Abstract
Introduction
The lateralization shoulder angle (LSA), the distalization shoulder angle (DSA) and the new “pentagon” concept are tools used in scheduled shoulder surgery to evaluate the positioning of reverse shoulder arthroplasty (RSA) implants. There is no information on the intra- and inter-rater reliability of these tools in the context of RSA for a proximal humerus fracture. The first hypothesis was the high reliability of the intra- and inter-rater analysis of the LSA and DSA angles. The second hypothesis was the reproductibility of the pentagon based on LSA and DSA analysis.
Methods
Forty-nine patients were evaluated retrospectively with a minimum of 2 years radiological follow-up after RSA surgery. Tuberosity healing was evaluated using an AP radiograph of the shoulder and their location analyzed within the said “pentagon” defined by the LSA/DSA angles and the maximum lengthening recommended.
Results
The intra-rater analysis found strong to an almost perfect agreement for the LSA and DSA. The agreement was moderate to strong for the pentagon. The inter-rater analysis found a fair agreement for the LSA and moderate agreement for the DSA and pentagon.
Conclusion
The LSA/DSA is used in patients undergoing RSA for glenohumeral OA. In this context, the tuberosities were intact and certain complications inherent to RSA for humeral fracture were not present. The population studied here (RSA after fracture) creates an interpretation bias due to the difficulty in analyzing tuberosity position.
Level of Evidence
4, retrospective study.
Keywords: Proximal humeral fracture, Reverse shoulder arthroplasty, Tuberosity healing, Observer variation
Introduction
Reverse shoulder arthroplasty (RSA) for proximal humerus fracture requires special attention on tuberosity fixation. In fact, the reattachment and healing of the tuberosities is a predictor of good functional outcomes and reduced postoperative complications (dislocation, loosening) [1, 2]. However, tuberosity reattachment is not always satisfactory, thus poor implant positioning can affect the outcome [2, 3]. Several studies have sought to define the ideal position based on humerus lengthening: acromion–lesser tuberosity distance, acromion–olecranon fossa distance, humeral head–epicondylar distance relative to the contralateral humerus [4–6]. This modification in the tuberosity position is a consequence and/or a driver of the alteration in the biomechanics of the deltoid and the RSA implants. Recently, Boutsiadis and al. proposed disregarding distances and focusing solely on two angles: lateralization shoulder angle (LSA) and distalization shoulder angle (DSA) [7]. However, Lädermann et al. emphasized that an acromion–tuberosity distance of more than 4 cm can compromise the axillary nerve and deltoid function after shoulder replacement [8]. Together, these measurements define the radiological concept of the pentagon, which must include the greater tuberosity.
The primary hypothesis was that the reliability of the intra- and inter-rater analysis of the LSA and DSA angles will be similar to that of the original study by Boutsiadis et al., who found a strong to almost perfect agreement. The secondary hypothesis was that the reproducibility of the pentagon concept is related to the reliability of the LSA and DSA analysis.
The aim of this study was to evaluate the intra- and inter-rater reliability of the radiographic analysis of the LSA/DSA and pentagon following primary RSA for proximal humerus fracture.
Materials and Methods
Study Design
This was a retrospective, multicenter cohort study of patients after RSA surgery for proximal humerus fracture, between January 2013 and May 2018. Included were patients over 65 years of age with a 3-part or 4-part fracture in the Neer classification [9], operated within 6 weeks of the fracture event and who had a minimum of 2 years of radiological follow-up. Excluded were patients who had a pathological fracture, prior surgery on the involved shoulder or post-traumatic neurological deficit. All the patients gave informed consent to having their epidemiological and radiological data analyzed for this study. The study protocol was developed in compliance with STROBE (Strengthening in Reporting of Observational Studies) guidelines. Our study population is summarized in Fig. 1.
Fig. 1.
