Orthopedics

Feature Article 

Osseous Integration of the Central Peg of an All-Polyethylene Glenoid With 3 Different Surgical Techniques

Patrick J. Denard, MD; Reuben Gobezie, MD; Justin W. Griffin, MD; Anthony A. Romeo, MD; Evan Lederman, MD

Abstract

All-polyethylene glenoid components designed for osseous integration of the central peg can be placed with no graft (NG), autogenous bone graft (ABG), or demineralized bone matrix (DBM). The purpose of this study was to compare osseous integration with these 3 techniques. A randomized controlled trial was performed of 153 total shoulder arthroplasties using a pegged allpolyethylene glenoid component designed for osseous integration. Central peg treatment included NG, ABG, or DBM. The primary outcome was central peg osseous integration defined as bone presence between the central fins 1 year postoperatively. Central osseous integration was observed in 90% of cases treated with ABG, 68% of cases treated with DBM, and 68% of cases treated with NG (P=.022). Postoperative Wirth grading revealed radiolucency around the central peg (grade 1) in 2.4% of cases with ABG, 5.4% of cases with DBM, and 9.8% of cases with NG (P=.134). At short-term follow-up, osseous integration of the central peg of an all-polyethylene glenoid designed for bony growth between the central fins appears to be highest when treating the central peg with ABG compared with leaving the central peg untreated or using DBM. [Orthopedics. 2020;43(5):278–283.]

Abstract

All-polyethylene glenoid components designed for osseous integration of the central peg can be placed with no graft (NG), autogenous bone graft (ABG), or demineralized bone matrix (DBM). The purpose of this study was to compare osseous integration with these 3 techniques. A randomized controlled trial was performed of 153 total shoulder arthroplasties using a pegged allpolyethylene glenoid component designed for osseous integration. Central peg treatment included NG, ABG, or DBM. The primary outcome was central peg osseous integration defined as bone presence between the central fins 1 year postoperatively. Central osseous integration was observed in 90% of cases treated with ABG, 68% of cases treated with DBM, and 68% of cases treated with NG (P=.022). Postoperative Wirth grading revealed radiolucency around the central peg (grade 1) in 2.4% of cases with ABG, 5.4% of cases with DBM, and 9.8% of cases with NG (P=.134). At short-term follow-up, osseous integration of the central peg of an all-polyethylene glenoid designed for bony growth between the central fins appears to be highest when treating the central peg with ABG compared with leaving the central peg untreated or using DBM. [Orthopedics. 2020;43(5):278–283.]

Total shoulder arthroplasty (TSA) is associated with good functional outcomes and reasonable survival in the majority of patients.1,2 However, glenoid component loosening remains a common cause for failure.3,4

In an effort to improve on long-term stability, several manufacturers offer the option of an all-polyethylene glenoid component with a large central peg designed for bony growth or integration between the central fins. Several studies have investigated bony growth between the central fins following the use of such components. However, treatment of the central peg at the time of implantation in these studies has varied from no treatment5,6 to the application of autogenous humeral head graft (ABG) around the central peg7–9 to the use of demineralized bone matrix (DBM). Each of these techniques may have advantages and disadvantages. Applying no graft is the quickest method of treatment. Demineralized bone matrix is easy to apply based on the consistency of the product, but it is an allograft and has increased cost. Autogenous humeral head graft is readily available but requires additional time for graft harvest and application to the central peg. While several studies have reported on bony growth between the central fins with an individual technique, to the authors’ knowledge no study has directly compared different techniques for managing the central peg.

The purpose of this study was to evaluate osseous integration of the central peg of an all-polyethylene glenoid designed for hybrid fixation with peripheral cement and central growth of bone between the fins. The hypothesis was that there would be no difference in osseous integration of the central peg between the 3 different surgical techniques.

