Radiologic, mechanical, and histologic evaluation of 2 glenoid prosthesis designs in a canine model

doi:10.1067/mse.2001.112021

Journal of Shoulder and Elbow Surgery

Volume 10, Issue 2, March–April 2001, Pages 140-148

https://doi.org/10.1067/mse.2001.112021 Get rights and content

Abstract

Aseptic loosening of glenoid components is a common problem associated with total shoulder arthroplasty. A new glenoid design aimed at improving fixation outcomes was compared with conventional keeled glenoids in weight-bearing canine shoulders. Radiographic, histologic, and mechanical tests were performed at 3 postoperative intervals (0, 3, and 6 months). The uncemented pegged glenoid achieved bone ingrowth around the peg flanges in each case. This result was confirmed histologically and radiographically. Mechanical results indicated that mean fixation strength increases significantly between 0 and 3 months after surgery and remains strong through 6 months. In contrast, conventional keeled glenoids were found to have partial or complete radiolucent lines around the keel in each instance, and mechanical testing demonstrated that mean fixation strength weakens significantly between 0 and 3 months after surgery and remains weak through 6 months. These results show that stem design changes can improve implant fixation. A cementless fluted peg stem was superior to a conventional cemented keel design in achieving osseous integration and fixation in a weight-bearing animal model. (J Shoulder Elbow Surg 2001;10:140-8.)

Introduction

Total shoulder replacement surgery results in good to excellent function in more than 90% of patients at early and midterm follow-up evaluations.1, 2, 3, 4 The majority of series reported to date have limited follow-up, however, and the incidence of glenoid component loosening50, 51 has been a concern. One third of all total shoulder-replacement complications involve symptomatic loosening of the glenoid and/or humeral components. The majority of these failures involve the glenoid.* Radiolucent lines at the bone-cement interface of the glenoid stem are common (30% to 96%1,2,4,7-10). The appearance or progression of these radiolucent lines may coincide with symptomatic component loosening.†

In a long-term follow-up report on 89 total shoulder-replacement arthroplasties at an average of 12 years after surgery (range 5 to 17 years), radiolucent lines had developed at the bone-cement interface in 84% of glenoid components, and 44% demonstrated definitive radiographic loosening.⁴⁴ There was also an association between radiographic loosening of the glenoid implant and shoulder pain (P =.0001).

Many methods have been advocated to improve fixation and long-term stability of the glenoid component. Preservation of the subchondral plate, concentric spherical reaming of the glenoid cavity, enhanced biomaterials, mismatching of the diameters of the glenoid and humeral head, and new glenoid designs have been tried.16, 23, 28, 42, 48, 49 Validation of these methods is based primarily on clinical trials and/or finite element modeling. Little is known about how fixation of the glenoid changes after implantation or how design features contribute to implant stability.

No accepted animal model exists for the study of shoulder implants. We undertook this study as a first step toward using the dog as a weight-bearing animal model to understand the effects of glenoid stem design on fixation. We choose the dog because bone remodeling kinetics in the dog have been well characterized and are similar to that of man.²⁵ This is why the dog is the principal animal model used for studying total hip1, 2, 3, 4, 5, 6, 7, 8 and, more recently, total knee prostheses.9, 10, 11, 12, 13 Furthermore, as in the human counterpart, stability of the canine shoulder joint is primarily dependent on the joint capsule.¹⁸

In this study, a weight-bearing canine model was used to evaluate glenoid implant-to-bone fixation strength and interface morphology. Changes over time were compared between a conventional keeled glenoid and an innovative peg design.

Section snippets

Implant design

Cadaver specimens from large breed dogs were used to design the glenoid implant. Implants were manufactured from Hylamer (DePuy AcroMed, Raynham, Mass), and the dimensions of the glenoid portion of the implant were identical between keel and peg designs. The glenoid component was oval (20.3 × 22.9 mm), with a radius of curvature of 14.5 mm and a component thickness of 2.5 mm (Figure 1).

. Appearance of the two glenoid components. Left, keel; right, peg.

The flanged peg stem had a large central peg

Clinical findings

The dogs began partial weight bearing 2 weeks after surgery and full weight bearing at 1 to 2 months. There was pronounced atrophy of the supraspinatus and infraspinatus muscles from 0 to 3 months after surgery. The muscle mass was restored by 6 months. In 2 dogs (1 with peg, 1 with keel implant), the implant was displaced in the soft tissues, and these dogs were excluded from the analysis. Two dogs (peg group) dislocated their shoulder joint within 2 weeks of surgery. These dogs had been using

Discussion

An animal model is essential to understand how glenoid fixation changes after implantation in a functional loaded environment. We found the dog model very useful in the study of 2 different types of glenoid fixation. Critics of this model will argue that dogs, and indeed all quadrupeds, are invalid models for studying shoulder prosthesis design because the forelimb is a major loadbearing joint. Although we do not know the load across the canine shoulder joint, we can be sure that after glenoid

Acknowledgements

The authors would like to express their appreciation to Carlton Southworth for his assistance with statistical evaluation of the data.