Flow chart summarizing the study design (RSA: reverse shoulder arthroplasty)
Surgical Technique
The procedure was carried out by 3 attending surgeons with significant experience in shoulder surgery. There were two level 4 surgeons and one level 3 surgeon, according to Tang’s classification (Table 1) [10]. An RSA implant with a self-stabilizing (press fit) and lockable stem designed specifically for fracture cases was used (Humelock Reversed 1 and 2, FX Solutions, France) [11]. A deep and modular metaphysis (OMS system) that could accept bone graft and had a 145° neck–shaft angle to protect the scapular pillar was impacted, screwed or cemented. A deltopectoral approach was made with the patient under general anesthesia in the beach chair position and a fluoroscopy unit was available. All the patients underwent biceps tenotomy and resection of the supraspinatus tendon [12]. The humeral head was excised and then fragmented for later use as a metaphyseal bone graft. The humeral shaft was prepared by inserting successively larger reamers, followed by metaphyseal rasps. Reaming of the glenoid was guided by a K-wire, inserted 12 mm from the inferior edge of the glenoid [13]. A 24 mm metaglenoid was impacted and secured with four screws. After verifying the height using the pectoralis major tendon as a landmark (as described by Muraschowsky et al. [14]) and 20° retroversion relative to the forearm, the stem was stabilized with screws inserted using a designated tool in the instrumentation set. Transosseous suturing of the tuberosities was done in every patient with three sets of double loop sutures; this made it possible to make self-locking knots as described by Lascar et al. [15].
Table 1.
Results of the intra-rater analysis based on Pearson’s correlation coefficient
Once the sutures had been passed through the tuberosities and the stem, the joint was reduced. Bone graft was added into the metaphyseal–epiphyseal cage (OMS system). The patient’s shoulder was immobilized in a sling with the elbow at the side for 1 month. Rehabilitation such as pendulum exercises were started on postoperative day 30.
Clinical Evaluation
The Constant-Murley, Quick-Dash and ASES scores were used. All patients were evaluated postoperatively at M1, M3, M6, and one year, and then every year [16–18]. Assessment of active shoulder mobility included anterior elevation, abduction, external rotation 1, and internal rotation.
Radiological Assessment
Anteroposterior views with the arm in neutral rotation, internal rotation and external rotation were made along with a Lamy view of the operated shoulder, then interpreted at the latest follow-up. At 2 years, the presence of scapular notching was evaluated and defined using the four stages in the Nerot-Sirveaux classification [19]. Healing, lysis and displacement of the greater tuberosity were evaluated on the four radiographic views. The greater tuberosity was considered healed when a bone bridge was visible.
Angles were measured by 3 independent evaluators (PT, IR, HH) using MicroDicom software on immediate postoperative AP radiographs with the shoulder in neutral rotation. A radiological analysis guide, inspired by the Boutsiadis study, was used to define the landmarks needed to measure the angles and the pentagon [7]. For the DSA, three landmarks were necessary: the most lateral edge of the acromion, the superior edge of the glenoid and the superior edge of the greater tuberosity, with an ideal angle described between 40 and 65° (Fig. 2). For the LSA, the three landmarks were the superior edge of the glenoid, the most lateral edge of the acromion and the most lateral edge of the greater tuberosity with an ideal angle described between 75 and 95° (Fig. 3).
Fig. 2.
Distalization shoulder angle (DSA)
Fig. 3.
Lateralization shoulder angle (LSA)
The maximum recommended lengthening corresponds to a parallel line located 4 cm from the inferior side of the acromion (Fig. 4) [4, 8]. The middle of the greater tuberosity was considered as the maximum limit for lengthening. The pentagon was constructed using three visual landmarks: the minimum and maximum values of the DSA, the minimum and maximum values of the LSA, and maximum recommended lengthening. This geometric figure corresponds to the optimal theoretical placement of the greater tuberosity (Fig. 5).
Fig. 4.
Maximum recommended lengthening (green line = 4 cm)
Fig. 5.
Optimal theoretical placement of the greater tuberosity “pentagon (Blue line: DSA, purple line: LSA, yellow line: maximum recommended lengthening, green line: pentagon, red circle: actual values)
Three raters participated in the reliability study: one upper limb surgeon (Medical Doctor) and two 5th year orthopedic surgery residents, with, respectively, one level 3 and two levels 1 according to Tang's classification [10]. To analyze the inter-rater reliability, each rater did the measurements a second time 15 days later.
Statistical Analysis
The qualitative variables were described by their number and percentage. Quantitative variables were described by their mean and standard deviation, their normality was verified by the Shapiro–Wilk test. For quantitative variables, the Wilcoxon nonparametric test was used. A p value < 0.05 was considered significant. The intra-rater agreement was determined with Pearson's correlation coefficient and its 95% confidence interval (CI). The agreement between the three raters was based on the intra-class correlation coefficient (ICC) with 95% CI. We defined the kappa value by κ.
