Keeled Components Research Articles

Polyethylene glenoid component fixation geometry influences stability in total shoulder arthroplasty

Glenoid component stability is essential to ensure successful long-term survivability following total shoulder arthroplasty. As such, this computational study assessed the stability of five all-polyethylene glenoid components (Keel, Central-Finned 4-Peg, Peripheral 4-Peg, Cross-Keel, and Inverted-Y), using simulated joint loading in an osteoarthritic patient cohort. Stability was assessed on the basis of component micromotion in the tangential and normal directions. Maximum tangential micromotion occurred in the Cross-Keel (146 ± 46 µm), which was significantly greater (p < .001) than the other components. Maximum normal micromotion occurred in the Inverted-Y (109 ± 43 µm), which was significantly greater (p ≤ .002) than the other four components. In general, the Central-Finned 4-Peg exhibited the least normal and tangential micromotion, while the keeled components shown the highest normal and tangential micromotion. This study suggests that modifications to keeled designs do not improve component stability under the conditions tested, and pegged components show superior computational stability.

Risk of Perforation Is High During Corrective Reaming of Retroverted Glenoids: A Computer Simulation Study

Corrective anterior reaming is an accepted method for addressing retroversion in a biconcave retroverted (Walch classification, type B2) glenoid in anatomic total shoulder arthroplasty. However, concern still exists regarding early glenoid component failure in the setting of severe retroversion, which may be related to loss of component containment and/or violation of subchondral bone resulting from reaming. The goal of this study was to determine what characteristics of B2 glenoids are less amenable to corrective reaming by virtually implanting anatomic glenoid components. (1) How much medial reaming is required to correct the version of a B2 glenoid to an acceptable position? (2) Are glenoids with more severe retroversion (> 25°) at higher risk of component perforation than less retroverted glenoids? (3) Is correcting to 10° of retroversion associated with greater risk as compared with reaming to 15°? (4) How does corrective reaming affect the underlying bone density on the glenoid face of B2 glenoids? A series of 71 patients with B2 glenoids (posterior subluxation of the humeral head with posterior bone loss) with CT scans who were indicated for shoulder arthroplasty were reviewed. Forty-four of 71 glenoids (62.5%) had < 25° of native retroversion. Anatomic glenoid implants were then virtually implanted using three-dimensional CT software that allows for preoperative shoulder arthroplasty planning to correct native retroversion to 15° or 10° of retroversion using both a central peg with an inverted triangle peg configuration or a keel. The amount of reaming of the anterior glenoid required to correct retroversion, perforation of peripheral pegs, or keel was compared. Additionally, assessment of the surface area of the glenoid that had poor bone density (defined as cancellous bone under the subchondral plate) was analyzed by the software after correction. Correction to 15° of retroversion required 5 ± 3 mm of reaming, and correction to 10° of retroversion required 8 ± 3 mm of reaming to obtain at least 80% seating. Peripheral peg perforation with correction to 15° occurred in 15 of 27 (56%) glenoids with > 25° of retroversion compared with 10 of 44 (23%) of glenoids with < 25° of retroversion (relative risk [RR], 2.4; 95% confidence interval [CI], 1.3-4.6; p = 0.006). There was no difference in perforation with keeled components. Increased correction to 10° did not increase the risk of component perforation. When correction to 15°, glenoids with higher native version (> 25°) had a greater risk of poor bone quality support (10 of 27 [37%]) when compared with glenoids with less version (four of 44 [9%]; RR, 4.1; 95% CI, 1.5-12.8; p = 0.006). Increased correction resulted in 13 of 27 (48%) glenoids with version > 25° having poor bone density versus 10 of 44 (23%) with ≤ 25° of version (RR, 2.1; 95% CI, 1.1-4.1; p = 0.028). There is a high risk of vault perforation after corrective reaming. Glenoid retroversions > 25° are at a higher risk of having poor bone quality supporting the component. When contemplating options for patients with severe retroversion, surgeons should consider alternatives other than corrective reaming if achieving normal glenoid version is desired.

