Classifications in Brief: The Nerot-Sirveaux Classification for Scapular Notching

History Anatomic total shoulder arthroplasty (TSA) can improve function and pain in patients with pathology of the glenohumeral articulation. However, rotator cuff deficiency can negatively impact patient function and component longevity after anatomic TSA [7, 24]. Studies have demonstrated the rotator cuff’s role as an important dynamic stabilizer of the glenohumeral joint [1, 8]. Therefore, rotator cuff deficiency directly increases the translational and frictional force burden on a TSA, which can lead to loosening and failure of the components [7, 12, 19]. Moreover, rotator cuff deficiency alters glenohumeral biomechanics, leading to loss of strength and ROM on arm flexion and abduction after TSA [16, 19]. Investigators set out to design a shoulder arthroplasty that would mitigate the problems associated with anatomic TSA in patients with cuff deficiency, leading to the development of the reverse total arthroplasty (RSA). In 1985, Grammont conceptualized the design from which modern RSA evolved [4, 20]. Although restricted to medium-term results, modern reverse shoulder arthroplasty appears to yield improvements in patient-reported outcome scores in a group of patients previously not well served by conventional implants, albeit at an increased risk of complications compared with anatomic TSA [2, 11, 18]. One of these complications, unique to reverse shoulder arthroplasty, is scapular notching. Scapular notching was described by Sirveaux et al. [20] in their analysis of the midterm results of the Delta (DePuy, Warsaw, IN, USA) shoulder prosthesis, which was a Grammont-style reverse design. When investigators compared preoperative and postoperative radiographs of 80 Grammont inverted total shoulders, they identified the phenomenon we now refer to as scapular notching as “a defect of the bone in the inferior part of the glenoid component.” Scapular notching is theorized to be caused by mechanical impingement of the medial side of the humeral polyethylene component against the inferior scapular neck. However, the notching sometimes extends beyond the extent of possible impingement, giving rise to the notion that polyethylene wear may lead to associated osteolysis [15]. It was eventually recognized that the symmetric geometry of the polyethylene humeral component and drastically medialized center of rotation may also contribute to this phenomenon. As a secondary aim to their 2004 study, Sirveaux et al. developed a classification system for their new discovery. We note that a very similar classification system was developed by Nerot’s group around the same time [21], yielding the commonly used combined reference, the Nerot-Sirveaux classification system. Classification System The Nerot-Sirveaux classification system for scapular notching is a radiographically based tool that describes the amount and extent of bone loss in patients with notching after RSA. To identify and classify scapular notching, Sirveaux et al. [20] utilized an AP radiographic view tangential to the baseplate (a true AP of the shoulder in the scapular plane), because this permits visualization of the glenosphere and scapular neck without superimposition of the humeral component. Sirveaux et al. and Nerot’s group both classified the scapular notch as Grades 1 to 4 based on the size of the defect seen on the radiograph. In Grade 1, the defect involved only the inferior pillar of the scapular neck. In Grade 2, the notch was in contact with the lower screw as a result of erosion of the scapular neck to the level of the screw. In Grade 3, erosion of the bone creating the notch extended over the lower screw. In Grade 4, the notch extended under the baseplate [14, 20, 21] (Fig. 1).Fig. 1: This is a rendition of the original figure portrayed by Sirveaux et al. in their article that described the Sirveaux classification of scapular notching [25]. Dotted white lines 1-4 indicate the various grades of scapular notching. In Grade 1, the defect involves only the inferior pillar of the scapular neck. In Grade 2, the notch contacts the lower screw. In Grade 3, erosion of the bone extends over the lower screw. In Grade 4, the notch extends under the baseplate.Grades 1 and 2 scapular notching generally are believed to be the result of mechanical impingement between the humeral polyethylene component and glenoid rim, whereas Grades 3 and 4 are thought to be caused by polyethylene-induced osteolysis, because mechanical erosion is unlikely to occur past the inferior screw [15]. This can lead to revision arthroplasty if the erosion compromises glenosphere fixation or the polyethylene geometry in such a way that instability results. Purpose The Nerot-Sirveaux classification has been used to communicate data in literature and deemed a prognostic indicator by some. For example, Sirveaux et al. found that Grades 3 and 4 notching correlated with lower Constant-Murley scores [20]. Alternatively, Werner et al. [22] found no such correlation between Grades 3 and 4 notching and Constant-Murley scores among 21 patients who underwent RSA. In addition, Mollon et al. [13] utilized the Nerot-Sirveaux classification to identify that patients with scapular notching had a higher occurrence of radiolucent humeral lines, which have been associated with radiologic evidence of component loosening [5]; however, a direct correlation between Nerot-Sirveaux grade and loosening has yet to be reported. Moreover, Levigne et al. [10] utilized the Nerot-Sirveaux classification to help show that scapular notching may be progressive. They found that the proportions of patients with scapular notching and those with higher grades of scapular notching increased over time after surgery. They also showed that higher grade was associated with severity of infraspinatus fatty infiltration and glenoid radiolucent lines. Alternatively, a study by Levigne et al. [9] also demonstrated the utility of the Nerot-Sirveaux classification system when they utilized the grading system to report that there was no correlation between the grade of scapular notching and postoperative pain score, ROM, or Constant-Murley score. Overall, it is evident