Abstract
Background
Calibration of shoulder radiographs is required for accurate preoperative planning. Current practice mostly uses an empirical fixed calibration factor of 5%, and limited information is available about how the magnification of the glenohumeral region differs among patients. This retrospective observational study analyzed the patient-specific magnification factor in total shoulder arthroplasty.
Methods
Radiographs of 94 patients with unilateral total shoulder arthroplasty (SMR Reverse Shoulder System, Lima Ltd., San Daniele del Friuli, Italy) were obtained from archives. The reverse humeral body diameter was used as internal reference. The measured radiographical magnifications were correlated with the patients’ sex, weight, and height.
Results
The average magnification factor of the glenohumeral region was 11.9% (standard deviation: 3.2%, range: 5.7–20.3%). No statistically significant difference in radiographic magnification was found between the male and the female patients. The magnification factor was higher in patients with higher weight (p < 0.05), but the explanatory power of the model was weak (R = 0.09).
Conclusions
The observed radiographic magnification was considerably higher than a commonly used fixed calibration factor of 5% and exhibited considerable variability among the patients. Therefore, standard radiographs might not be appropriate for accurate preoperative templating, and we recommend using either computer tomography data or calibrating radiographs through external calibration markers for each patient.
Zusammenfassung
Hintergrund
Für eine genaue präoperative Planung ist die Kalibrierung von Röntgenaufnahmen der Schulter erforderlich. Praktisch wird aktuell zumeist ein empirisch festgelegter Kalibrierungsfaktor von 5 % verwendet, und es gibt nur begrenzt Informationen darüber, wie sich die Vergrößerung der Glenohumeralregion zwischen den Patienten unterscheidet. In der vorliegenden retrospektiven Beobachtungsstudie wurde der patientenspezifische Vergrößerungsfaktor bei totaler Schulterarthroplastik untersucht.
Methoden
Aus Archiven wurden Röntgenaufnahmen von 94 Patienten mit unilateraler totaler Schulterarthroplastik (SMR Reverse Shoulder System, Fa. Lima Ltd., San Daniele del Friuli, Italien) entnommen. Als interne Referenz wurde der Durchmesser des hinteren Humerusschafts verwendet. Die gemessenen radiographischen Vergrößerungen wurden mit Geschlecht, Gewicht und Körpergröße der Patienten korreliert.
Ergebnisse
Der durchschnittliche Vergrößerungsfaktor der Glenohumeralregion betrug 11,9 % (Standardabweichung: 3,2 %; Spannbreite: 5,7–20,3 %). Es fand sich kein statistisch signifikanter Unterschied bei der radiographischen Vergrößerung zwischen männlichen und weiblichen Patienten. Ein höherer Vergrößerungsfaktor lag bei Patienten mit höherem Gewicht vor (p < 0,05), aber die Aussagekraft des Modells war schwach (R = 0,09).
Schlussfolgerung
Die ermittelte radiographische Vergrößerung war beträchtlich höher als der gewöhnlich verwendete feste Kalibrierungsfaktor von 5 % und zeigte eine erhebliche Variabilität zwischen den Patienten. Daher sind Standardröntgenaufnahmen möglicherweise nicht als genaue präoperative Schablone geeignet, und die Autoren empfehlen, entweder Computertomographiedaten zu verwenden oder Röntgenaufnahmen mittels externer Kalibrierungsmarker für jeden Patienten zu kalibrieren.
Similar content being viewed by others
Avoid common mistakes on your manuscript.
Background
Reverse total shoulder arthroplasty (RTSA) represents an efficacious surgical intervention for the alleviation of incapacitating shoulder pain. Initially introduced for the treatment of rotator cuff insufficiency, it has demonstrated success in managing various conditions such as glenohumeral osteoarthritis, proximal humerus fractures and malunions, inflammatory arthritis, tumor reconstruction, and irreparable rotator cuff tears [1, 2]. With the aging population, the demand for RTSAs is increasing, and projections indicate a continued rise in the coming decade [3]. Nonetheless, the implantation of RTSA remains a challenging procedure, even for experienced shoulder surgeons [2].
Preoperative planning plays a crucial role in achieving optimal implant size selection and accurate placement of the glenosphere and humeral component [4]. Conventional preoperative planning methods typically involve the utilization of either physical or digital templates on radiographs [5]. These templates need to be calibrated to accurately correspond to the actual size of the shoulder bones. However, in the case of RTSA, both digital and physical radiographic templates commonly employ a fixed 5% magnification factor [6].
Previous studies have demonstrated significant variability in image magnification among different patients. For instance, in the context of hip imaging, magnification levels have been reported to range from 12 to 35% [7, 8]. Similarly, investigations involving trauma patients undergoing humeral nailing or plating have indicated a magnification range of 2–22% for the humerus [9]. It is important to note that radiographic magnification is influenced by various factors, including radiographic techniques and the size of the patient, which can affect both the focus–film distance and the shoulder–film distance [10, 11].
