Analysis of impingement-free range of motion of the glenohumeral joint after reverse total shoulder arthroplasty using three different implant models.

ABSTRACT

BACKGROUND: This study aimed to investigate impingement-free range of motion (ROM) of the glenohumeral joint following reverse total shoulder arthroplasty (RTSA) with three types of implant models using computational motion analysis. METHODS: Three-dimensional (3D) scapulohumeral models were created from preoperative computed tomography (CT) images of seven patients by using visualization and computer-aided design software. Three types of implant designs, namely, typical medialization, in between, and lateralization implants, were used for the reconstruction of 3D model; each design was designated as group I, II, and III, respectively. All possible combinations of virtual surgeries were evaluated for impingement-free ROM in all three groups. Maximal ROMs were compared. The effect of implant positions on ROM of the shoulder joints were investigated in each group. RESULTS: The all lateralization group (group III) showed significantly greatest maximal adduction, abduction and external rotation (ER). Adduction and abduction were significantly increased by the glenoid component inferior translation in all three groups. (In group I, p < 0.001 for adduction, p = 0.002 for abduction, respectively; in group II, p = 0.025, p < 0.001, respectively; in group III, p = 0.038, p = 0.011, respectively). Increasing humerus retroversion might have some effect on increasing abduction. In group II and III, internal rotation (IR) and ER were significantly affected by the humerus retroversion (in group II, p = 0.033 for IR, p = 0.007 for ER, respectively; in group III, p = 0.004, p < 0.001, respectively). In group III, ER was also significantly affected by the glenoid component inferior translation (p = 0.003). CONCLUSIONS: Lateralization design model showed greatest ROM of the shoulder joint. The effects of implant positions on impingement-free ROM exhibited different tendencies between medialization and lateralization implant models. Humerus retroversion affected both IR and ER, especially in lateralization design. Increasing glenoid inferior translation increases both adduction and abduction regardless of implant designs.