Effect of the critical shoulder angle on severe cranialization following total shoulder arthroplasty

Matthias Wolf; Matthias Bülhoff; Patric Raiss; Felix Zeifang; Michael W Maier

doi:10.1016/j.jor.2020.03.024

. 2020 Mar 25;21:240–244. doi: 10.1016/j.jor.2020.03.024

Effect of the critical shoulder angle on severe cranialization following total shoulder arthroplasty

Matthias Wolf ^a,^∗∗, Matthias Bülhoff ^a, Patric Raiss ^b, Felix Zeifang ^c, Michael W Maier ^a

PMCID: PMC7136606 PMID: 32280160

Abstract

Purpose

This study assesses the relationship of CSA, cranialization and radiographic glenoid loosening following TSA in the long-term follow-up.

Methods

26 shoulders with TSA were examined radiographically postoperatively and after a mean 12.6 years. Severe cranialization was defined as direct humeral contact with the acromion and/or acetabularization of the acromion.

Results

A CSA ≥35° was associated with severe cranialization. Glenoid loosening was present in 6/24 shoulders (25%). Severe cranialization was associated with glenoid loosening (p = 0.003).

Conclusion

A postoperative CSA ≥ 35° was associated with severe humeral cranialization after TSA in the long-term follow-up. Severe cranialization correlated with glenoid loosening.

Level of evidence IV – retrospective cohort study.

Keywords: Critical shoulder angle, Cranialization, Total shoulder arthroplasty, Glenoid loosening, Rotator cuff insufficiency

Abbreviations: CSA, Critical Shoulder Angle; TSA, Total Shoulder Arthroplasty

1. Introduction

Total shoulder arthroplasty (TSA) is a successful treatment for the degenerated shoulder joint. While the outcome in long-term follow-up is generally satisfactory, complications seem to arise after 10 years, among which glenoid loosening and cranialization of the humerus, indicating rotator cuff insufficiency, are the most frequent.1, 2, 3, 4, 5 In the majority of studies severe humeral cranialization, which in the literature is generally defined as cranial migration of the humeral head of more than half of its diameter, is reported with a frequency of approximately 10% after 10 years and seems to increase throughout follow-up time.¹^,²^,⁴^,⁵ Radiological glenoid loosening is reported in 20%–52% of cases after 10 years2, 3, 4, 5 with inconsistent reports on the correlation with clinical symptoms.¹^,²^,⁴ The resulting clinical symptoms are a major reason for surgical revision, which is necessary in 9–29% of cases after 15 years following TSA.¹^,³^,⁵ Humeral cranialization following TSA is associated with glenoid loosening,⁵ which could be a result of increased eccentric glenoid loading as a result of rotator cuff tear.⁶ Franklin and Matsen have compared this mechanism to a “rocking-horse”.⁷^,⁸ Consequently, reducing the rate of secondary rotator cuff tear should also avoid some of the cases of glenoid loosening.

The critical shoulder angle (CSA) was introduced by Moor et al. in 2013 and measures glenoid inclination and acromiohumeral coverage in one parameter.⁹ When CSA ≥35° patients are at increased risk for rotator cuff tear, while when <30° they have a higher likelihood of osteoarthritis.⁹ The parameter was verified and a biomechanical foundation was established in subsequent studies.10, 11, 12 Due to its predictive capabilities, Cerciello et al. hypothesized that in patients with TSA, CSA would predict secondary rotator cuff failure. However, they could not confirm this hypothesis in a retrospective study of 19 patients receiving revision surgery after a mean 45 months due to a failed rotator cuff in comparison to 29 subjects without symptoms.¹³

Within a previous study in our center severely cranialized TSA's were discovered after ten years of follow-up, as shown in Fig. 1 ² They were considered to have a torn rotator cuff with a high certainty, since they all showed either direct contact of the humeral component with the acromion and/or acetabularization of the acromion. Alongside severe cranialization, glenoid loosening or glenoid destruction was often discovered, raising the interest in this particular entity in our study group. The primary purpose of this study was to investigate whether the postoperative CSA is larger in patients with severe cranialization, which was used as an indirect measure of rotator cuff tear following TSA. The secondary goal was to evaluate the rate of glenoid loosening and whether severe cranialization correlates with glenoid loosening.