Paper #2 - Radiographic and Clinical Comparison of Pegged and Keeled Glenoid Components Using Modern Cementing Techniques: Midterm Results of a Prospective Randomized Study

Background: Glenoid component loosening remains a significant issue after anatomic shoulder arthroplasty. Pegged glenoid components have shown better lucency rates than keeled components in the short term, however, mid to long-term results have not fully been determined. We previously reported early outcomes of this randomized, controlled group of patients, with higher glenoid lucency rates in patients with a keeled glenoid. The purpose of this study was to evaluate the radiographic and clinical outcomes of pegged and keeled glenoid components at midterm follow-up.

Radiographic and clinical comparison of pegged and keeled glenoid components using modern cementing techniques: midterm results of a prospective randomized study

Glenoid component loosening remains a significant issue after anatomic shoulder arthroplasty. Pegged glenoid components have shown better lucency rates than keeled components in the short term; however, midterm to long-term results have not fully been determined. We previously reported early outcomes of the current randomized controlled group of patients, with higher glenoid lucency rates in those with a keeled glenoid. The purpose of this study was to evaluate the radiographic and clinical outcomes of these components at minimum 5-year follow-up. Fifty-nine total shoulder arthroplasties were performed in patients with primary glenohumeral osteoarthritis. Patients were randomized to receive either a pegged or keeled glenoid component. Three raters graded radiographic glenoid lucencies. Clinical outcome scores and active mobility outcomes were collected preoperatively and at yearly postoperative appointments. Of the 46 shoulders meeting the inclusion criteria, 38 (82.6%) were available for minimum 5-year radiographic follow-up. After an average of 7.9 years, radiographic lucency was present in 100% of pegged and 91% of keeled components (P = .617). Grade 4 or 5 lucency was present in 44% of pegged and 36% of keeled components (P = .743). There were no differences in clinical outcome scores or active mobility outcomes between shoulders with pegged and keeled components at last follow-up. Within the initial cohort, 20% of the keeled shoulders (6 of 30) and 7% of the pegged shoulders (2 of 29) underwent revision surgery (P = .263). Kaplan-Meier analysis showed no significant difference in survival rates between groups (P = .560). At an average 7.9-year follow-up, non-ingrowth, all-polyethylene pegged glenoid implants are equivalent to keeled implants with respect to radiolucency, clinical outcomes, and need for revision surgery.

No correlation between radiolucency and biomechanical stability of keeled and pegged glenoid components

BackgroundThe purpose of this study was to examine biomechanical properties and the degree of radiolucency of two cemented basic glenoid designs for total shoulder arthroplasty. Our hypothesis was that a component with increased micro-motion in the laboratory at time zero would also exhibit a greater amount of radiolucency in patients at a minimum of 2 years post total shoulder arthroplasty.MethodsThirty cadaveric shoulders were divided into 2 groups (keel vs. peg). The glenoid components were first loaded with a single axial eccentric force of 196 N in all orientations and then with a transversal load of 49 N to simulate in vivo loads with abduction. Displacement of the glenoid component was determined with four different linear variable-differential transducers. In the second phase, 56 antero-posterior x-rays of 52 patients with either the same keeled (n = 24) or pegged (n = 32) glenoid component with a minimum of 24 months follow-up were evaluated for radiolucency.ResultsBiomechanically the pegged glenoid showed a significant increase in micro-motion during eccentric axial loading as well as during combined loading in the anterior, posterior, and inferior position as compared to the keeled glenoid (p < 0.05). In contrast all results were significant with greater radiolucency for the keeled glenoid component (p = 0.001).ConclusionWhile the pegged component exhibited a greater amount of micro-motion during biomechanical testing, radiolucency was greater in patients with a keeled component. These findings provide support for both components from different perspectives and highlight the need for well-constructed studies to determine whether glenoid design has an effect on clinical outcome, because influences are multifactorial and biomechanical forces may not recreate forces seen in vivo.