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This study introduces a radiographic assessment method developed specifically for an FCP glenoid component. Results show high interobserver and acceptable intraobserver reliability for the method presented in this study. The new scales provide a more accurate description of radiographic findings, helping to identify glenoid components that may be at risk for loosening.
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In a comparative retrospective case series, all patients who underwent TSA-to-reverse TSA revision between 2014 and 2022 were reviewed. Demographic varibles as well as clinical and radiographic outcomes were collected. Ingrowth central peg and noningrowth pegged glenoid groups were compared using t-test, Mann-Whitney U, Chi-Square, or Fisher’s exact tests where indicated.
Overall, 49 patients were included: 27 underwent revision from noningrowth and 22 from central ingrowth components. Females more commonly had noningrowth components (74% vs. 45%, P = .04) and preoperative external rotation was higher in central ingrowth components (P = .02). Time to revision was significantly earlier in central ingrowth components (2.4 vs. 7.5 years, P = .01). Structural glenoid allografting was required more with noningrowth components (30% vs. 5%, P = .03) and time to revision in patients ultimately requiring allograft reconstruction was significantly later (9.96 vs. 3.68 years, P = .03).
Central ingrowth pegs on glenoid components were associated with decreased need for structural allograft reconstruction during revision; however, time to revision was earlier in these components. Further research should focus on whether glenoid failure is due to glenoid component design, time to revision, or both.
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Citation Excerpt :
A “loose” component was defined as a component with radiolucency grade 3 or greater. The appearance of the central peg was graded from 1 to 3 as described by Wirth et al33: grade 3, bone in contact with the central peg accompanied by increased radiodensity between the fins; grade 2, bone in contact with the central peg without increased density between the fins; and grade 1, osteolysis about the central peg. Cemented central pegs were not included in the Wirth grading system as the cement would be expected to interfere with any bone contact between the implant and central peg.
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We performed a multicenter retrospective review of patients who underwent TSA with the same hybrid all-polyethylene glenoid and had minimum 2-year follow-up. Patient-reported outcomes and radiographic outcomes were analyzed based on preoperative Walch morphology and central peg technique. Radiographic analysis included preoperative glenoid morphology; preoperative and postoperative glenoid version, glenoid inclination, and posterior humeral head subluxation; and postoperative glenoid radiolucencies according to the Wirth and Lazarus classifications.
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In the fully cemented condition, the 2 component designs had comparable performance; however, the differences in designs could be better observed in the uncemented group. The self-pressurizing all-polyethylene design studied has superior biomechanical stability. Clinically, the improved stability of the glenoid component correlated with a reduction of radiolucent lines and will likely lead to a reduction in glenoid component loosening.

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^☆: Reprint requests: Charles A. Rockwood, Jr, MD, Department of Orthopaedics, The University of Texas Health Science Center at San Antonio, Orthopaedics Mail Code-7774, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900.

^☆☆: J Shoulder Elbow Surg 2001;10:140-8.

^★: *References 2-5, 7-10, 12, 13, 15, 17-21, 24, 26, 27, 29,31-41, 43-46.

^★★: †References 1, 4, 9, 14, 15, 26, 44, 47.

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Original ArticlesRadiologic, mechanical, and histologic evaluation of 2 glenoid prosthesis designs in a canine model☆,☆☆,★,★★

Abstract

Introduction

Section snippets

Implant design

Clinical findings

Discussion

Acknowledgements

J Arthroplasty

J Shoulder Elbow Surg

Orthop Clin North Am

J Arthroplasty

Orthop Clin North Am

J Arthroplasty

J Arthroplasty

J Shoulder Elbow Surg

Prosthetic replacement of the shoulder for the treatment of defects in the rotator cuff and the surface of the glenohumeral joint

J Bone Joint Surg Am

Neer total shoulder arthroplasty [abstract]

Orthop Trans

Long-term results of Neer total shoulder replacement

Total shoulder arthroplasty

J Bone Joint Surg Am

Non-constrained total shoulder arthroplasty in patients with polyarticular rheumatoid arthritis [abstract]

Orthop Trans

Effects of fixation technique on displacement incompatibilities at the bone-implant interface in cementless total knee replacement in a canine model

J Appl Biomater

Survivorship of unconstrained total shoulder arthroplasty

J Bone Joint Surg Am

Should the glenoid be placed in shoulder arthroplasty with an unconstrained Dana or St Georg prosthesis?

Ann Chir Gynaecol

Total shoulder replacement arthroplasty: a clinical review of 21 cases

Orthop Trans

The effect of the medial collar in total hip arthroplasty with porous-coated components inserted without cement: an in vivo canine study

J Bone Joint Surg Am

Prosthetic arthroplasties of the shoulder

Clin Orthop

Unconstrained total shoulder prosthesis

Clin Orthop

Total shoulder arthroplasty with the Neer prosthesis

J Bone Joint Surg Am

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

Shoulder resurfacing according to the method of Neer. Proceedings of the British Orthopaedic Association

J Bone Joint Surg Br

Cementless total shoulder arthroplasty: preliminary experience with thirteen cases

Orthopedics

Shoulder arthroplasty with the Neer Mark-II prosthesis

Arch Orthop Trauma Surg

Original Articles
Radiologic, mechanical, and histologic evaluation of 2 glenoid prosthesis designs in a canine model☆,☆☆,★,★★