The stabilizing role of the shoulder girdle muscles during the shoulder arthroplasty

Purpose. To detect reliable preoperative markers of the shoulder hemi-implant instability by the results of electromyographic study in patients with proximal humerus (PH) injuries. Materials and Methods. We performed surgical treatment of 50 patients, among them: 23 patients with chronic factures, 20 patients with PH fracture-dislocations, 7 patients with avascular necrosis of the head who underwent hemiarthroplasty. Methods of studying: clinical, radiological, multispiral CT with evaluation of the state of the shoulder bone structures, rotator cuff and ligaments, in some cases we performed MRI of the shoulder. All the patients underwent electromyography (EMG) of the shoulder girdle muscles of both upper limbs with determination of their functional state preoperatively. Periods of observation were from six months to 7.5 years after surgery. The patients were divided into two groups: those with a stable implant (Group 1) and those with an unstable implant (Group 2). Results. Before surgery the muscle functions in patients of Group 1 and Group 2 revealed to be different. In patients of Group 2 EMG parameters before surgery were reduced on both sides with respect to Group 1 patients. The asymmetry between the sides was more marked in the group with unstable implants. We have obtained the reliable preoperative criteria of hemi-implant instability in the long-term periods by electromyography results. The mean frequency (MF) of the biceps bioelectric activity (BA) can serve as a quantitative criterion of implant instability. The less MF of m. biceps BA (below 174 Hz) and the smaller MF difference between the sides (