These analyses were done using the software R version 3.6.3 (www.cran.r-project.org). The results were interpreted as recommended by Landis and Koch [20]:
| Value of kappa (κ) | Interpretation |
|---|---|
| < 0 | No agreement |
| 0–0.20 | Slight agreement |
| 0.21–0.40 | Fair agreement |
| 0.41–0.60 | Moderate agreement |
| 0.61–0.80 | Strong agreement |
| 0.81–1.00 | Almost perfect agreement |
The Kappa coefficient could be negative, indicating that the result is no better than that expected by chance.
Results
Descriptive Analysis
Of the 78 eligible patients, 49 patients who had at least 24 months follow-up were reviewed for this study (63% of starting population). Sixteen patients were excluded because they met at least one exclusion criterion and 13 were excluded because they did not have radiographs at 2+ years postoperative. The stems were locked and uncemented in 100% of patients. The average follow-up was 46 ± 20 months (24–88 months). The mean patient age at the time of surgery was 76 ± 7 years (68–97 years); 45% of the population was older than 80 years at the time of the last clinical evaluation; 92% were women. Based on the Neer classification (5), 3-part and 4-part fractures had a 14% and 86% share, respectively. No intraoperative complications were found. Eight patients had postoperative complications, a rate of 16%, with 1 dislocation, 6 acromial fractures, and 1 axillary neurapraxia (with complete recovery at six months post-op).
Functional Analysis
The mean QDash, ASES, Constant, and weighted Constant scores were 37 ± 21, 63 ± 22, 52 ± 16, and 84 ± 24, respectively. There was a significant improvement in the Constant and Weighted Constant scores when the tuberosities were included in the DSA (p = 0.03 and p = 0.01 respectively). Properly performed distalization appears to partially improve functional outcomes in patients regardless of tuberosity status.
Intra-rater Analysis (Table 1)
For the LSA, agreement between raters 1, 2 and 3 was κ = 0.81 [0.69–0.89]; κ = 0.77 [0.62–0.86]; κ = 0.98 [0.97–0.99]. For the DSA, agreement between raters 1, 2 and 3 was κ = 0.95 [0.92–0.97]; κ = 0.85 [0.76–0.91]; κ = 0.99 [0.98–0.99]. For the pentagon, agreement between raters 1, 2 and 3 was κ = 0.79 [0.66–0.88]; κ = 0.48 [0.24–0.67]; κ = 0.80 [0.66–0.88].
Inter-rater Analysis (Table 2)
Table 2.
Results of the inter-rater analysis based on the intra-class correlation coefficient
For the LSA, the level of agreement between the first and second reading was κ = 0.37 [0.19–0.55]; κ = 0.40 [0.22–0.58]. For the DSA, the level of agreement between the first and second reading was κ = 0.51 [0.35–0.67]; κ = 0.54 [0.38–0.69]. For the pentagon, the level of agreement between the first and second reading was κ = 0.43 [0.26–0.60]; κ = 0.43 [0.25–0.60].
Discussion
While the reproducibility of these measurements has only been validated in the context of RSA for omarthrosis, the aim of this study was to validate the reliability of LSA and DSA analysis in the context of RSA for proximal humerus fractures [7]. These radiographic tools are fairly recent, with only two studies reporting on their use [6, 7]. The study by Boutsiadis et al. was the only one to evaluate the inter- and intra-rater agreement [7]. Their intra-rater analysis found a strong agreement for the LSA (κ = 0.8 [0.7–0.86]) and almost perfect agreement for the DSA (κ = 0.9 [0.83–0.93]). Our intra-rater analysis was consistent with their findings since we found an almost perfect agreement for both the LSA and the DSA.
Their inter-rater analysis found a strong agreement for the LSA (κ = 0.78 [0.73–0.84]) and almost perfect agreement for the DSA (κ = 0.81 [0.78–0.85]). The results of our inter-rater analysis were different from those described by Boutsiadis et al. [7]. In fact, the agreement was low for the LSA and moderate for the DSA. The results of our study and the Boutsiadis et al. study are compared in Table 3 [7].
Table 3.
Comparison of the intra- and inter-rater reliability between our study and the Boutsiadis study
We added an analysis of the pentagon, which corresponds to the geometric shape formed by the LSA and DSA. The intra-rater analysis of the pentagon found only strong agreement, while the angle measurements had an almost perfect agreement. Contrary to our secondary hypothesis, the pentagon analysis does not appear to be related solely to the strength of the LSA and DSA analysis.
We also found that the inter-rater reliability did not improve between the first and second readings. The agreement was moderate in both situations. Surgeon experience appears to play an important role when it comes to reproducibility when reading radiographs. Indeed, the attending surgeon in our study had a higher mean Kappa coefficient than the two residents. We chose a 2-week interval between the two readings, which we felt was sufficient to eliminate any carryover effect. Other publications analyzing the inter-rater agreement used a 2-week interval [21], while some used 6 months [22].