Materials and Methods

Study Cohort

A multicenter prospective randomized controlled trial was performed of patients undergoing TSA to determine the rate of osseous integration of the central peg of an all-polyethylene glenoid with peripheral cement and 3 different central peg techniques: (1) ABG, (2) DBM, or (3) no central graft (NG). Institutional review board approval was obtained prior to commencing the study. The surgeries were performed by 3 fellowship-trained shoulder surgeons (P.J.D., R.G., E.L.) practicing at different centers. The inclusion criteria were a primary TSA with an intact rotator cuff and a minimum follow-up of 1 year. The exclusion criteria were revision arthroplasty, a Walch type C glenoid, and incomplete follow-up.

A power analysis was performed prior to enrollment based on previous non-comparative studies reporting up to a 68% difference in osseous integration of the central peg between different techniques. It was determined that a total of 41 patients were required in each group to have an 80% power to detect a 25% difference in osseous integration. On the basis of this analysis, 51 patients were enrolled in each group to account for potential loss to follow-up. Patients scheduled for a TSA who met the study criteria were invited to participate, consented, and were then randomized to 1 of the 3 treatment groups. No patient refused to participate. Overall, follow-up was obtained for 79% of the patients (119 of 151). In the ABG group, 1 patient was revised to a reverse shoulder arthroplasty prior to 1 year and 9 patients were lost to follow-up, for a total follow-up of 80%. In the DBM group, 14 patients were lost to follow-up, leaving 73% with complete follow-up. In the NG group, 10 patients were lost to follow-up, leaving 80% with complete follow-up. Baseline characteristics of the patients are presented in Table 1.

Baseline Characteristics

Table 1:

Baseline Characteristics

Surgical Technique

A deltopectoral approach was used to expose the shoulder. In all cases, the biceps was tenodesed to the pectoralis major tendon. A lesser tuberosity osteotomy or subscapularis peel, depending on surgeon preference, was used to access the glenohumeral joint. A complete release of the subscapularis tendon was performed. Next, the humeral head was resected with a free-handed anatomic cut, respecting native humeral head version and inclination. The humerus was prepared for placement of a short stem press-fit component (Univers Apex; Arthrex, Inc, Naples, Florida). The glenoid was then exposed and an allpolyethylene pegged glenoid (VaultLock; Arthrex, Inc) was placed (Figure 1). This implant has an in-line design with 3 pegs. The inferior and superior pegs are designed for cement fixation, while the central peg is designed for press-fit fixation with a drill size of 6.0 mm and central fin size of 7.5 mm. The implant is approved by the Food and Drug Administration for peripheral cement; treatment of the central peg is not specified in the approval. In all cases, the superior and inferior pegs were filled with cement and pressurized multiple times prior to implantation. The central peg was then treated according to 3 different techniques. In the ABG group, the resected humeral head was reamed to obtain cancellous bone graft, which was then compressed to the central peg using a dedicated bone graft application clamp. The reaming step was used to produce a slurry of bone that could be compressed between the fins. Bone graft was applied until all spaces between the central fins were filled. In the second group, DBM was compressed around the central peg. In the third group (NG), the polyethylene was untreated and implanted without bone graft or DBM. No cement was placed on the backside of the implant.

The all-polyethylene component used in this study had 3 inline pegs with an inner central peg diameter of 6.0 mm and outer fin diameter of 7.5 mm.

Figure 1:

The all-polyethylene component used in this study had 3 inline pegs with an inner central peg diameter of 6.0 mm and outer fin diameter of 7.5 mm.

Radiographic Evaluation

Osseous integration of the central peg was assessed on plain radiographs by 2 independent examiners (P.J.D., J.W.G.). Discrepancies in grading were rectified by re-review together and mutual agreement. Grashey (true glenohumeral antero-posterior view) and axillary radiographs were obtained preoperatively, immediately postoperatively, and 1 year postoperative. Glenoid loosening was assessed on a scale of 0 to 5 based on the Lazarus et al10 criteria for a pegged glenoid. Osseous integration was assessed on plain radiographs according to the Churchill et al5 and the Wirth et al11 criteria. In the former, bone between the central fins was graded as yes or no. This was used as the primary outcome of the study. In the latter, the bone presence around the central peg is graded 1 to 3, where bone in contact with the central peg accompanied by increased radiodensity between the fins is grade 3 (Figure 2), bone in contact with the central peg without increased density between the fins is grade 2, and osteolysis about the central peg is considered grade 1 (Figure 3).