Survival of the pegged glenoid component in shoulder arthroplasty: part II

Loosening of the glenoid component is a primary reason for failure of an anatomic shoulder arthroplasty. Pegged glenoids were designed in an effort to outperform keeled components. This study evaluated the midterm clinical and radiographic survival of a single implant design with implantation of an in-line pegged glenoid component and identified risk factors for radiographic loosening and clinical failure. There were 330 total shoulder arthroplasties that had been implanted with a cemented, all-polyethylene, in-line pegged glenoid component evaluated with an average clinical follow-up of 7.2 years. Of these shoulders, 287 had presurgical, initial postsurgical, and late postsurgical radiographs (mean radiographic follow-up, 7.0 years). At most recent follow-up, 30 glenoid components had been revised for aseptic loosening. This translated to a rate of glenoid component survival free from revision for all 330 shoulders of 99% at 5 years and 83% at 10 years. Of 287 glenoid components, 120 were considered loose on the basis of radiographic evaluation. Four humeral components were considered loose. Component survival (Kaplan-Meier) free from radiographic failure at 5 and 10 years was 92% and 43%. Severe presurgical glenoid erosion (Walch A2, B2, C) and patient age <65 years were risk factors for radiographic failure. Late humeral head subluxation was associated with radiographic failure. Despite the predominant thinking that pegged glenoid components may be superior to keeled designs, midterm radiographic and clinical failure rates were high with this pegged component design, particularly after 5 years. Advanced presurgical glenoid erosion and younger patient age are risk factors for radiographic loosening. Revision rates underestimate radiographic glenoid loosening.

Failure of the Glenoid Component in Anatomic Total Shoulder Arthroplasty

Although glenoid component failure is one of the most common complications of anatomic total shoulder arthroplasty, substantial evidence from the recent published literature is lacking regarding the temporal trend in the rate of this complication and the risk factors for its occurrence. We conducted a systematic review and identified twenty-seven articles presenting data on glenoid component failure rates that met the inclusion criteria. These articles represented data from 3853 total shoulder arthroplasties performed from 1976 to 2007. Asymptomatic radiolucent lines occurred at a rate of 7.3% per year after the primary shoulder replacement. Symptomatic glenoid loosening occurred at 1.2% per year, and surgical revision occurred at 0.8% per year. There was no significant evidence that the rate of symptomatic loosening has diminished over time. Keeled components had greater rates of asymptomatic radiolucent lines compared with pegged components in side-by-side comparison studies. However, as a result of wide variability in outcomes reporting, only sex, Walch class, and diagnosis were significantly associated with the risk of glenoid component failure in the overall analysis. This is the first systematic review of the published evidence on glenoid component failure. Although the authors of individual articles proposed various risk factors for glenoid component failure, many of these relationships were not significant in the present study. A consistent methodological approach to future investigations is likely to improve the quality of the evidence on which patients, techniques, and prostheses are selected for total shoulder arthroplasty.

Fully uncemented glenoid component in total shoulder arthroplasty

Loosening of the glenoid component remains the most common problem in total shoulder arthroplasty. It has been described that the round-backed, all-polyethylene components with cemented peg fixation perform better biomechanically and clinically than flat-backed, metal-backed, or keeled components. However, side effects of cementing have been described. We hypothesized that cementing of a specific type of all-polyethylene glenoid component with 3 peripheral pegs and 1 central anchor peg is not necessary to obtain good clinical and radiologic results. Thirty-four shoulders (34 patients), with a mean follow-up of 28.3 months, were evaluated clinically with the Constant-Murley score and the SF-12 Health Survey score. The fixation of the glenoid component was evaluated with computed tomography scan. The Constant-Murley score increased from 40.2 points (range, 13-73 points) preoperatively to 72points (range, 54-93 points) postoperatively. The SF-12 Physical Component Summary score was 45, and the SF-12 Mental Component Summary score was 50. No signs of loosening were seen around the pegs or glenoid in 30 shoulders. Signs of loosening were seen around the central anchor peg and the peripheral pegs in 4 shoulders. There was no statistical difference between the clinical outcome of patients with and without signs of loosening. The clinical and radiologic evaluation of an uncemented all-polyethylene glenoid is promising, with good clinical results and with no signs of loosening in 88% of the patients on computed tomography scans.