2. Methods

Between 1995 and 2000, 125 patients underwent shoulder arthroplasty in our institution and were prospectively entered into a registry.² TSA was performed in 60 cases, while 43 underwent hemiarthroplasty, 19 received a fracture prosthesis and three underwent a reverse shoulder arthroplasty.² From this registry segment 36 patients (39 shoulders) were identified, who initially received TSA due to osteoarthritis, for their long-term follow-up study 2. We evaluated the available conventional postoperative imaging data of this registry segment for possible study inclusion. Ethics committee approval was given for conducting studies on this cohort.

Inclusion criteria in radiographs acquired within 1 year postoperatively were (1) sufficient ap-radiograph quality with visible glenohumeral joint space and the apparent ante/retroversion of less than 10° compared to the images published by Moor et al. and Suter et al.,⁹^,¹⁴ to reduce the bias due to radiograph quality. (2) intact glenoid component without signs of loosening. Only for evaluation of cranialization at follow-up, ap-radiographs with larger ante-/retroversions were accepted, since quantitative measurements were not performed.

Exclusion criteria after preliminary analysis were (1) a difference of CSA in the bony plane and the glenoid component plane of more than 10° to reduce a bias due to faulty implantation or remaining cranial osteophytes.

Radiographs were only available on film for the period up to the year 2008. Thus, measurements for this section had to be conducted manually. Whenever radiographs were available digitally, values were measured using the PACS-Software by GE healthcare. Measurements were rounded to the nearest degree. Two surgeons conducted the qualitative measurements and a consensus was reached for differing results. Measurement of CSA was originally defined by Moor et al.⁹ in non-arthroplasty shoulders. We chose to measure the glenoid component plane and draw a line from the inferior glenoid component lateral rim to the inferior edge of the lateral acromion, a method also used by Watling et al.¹⁵ Images within the first postoperative year without radiographic loosening were accepted.

Following TSA, rotator cuff insufficiency is often reported indirectly using the humeral head cranialization in relation to its center, according to the grading published by Torchia et al.¹⁶ However, rotator cuff tear cannot be definitely diagnosed with this method. Thus, in this study we chose to measure RCT qualitatively applying the morphologic findings of conventional radiography generally used to define a grade 3 in the Hamada classification for RCT arthropathy.¹⁷

Cranialization of the humeral head was evaluated qualitatively on most recent imaging material, or in case of revision preoperative imaging material, and defined as severe when the humeral head was in direct contact with the inferior acromial border and/or acromial acetabularization was present.

At follow-up, glenoid loosening was evaluated using a radiolucent line score as previously described by Molé et al. and modified by Raiss et al. adding the axillary view.²^,¹⁸ The glenoid component was considered loose, when radiolucent line score was >12 points on either ap or axillary view and considered at risk when between 7 and 12 points. Glenoid tilt and subsidence were measured qualitatively comparing the radiographs of the patients’ follow-up series.

A reproducible glenoid tilt or subsidence throughout follow-up, or an obvious destruction of glenoid integrity resulted in a score of 18 points and the glenoid was considered loose.

Statistical counselling was obtained by the institute for medical biometry. The data was analyzed using IBM® SPSS® statistics software (Version 25) and R-Studio. Descriptive statistics were illustrated using mean, standard deviation, 95% confidence interval (CI), minimum and maximum or totals and percentage where applicable. Confirmative testing was performed using logistic regression. Area under the curve was calculated and receiver operating characteristics illustrated. Student's T-Test was performed on the difference in mean CSA, Pearson's χ²-test was performed on CSA ≥35° and severe cranialization, on CSA ≥35° and glenoid loosening, as well as severe cranialization and glenoid loosening. P-values <0.05 were considered statistically significant. Figures were created using Microsoft Power Point Professional 2018 and IBM® SPSS® statistics software.