One-year postoperative anteroposterior radiograph of a glenoid placed with autogenous bone graft around the central peg. There is complete osseous integration of the central peg (A). Anteroposterior up-close view showing bone presence between the central fins (B).

Figure 2:

One-year postoperative anteroposterior radiograph of a glenoid placed with autogenous bone graft around the central peg. There is complete osseous integration of the central peg (A). Anteroposterior up-close view showing bone presence between the central fins (B).

One-year postoperative anteroposterior up-close radiograph of a glenoid without bone graft with postoperative lucency around the central peg (arrowhead).

Figure 3:

One-year postoperative anteroposterior up-close radiograph of a glenoid without bone graft with postoperative lucency around the central peg (arrowhead).

Patient Evaluation

Function and range of motion were assessed preoperatively and 12 months postoperatively. Function was determined with the single assessment numeric evaluation score, American Shoulder and Elbow Surgeons score, Constant score, and visual analog scale pain score at each time point. Range of motion was assessed by an independent examiner using a goniometer to determine forward flexion and external rotation with the arm at the side. Internal rotation was estimated to the nearest spinal level.

Statistical Analysis

Continuous data were described by means and standard deviations. Chi-square tests were used to assess differences in osseous integration, Wirth grade, and Lazarus score. A univariate analysis was done to evaluate outcomes according to radiographic findings (osseous integration and glenoid loosening). A paired t test or sign test or Wilcoxon rank sum test was performed (depending on variable distribution) to analyze the difference in pre- and postoperative range of motion and functional outcome scores. Statistical analyses were conducted using SAS version 9.4 software (SAS Institute, Cary, North Carolina) and performed by a trained statistician. Two-tailed P<.05 was considered significant.

Results

Radiographic Results

Postoperative glenoid scores are presented in Table 2. Osseous integration or bone growth between the fins of the central peg was observed in 90% of cases treated with ABG, 68% of cases treated with DBM, and 68% of cases treated with NG (P=.022). There was no difference in osseous integration between the NG and DBM groups.

Postoperative Glenoid Scores

Table 2:

Postoperative Glenoid Scores

Postoperative Wirth grades revealed radiolucency around the central peg (grade 1) in 2.4% of cases with ABG, 5.4% of cases with DBM, and 9.8% of cases with NG (P=.134).

There was no difference in glenoid radiolucency between the groups according to the Lazarus classification.

There was no association between osseous integration of the central peg and functional outcome (P>.05). Furthermore, there was no association between osseous integration in the central peg and glenoid radiolucent lines (P>.05).

Clinical Results and Complications

There was no difference between the groups regarding range of motion or functional outcome (Table 3).

Postoperative Outcomes

Table 3:

Postoperative Outcomes

In the ABG group, there were 3 complications in 3 patients (7.3%), including 1 case of postoperative stiffness requiring capsular release, 1 case of anterior subluxation due to presumed subscapularis failure that was treated nonoperatively, and 1 case of polyethylene fracture that was treated with revision to reverse shoulder arthroplasty. In the NG group, there was 1 complication (2.4%) of a subscapularis failure that was treated with revision repair. In the DBM group, there were 2 cases (5.4%) of subscapularis failure that were treated conservatively.

Discussion

The results of this study refute the hypothesis that there would be no difference in osseous integration of the central peg of an all-polyethylene glenoid using 3 different treatments for the central peg. Contrary to the hypothesis, bone presence between the central peg was highest when ABG was applied to the central peg prior to insertion, with the rate of integration being 90.2%, compared with 67.6% with DBM and 68.3% with NG.

