Biomechanical effects of humeral neck-shaft angle and subscapularis integrity in reverse total shoulder arthroplasty

Joo Han Oh, Sang Jin Shin, Michelle H. McGarry, Jonathan H. Scott, Nathanael Heckmann, Thay Q. Lee

Research output: Contribution to journalArticlepeer-review

71 Scopus citations

Abstract

Background: The variability in functional outcomes and the occurrence of scapular notching and instability after reverse total shoulder arthroplasty remain problems. The objectives of this study were to measure the effect of reverse humeral component neck-shaft angle on impingement-free range of motion, abduction moment, and anterior dislocation force and to evaluate the effect of subscapularis loading on dislocation force. Methods: Six cadaveric shoulders were tested with 155°, 145°, and 135° reverse shoulder humeral neck-shaft angles. The adduction angle at which bone contact occurred and the internal and external rotational impingement-free range of motion angles were measured. Glenohumeral abduction moment was measured at 0° and 30° of abduction, and anterior dislocation forces were measured at 30° of internal rotation, 0°, and 30° of external rotation with and without subscapularis loading. Results: Adduction deficit angles for 155°, 145°, and 135° neck-shaft angle were 2° ± 5° of abduction, 7° ± 4° of adduction, and 12° ± 2° of adduction (P < .05). Impingement-free angles of humeral rotation and abduction moments were not statistically different between the neck-shaft angles. The anterior dislocation force was significantly higher for the 135° neck-shaft angle at 30° of external rotation and significantly higher for the 155° neck-shaft angle at 30° of internal rotation (P < .01). The anterior dislocation forces were significantly higher when the subscapularis was loaded (P < .01). Conclusions: The 155° neck-shaft angle was more prone to scapular bone contact during adduction but was more stable at the internally rotated position, which was the least stable humeral rotation position. Subscapularis loading gave further anterior stability with all neck-shaft angles at all positions.

Original languageEnglish
Pages (from-to)1091-1098
Number of pages8
JournalJournal of Shoulder and Elbow Surgery
Volume23
Issue number8
DOIs
StatePublished - Aug 2014

Keywords

  • Anterior dislocation
  • Arthroplasty
  • Biomechanics
  • Notching
  • Reverse shoulder

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