Rates of Radiolucency and Loosening After Total Shoulder Arthroplasty with Pegged or Keeled Glenoid Components

The objective of this study was to conduct a meta-analysis and cost-effectiveness analysis of the effect of glenoid design on radiolucency, loosening, and revision after total shoulder arthroplasty. We conducted a systematic review of PubMed, MEDLINE, Embase, the Cochrane Central Register of Controlled Trials, and CINAHL with use of a search for the terms arthroplasty AND shoulder AND (peg OR keel). Data on study design and on the end points of radiolucency, loosening, and revision were extracted independently and in duplicate. Random-effect models were used to calculate the pooled risk ratio and risk difference. The risk difference was used to estimate the number needed to treat (the number of individuals who would have to receive a pegged component to avoid one loosening or revision). Eight studies with a total of 1460 patients (mean age, sixty-seven years) were included. The mean study quality was 1.75 points (95% confidence interval [CI], 1.26 to 2.24) on the 3-point modified Jadad scale. There was no significant difference in the risk of any radiolucency (risk ratio, 0.42; 95% CI, 0.12 to 1.42) or in the risk of severe radiolucency (risk ratio, 0.65; 95% CI, 0.23 to 1.82) between pegged and keeled components. The pooled risk ratio for revision was 0.27 (95% CI, 0.08 to 0.88) in favor of pegged components (p = 0.028). At a cost-effectiveness threshold of $50,000 per quality-adjusted life year, pegged components can be between $2325 and $40,920 more expensive than keeled components and still be cost-effective. Our study produced evidence that pegged glenoid components were associated with a lower revision risk compared with keeled components. However, the difference was rather small and will therefore be most meaningful to high-volume shoulder arthroplasty centers. Because of the similarity between primary and secondary costs, pegged glenoid designs were more cost-effective than keeled glenoid designs.

Radiographic comparison of pegged and keeled glenoid components using modern cementing techniques: A prospective randomized study

Modern cementing techniques have improved glenoid fixation, reduced glenoid lucency seen with keeled components, and may eliminate differences attributable to glenoid design. The purpose of this study was to determine the effect of glenoid design on immediate and follow-up radiographic lucency of pegged and keeled glenoid components, using modern cementing techniques. Fifty-three total shoulder arthroplasties were performed in patients with primary glenohumeral osteoarthritis. Patients were randomized prospectively to receive either a pegged or keeled glenoid component. Three raters graded radiographic glenoid lucencies. On immediate radiographs, there was no significant difference in the rate of glenoid lucency between pegged (0%) and keeled (15%) glenoid components (P = .128). However, after an average of 26 months, the rate of glenoid lucency was significantly higher in patients with keeled components (46%) compared to patients with pegged components (15%) (P = .003). Even with modern cementing techniques, pegged glenoid components remain radiographically superior to keeled glenoid components.

Stability of Cemented in-Line Pegged Glenoid Compared with Keeled Glenoid Components in Total Shoulder Arthroplasty

Considerable interest has been focused on the design of the glenoid component used in total shoulder arthroplasty in order to reduce the risk of loosening. One design-related feature that has attracted attention is whether to use pegged or keeled cemented glenoid components. The main purpose of this study was to compare the fixation of cemented keeled glenoid components with that of cemented in-line pegged glenoid components. In a prospective randomized study, we compared the stability of cemented, all-polyethylene, keeled glenoid components and cemented, all-polyethylene, in-line three-pegged glenoid components by radiostereometric analysis. Twenty-seven shoulders in twenty-five patients with osteoarthritis (twenty-two shoulders had primary and five shoulders had secondary osteoarthritis) were included. There were sixteen women and nine men, and the mean age was sixty-four years. Radiostereometric analysis and conventional radiographs were carried out at five days, at four months, and at one and two years postoperatively. The mean Constant and Murley score preoperatively and two years postoperatively was 25 and 70, respectively, for shoulders with the keeled glenoid component and 22 and 70 for the shoulders with a pegged component. No significant difference was detected between groups with regard to the average micromigration of the glenoid components at any of the time points. The average translation was <1 mm, while the median value was <0.3 mm at two years, with no significant difference between the different axes. In five shoulders (three with the keeled component and two with the pegged component), translation at two years was >1 mm. In fourteen shoulders (eight with the keeled and six with the pegged component), the rotation around one or several axes was >2 degrees . We were not able to detect any specific pattern with regard to movement for either type of component nor were we able to detect any difference between the two types of components in the way they migrated, if migration occurred. Cemented all-polyethylene keeled or in-line three-pegged glenoid components appear to have similar stability during the first two years after surgery. Studies with a longer follow-up period are needed to relate these findings to long-term clinical and radiographic outcomes.