Traditionally, glenoid fixation of an all-polyethylene component has most commonly been achieved with cement. Survivorship of such components has been reported to be more than 90% at 10 years following surgery. In a series of more than 2000 patients with a variety of implants, Singh et al1 reported that the survival of a TSA with a cemented glenoid was 90.6% at 10 years. Raiss et al3 reported 89% survival at 10 years in 63 TSAs with a cemented keeled glenoid. However, 73% of the components were considered radiographically loose at final follow-up. Similarly, Kasten et al4 observed that 33% of cemented keeled glenoids were radiographically loose after 9 years. In an effort to improve long-term survival and decrease the rate of loosening, alternatives to completely cemented fixation have been developed. Given the high failure rates reported to date for metal-backed components, most of the focus has been on maximizing fixation of an allpolyethylene glenoid.

One concept has been the development of an all-polyethylene glenoid with hybrid fixation in which the peripheral pegs are cemented and the central peg is designed for osseous integration. The goal of this type of design is to achieve immediate stability, decrease the need for cement and thus the potential for thermal necrosis, and ultimately obtain growth between the central fins for long-term durability. Initially this concept was shown to be promising in a canine model in which mechanical fixation was stronger and radiolucent lines were decreased with a pegged central finned component compared with a fully cemented keeled component.12 Subsequent clinical studies have validated the concept. Noyes et al8 reported 97% survivorship in 42 components (Anchor Peg; DePuy, Warsaw, Indiana) evaluated at a mean of 80 months postoperative. Most importantly, 81% had complete incorporation without the development of radio-lucent lines. In this study, the central peg was treated with ABG. However, there is no consensus in the literature as to the ideal method for treating the central peg.

Churchill et al5 reported on 20 hybrid glenoids (Anchor Peg) secured with peripheral cement and press-fit fixation without the use of graft centrally. At a minimum follow-up of 5 years, 75% were found to have central osseous integration. Conversely, Kilian et al13 found that only 25% of a similarly designed glenoid (CortiLoc; Wright Medical, Memphis, Tennessee) had central integration at 2 years postoperative when the central peg was placed with press-fit fixation without bone graft.

The highest rates of osseous integration have been reported when bone graft is applied to the central peg. Wirth et al11 reported that 93% of 44 glenoids (Anchor Peg) had central osseous integration at a minimum follow-up of 4 years when bone graft was applied to the central peg at the time of implantation. Similarly, Arnold et al7 found that 91% of the same glenoid component implanted with ABG centrally had osseous integration based on computed tomography scans obtained at a minimum follow-up of 2 years postoperative. These two studies are consistent with the 90% rate of osseous integration that the current authors observed with ABG. On the other hand, in the current study, the rate of integration was much lower without bone graft or with the use of DBM. Although the authors did not observe an association between glenoid loosening and integration, this may have been due to their short-term follow-up. Studies with longer follow-up have suggested a relationship. Arnold et al7 found that postoperative radiolucent lines were decreased when osseous integration was achieved. In a report of 83 TSAs with a mean follow-up of 47 months, Wijeratna et al14 also found that radiolucent lines were decreased when osseous integration occurred. Together, these studies lend support to the concept that osseous integration is important for lowering the risk of loosening with a hybrid polyethylene component. On the basis of the difference in the rate of integration achieved with the 3 different techniques in the current study, the authors believe that applying ABG to the central peg should be the standard of care for a hybrid all-polyethylene glenoid implant.

The major strengths of this study included the randomized controlled design and the cohort size. However, there were several weaknesses. First, the follow-up was short. The primary outcome of this study was osseous integration of the central peg. One-year follow-up is sufficient to evaluate this outcome, based on a previous study.14 However, longer follow-up is needed to investigate the relationship between osseous integration and glenoid loosening. The authors intend to re-evaluate these patients at 5 years postoperative to evaluate this variable. Second, the evaluation of osseous integration was based on plain radiographs and did not involve computed tomography scans. On one hand, computed tomography would provide more detailed information and better interpretation of glenoid loosening (as opposed to integration). On the other hand, computed tomography involves additional cost and radiation; further, plain radiographs have been used in the majority of studies evaluating osseous integration and have been suggested to correlate with computed tomography scans for evaluation of osseous integration.5 Third, the authors did not evaluate the relationship between glenoid implant position or glenoid retroversion and osseous integration. Such an investigation would require serial computed tomography scans preoperatively, immediately postoperatively, and at final follow-up. Future studies should evaluate the influence of glenoid version on ingrowth as well as long-term clinical outcomes.

