Introduction.The results of using various reconstructive technologies in the 1980–1990’s to replace post-resection bone defects determined oncological endoprosthetics as the most promising onco-orthopedics trend, due to the quality-of-life and functional potential restoration in a short time. Despite the constant improvement of the design and technology of oncological endoprosthesis at the moment, complications such as aseptic instability, mechanical failure and infection of the endoprosthesis significantly affect the reduction of implant survival. It is impossible to reduce the frequency of endoprosthesis aseptic instability without developing a unified strategy for the prevention and treatment of this type of complication.

The study objective – to examine the main causes of early and late aseptic loosening, analyze complication rate in various periods after endoprosthesis using literature data and results of treatment of a large patient group who underwent primary and repeat endoprosthesis for different post-resection bone defects.

Materials and methods. The study included 1292 patients aged 10 to 81 years with primary bone and soft tissues sarcomas, metastatic, benign lesions of the bone, who since January 1992 to January 2020 were performed 1671 primary and revision endoprosthetics of various bone segments. The age of the patients ranged from 10 years to 81 years. The mean age of the patients was 34.7 years. In the study group of patients, most often endoprosthetics was performed at the age of 21 to 30 years and accounted for 29 % of cases. The mean follow-up period after primary arthroplasty of various segments was 82.8 months (from 0 to 335.7 months). The mean follow-up period after revision arthroplasty was 54.2 months (from 0 to 282.8 months). In 1594 (95.4 %) cases were used bone cement stem fixation.

Results. The results of the study show that the optimal shape of the endoprosthesis stem for primary and revision endo-prosthesis replacement is conical and cylindrical figured (made in the shape of the bone marrow canal). The most stable endoprosthesis stems are 60–100 mm long for upper limb arthroplasty and 110–150 mm for lower limb arthroplasty. Endoprosthesis stems longer than 160 mm can only be used in revision endoprosthetics. The length of the bone resection does not affect the incidence of endoprosthesis instability. The quality of the formed cement mantle affects the frequency of endoprosthesis instability. The presence of at least one revision arthroplasty with replacement of the endoprosthesis stem increases the risk of developing subsequent early instability (type IIA) about 4 times and the risk of late instability (type IIB) about 6 times compared with primary arthroplasty. The occurrence of late aseptic instability of the endoprosthesis (type IIB) will lead to the development of breakage/destruction of the endoprosthesis (type IIIA) in a shorter period than the breakage/ destruction of the endoprosthesis will lead to the development of late instability of the endoprosthesis (type IIB).

Conclusion. The choice of an endoprosthesis, taking into account the optimal biomechanics of the endoprosthesis design, the shape of the stem, methods of fixation, the introduction of innovative technological solutions, adherence to the principles of oncological endoprosthesis replacement, is a means of reducing the incidence of this type of complications.

For many decades, in the literature there has been a discussion about the role of skin scars in the development of tumors. Despite this, the distinctive features of their formation and pathogenetic mechanisms remain not fully revealed. The princ-i ples of malignant tumors’ development of healthy and pathologically altered skin remain unresolved. There are conflicting data on the influence of climatogeographic and social factors on the development of skin cancer. It has been established that ultraviolet irradiation plays an important role in the development of malignant skin neoplasms. Intensive insolation is the cause of the development of pathological changes in the skin and vascular tissue. Perhaps one of the probable patho-genic factors is the influence of damaging doses of solar energy. On the skin structure in Central Asian countries, where skin cancer occupies the leading rank among all malignant tumors. The results of treatment in skin cancer that has developed in the area of scarring of various origins – mechanical, traumatic injuries, or chemical, thermal burns – remain disappointing. The development of relapses and metastases in the nearby anatomic structures after treatment worsen the quality of life in the patients; dictate the selection of adequate methodological approaches to this group of patients.

Introduction. The article presents the results of validation of the Russian language version of the fatigue (FA12) module of the specialized Quality of Life Questionnaire – Core 30 (QLQ-C30) developed by the Study Group of Quality of Life of the European Organization for Research and Treatment Cancer (EORTC). The questionnaire has been successfully applied in Russian and international trials.