Photoelastic comparison of strains in the underlying glenoid with metal-backed and all-polyethylene implants

An alteration in the stress and strain environment following arthroplasty is believed to lead to bone remodeling, which can trigger implant loosening and subsequent failure. Bone remodeling, while well-studied in hip arthroplasty, has received less attention in total shoulder replacement. This study examines differences in strain states between intact glenoids and following replacement with an uncemented metal backed keeled component and a cemented all polyethylene pegged component with the same articular geometry, using the photoelastic method. Strain measurements were taken in glenoids before and after implantation under 4 loading conditions corresponding to 4 abduction angles: 0 degrees, 30 degrees, 60 degrees, and 90 degrees. Shear strains increased at most locations following reconstruction with both of the implants. Uncemented, keeled metal backed implants produced areas of higher cortical shear strains compared to cemented, all PE pegged implants.

A study of the micromovement of pegged and keeled glenoid components compared using radiostereometric analysis

In a prospective, randomized study between 2000 and 2004, 20 patients with primary osteoarthritis of the shoulder had a total shoulder arthroplasty with radiostereometric analysis, 10 with keeled and 10 with pegged glenoid components. The relative movement of the glenoid component with respect to the scapula was measured over a 24-month period. Three keeled and five pegged glenoids needed reaming for erosion. The largest translations occurred along the longitudinal axis (mean of 1.35 mm for keeled eroded components) (P = .017 for keeled vs pegged components and P = .013 for eroded vs non-eroded components). Both of the other translation axes showed no significant differences. The highest maximum total point movement at 24 months was 2.57 mm for keeled eroded components and 1.64 mm for pegged eroded components (P = .029 for keeled vs pegged components and P = .023 for eroded vs non-eroded components). The largest rotation was anteversion, with mean values of 5.5 degrees for keeled eroded components and 4.8 degrees for pegged eroded components (P = .658 for keeled vs pegged components and P = .90 for eroded vs non-eroded components). The mean varus tilt was 4.5 degrees for keeled eroded components compared with 2.3 degrees for pegged eroded components (P = .004 for keeled vs pegged components and P = .016 for eroded vs non-eroded components), and finally, anterior-posterior rotation mean values were 3.5 degrees for keeled eroded components and 1.1 degrees for pegged eroded components (P = .022 for keeled vs pegged components and P = .04 for eroded vs non-eroded components). In conclusion, whereas all components moved, radiostereometric analysis revealed increased migration with keeled components, exacerbated by glenoid erosion. Furthermore, a distinctive pattern of migration was identified over the 2-year period.

The mechanism of failure in cemented glenoid components — an in vitro study

Loosening of the glenoid component is a primary reason for failure of an anatomic shoulder arthroplasty. Pegged glenoids were designed in an effort to outperform keeled components. This study evaluated the midterm clinical and radiographic survival of a single implant design with implantation of an in-line pegged glenoid component and identified risk factors for radiographic loosening and clinical failure.There were 330 total shoulder arthroplasties that had been implanted with a cemented, all-polyethylene, in-line pegged glenoid component evaluated with an average clinical follow-up of 7.2 years. Of these shoulders, 287 had presurgical, initial postsurgical, and late postsurgical radiographs (mean radiographic follow-up, 7.0 years).At most recent follow-up, 30 glenoid components had been revised for aseptic loosening. This translated to a rate of glenoid component survival free from revision for all 330 shoulders of 99% at 5 years and 83% at 10 years. Of 287 glenoid components, 120 were considered loose on the basis of radiographic evaluation. Four humeral components were considered loose. Component survival (Kaplan-Meier) free from radiographic failure at 5 and 10 years was 92% and 43%. Severe presurgical glenoid erosion (Walch A2, B2, C) and patient age <65 years were risk factors for radiographic failure. Late humeral head subluxation was associated with radiographic failure.Despite the predominant thinking that pegged glenoid components may be superior to keeled designs, midterm radiographic and clinical failure rates were high with this pegged component design, particularly after 5 years. Advanced presurgical glenoid erosion and younger patient age are risk factors for radiographic loosening. Revision rates underestimate radiographic glenoid loosening.

