Study of changes in the balance of the pelvic girdle muscles in patients with dysplastic coxarthrosis after arthroplasty

Background. Dysplastic coxarthrosis is a special medical and social problem in the treatment of adult patients, often leading to disability, limiting the human’s ability to self-care. Arthroplasty for dysplastic coxarthrosis is only a certain stage in the restoration of the patient’s musculoskeletal function. Considering the large number of unsatisfactory results of arthroplasty in dysplastic coxarthrosis, a very important factor is the construction of a rehabilitation prognosis — the estimated probability of achieving the intended goals of rehabilitation or realization of rehabilitation potential, taking into account disease features and the patient’s capabilities. Objective: to determine the significant parameters of the dysplastic hip joint whose change affects the deficit of lower limb muscle strength after arthroplasty and the prospects for rehabilitation potential. Materials and methods. An X-ray examination of 23 dysplastic hip joints was performed. The following radiometric parameters were measured: acetabular depth; floor thickness; acetabular depth index; abductor moment arm; gravity moment arm; height and lateralization of the center of rotation of the femoral head relative to the center of the acetabulum rotation. To objectify the balance of muscle forces required to maintain pelvic balance when standing on one leg, a mathematical model was used created by the authors, which reflects the pelvis with the femur and the action vectors of the muscles of two groups: abductors and adductors of the hip. Results. Using the model of horizontal balance of the pelvis, the level of muscle strength deficit was calculated in patients before and after arthroplasty. It was found that in some of them the muscle strength deficit remained. With a linear regression model, an equation was created to determine the muscle strength deficit. According to the statistical analysis, no difference was found between the results of the regression equation and the mathematical model (p >> 0.05). The regression analysis has shown that the most significant factors for the result are the neck shaft angle, floor thickness, and head height. To determine the limits of radiometric parameters that affect the outcome of arthroplasty, patients were divided into 4 groups according to the level of calculated muscle strength deficit: group I — deficit of more than 20 %, group II — deficit of less than 20 %, group III — surplus of 20 % and group IV — surplus of more than 20 %. In general, patients improve their muscle strength, but the initial deficit greatly affects the outcome after arthroplasty. For patients in group I, pre- and postoperative rehabilitation is necessary to achieve a positive result. In group II, the main direction of rehabilitation is to increase muscle strength. For patients of groups III and IV, general rehabilitation measures can be used. Conclusions. The most important parameter that affects muscle strength after arthroplasty is the patient’s muscle strength before surgery and weight. Another important indicator is the thickness of the acetabular floor. Weight loss is the main criterion for successful treatment of patients after any arthroplasty.