Materials and methods. A sample of 55 patients (mean age 53.23±  2.01 years; 52.7 % men and 47.3 % women) at the N.N. Blokhin National Medical Research Center of Oncology was used to perform psychometric review of the fatigue module (FA12) of the QLQ-C30 questionnaire which confirmed its convergent validity and reliability – consistency (Cronbach coefficient α is 0.768).

Results. The results of factor analysis confirmed adequacy of the structure of the Russian version of the fatigue module and its conformity with the basic factor model.

Conclusion. The obtained results allow to state that the Russian version of the fatigue module is a reliable and valid instrument which can be used both in national and cross-cultural trials.

Introduction. Surgical treatment of tumors of the distal part of the forearm has always been complicated. Though there are many methods of reconstruction of defects of the long bones of this area after resection, the optimal technique is still debated.

The study objective is to analyze the results of surgical treatment of tumors and tumor-like conditions of the forearm long bones, rate of postoperative complications, and techniques of their correction.

Materials and methods. The article presents data on 75 patients with tumor and tumor-like conditions of the forearm long bones. Diagnosis was histologically verified. In 58 (77.3 %) patients, benign giant cell tumor was diagnosed, in 3 (4 %) patients – malignant giant cell tumor, in 3 (4 %) patients – osteogenic sarcoma, in 3 (4 %) patients – chondrosarcoma, in 6 (8 %) patients – fibrous dysplasia. All patients underwent surgical treatment of varying volume. During the study, analysis of complications of surgical treatment was performed.

Results. Postoperative complications of various nature developed in 17 (22.7 %) of 75 patients between 2 weeks and 2 years after treatment. They mostly developed after segmental resection of the forearm bones with autoplasty (38.1 %) and segmental bone resection (21.4 %), as well as after excochleation with cementoplasty (16.1 %). The most frequent complications were autotransplant lysis (in 4 (19.1 %) cases), its fracture (in 2 (9.5 %) cases), and infections and inflammatory complications (in 2 (9.5 %) cases). After segmental resection with endoprosthesis, only 1 (11.1 %) patient experienced endoprosthesis head instability in the early postoperative period which led to re-endoprosthesis. Local recurrence was observed in 6 (19.4 %) of 31 patients with gigantic-cell tumors after excochleation and in 4 (28.6 %) of 14 patients after segmental resection. In 2 (14.3 %) cases, progression of the main disease was observed in the form of pulmonary metastases.

Conclusion. Excochleation with cementoplasty is the method of choice in benign tumors of the forearm bones in the absence of soft-tissue component, destruction of the cortical layer, advancement of the tumor to the joint surface. In case of benign tumors in the absence of soft-tissue component and destruction of the cortical layer, and in the presence of tumor advancement to the joint surface, the optimal technique is segmental bone resection with substitution of the defect with endoprosthesis.

Phosphaturic mesenchymal tumor inducing development of phosphopenic osteomalacia is manifested as deformations and multiple fractures of the bones which decreases patients’ quality of life and leads to disability. Insufficient awareness about this pathology among doctors and absence of symptoms allowing its diagnosis cause late diagnosis of the disease despite application of up-to-date high-tech diagnostic methods. The optimal treatment of phosphaturic mesenchymal tumors is radical resection. However, strong connection of the tumor with the surrounding tissues and, in many cases, absence of a capsule or sclerosis (if located in the bones) complicate surgery leading to high recurrence rate. Radical resection of phosphaturic mesenchymal tumors is especially complicated in cases of localization in complex anatomical areas of the lower limbs.

The disease is characterized by long timespan between first clinical signs, diagnosis, and start of treatment (sometimes, several years). Diagnosis confirmation and visualization of the details of phosphaturic mesenchymal tumor requires magnetic resonance imaging. This method allows to examine connection between the tumor and surrounding tissues and the presence of a capsule. Magnetic resonance imaging also allows to accurately determine the area of surgical intervention. Radical tumor resection leads to normalization of blood and urine biochemistry in the span of several weeks. Restoration of bone density and muscle function requires 3–6 months after the operation.