Consequently, certain hospitals employ external markers to estimate magnification and enhance the precision of preoperative templating. Nevertheless, in cases where such markers are unavailable, a fixed magnification value is universally applied to all patients. We hypothesize that (1) the actual magnification significantly deviates from the commonly adopted value of 5%, and (2) notable variations in radiographic magnification exist among patients. To address these hypotheses, we conducted a retrospective observational study wherein the magnification of the shoulder joint was ascertained by employing the implant as an internal calibration marker.
Methods
A retrospective study was conducted at Motol University Hospital, Czechia, involving patients who had previously undergone total glenoid arthroplasty. The analysis focused exclusively on the SMR Reverse Shoulder System implants (Lima Corporate, San Daniele del Friuli, Italy; [6]). The study inclusion criteria encompassed the following parameters: unilateral RTSA, documented information regarding implant size and type, recorded patient height and weight, availability of digital anteroposterior (AP) radiographs of the shoulder in a neutral position from the hospital archives, and clear visibility of the humeral and glenoid components of the RTSA. A total of 98 digital AP radiographs from a consecutive cohort of 98 patients, taken during the first follow-up after glenoid arthroplasty, were obtained as DICOM files. Three patients were excluded from the study due to evident arm rotation in the radiographic images, and one patient was excluded due to missing information on the radiographic setup in the DICOM file. The final cohort comprised 94 patients, including 62 female and 32 male patients. The average age of patients at the time of surgery was 69.4 years (±8.7 years, ranging from 38 to 85 years). The data were collected during the period 2014–2017, with the actual study being conducted in April 2023. This noninterventional retrospective study based on an anonymized dataset was approved by the ethics committee of Motol University Hospital (reference no. EK-1204/18). The authors did not have access to any information that could potentially identify individual participants either during or after the process of data collection.
For reference, the diameter of the proximal part of the reverse humeral body (component no. 1352.20.010) was used (Fig. 1). This component possesses a cylindrical shape, and its diameter remains consistent regardless of internal or external rotation. The cylindrical geometry was confirmed by fitting a cylinder to a 3D scan of a nonimplanted specimen using an optical coordinate measuring system (Omnilux, RedLux Ltd., Romsey, UK). The physical diameter of 36.6 mm was obtained from the cylindrical fit and verified by measuring the component using a digital caliper (Mahr GmbH, Göttingen, Germany). The component dimension on the radiographs was estimated from the DICOM files using the Fiji platform for biological-image analysis [12]. Specifically, two points on each side of the cylindrical portion of the component were defined and used to construct the lateral and medial edges of the component. A custom MATLAB script (MATLAB R2020b, The MathWorks, Inc., Natick, MA, USA) was developed to calculate the diameter of the component as the mean perpendicular distance between the lines measured at the defined points (Fig. 1). A single observer (A. K.) analyzed all radiographs. To assess the reliability of the method for estimating radiographic magnification, five independent and blinded observers (postgraduate students of biomechanics at CTU in Prague) analyzed a set of 20 randomly selected radiographs.
The radiographic magnification (M) of the implants was calculated as
where 0% magnification correspond to exact match between the image size and implant size.
Statistical analysis
Data analysis was performed utilizing R (version 4.1.2; R Foundation for Statistical Computing, Vienna, Austria). To assess interobserver variability, the intraclass correlation coefficient (ICC) was calculated using model 2.1 as described by Shrout and Fleiss [13]. The Shapiro–Wilk test was employed to assess the normal distribution of radiographic magnification. The analysis was conducted for the entire cohort as well as separately for male and female patients. An unpaired Welch t test was used to compare radiographic magnification between male and female patients. Multiple linear regression was employed to investigate whether patient weight and height significantly predicted magnification [14]. The computation of 95% confidence intervals (Cis) and p values was carried out using the Wald approximation. An alpha value of 0.05 was applied to evaluate the statistical significance. In the post hoc power analysis, based on the sample size for the primary outcome, the power was determined to be 0.99 for a two-tailed comparison, with an effect size of 0.5 and an alpha error of 0.05.
Results
There was an excellent agreement between the observers in evaluating the magnification of the radiographs (inter-rater ICC = 0.997, 95% confidence interval: 0.991–0.999). The average magnification factor was 11.9% (standard deviation [SD]: 3.2%, range: 5.7–20.3%). The magnification factor was normally distributed (Shapiro–Wilk normality test p = 0.209; Fig. 2).