Conclusion

At short-term follow-up, osseous integration of the central peg of an allpolyethylene glenoid designed for bone ingrowth appears to be highest when treating the central peg with ABG compared with leaving the central peg untreated or using DBM.

References

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  2. Fox TJ, Foruria AM, Klika BJ, Sperling JW, Schleck CD, Cofield RH. Radiographic survival in total shoulder arthroplasty. J Shoulder Elbow Surg. 2013;22(9):1221–1227. doi:10.1016/j.jse.2012.12.034 [CrossRef] PMID:23473606
  3. Raiss P, Bruckner T, Rickert M, Walch G. Longitudinal observational study of total shoulder replacements with cement: fifteen to twenty-year follow-up. J Bone Joint Surg Am. 2014;96(3):198–205. doi:10.2106/JBJS.M.00079 [CrossRef] PMID:24500581
  4. Kasten P, Pape G, Raiss P, et al. Mid-term survivorship analysis of a shoulder replacement with a keeled glenoid and a modern cementing technique. J Bone Joint Surg Br. 2010;92(3):387–392. doi:10.1302/0301-620X.92B3.23073 [CrossRef] PMID:20190310
  5. Churchill RS, Zellmer C, Zimmers HJ, Ruggero R. Clinical and radiographic analysis of a partially cemented glenoid implant: five-year minimum follow-up. J Shoulder Elbow Surg. 2010;19(7):1091–1097. doi:10.1016/j.jse.2009.12.022 [CrossRef] PMID:20382041
  6. De Wilde L, Dayerizadeh N, De Neve F, Basamania C, Van Tongel A. Fully uncemented glenoid component in total shoulder arthroplasty. J Shoulder Elbow Surg. 2013;22(10):e1–e7. doi:10.1016/j.jse.2013.01.036 [CrossRef] PMID:23619247
  7. Arnold RM, High RR, Grosshans KT, Walker CW, Fehringer EV. Bone presence between the central peg’s radial fins of a partially cemented pegged all poly glenoid component suggest few radiolucencies. J Shoulder Elbow Surg. 2011;20(2):315–321. doi:10.1016/j.jse.2010.05.025 [CrossRef] PMID:20863718
  8. Noyes MP, Meccia B, Spencer EE Jr, . Five- to ten-year follow-up with a partially cemented all-polyethylene bone-ingrowth glenoid component. J Shoulder Elbow Surg. 2015;24(9):1458–1462. doi:10.1016/j.jse.2015.02.018 [CrossRef] PMID:25842027
  9. Parks DL, Casagrande DJ, Schrumpf MA, Harmsen SM, Norris TR, Kelly JD II, . Radiographic and clinical outcomes of total shoulder arthroplasty with an all-polyethylene pegged bone ingrowth glenoid component: prospective short- to medium-term follow-up. J Shoulder Elbow Surg. 2016;25(2):246–255. doi:10.1016/j.jse.2015.07.008 [CrossRef] PMID:26422526
  10. 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(7):1174–1182. doi:10.2106/00004623-200207000-00013 [CrossRef] PMID:12107318
  11. Wirth MA, Loredo R, Garcia G, Rockwood CA Jr, Southworth C, Iannotti JP. Total shoulder arthroplasty with an all-polyethylene pegged bone-ingrowth glenoid component: a clinical and radiographic outcome study. J Bone Joint Surg Am. 2012;94(3):260–267. doi:10.2106/JBJS.J.01400 [CrossRef] PMID:22298059
  12. Wirth MA, Korvick DL, Basamania CJ, Toro F, Aufdemorte TB, Rockwood CA Jr, . Radiologic, mechanical, and histologic evaluation of 2 glenoid prosthesis designs in a canine model. J Shoulder Elbow Surg. 2001;10(2):140–148. doi:10.1067/mse.2001.112021 [CrossRef] PMID:11307077
  13. Kilian CM, Morris BJ, Sochacki KR, et al. Radiographic comparison of finned, cementless central pegged glenoid component and conventional cemented pegged glenoid component in total shoulder arthroplasty: a prospective randomized study. J Shoulder Elbow Surg. 2018;27(6S):S10–S16. doi:10.1016/j.jse.2017.09.014 [CrossRef] PMID:29246679
  14. Wijeratna M, Taylor DM, Lee S, Hoy G, Evans MC. Clinical and radiographic results of an all-polyethylene pegged bone-ingrowth glenoid component. J Bone Joint Surg Am. 2016;98(13):1090–1096. doi:10.2106/JBJS.15.00475 [CrossRef] PMID:27385682

