title: Scapular Notching on Kinematic Simulated Range of Motion After Reverse Shoulder Arthroplasty Is Not the Result of Impingement in Adduction.
abstract: Impingement after reverse shoulder arthroplasty (RSA) is believed to occur from repetitive contact in adduction between the humeral component and the inferior scapular pillar. The primary purpose of this biomechanical study was to confirm the presence of different types of impingement and to examine which daily-life movements are responsible for them. A secondary aim was to provide recommendations on the type of components that would best minimize notching and loss of range of motion (ROM). The study included 12 fresh frozen shoulder specimens; each had a computed tomography (CT) image of the entire scapula and humerus in order to acquire topological information of the bones before RSA implantation. Cyclic tests were run postimplantation with 3 shoulders in each modalities. To quantify bone loss due to impingement, 3-dimensional anatomical models of the scapula were reconstructed from the CT scans and compared to their intact states. We found 8 bony impingements in 7 specimens: 2 at the lateral acromion, 1 at the inferior acromion, 4 scapular notching, and 1 with the glenoid resulting to wear at the 3:00 to 6:00 clock-face position. Impingements occurred in all kinds of tested motions, except for the internal/external rotation at 90° of abduction. The 3 specimens tested in abduction/adduction presented bone loss on the acromion side only. Scapular notching was noted in flexion/extension and in internal/external rotation at 0° of abduction. The humeral polyethylene liner was worn in 2 specimens--1 at the 6:00 to 8:00 clock-face position during internal/external rotation at 0° of abduction and 1 at the 4:00 clock-face position during flexion/extension. The present study revealed that 2 types of impingement interactions coexist and correspond to a frank abutment or lead to a scapular notching (friction-type impingement). Scapular notching seems to be caused by more movements or combination of movements than previously considered, and in particular by movements of flexion/extension and internal/external rotation with the arm at the side. Polyethylene cups with a notch between 3 and 9 o'clock and lower neck-shaft angle (145° or 135°) may play an important role in postoperative ROM limiting scapular notching.
authors.affiliation: From the Division of Orthopaedics and Trauma Surgery, La Tour Hospital, Meyrin (AL); Faculty of Medicine, University of Geneva (AL); Division of Orthopaedics and Trauma Surgery, Department of Surgery, Geneva University Hospitals, Geneva (AL); AO Research Institute Davos, Davos (BG, IZ, JH); Artanim Foundation, Medical Research Department (CC); Faculty of Medicine, Department of Cellular Physiology and Metabolism, Anatomy Sector, University of Geneva, Geneva, Switzerland (BVS, JHF); and Department of Orthopaedics, Shoulder Unit, Santy Orthopaedic Center and Jean Mermoz Hospital GDS, Lyon, France (GW).
authors.forename: Alexandre
authors.initials: A
authors.lastname: Lädermann
authors.forename: Boyko
authors.initials: B
authors.lastname: Gueorguiev
authors.forename: Caecilia
authors.initials: C
authors.lastname: Charbonnier
authors.forename: Bojan V
authors.initials: BV
authors.lastname: Stimec
authors.forename: Jean H D
authors.initials: JHD
authors.lastname: Fasel
authors.forename: Ivan
authors.initials: I
authors.lastname: Zderic
authors.forename: Jennifer
authors.initials: J
authors.lastname: Hagen
authors.forename: Gilles
authors.initials: G
authors.lastname: Walch
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001178:Arthroplasty / Q000009:adverse effects*; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology; D058996:Quality Improvement; D016059:Range of Motion, Articular; D012540:Scapula / Q000473:pathology*; D019534:Shoulder Impingement Syndrome / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology