This computational modeling study asks whether reverse shoulder arthroplasty ROM simulation changes when you account for scapulothoracic orientation. Six surgeons planned rTSA in ten statistical shape models using prototype software. ROM was compared with and without adjustment for posture types A, B, and C in a global reference frame.
When a planning screen tells you an rTSA construct gives 60° of external rotation, remember it references the scapula in isolation, not the scapula's real position on a kyphotic thorax. This study shows conventional software overestimates external rotation, extension, and high internal rotation by roughly 33° to 38° on average, and up to ~50° in type C patients.
The mental model: the more a patient's scapula is internally rotated and protracted (type C, thoracic kyphosis), the more the scapular axis diverges from the true body axis, and the less trustworthy the simulated numbers become.
Clinically this explains why patients struggle with reaching behind the back and adducted external rotation after rTSA, motions that combine rotation with coracoid impingement. The authors go further, arguing that prior studies optimizing component placement using conventional software should be re-examined.
Note the heavy industry involvement (Arthrex funding, employee co-author, patent) and that the model captures only glenohumeral motion, not scapulothoracic contribution or soft tissue.
This computational modeling study asks whether reverse shoulder arthroplasty ROM simulation changes when you account for scapulothoracic orientation. Six surgeons planned rTSA in ten statistical shape models using prototype software. ROM was compared with and without adjustment for posture types A, B, and C in a global reference frame.
When a planning screen tells you an rTSA construct gives 60° of external rotation, remember it references the scapula in isolation, not the scapula's real position on a kyphotic thorax. This study shows conventional software overestimates external rotation, extension, and high internal rotation by roughly 33° to 38° on average, and up to ~50° in type C patients.
The mental model: the more a patient's scapula is internally rotated and protracted (type C, thoracic kyphosis), the more the scapular axis diverges from the true body axis, and the less trustworthy the simulated numbers become.
Clinically this explains why patients struggle with reaching behind the back and adducted external rotation after rTSA, motions that combine rotation with coracoid impingement. The authors go further, arguing that prior studies optimizing component placement using conventional software should be re-examined.
Note the heavy industry involvement (Arthrex funding, employee co-author, patent) and that the model captures only glenohumeral motion, not scapulothoracic contribution or soft tissue.