December 1st, 2018 , Clinical Orthopaedics and Related Research

The Nerot-Siveaux Classification for Scapular Notching (Excerpt)

Authors: Young BL, Cantrell CK, Hamid N.

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).

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