Our study featured a patient population who had undergone RSA for proximal humerus fracture, causing a selection bias. Indeed, Boddapati et al. compared epidemiological data relative to the indication for arthroplasty: fracture, glenohumeral OA, and irreparable rotator cuff tear [23]. Their fracture group consisted of older, more fragile patients (diabetes, chronic obstructive pulmonary disease, dependent) and mostly women. The operative time and length of hospital stay were longer and the transfusion rate higher [23]. Our study population is comparable to the fracture group in the Boddapati study [23]. However, the population used to define the LSA/DSA angles consisted of patients undergoing RSA for glenohumeral OA [7]. In this context, the tuberosities are intact and some complications inherent to RSA for humeral fracture are not present (lysis, nonunion, malunion). This bias is important and likely made it more difficult to interpret the positioning of the greater tuberosity following a proximal humerus fracture in our study.
The SOFCOT study group looked at postoperative mortality in patients undergoing RSA for a proximal humerus fracture. They found a significant survival rate (73%) at 5 years, confirming the value of this surgery in the elderly. The presence of cognitive impairment and/or several comorbidities (ASA > 3) were risk factors for early mortality, which should be taken into account before considering this type of surgery [24].
Beyond the radiographic analysis, the DSA, LSA and pentagon are used to predict the functional outcomes of RSA over the long term. The primary goal of RSA is to improve mobility and functional scores. This guarantee of improved functional outcomes based on these angles has only been demonstrated in a population of patients undergoing RSA for glenohumeral OA [7].
While our study is the first to analyze the LSA/DSA after proximal humerus fracture, it has its limitations. The radiographic analysis was standardized with an imaging interpretation protocol. The intra- and inter-rater analysis found an almost perfect intra-rater agreement for the analysis of angles, confirming that the landmarks selected were the correct ones. However, the moderate inter-rater reliability leads us to believe that the radiological analysis protocol was not precise enough.
There are also significant biases to a radiological analysis: variable quality of radiographs, projection or incidence errors, difficult to distinguish between tuberosity osteolysis and ossifications, acromial fracture and morphological variation of the acromion [25]. Moreover, our implant system had a lateral cage packed with bone graft. This feature complicated the interpretation. Fortané et al. found a higher rate of consolidation when using a modular cage, without improving functional results [26].
Doing an AP radiograph in neutral rotation appears essential to avoid influencing the LSA and DSA. The basis of this work was the analysis of different angles on an AP view. While a CT scan is the gold standard to assess tuberosity healing, osteolysis and calcifications, we felt that its benefits to the analysis were not sufficient to justify doing one in our study. The invasiveness of the CT scan may lead to a discussion of an EOS, which is less invasive, superimposes several images and allows 3D reconstruction.
Conclusion
The reproducibility of the DSA and LSA angles in patients who have undergone RSA following proximal humerus fracture is debatable. While the intra-rater analysis was reliable with an almost perfect agreement, the inter-rater analysis had fair to a moderate agreement. Reproducibility of the pentagon analysis was not solely dependent on the LSA and DSA. The population studied here (RSA after fracture) creates an interpretation bias given the difficulty in analyzing the position of the tuberosities. We hope that in the near future, surgical navigation will allow us to determine these angles intraoperatively—even in a fracture context—and to optimize RSA implant positioning.
Acknowledgements
We thank the university hospital of Besançon and the whole department of orthopaedic surgery.
Author Contributions
All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by PT, IR and HH. The first draft of the manuscript was written by PT and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.
Funding
The authors did not receive support from any organization for the submitted work. No funding was received to assist with the preparation of this manuscript. No funding was received for conducting this study. No funds, grants, or other support was received.
Declarations
Conflict of interest
The authors declare financial interests with the following organizations: LO: FX solutions, Medartis, Keri Médical, Evolutis, Elsevier, CHRU de Besancon, Université de Bourgogne Franche Comté. PT: Arthrex SAS. HH: FX solutions. TL: Johnson & Johnson medical SAS. FL: Medartis, Évolutis, Zimmer, Arthrex. IP, IR, FS : none.
Ethical Approval
The experiments comply with the current laws of the country. The study protocol was developed in compliance with STROBE (Strengthening in Reporting of Observational Studies) guidelines. Ethical approval was not required.
Informed Consent
Written informed consent was obtained from all patients and/or families.
Footnotes
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
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