3. Results

After preliminary analysis 10 shoulders were excluded due to inadequate ap-projection of the immediate postop image and no further available image within the first postoperative year, available at our institution. Three subsequent shoulders were excluded due to a mismatch of bony glenoid plane and implanted glenoid plane of more than 10°. Twenty-one patients and 26 shoulders were included into the analysis (see Fig. 2). Thirteen patients (48%) were female and 5 female patients (24%) had bilateral shoulder replacement. Mean age at the time of arthroplasty was 62 years (range 31–76 years). Mean follow-up was 12.6 years (±2.9, range 8.2–19.1 years). Mean postoperative CSA was 33.6° (±6.1°, 95% CI 24.0°–50.0°).

Fig. 2 — Flow-chart of the study cohort. Of 39 patients available at follow-up, 26 patients could be entered into the analysis at 12.6 years of follow-up due to the inclusion criteria. Throughout Follow-up 8 patients showed *severe* cranialization, while 6 of these patients had a CSA ≥35° postoperatively. This finding was statistically significant (p = 0.011). Of the 18 patients classified as *not severe* at follow-up, 14 had a CSA <35°.

Acromial contact was present in 6 shoulders (23%) and acromial acetbularization occurred in 7 shoulders (27%). One patient received glenoid component removal and head replacement at an external institution due to glenoid loosening after 12.2 years, presenting with acromial contact and acetabularization preoperatively. Consequently, severe cranialization was present in 8 cases (31%). One shoulder didn't show acromial contact but severe acromial acetabularizaion with lysis of the acromial bone which created an apparent acromiohumeral distance.

Mean postoperative CSA was larger in patients with severe cranialization at follow-up (difference 6.4° ± 2.3°, 95% CI 1.67–11.1, p = 0.01, see Fig. 3). Of the 8 shoulders showing severe cranialization at follow-up, the CSA of 6 shoulders was ≥35° (chi-square test p = 0.011) detecting severe cranialization with a sensitivity of 75% and a specificity of 78%. While the positive predictive value of a CSA ≥35° for severe cranialization was only 0.6, the negative predictive value was 0.88. Logistic regression predicted severe cranialization with an acceptable area under the curve (AUC) of 0.774 (p = 0.028).

At follow-up 24 shoulders had sufficient image quality (glenoid version) to allow for glenoid interpretation in the ap-radiograph. Of these, 6 glenoid components (25%) were classified as loose, due to subsidence, tilt, or destruction leading to an immediate radiolucent line score of 18 points. Another 7 shoulders showed a radiolucent line score from 7 through 12 and thus were classified as at risk. The remaining 11 shoulders showed a radiolucent line score ≤7 and were classified as not at risk.

Glenoid loosening or radiolucency score >7 did not correlate with a CSA ≥35° although logistic regression showed suggestive values that could lead to significance in larger cohorts. Severe cranialization was associated with glenoid loosening (p = 0.003).

4. Discussion

Since our cohort is small it is paramount to know that its structure is comparable to previous studies on this topic. Mean age at the time of arthroplasty was 62 years, which is comparable to Cerciello et al. (mean age 62.6 years [study group] and 67.6 years [control group]) and Moor et al. (mean age 58.1 years [RCT group] and 65.9 years [control group]). The mean CSA in our cohort was 33.6° (±6.1°, 95% CI 24.0°–50.0°), which is in line with Moor's original study, who reported a mean CSA of 33.3 (±2.2°, 95% CI 28.8°–38.6°), and Cerciello's study following TSA, who reported a mean CSA of 29°–30° for TSA.¹³ Two groups also found a larger standard deviation than Moor et al., which is in line with our findings.⁹^,¹³^,¹⁵ The large standard deviation could either be due to the larger size of Moor's cohort, or a systematic error of glenoid implantation, which might have a greater variation of superoinferior angulation than scapular anatomy.