A slightly higher radiographic magnification was observed in male (mean: 12.7%, SD: 3.5%) than in female patients (mean: 11.4%, SD: 3.1%), the difference was not significant (Welch two-sample t test p = 0.077). A linear model was fitted to predict radiographic magnification with patient height and weight. The model’s explanatory power was weak (R = 0.09), indicating large inter-individual variability among patients (Fig. 3). The effect of weight was statistically significant and positive (p = 0.017), while the effect of height was not statistically significant (p = 0.648).
Discussion
Previous studies have established a correlation between radiographic magnification in preoperative planning for hip arthroplasty and patient factors such as sex, age, weight, or body mass index [15, 16]. In our study, the only statistically significant factor was patient weight, as higher weight correlated with larger radiographic magnification (Fig. 3). The slightly higher magnification observed in male patients (Fig. 2) can be attributed to the observation of higher weight in male compared to female patients (Fig. 3). However, due to the significant inter-individual differences, this correlation (Fig. 3) is not applicable for clinically practical correction.
A limitation of this study is its reliance primarily on data obtained from a single clinical workplace and a single X‑ray machine, which limited the cohort size. Extending the study to multiple clinical workplaces would provide a lager cohort, but it could introduce additional variability related to the specific radiographic setup. Hornova et al. in 2017 [8] demonstrated considerable variations in hip radiographic magnification ranging from 16 to 24% between different clinical workplaces. It should also be noted that the radiographic device used in this study performed an intrinsic magnification correction of 5.2% according to DICOM image headers, where the imager pixel spacing of 0.143 mm appeared as a radiographic image with a pixel spacing of 0.136 mm.
The magnification was estimated from the cylindrical component of RTSA as shown in Fig. 1. The distortion of the cylindrical section due to shoulder flexion or extension was corrected by averaging its dimension along the length of the component. However, the magnification obtained at the cylindrical component might differ from the magnification at the glenosphere, as these two components might not be aligned in the sagittal plane.
Three-dimensional planning techniques using computed tomography (CT) imaging have been proposed for enhancing precision in preoperative planning [17, 18]. However, recent investigations have indicated minor discrepancies between 3D planning and traditional 2D methods [4]. Additionally, careful consideration must be given to the potential risks associated with increased radiation exposure, as higher effective doses during CT shoulder examinations may increase the risk of developing cancer [19]. Nevertheless, one advantage of CT scans is the absence of a need for external calibration markers. Moreover, CT scans are typically readily available, and the radiation dosage from modern CT machines continues to decrease.
Plain radiographs serve as the initial assessment method for evaluating the glenohumeral joint [20]. It has been shown that the use of external markers can enhance the accuracy of preoperative templating. A spherical external calibration marker should be positioned at the anticipated joint height above the detector [5].
Practical conclusion
-
The commonly assumed standard magnification for shoulder radiographs is 5%; however, our findings demonstrate that radiographic magnification in the glenohumeral region can range as high as 20% in certain patients.
-
In the majority of patients, magnification surpassed 10%, revealing significant inter-individual variability.
-
Therefore, we recommend employing an external calibration marker placed in the frontal plane crossing the acromion process when utilizing plain radiographs for shoulder arthroplasty templating.
-
In instances where a calibration marker is unavailable, our results indicate that relying on a fixed 5% magnification may introduce systematic bias in preoperative planning.
References
Best MJ, Aziz KT, Wilckens JH, McFarland EG, Srikumaran U (2021) Increasing Incidence of Primary Reverse and Anatomic Total Shoulder Arthroplasty in the United States. J Shoulder Elbow Surg 30(5):1159–1166. https://doi.org/10.1016/j.jse.2020.08.010
Kozak T, Bauer S, Walch G, Al-karawi S, Blakeney W (2021) An Update on Reverse Total Shoulder Arthroplasty: Current Indications, New Designs, Same Old Problems. Efort Open Rev 6(3):189–201. https://doi.org/10.1302/2058-5241.6.200085
