KNEE CARTILAGE AND SYNOVIAL MEMBRANE STRUCTURAL CHANGES DURING TIBIA DISTRACTION WITH PLATING

Purpose of the study — to analyze the changes in knee articular cartilage and synovial membrane during distraction external fixation of the tibia in combination with plating.

Material and methods. Articular cartilage and synovial membrane of the knee joint were studied using histomorphometry methods in 9 mongrel dogs during distraction external fixation of the tibia combined with plating. Tibia and fibula osteotomies were performed at the border of middle and upper third, plate was fixed on tibia diaphysis. Lengthening was achieved at rate of 1 mm per day in four stages during 21–28 days. Animals were withdrawn from experiment in 30 and 90 days. After autopsy of knee joints the authors excised sections of synovial membrane from suprapatellar area, articular cartilage with underlying subchondral bone from loadable surface of femoral condyles. Thickness of articular cartilage, its area and volumetric density of chondrocytes was measured, proportion of chondrocytes within isogenic groups from the overall number of chondrocytes as well as proportion of empty lacunae. In synovial membrane the authors measured thickness of surface layer and numeric density of micro vessels. Articular cartilage of 5 intact animals was used as a control group.

Results. After 30 days of plate fixation a hyperplasia of the integument layer, mild synovitis, and hypervascularization were observed in synovial membrane. Density of micro vessels increased to 363.93±33.71 (control group — 335.05±28.88). The authors also observed subperineural and endoneural edema as well as destruction of nerve fibers in subsynovial layer. Articular cartilage retained the zonal structure. Destructive changes were manifested by fibers separation in the superficial part of surface zone and by partial loss of chondrocytes. The following parameters were reduced: cartilage thickness, area and volumetric density of chondrocytes, proportion of isogenic groups; empty lacunae exceeded the values in controls by 18.2%. After 90 days of plate fixation, thinning of the cover layer of synovial membrane was reported. The numerical density of micro vessels decreased to 325.81±36.39. In nerves of subsynovial layer the edema and vacuolization of myelin sheaths of preserved nerve fibers as well as the formation of Büngner bands in place of degenerating ones were detected. Synovitis was not observed. Fibers separation of extracellular substance in upper superficial part of the surface cartilage zone was retained. There was a tendency to increase in cartilage thickness, area and volumetric density of chondrocytes, proportion of isogenic groups; and to decrease of empty lacunae number.

Conclusion. The histological changes in the articular cartilage during distraction external fixation of the tibia in combination with plating corresponded to the initial stages of osteoarthritis of grades 1—2 according to histological classification of International Society for Study of Osteoarthritis (2006) and were accompanied by hypovascularization and denervation of synovial membrane.

distraction external fixation, plate, articular cartilage, synovial membrane, histomorphometry