Severe cranial migration has been reported in 2–12.8% after 10 years²^,⁴ and in 12.8–35.6% after more than 15 years of follow-up.¹^,⁴^,⁵ In patients under 50 years at implantation it was reported with 11.7% even after 20 years of follow-up.³ In our cohort with a stricter endpoint definition, severe cranial migration was present in 31% of cases after a mean follow-up of 12.5 years. This increased frequency could partly be due to a selection bias, since Raiss et al. reported severe cranialization in 12.8% at ten years in a larger portion of the same registry segment with partly shorter follow-up.² Our cohort size is smaller due to the inclusion criteria of the postoperative image quality, which were necessary to reliably measure the scapular parameters. Overall the data is in keeping with the reported literature that suggests that cranialization is progressive over time. It could be increasing more slowly in younger patients under 50 years at implantation. In our view this could be due to the better stabilization through greater rotator cuff strength and better subscapularis healing in younger patients.

Logistic regression was able to predict severe cranialization using CSA with an AUC of 0.774. Because of the inferior AUC and the low predictable capabilities of the test in our cohort we found our results to be inferior to Moor et al.⁹ which can be explained by the small cohort size. In consequence a threshold was not calculated in this cohort regardless of the seemingly positive statistical result. In our cohort, a CSA ≥35° was predictive of severe cranialization. Cerciello et al. previously reported no significant difference in mean CSA values of patients being revised for rotator cuff failure with preoperative confirmatory CT-arthrograms compared to a matched cohort for age, sex and initial gleno-humeral diagnosis.¹³ Due to the nature of their study the follow-up between groups differed. The RCT group had a follow-up of 3.75 years showing early failure of the rotator cuff in their study, while the control group was followed a mean of 8.8 years.¹³ Due to strong tendencies they did suggest studies in larger cohorts could find significant differences.¹³ While the small cohort size makes it difficult to generalize our findings, we believe the longer follow-up in our study is responsible for the reported differences to Cerciello et al., since it appears that complications become apparent especially between 10 and 15 years of follow-up.1, 2, 3, 4, 5

While a CSA ≥35° did predict severe cranialization in our study, the positive predictive value was not good. However, a negative predictive value of 0.88 according to our dataset offers the interpretation that 88% of patients with a postoperative CSA <35° do not have severe cranialization after a mean of 12.5 years. However, due to the small cohort size and the follow-up time, we find it difficult to generalize these findings that require further verification. Furthermore, future studies should also address whether the 35° threshold discovered by Moor et al. can be applied following TSA. A positive correlation of CSA and glenoid inclination has been shown, while the lateral acromial roof extension seems to have the larger effect size within CSA.¹⁹^,²⁰ Still, if modification of either glenoid inclination or acromial coverage during the arthroplasty procedure could influence postoperative outcome remains to be determined.

Moreover, our data showed glenoid loosening in 25% (6/24) of TSAs which despite its small count is in keeping with several contemporary studies, reporting glenoid loosening in 19.7%–51.5% of cases after 10 years.2, 3, 4, 5 In our series an additional 29% of glenoids were at risk. This complements studies with follow-up periods of 15 years or more that reported high rates of glenoid loosening of about 70%.¹^,⁵ In young patients the frequency seems to be less with 35% of glenoids “at risk”, showing a radiolucency score greater or equal to 12 in young patients >15 years after TSA.³

Glenoid loosening or radiolucency score >7 did not correlate with a CSA ≥35° in our study, although logistic regression showed a suggestive tendency and severe cranialization was associated with glenoid loosening. Watling et al. had recently shown that CSA correlates with glenoid loosening in pegged polyethylene glenoids.¹⁵ It is to be expected that this would translate well to comparable cohorts with keeled glenoids, like ours, since keeled glenoids have higher rates of loosening, malposition, dislocation and early failure.²¹ Probably our sample size was too small to detect statistically significant differences for this parameter.

