prognosis to components with grade B seating (<25% incomplete contact, single radiograph). This disagreement with the rating system arose because Lazarus defines ‘‘a component that was backed by an intervening layer of cement was deemed as unsupported,’’ according to a single AP radiograph. While we agree with this principle, difficulties arise using the classification system when a small amount of cement remains on the posterior rim of the glenoid (Figure 4). We consider the component in Figure 4 well seated with at least 90% component-bone seating; however, this cement rim appears as a long cement line along the component-bone interface on the AP radiograph and may appear often to pass the entire length of the component (Figure 5). We considered that this AP appearance was, therefore, classified as >50% incomplete contact based on this single radiograph; however, the axillary lateral radiograph findings of > 90% complete seating with a small posterior rim of cement are not accounted for. We suggest that the classification system be modified to account for both the AP and the axillary radiograph appearances in all grades. There was no difference in seating grades for the subgroup with preoperative posterior glenoid wear. We attribute this to the ability of the component to be accurately sized to the available glenoid bone stock in all cases using, when required, the dual size glenoid. The main limitations of our study include the use of plain radiographs. The accuracy of plain radiographs has been questioned when interpreting radiolucencies
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about a glenoid component9,11 An analysis using fluoroscopy or computerized tomography would be a more accurate method of assessing component fixation and seating. Plain radiography is still the most common imagining method used to review TSA components. The axillary lateral radiograph is difficult to standardize; however, we feel that it is important to use these to obtain imaging in two planes. The amount of cement used for pegged components is less than for traditional keeled components, and is potentially more difficult to assess on radiographs. The use of high quality radiographs in this study should minimize these issues. A second limitation of this study is that it does not determine the relative importance of each individual technique or design described to improve glenoid fixation but reports on their combined results. The relative importance of the glenoid reaming, instrumented cementing technique, pegged design, dual radius design, or other factors cannot be ascertained from this study. Early radiolucencies about a glenoid component are a common finding in TSA. This study demonstrates that the use of surgical techniques to improve glenoid fixation (glenoid reaming, instrumented cement pressurization, and a size-matched polyethylene pegged glenoid) leads to a low incidence of early radiolucencies. The long-term effect of reduced early radiolucencies in these patients remains to be determined.
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