Object: lumbar-pelvic muscular balance in patients with diseases and consequences of hip joint injuries before surgery and after cementless total hip arthroplasty for different total femoral offset; graph-analytical model of the pelvic girdle muscles to ensure horizontal pelvic equilibrium in normal and at different values of total femoral offset after cementless total hip replacement. Aim: to establish the causes of postural balance impairment in patients after surgery for hip joint arthroplasty on the basis of studying the features of the pelvic girdle muscles and to develop methods for their prevention. Methods: clinical, X-ray, biomechanical (stabiliography), mathematical modeling, statistical. On the basis of retrospective analysis and X-ray examination of the results of non-cemented total hip arthroplasty of patients with various diseases of the hip joint, it has been established that the anatomic-functional and biomechanical changes of the hip joint structures, as well as the imbalance of the pelvic girdle muscles, negatively affect the positional adaptation of the components of the prosthesis due to the reduction of the moment arm of abductors. It is proved that men have the reduction of the arm of the abductor forces more than three times more often than women have. For the first time, with the help of mathematical modeling, it has been established that reducing the size of the arm of the hip abductors by more than 5 mm sharply reduces the effectiveness of the pelvic girdle muscles in maintaining of postural balance. Excessive weight of the patient is defined as a factor of negative influence on the work of the abduction mechanism. Under conditions of reduction of the size of the moment arm of the abductors of the hip for 10 mm and more, the critical influence of the muscle weakness of the abductors on the work of the abduction mechanism has been proved, and the increase in the body weight of the patient by 30% - to maintaining of the pelvic balance. On the basis of the estimation of the results of stabilography, it was first established that the reduction of the length of the arm of the abductors after the hip arthroplasty leads to a significant change in the shape of the pressure spot in the case of single-support standing, namely: an increase in its sagittal size and a decrease in the frontal size of the displacement spot of the projection of the common center of mass, which indicates a greater amplitude of body oscillation in the sagittal plane. It was first established that reducing the length of the arm of the abductors after the arthroplasty leads to a significant increase in the spot area of displacement of the projection of the common center of mass, which indicates a deterioration in stability; as well as to increase the speed and frequency of oscillations of its projection, which leads to a significant increase in power inputs in maintenance of vertical posture (more than 2 times). The method of evaluation of the function of the pelvic girdle muscles, responsible for maintaining the pelvic horizontal balance (postural balance) is improved, which makes it possible to analyze the effectiveness of these muscles in the treatment of the patient. A complex of prophylactic presurgical exercises of medical physical education aimed at reducing the muscle imbalance responsible for preserving the postural balance was developed, which enabled to improve the positional adaptation of the components of the prosthesis and the work of the abduction mechanism in patients after the hip arthroplasty. Clinical use of the proposed methods and methodological approaches allowed to optimize the rehabilitation period after the operation of the hip arthroplasty, improve the recovery of muscle function that is responsible for the postural balance. The results of the study were introduced into the clinical practice of the Research Institute of Traumatology and Orthopedics of the Donetsk National Medical University of the Ministry of Health of Ukraine, SI "Sytenko Institute of Spine and Joint Pathology National Ukranian Academy of Medical Sciences", KU "I.K. Matsuka Mariupol City Hospital № 4", KZ "Mariupol City Hospital № 1", KOZZ "Regional Hospital of Intensive Care in Mariupol". Traumatology and Orthopaedics