In our study only one Patient was surgically revised throughout follow-up. While in two studies an association of clinical symptoms with glenoid loosening was not found,¹^,² the clinical impression of the authors differed and other studies had already shown an association of glenoid loosening and clinical worsening in a medium-term follow-up.⁴

The revision rate for glenoid loosening has been reported with 9.1% after 15 years, with revision incidence increasing throughout follow-up,⁵ while the overall revision rate in a different study was 31% after more than 15 years in a french cohort, in which painful glenoid loosening was the main reason for revision.¹

In a more than 15-year follow-up of patients younger than 50 years at implantation, Schoch et al. reported a rate of surgical revision to Hemiarthroplasty in 11.4% of cases with TSA, with a revision-free survival of 83% in TSA.³

The present study has some limitations. Sonography assessment of the rotator cuff, CT-Scans or MRIs were not obtained during follow-up, thus only indirect measures via severe cranialization were taken. However, the applied measure of severe cranialization was chosen strictly, erring rather on the side of underdiagnosis than overdiagnosis. Still, on formal grounds it is unclear whether the diagnosis of rotator cuff insufficiency was truly made, which is why the phrasing of severe cranialization was used. Since it appears that complications become apparent especially between 10 and 15 years of follow-up, diagnosis might have been missed in our cohort whose mean follow-up was close to the center of this range. However, the follow-up duration of this study is much longer than in other studies on the topic of secondary rotator cuff insufficiency in TSA. Due to the inclusion criteria of the postoperative radiograph, the sample size was relatively small; generalization is therefore not advised. The large standard deviation of CSA found in our cohort and other published cohorts following TSA could be an indicator of relevant outliers influencing results. We have tried to minimize this bias through the inclusion criteria but cannot deny its relevance raising the importance of a confirmation study in a larger cohort.

5. Conclusion

The results of this small cohort suggest that a postoperative CSA ≥35° is associated with severe cranialization of the humeral head in the long-term following TSA, with a larger mean CSA postoperatively in shoulders with severe cranialization. Additionally, severe cranialization correlated with glenoid loosening. Our findings support the impact of postoperative joint geometry on the radiographic long-term follow-up following TSA underlining the continuous need to strive for ideal component placement.

Disclosures

All Authors, their immediate family and any research foundation with which they are affiliated did not receive any financial payments or other benefits from any commercial entity related to the subject of this article.

Source of funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee (Ethics committee of the Heidelberg University Medical Faculty, reference no. S-305/2007).

Declaration of competing interests

None.

References

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[bib2] 2.Raiss P., Schmitt M., Bruckner T. Results of cemented total shoulder replacement with a minimum follow-up of ten years. J Bone Joint Surg Am. 2012;94 doi: 10.2106/JBJS.K.00580. e1711-1710. [DOI] [PubMed] [Google Scholar]

[bib3] 3.Schoch B., Schleck C., Cofield R.H., Sperling J.W. Shoulder arthroplasty in patients younger than 50 years: minimum 20-year follow-up. J Shoulder Elbow Surg. 2015;24:705–710. doi: 10.1016/j.jse.2014.07.016. [DOI] [PubMed] [Google Scholar]

[bib4] 4.Walch G., Young A.A., Melis B., Gazielly D., Loew M., Boileau P. Results of a convex-back cemented keeled glenoid component in primary osteoarthritis: multicenter study with a follow-up greater than 5 years. J Shoulder Elbow Surg. 2011;20:385–394. doi: 10.1016/j.jse.2010.07.011. [DOI] [PubMed] [Google Scholar]