Baseline Characteristics

CharacteristicABG (N=41)NG (N=41)DBM (N=37)P
Age, mean±SD (range), y64.9 (40–84)63.8 (43–74)64.3 (47–79).467
Male, No.24 (58.5%)26 (63.4%)21 (56.8%).834
Dominant arm, No.20 (48.8%)17 (41.5%)23 (62.2%).130
Forward flexion, mean±SD106°±35°105°±40°114°±30°.523
External rotation, mean±SD28°±19°32°±22°27°±19°.671
Internal rotationL5L5L5.666
VAS pain score, mean±SD5.9±2.26.4±2.66.3±1.8.489
ASES score, mean±SD41.5±17.338.9±16.838.6±16.5.712
Constant score, mean±SD39.0±15.437.9±16.944.7±17.4.229
SANE score, mean±SD31.8±18.130.6±18.434.9±21.4.760

Postoperative Glenoid Scores

ParameterABG (N=41)NG (N=41)DBM (N=37)PP ABG vs NGP ABG vs DBMP NG vs DBM
Lazarus score, mean±SD0.5±0.80.5±0.80.4±0.5.767NANANA
Wirth grade, No.
  11 (2.4%)4 (9.8%)2 (5.4%)
  23 (7.3%)9 (21.9%)10 (27.0%)
  337 (90.2%)28 (68.3%)25 (67.6%).134.063.115.808
Central bone between fins, No.37 (90.2%)28 (68.3%)25 (67.6%).022.014.013.948

Postoperative Outcomes

OutcomeABG (N=41)NG (N=41)DBM (N=37)Pa
Forward flexion, mean±SD139°±27°141°±18°140°±26°.236
External rotation, mean±SD52°±14°49°±15°52°±16°.548
Internal rotationL3L3L2.988
VAS score pain, mean±SD1.2±1.51.4±1.71.0±2.0.433
ASES score, mean±SD82.9±16.081.1±15.587.3±19.2.386
Constant score, mean±SD69.0±11.065.8±11.570.5±16.2.568
SANE score, mean±SD75.6±19.678.5±22.378.2±24.9.599
Authors

The authors are from Southern Oregon Orthopedics, Medford, and the Department of Orthopaedics & Rehabilitation, Oregon Health & Science University, Portland, Oregon (PJD); The Cleveland Shoulder Institute (RG), Beachwood, Ohio; Jordan Young Institute (JWG), Virginia Beach, Virginia; Rothman Institute (AAR), New York, New York; and the University of Arizona College of Medicine–Phoenix and The Orthopedic Clinic Association, Phoenix, Arizona (EL).

Dr Denard is a paid consultant for and receives royalties from Arthrex, Inc. Dr Gobezie is a paid consultant for and receives royalties from Arthrex, Inc. Dr Griffin is a paid consultant for Arthrex, Inc. Dr Romeo is a paid consultant for and receives royalties from Arthrex, Inc. Dr Lederman is a paid consultant for and receives royalties from Arthrex, Inc.

Correspondence should be addressed to: Patrick J. Denard, MD, Southern Oregon Orthopedics, 2780 E Barnett Rd, Ste 200, Medford, OR 97530 ( pjdenard@gmail.com).

Received: January 17, 2020
Accepted: April 23, 2020
Posted Online: August 06, 2020

10.3928/01477447-20200721-04

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