Wagner ER, Farley KX, Higgins I, Wilson JM, Daly CA, Gottschalk MB (2020) The Incidence of Shoulder Arthroplasty: Rise and Future Projections Compared with Hip and Knee Arthroplasty. J Shoulder Elbow Surg 29(12):2601–2609. https://doi.org/10.1016/j.jse.2020.03.049
Olaiya OR, Nadeem I, Horner NS, Bedi A, Leroux T, Alolabi B et al (2020) Templating in Shoulder Arthroplasty—A Comparison of 2D CT to 3D CT Planning Software: A Systematic Review. Shoulder Elbow 12(5):303–314. https://doi.org/10.1177/1758573219888780
Archibeck MJ, Cummins T, Tripuraneni KR, Carothers JT, Murray-Krezan C, Hattab M et al (2016) Inaccuracies in the Use of Magnification Markers in Digital Hip Radiographs. Clin Orthop Relat Res 474(8):1812–1817. https://doi.org/10.1007/s11999-016-4704-8
Bloch HR (2016) The SMR® Shoulder System of Lima Corporate. In: Frankle M, Marberry S, Pupello D (eds) Reverse Shoulder Arthroplasty. Springer, Cham, pp 417–424
Descamps S, Livesey C, Learmonth ID (2010) Determination of Digitised Radiograph Magnification Factors for Pre-Operative Templating in Hip Prosthesis Surgery. Skelet Radiol 39(3):273–277. https://doi.org/10.1007/s00256-009-0732-8
Hornová J, Růžička P, Hrubina M, Šťastný E, Košková A, Fulín P et al (2017) Magnification of Digital Hip Radiographs Differs between Clinical Workplaces. PLoS ONE 12(11):e188743. https://doi.org/10.1371/journal.pone.0188743
King RJ, Craig PRS, Boreham BG, Majeed MA, Moran CG (2009) The Magnification of Digital Radiographs in the Trauma Patient: Implications for Templating. Injury 40(2):173–176. https://doi.org/10.1016/j.injury.2008.06.027
Hafez MA, Schemitsch EH (2008) Digital Templating for Revision Total Hip Arthroplasty. In: Operative Techniques: Hip Arthritis Surgery. Elsevier, pp 215–225
Loweg L, Trost M, Kutzner KP, Ries C, Boese CK (2020) A Novel Calibration Method for Digital Templating of Total Hip Arthroplasty: A Prospective Clinical Study of Dual Scale Type Single Marker Calibration in Supine Radiographs. Int Orthop (sicot) 44(9):1693–1699. https://doi.org/10.1007/s00264-020-04597-8
Schindelin J, Arganda-Carreras I, Frise E, Kaynig V, Longair M, Pietzsch T et al (2012) Fiji: An Open-Source Platform for Biological-Image Analysis. Nat Methods 9(7):676–682. https://doi.org/10.1038/nmeth.2019
Shrout PE, Fleiss JL (1979) Intraclass Correlations: Uses in Assessing Rater Reliability. Psychol Bull 86(2):9. https://doi.org/10.1037//0033-2909.86.2.420
Fox J (2016) Applied Regression. Analysis (and Generalized Linear Models. Third edition, Los Angeles: SAGE)
Jahnke A, Engl S, Seeger JB, Basad E, Rickert M, Ishaque BA (2015) Influences of Fit and Fill Following Hip Arthroplasty Using a Cementless Short-Stem Prosthesis. Arch Orthop Trauma Surg 135(11):1609–1614. https://doi.org/10.1007/s00402-015-2302-y
Pourmoghaddam A, Dettmer M, Freedhand AM, Domingues BC, Kreuzer SW (2015) A Patient-Specific Predictive Model Increases Preoperative Templating Accuracy in Hip Arthroplasty. J Arthroplast 30(4):622–626. https://doi.org/10.1016/j.arth.2014.11.021
Cho SH, Jeong J (2020) Radiologic Results of Three-Dimensional Templating for Total Shoulder Arthroplasty. Clin Orthop Surg 12(2):232. https://doi.org/10.4055/cios19100
Min KS, Fox HM, Bedi A, Walch G, Warner JJP (2020) Influencing the Learning Curve for Assessment of the Glenoid and Surgical Planning. Bone Jt J 102(3):6. https://doi.org/10.1302/0301-620X.102B3.BJJ-2019-1153.R1
Iordache SD, Goldberg N, Paz L, Peylan J, Hur RB, Steinmetz A (2017) Radiation Exposure From Computed Tomography Of The Upper Limbs. Acta Orthop Belg 83(4):581–588
Gates S, Sager B, Khazzam M (2020) Preoperative Glenoid Considerations for Shoulder Arthroplasty: A Review. Efort Open Rev 5(3):126–137. https://doi.org/10.1302/2058-5241.5.190011
Acknowledgements
This work was supported by Czech Health Research Council, Project No. NU21-06-00084.
Funding
Open access publishing supported by the National Technical Library in Prague.
Author information
Authors and Affiliations
Corresponding author
Ethics declarations
Conflict of interest
A. Kratochvíl, M. Daniel, P. Fulín and D. Pokorný declare that they have no competing interests.
This study was approved by the ethics committee of Motol University Hospital (reference no. EK-1204/18).
Additional information
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Scan QR code & read article online
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Kratochvíl, A., Daniel, M., Fulín, P. et al. Radiographical magnification of the shoulder region. Obere Extremität (2024). https://doi.org/10.1007/s11678-024-00802-x
Received:
Accepted:
Published:
DOI: https://doi.org/10.1007/s11678-024-00802-x