1 Introduction

Shoulder arthroplasty has been performed for treatment of glenohumeral arthritis (GHOA)¹1GHOA: Glenohumeral osteoarthritis. for the last decades with significant clinical and functional improvement. However, the problem of glenoid deformity and retroversion, in particular, remains a challenge.¹ Glenoid bone loss and deformity are frequently relevant to GHOA due to chondral and bone wear.² Glenoid morphology is a considerable factor affecting clinical outcomes after shoulder arthroplasty for arthrosis.

In accordance with the Walch classification³ of glenoid morphology, there are three types: type A is central glenoid erosion, type B is posterior glenoid erosion, type C is dysplastic glenoid and excessive posterior erosion, and each of these has subclasses. In their published study, Walch et al. stated that GHOA exhibited the majority of the type B deformity.³ In the axial plane, type B glenoid morphology exhibits glenoid retroversion of up to 25°.

Retroverted glenoids or posterior defects can be treated with hemiarthroplasty, anatomical total shoulder arthroplasty (aTSA),²2aTSA: Anatomic total shoulder arthroplasty. or reverse shoulder arthroplasty (RSA).³3RSA: Reverse shoulder arthroplasty. Hemiarthroplasty, which lacks a glenoid component, is relatively less prone to complications. However, it is associated with suboptimal functional outcomes and inadequate pain relief.⁴ Options for aTSA applications include augmented glenoid implants, bone block grafts, and asymmetric reaming.⁵ The incorporation of augmented glenoid components can help conserve bone stock, but further research is necessary to establish the long-term implant survival rates.⁵ Another approach to maintain bone stock in cases of posterior defects involves bone grafting with an aTSA. Nevertheless, it is important to note that graft-related complications are frequently observed in this procedure.⁶ By using a procedure known as BIO-RSA (bony increased offset RSA), a bone graft could be placed below of the glenoid baseplate to achieve lateralization in cases of retroversion and excessive medialization of the glenoid.⁷

Performing aTSA can be challenging in posterior glenoid bone loss. It is vital to insert the glenoid component in native version the for avoiding instability and loosening.⁵ In recent years, RSA has been performed in such challenging cases and good clinical results have been reported.^8–11 The treatment of severe glenoid bone loss, which frequently leads to excessive retroversion in RSA, is necessary to improve outcomes and lower complications.^8,12,13 At this cases, the baseplate should be located somewhere between the neutral version and 10° of retroversion.¹⁴ Eccentric reaming, bone graft, or a combination of these are applied with the purpose of correction of the retroversion. Depending on how serious the retroversion is, one of these methods is distinguished.

Our hypothesis posits that RSA surgery employing eccentric glenoid reaming can potentially achieve significant version correction in patients with GHOA. To substantiate this hypothesis, we conducted a comparative analysis between GHOA patients undergoing RSA surgery and those treated with CTA.⁴4CTA: Cuff tear arthropathy. Our objective was to assess and compare the angular differences in glenoid version between the two groups, aiming to radiologically demonstrate the effectiveness of the eccentric reaming technique.

2 Methods

This study was conducted in a tertiary university hospital clinic that serves as a referral center for shoulder disorders. Data collected from patients who underwent RSA surgery from January 2018 to December 2022 formed the basis of this retrospective study. Patient information was obtained from the clinical file archive and the hospital computer network system. Institutional review board approval was obtained from the relevant academic board.

2.2

2.2 Radiologic evaluation

All patients had a routine CT scan no more than one week before the operation and no more than 2 days after the operation. It was applied in 120 kV and 0.75 mm thick slices with a computed tomography device (Aquilion 16; Toshiba Medical Systems, Japan). Images scanned from records were analyzed in a program (Radiant DICOM Viewer; Medixant, Pdoland) with DICOM format. Radiological measurement and classification was performed by an experienced surgeon (MK) fort this study plan. First, patients in the GHOA and CTA groups were classified according to the Walch classification³ and Hamada classification,¹⁵ respectively, based on radiologic images. Preoperative and postoperative glenoid version angles were measured via CT recordings using the method previously described by Friedman et al.¹⁶

The angle measurements were performed on axial sequences derived from CT images. A perpendicular line was drawn, connecting the midpoint of the anterior-posterior axis of the glenoid fossa with the medial edge of the scapula on the axial section. Subsequently, the angle between this line and the one connecting the anterior and posterior lips of the glenoid fossa was measured. Retroversion was designated by a negative angle value. Preoperative and postoperative drawings are illustrated with photographs (Fig. 1).

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Fig. 1 Friedman angle measurement. A. Preoperative CT-scan image, axial section. B. Postoperative CT-scan image, axial section.

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The angle between this axis and the line drawn on the glenoid surface was measured manually in the preoperative and postoperative periods, without using any preoperative template or planning program. In recent studies, it has been suggested that there is no significant difference in 2D measurements compared to 3D verification.¹⁷ 3D images of the patients in the study were obtained, but since there was no 3D measurement software, it was sufficient to make measurements on only 2D images. The changes between the preoperative and postoperative angles and the angle differences between the CTA group and the GHOA group were compared.

3 Results

The CTA group consisted of 40 patients and the GHOA group consisted of 17 patients. In both groups, the number of female patients was higher than that of males and male patients percentage was %17 (Table 1). The mean age was 67.1 in total. In the GHOA and CTA group, they were dispersed as 69.1 and 66.3, respectively.

Preoperative X-ray images of the CTA group were classified according to the Hamada classification.¹⁵ The GHOA group's data were examined in a similar manner and classified using the Walch classification. The most prevalent variation was a glenoid of type B2. Table 1 lists the patients' preoperative classifications and demographic details.

The mean preoperative glenoid version of the GHOA group was 17° and that of the CTA group was 4°. As a result of the comparison, it was observed that the GHOA group had a significantly higher retroversion degree (p < 0.001) (Table 2) (Fig. 2).

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Fig. 2 Comparison of preoperative and postoperative glenoid versions.

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The mean postoperative version degrees of both groups; It was 7° in the GHOA group and 4° in the CTA group. There was no significant difference between the two groups in terms of mean postoperative version degrees (p = 0.055) (Fig. 2).

Glenoid version change achieved by eccentric reaming was observed to be significantly higher in the GHOA group. The mean version change was 8 in the GHOA group and 0.075 in the CTA group (p = 0.001) (Fig. 2).

It was discovered that the version change differences between the two groups varied significantly (p < 0,001).

4 Discussion

The main finding of this study is that the glenoid retroversion in GHOA, adequate version correction can be achieved with the eccentric reaming technique. Performing RSA together eccentric reaming on GHOA patients had similar radiologic success as the postoperative glenoid baseplate versions of CTA patients, according to the results.

Numerous studies about RSA for GHOA patients are available in the literature.^{10,12,18–23} Based on a study in GHOA patients, RSA and eccentric anterior superior reaming compensated for glenoid bone loss.¹⁰ The preoperative morphology of the glenoid was not significantly related to the results of the surgery. Regardless of the level of glenoid deformity present prior to surgery, primary RSA has been demonstrated to offer perfect short-term outcomes for patients with GHOA.^10,23 Another study reported that GHOA patients had superior clinical outcomes compared to CTA patients, indicating that RSA could be an option for these patients.²² The semi-constrained design overcomes the issues related to possible posterior instability and repetitive posterior humeral head displacement. The secure fixation of the glenoid base plate reduces the theoretical possibitily of glenoid baseplate loosening.²⁰ The present study lacks clinical outcome data, however postoperative CT scan results showed that eccentric reaming could successfully correct high degrees of retroversion.

The use of RSA with eccentric reaming in B2 glenoids may raise issues like excessive medialization and increased scapular notching. Compared to neutral baseplates, the use of half-wedges might considerably alleviate scapular neck impingement.²⁴ On the other hand, another study indicates that eccentric reaming in patients with degenerative arthrosis and glenoid bone loss may produce satisfying short-term outcomes when a lateralized RSA system is utilized.²¹ At the same study, they were unable to show any risk of scapular notching according to the level of medialization.

During a aTSA, a number of methods can be performed to treat asymmetric posterior glenoid wear brought on by degenerative GHOA. In the study by Walch et al., asymmetric reaming and total shouler arthroplasty produced satisfactory long-term clinical results, but frequent reports of component dislocation and loosening were also made.⁶ Bone grafting can be used to fill the posterior glenoid defect when the retroversion angle is too high to be treated with eccentric reaming. In the study conducted by Steinmann et al., involving 27 patients who underwent aTSA with posterior glenoid bone grafting, 13 excellent and 5 poor results were reported.²⁵ In our study, the posterior glenoid defect was filled with a bone graft in cases where it was foreseen that the insufficient asymmetric reaming for glenoid version correction. In these circumstances, eccentric reaming can cause to more bone loss or penetration of the glenoid vault, both of which are undesirable outcomes. According to the study by Klika et al. two out of every 25 patients had poor outcomes.²⁶ The ten patients' radiological findings were potentially loosening. Following bone grafting and aTSA implementation to the posterior glenoid, it is challenging to monitor the graft union and loosening of the implant radiographically. The augmented glenoid component has been used in a number of different ways in search for a solution for large posterior glenoid defects. Rice et al. found that 14 % of patients who underwent aTSA with posterior augmented glenoid had poor outcomes in their long-follow-up study.²⁷ The outcome was excellent in 36 % rate. Long-term survival rates were reported at 31 % in another study with a posterior augmented metal-backed glenoid component.²⁸ Although augmented glenoid components have presented encouraging results, more extensive studies are needed.