that the debate remains open concerning the clinical relevance of scapular notching and using the Nerot-Sirveaux classification to guide treatment remains controversial. By implementing the Nerot-Sirveaux classification in future studies, investigators may be able to portray how the extent of notching affects ROM, pain, and patient-reported outcome scores in patients who undergo revision or subsequent surgery and help shed light on the aforementioned debate. Importantly, we are just now beginning to reach long-term followup for many of the first Grammont-type implants, and a well-established, reliable, validated classification system will be crucial for analyzing the effect of scapular notching on long-term failure rates, component loosening, patient-reported outcomes, pain, and ROM. The Nerot-Sirveaux classification system also can be used by investigators in studies of implant development and technique modification, as exemplified in the study by Irlenbusch and Kohut [6], which showed that only Grades 1 and 2 notching were evident in their evaluation of a novel baseplate design. Current concepts of reverse shoulder arthroplasty have evolved to reduce the frequency of notching, and so a classification system like Nerot-Sirveaux is potentially useful to assess those designs. Validity and Reliability Although there are many papers about scapular notching, none have aimed to quantify the validity of the Nerot-Sirveaux classification system despite it being the primary system of classifying scapular notching. This is likely secondary to the fact that measuring the validity of a classification system relies on comparing the radiographic classification with a gold standard measurement, which in this case would be an intraoperative assessment of glenoid bone loss. In their review article, Garbuz et al. [3] go further, discussing that invalidated musculoskeletal classification systems would benefit from at least having a high degree of reliability. Sadoghi et al. [17] assessed the reliability of the Nerot classification system in their study of 60 shoulders that underwent RSA, which we believe should apply equally to the Nerot-Sirveaux classification. In their study, each radiograph was assessed two times by two separate orthopaedic surgeons, totaling four radiographic evaluations. Interobserver and intraobserver reliability of the system as it pertained to scapular notching was found to be “almost perfect” with a κ coefficient value of > 0.86. However, the reliability testing of the Nerot-Sirveaux classification has been limited to that single study, and some may say that a weighted Cohen’s κ coefficient may have been more useful in this study; therefore, further studies are needed to assess the reliability of the Nerot-Sirveaux classification. Limitations In their review article, Garbuz et al. [3] discussed that a successful classification system should be reliable and valid. Reliability pertains to interobserver and intraobserver agreement, and validity pertains to the accuracy of the classification to truly describe the pathology. As stated in the previous section, there is room for improvement when it comes to assessing the reliability and validity of the Nerot-Sirveaux classification. Although it may be difficult to assess the validity of the Nerot-Sirveaux classification system by comparing radiographic grade with intraoperative degree of bone loss, it is critical that future investigations strive to establish that the classification have a high degree of reliability. Until then, clinicians and investigators should be vigilant when interpreting published results based on the Nerot-Sirveaux classification. In addition, the ability of the Nerot-Sirveaux classification to guide treatment is controversial. Although the classification system has been associated with frequency of radiolucent lines, severity of infraspinatous fatty infiltration, pain scores, ROM, and Constant-Murley score, we do not know of a study that has directly assessed the ability of the Nerot-Sirveaux classification to guide treatment or serve as an indication for revision surgery [9, 10, 13, 20]. The reliability of classification systems can also be impeded by procedural variability leading to measurement variability, which in the case of the Nerot-Sirveaux classification pertains to variability in positing or beam angle for true AP shoulder radiographs subsequently affecting the grade measured by the clinician [23]. For example, although Sadoghi et al. [17] demonstrated that the Nerot-Sirveaux classification has excellent interobserver and intraobserver reliability, they note in their study that the classification system may be limited by the radiographic beam angle, which can hide the notch behind radiopaque components or superimposed ribs. Levigne et al. [10] discussed the importance of precise patient positioning and x-ray beam alignment to fully and accurately assess the grade of scapular notching. Several methods have been proposed for reducing procedural variability such as describing standardized procedural methods in detail to the technician performing the procedure, using identical equipment for each procedure, and using positional jigs to standardize limbs while obtaining radiographs [23]. Overall, the Nerot-Sirveaux classification is widely used and accepted by clinicians and investigators; however, caution should be used when using the classification for clinical purposes, because we are not aware of any study that has found that the degree of scapular notching is an indication for intervention. Conclusions The Nerot-Sirveaux classification was formed to grade the extent of scapular notching after RSA. It has been used for communicating data in the literature and deemed a prognostic tool by some investigators and clinicians. However, the clinical relevance of scapular notching remains widely unknown, and the validity and reliability of the classification system have not been well established. Therefore, vigilance and caution should be taken when interpreting results or deciding to use the system to guide treatment. Future studies are needed to determine whether this classification earns a permanent role in clinical research and practice.