Histomorphometric evaluation of the synovial membrane during osteosynthesis of intra-articular metaepiphyseal fractures with titanium screws in lambs (an experimental morphological study)

Introduction The complexity of treating intra-articular fractures in children is due to the anatomical features of the joint, its biomechanics, and the tendency to develop post-traumatic arthritis. This necessitates a detailed study of the structural organization of all elements of the joint synovial environment. The aim of this study was to evaluate, using an experimental model, the severity of structural changes in the synovial membrane of the carpal joint during osteosynthesis of intra-articular metaphyseal fractures with titanium screws. Materials and Methods The study was performed on six outbred male lambs (46.1 ± 3.0 days old, weighing 15.7 ± 2.0 kg). An oblique intra-articular metaphyseal fracture of the radius on the right limb was modeled. Fracture fixation was performed with two cannulated cancellous bone screws made of Ti6AL4V titanium. The experimental periods were 120 (n = 3) and 365 (n = 3) days after surgery. Histomorphometric analysis of the synovial membrane was performed using an AxioScope.A1 microscope and Zenblue software (CarlZeissMicroImagingGmbH, Germany). The synovium of the contralateral joint served as a control. Results In the control joint, fibroblast-like synoviocytes predominated in the synovial membrane lining layer; no signs of synovitis were detected. After 13.5 months, a decrease in lining layer thickness (p = 0.0326) and synoviocyte density (p = 0.0009) was noted. In the experimental joint, mild synovitis, hyperplasia of the lining layer, increased synoviocyte density and macrophage-like synoviocyte representation (more than 50 % per field of view), formation of synovial villi, and the presence of focal and diffuse lymphohistiocytic infiltrates were detected after 120 days. After 365 days, signs of synovitis were absent, fibroblast-like synoviocytes predominated in the lining layer; elevated synoviocyte density values persisted (p = 0.0141), and lining layer thickness values were comparable to the control (p = 0.1301). Discussion Non-bioresorbable fixators used for osteosynthesis of intra-articular fractures can cause a number of complications, including infection, pain, and arthritis. It was established that macrophage and fibroblastic synoviocytes perform various pro- and anti-inflammatory functions and can both prevent inflammation by forming an anti-inflammatory barrier and contribute to the development of synovitis. Conclusion Osteosynthesis of intra-articular metaepiphyseal fractures of the distal articular end of the radius in lambs using titanium screws provoke mild synovitis after 120 days of the experiment. This synovitis was characterized by thickening of the lining layer, an increase in the numerical density of synoviocytes and in macrophage synoviocytes, and the presence of a lymphohistiocytic infiltrate. By the end of the experiment, the synovial membrane inflammation revered, and histological signs of synovitis were absent.