Short stem humeral components in reverse shoulder arthroplasty: stem alignment influences the neck-shaft angle

• Published in: Archives of orthopaedic and trauma surgery 2021-02, Vol.141 (2), p.183-188
• Main Authors: Abdic, Sejla, Athwal, George S., Wittmann, Thomas, Walch, Gilles, Raiss, Patric
• Format: Article
• Language: English
• Subjects: Joint surgery; Medicine; Medicine & Public Health; Orthopaedic Surgery; Orthopedics; Shoulder; Transplants & implants
• ISSN: 0936-8051; 1434-3916
• DOI: 10.1007/s00402-020-03424-4

Introduction Shorter humeral reverse total shoulder arthroplasty (RTSA) stems may reduce stress shielding, however, potentially carry the risk of varus/valgus malalignment. This radiographic study’s purpose was to measure the incidence of stem malalignment and thus the realized neck-shaft angle (NSA). The hypothesis was that malalignment of the stem is a frequent postoperative radiographic finding. Methods Radiographs of an uncemented curved short stem RTSA with a 145° NSA were reviewed. The study group included 124 cases at a mean age of 74 (range 48–91) years. The humeral stem axis was measured and defined as neutral if the value fell within ± 5° of the longitudinal humeral axis. Angular values > 5° were defined as malaligned in valgus or varus. The filling ratio of the implant within the humeral shaft was measured at the level of the metaphysis (FR met ) and diaphysis (FR dia ). Results The average humeral stem axis angle was 4 ± 3° valgus, corresponding to a true mean NSA of 149 ± 3°. Stem axis was neutral in 73% ( n =  90) of implants. Of the 34 malaligned implants, 82% ( n =  28) were in valgus (NSA = 153 ± 2°) and 18% ( n =  6) in varus (NSA = 139 ± 1°). The average FR met  and FR dia were 0.68 ± 0.11 and 0.72 ± 0.11, respectively. A low positive association was found between stem diameter and filling ratios ( r  = 0.39; p   5° malaligned. The majority of malaligned components (86%) were implanted in valgus, corresponding to an NSA of > 150°. As such, surgeons must be aware that shorter and smaller stems may lead to axial malalignment influencing the true SA. Level of evidence Level IV, retrospective study.