[bib5] 5.Young A., Walch G., Boileau P. A multicentre study of the long-term results of using a flat-back polyethylene glenoid component in shoulder replacement for primary osteoarthritis. J Bone Joint Surg Br. 2011;93:210–216. doi: 10.1302/0301-620X.93B2.25086. [DOI] [PubMed] [Google Scholar]

[bib6] 6.Hopkins A.R., Hansen U.N., Amis A.A., Taylor M., Emery R.J. Glenohumeral kinematics following total shoulder arthroplasty: a finite element investigation. J Orthop Res. 2007;25:108–115. doi: 10.1002/jor.20290. [DOI] [PubMed] [Google Scholar]

[bib7] 7.Franklin J.L., Barrett W.P., Jackins S.E., Matsen F.A., 3rd Glenoid loosening in total shoulder arthroplasty. Association with rotator cuff deficiency. J Arthroplasty. 1988;3:39–46. doi: 10.1016/s0883-5403(88)80051-2. [DOI] [PubMed] [Google Scholar]

[bib8] 8.Matsen F.A., 3rd, Clinton J., Lynch J., Bertelsen A., Richardson M.L. Glenoid component failure in total shoulder arthroplasty. J Bone Joint Surg Am. 2008;90:885–896. doi: 10.2106/JBJS.G.01263. [DOI] [PubMed] [Google Scholar]

[bib9] 9.Moor B.K., Bouaicha S., Rothenfluh D.A., Sukthankar A., Gerber C. Is there an association between the individual anatomy of the scapula and the development of rotator cuff tears or osteoarthritis of the glenohumeral joint?: a radiological study of the critical shoulder angle. Bone Joint Lett J. 2013;95-B:935–941. doi: 10.1302/0301-620X.95B7.31028. [DOI] [PubMed] [Google Scholar]

[bib10] 10.Heuberer P.R., Plachel F., Willinger L. Critical shoulder angle combined with age predict five shoulder pathologies: a retrospective analysis of 1000 cases. BMC Muscoskel Disord. 2017;18:259. doi: 10.1186/s12891-017-1559-4. [DOI] [PMC free article] [PubMed] [Google Scholar]

[bib11] 11.Moor B.K., Wieser K., Slankamenac K., Gerber C., Bouaicha S. Relationship of individual scapular anatomy and degenerative rotator cuff tears. J Shoulder Elbow Surg. 2014;23:536–541. doi: 10.1016/j.jse.2013.11.008. [DOI] [PubMed] [Google Scholar]

[bib12] 12.Viehofer A.F., Gerber C., Favre P., Bachmann E., Snedeker J.G. A larger critical shoulder angle requires more rotator cuff activity to preserve joint stability. J Orthop Res. 2016;34:961–968. doi: 10.1002/jor.23104. [DOI] [PubMed] [Google Scholar]

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[bib14] 14.Suter T., Gerber Popp A., Zhang Y., Zhang C., Tashjian R.Z., Henninger H.B. The influence of radiographic viewing perspective and demographics on the critical shoulder angle. J Shoulder Elbow Surg. 2015;24:e149–158. doi: 10.1016/j.jse.2014.10.021. [DOI] [PMC free article] [PubMed] [Google Scholar]

[bib15] 15.Watling J.P., Sanchez J.E., Heilbroner S.P., Levine W.N., Lu Bigliani, Jobin C.M. Glenoid component loosening associated with increased critical shoulder angle at midterm follow-up. J Shoulder Elbow Surg. 2018;27:449–454. doi: 10.1016/j.jse.2017.10.002. [DOI] [PubMed] [Google Scholar]

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PERMALINK

Effect of the critical shoulder angle on severe cranialization following total shoulder arthroplasty

Matthias Wolf, Dr.

Matthias Bülhoff, Dr.

Patric Raiss, Prof. Dr.

Felix Zeifang, Prof. Dr.

Michael W Maier, Prof. Dr.