Even with the adoption of new aTSA procedures, the posterior subluxation of the humeral head, retroversion of the glenoid surface, and posterior glenoid defect still exist as a problem. In patients with old age, limited expectations, and perhaps severe aTSA risks, RSA is a suitable alternate option. Collin et al. reported excellent results after observing individuals with type B glenoids without a rotator cuff tear for at least five years following RSA. 16 of the 45 patients reportedly had grafting, and every single one of them had union.²⁹ RSA offers promising short- and midterm results because of the benefit of a more stable fixation as well as a constrained design to prevent posterior subluxation.³⁰ For eccentric reaming to be successful, there must be enough glenoid bone, especially in RSA. Therefore, eccentric reaming can be used to safely treat small posterior glenoid abnormalities with little retroversion. More severe abnormalities or significant retroversion require the use of bone graft or metal augments to ensure the joint line and reliable fixation.³¹ It is possible to partially repair bone loss and retroversion in the posterior glenoid using procedures including eccentric reaming, bone grafting, and baseplate augmentation, and the preliminary outcomes are affirmative.³¹ Despite the above-mentioned studies, it is unclear to what extent a retroverted glenoid can be corrected with eccentric reaming. In this study, the cases with glenoid retroversion greater than 35° were treated by bone grafting. The glenoids that have values below 35° were reammed eccentrically. It was intended to normalize the version during the application of the technique. Nevertheless, since it was clear that this would not be possible in cases of extreme retroversion, degrees close to normal were accepted and no further reaming was done.

Eccentric reaming is a straightforward technique with a number of advantages. It is simple, inexpensive, and requires no additional time or no instrument. The anterior site bone of the glenoid is reamed to the same depth as the worn posterior site. In the technique, a guide pin is placed on the glenoid surface at a specific angle oriented posteriorly, according to the desired correction angle, and the reaming process is then continued. The size of the remaining glenoid restricts the amount of asymmetric reaming that can be done³² With preoperative CT, the amount of eccentric reaming can be planned and applied in advance. Thereby, there is a decreased risk of glenoid base perforation and maximum bone reserve preservation.^33,34 For aTSA procedure with eccentric reaming, the glenoid version angle must be set to less than 10°; otherwise, glenoid component loosening occurs.³⁵ For RSA, fixing the retroversion is advised but not essential. Higher than 15° retroversion angles can be tolerated by RSA.³⁶ In this study, the median value of postoperative residual angles was 7, which was below of the acceptable limit.

This study has several limitations that should be acknowledged. Firstly, the retrospective nature of the study might have introduced inclusion bias. Secondly, a notable limitation is the small number of patients included in the cohort. The study lacks comprehensive clinical outcome data and long-term radiological results, which could differ from the short-term radiological findings presented. The limited sample size and absence of functional outcomes render the study insufficient in elucidating the influence of radiological measurements on clinical importance. This results only demonstrated the radiological efficacy of the eccentric reaming technique. However, larger-scale prospective randomized controlled trials are needed to understand the clinical significance of this technique or the correction of retroversion.

5 Conclusion

In conclusion, RSA surgery utilizing eccentric reaming emerges as a viable option for patients with Glenohumeral Osteoarthritis (GHOA), particularly those with high retroversion and a heightened risk of complications associated with anatomic Total Shoulder Arthroplasty (aTSA). The radiological assessments in our study indicate that eccentric reaming effectively corrects retroversion. When comparing the measurements of patients undergoing eccentric reaming with those of patients treated with CTA, a similar glenoid component angle is achieved. Nevertheless, further randomized controlled trials are imperative to explore optimal management strategies for GHOA patients with posterior glenoid defects.

Funding

None.

Conflict of Interest

None.

Academic board approval name and number

T.C. Bezmialem Foundation University, Faculty of Medicine, Head of orthopedics and traumatology department/45446446-010.99-6293.

CRediT authorship contribution statement

Tolga Keçeci: Methodology, Formal analysis, Writing – original draft. Vahdet Uçan: Validation, Investigation. Rodi Ertogrul: Validation, Writing – review & editing. Koray Şahin: Formal analysis, Writing – review & editing. Kerem Bilsel: Conceptualization, Investigation, Project administration. Mehmet Kapıcıoğlu: Methodology, Supervision.