Kinematic analysis of the scapula after total anatomic and reverse shoulder arthroplasty.

OBJECTIVE: Scapular motion is essential for full, functional mobility of the arm. Many shoulder pathologies are associated with alterations of scapular kinematics which have been only little studied in total shoulder arthroplasties. The aim of this study was to compare the 3D scapula kinematics in two groups of patients with total shoulder anatomic (aTSA) or reverse (rTSA) arthoplasties to asymptomatic controls of comparable age during two arm elevation tasks (abduction and flexion) and two simulations of activity of daily living ("hair combing" and "back washing").

MATERIAL/PATIENTS AND METHODS: Scapular kinematics was assessed using a Polhemus Fastrak electromagnetic device in 14 patients with aTSA (and 14 controls) and 9 patients with rTSA (and 9 controls). The 3D rotations and the 3D displacements of the barycenter of the scapula were measured at 30°, 60° and 90° of humero-thoracic (HT) elevation. Patient groups were compared with each other by Mann-Whitney U test and with their respective controls by Wilcoxon test.

RESULTS: Scapulohumeral rhythm was reduced in both patient groups as compared with controls. Patients with aTSA showed more lateral rotation and more linear displacements of the scapula compared to rTSA and control groups. Nevertheless, the global kinematics pattern remained unchanged in both groups of patients.

DISCUSSION-CONCLUSION: Patients showed a greater participation of the scapula in HT elevation movements and kinematic modifications of small amplitude that could suggest a compensation mechanism for patients with aTSA. However, having a total shoulder arthroplasty does not alter the global kinematic pattern of the scapula.