Remodeling of articular cartilage and subchondral zone of the tibia in exo‑prosthetics of the limb

Introduction Exo-prosthetics of limbs through osseointegration opens up new possibilities in prosthetics. Modern prostheses are becoming more high-tech, which requires deep understanding of the anatomical and functional features of the bone-joint system. Aim To identify features of structural reorganization of articular cartilage and subchondral zone of the tibia in lower leg prosthetics using an implant with calcium phosphate coating and an implant without additional coating. Materials and methods The study was performed on 5 intact (control) and 6 experimental dogs (age 1.8 ± 0.5 years, weight 19 ± 1.2 kg). A tibial stump was modeled in the animals at the border of the middle and upper third of the diaphysis. After 2.5 months a PressFit type implant was installed. Depending on the Press‑Fit type, the animals were divided into groups: group 1 made of Ti6Al4V alloy (n = 3); group 2 of Ti6Al4V alloy with calcium phosphate coating (n = 3). Duration of the experiment was 180 days after prosthesis fitting. Histomorphometric study of the articular cartilage and subchondral zone was performed on paraffin sections using an AxioScope.A1 microscope supplied with AxioCam camera and Zenblue software (CarlZeissMicroImagingGmbH, Germany). Results Bone tissue remodeling was expressed by thinning of the subchondral bone plate, osteolysis, changes in the architecture of bone trabeculae in the subchondral trabecular bone, and a decrease in bone tissue mineralization. These signs were more intense in group 1. Signs of reparative osteogenesis with osteoblasts on the surface of bone trabeculae were noted in group 2. Subchondral bone plate thickness reduced twofold in group 1, and by 1.5 times in group 2 relative to the control. The values of the parameter of trabecular area were reduced in group 1 by 17 % and in group 2 by 10 %. Statistically significant decrease in the values of articular cartilage thickness was recorded in group 1 and was accompanied by a higher (by 1.8 times) frequency of vessels been found in the deep zone of cartilage compared to group 2. Discussion The identified changes in the subchondral zone corresponded to stage 0 (according to the O‑M classification. Aho et al., 2017): very early signs of osteoarthritis, when subchondral sclerosis is not pronounced, the subchondral bone plate is thin. Structural changes in articular cartilage corresponded to grade 0–1 according to the histological classification of the International Society for the Study of Osteoarthritis OARSI. Conclusion Histomorphometric changes in the osteochondral component of the tibial plateau during lower leg prosthetics (thinning of the subchondral bone plate, rarefaction of the subchondral trabecular bone, penetration of vessels into non-calcified cartilage) are predictors of arthrosis. The use of implants made of Ti6Al4V alloy coated with a calcium phosphate provides reduction of bone resoption intensity and activates reparative osteogenesis.