Incidence of Early Radiolucent Glenoid Lines in Patients Having Total Shoulder Replacements

Glenoid loosening is the most common long-term complication occurring after total shoulder replacement. Imprecise cement technique and glenoid preparation may result in early radiolucent glenoid line formation. Early radiolucent lines may indicate inadequate initial fixation, which may contribute to early loosening. Improved cement techniques, refined instrumentation, and glenoid component design all may reduce early radiolucent lines. In our study, postoperative anteroposterior and axillary radiographs were obtained after 68 total shoulder replacements done by one surgeon using either an old free-hand, manual packing technique before November 1998 (n = 28) or a new instrument preparation and pressurization technique since November 1998 (n = 40). Three orthopaedic surgeons blindly reviewed the radiographs for the presence and thickness (mm) of radiolucent lines. The newer instrumented pressurization group had a lower incidence of radiolucent lines than the old manually packed group. In the new subgroup, pegged components had a lower incidence of radiolucent lines than keeled components. The incidence of radiolucent lines seems to be reduced using specially designed instruments, new glenoid designs, and modern cement techniques, which may lead to reduced long-term glenoid loosening. Therapeutic study, Level III-2 (retrospective cohort study). See the Guidelines for Authors for a complete description of levels of evidence.

Radiographic comparison of pegged and keeled glenoid components

Glenoid loosening is one reason for failure of total shoulder arthroplasty. Several factors, including radiographic lucency, have been shown to be associated with glenoid loosening. The purpose of this study was to assess the correlation between glenoid design and immediate radiographic lucency in a prospective randomized clinical trial. Total shoulder arthroplasty was performed in 43 patients over a 2-year period. Twenty-three patients were randomized into the keel group and twenty patients into the pegged group. Postoperative radiographs obtained within 6 weeks of surgery were evaluated by 3 raters to determine glenoid lucency. On a scale from 0 (no lucency) to 5 (gross lucency and component loosening), the rate of lucency was 39% (9/23) in the keeled components, which was significantly higher than the rate of 5% (1/20) observed in the pegged components (P = .026). Patient age, gender, and glenoid size did not significantly affect glenoid component lucency (P > .05). The consistency reliability among raters (Cronbach alpha) was 0.87, and the intertester reliability was 0.87. Pegged glenoid components have less radiographic lucency when compared with keeled glenoid components in the immediate postoperative period.

The radiographic evaluation of keeled and pegged glenoid component insertion.

Radiolucent lines about the glenoid component of a total shoulder replacement are a common finding, even on initial postoperative radiographs. The achievement of complete osseous support of the component has been shown to decrease micromotion. We evaluated the ability of a group of experienced shoulder surgeons to achieve complete cementing and support in a series of patients managed with keeled and pegged glenoid components. We reviewed the initial postoperative radiographs of 493 patients with primary osteoarthritis who had been managed with total shoulder arthroplasty by seventeen different surgeons. One hundred and sixty-five patients were excluded because of inadequate radiographs, leaving 328 patients available for review. Of these, thirty-nine patients had a keeled component and 289 had a pegged component. The method of Franklin was used to grade the degree of radiolucency around the keeled components, and a modification of that method was used to grade the degree of radiolucency around the pegged components. The efficacy of component seating on host subchondral bone was evaluated with a newly constructed five-grade scale based on the percentage of the component that was supported by subchondral bone. Each radiograph was graded four times, by two separate reviewers on two separate occasions. Radiolucencies were extremely common, with only twenty of the 328 glenoids demonstrating no radiolucencies. On a numeric scale (with 0 indicating no radiolucency and 5 indicating gross loosening), the mean radiolucency score was 1.8 +/- 0.9 for keeled components and 1.3 +/- 0.9 for pegged components (p = 0.0004). After defining categories of "better" and "worse" cementing, we found that pegged components more commonly had "better cementing" than did keeled components (p = 0.0028). Incomplete seating was also common, particularly among patients with keeled components. Ninety-five of the 121 pegged components that had been inserted by the most experienced surgeon had "better cementing," compared with eighty-five of the 168 pegged components that had been inserted by the remaining surgeons (p < 0.00001). Perfectly cementing and seating a glenoid replacement is a difficult task. Radiolucencies and incomplete component seating occur more frequently in association with keeled components compared with pegged components. Surgeon experience may be an important variable in the achievement of a good technical outcome.