| Background and objectives:Knee osteoarthritis(OA) is the most common degenerative joint disease, which ischaracterized by progressive cartilage degeneration and subchondral bone remodeling, and iscaused by imbalance between synthesis and degradation of the chondrocyte, extracellularmatrix and subchondral bone due to mechanical and biological factors. Knee osteoarthritis isclinically featured by continuous pain, deformity and dysfunction, which is the main cause ofjoint pain and disability in elderly. Until recently, there is no drug and therapeutic tool whichcan delay the course of osteoarthritis. Total knee arthroplasty(TKA) is widely used in thetreatment of severe knee osteoarthritis, imposing huge economic brudern on the patients andtheir families.Normal osteochondral structure from articular surface to the bone marrow cavity iscomposed of hyaline cartilage, calcified zone and subchondral bone, and the subchondralbone further consists of subchondral bone plate and trabecular bone. Most researchesconcentrated on hyaline cartilage previously, and the chondrocyte apoptosis and matrixdegradation were considered the primary cause of osteoarthritis. However, with thedevelopmental understanding of the structure and function of osteochondral component, theresearchers have found that the hyaline cartilage, calcified zone and subchondral bone form afunctional unit as a whole. In the development of osteoarthritis, the calcified zone andsubchondral bone also undergo specific pathologic changes, which are closely related todegeneration of hyaline cartilage. In fact, since Radin and his group first proposed thatsubchondral bone sclerosis may be the initiating factor of cartilage degeneration, moreattention has been paid to the role of subchondral bone in the pathogenesis of osteoarthritis.Therefore, it is necessary to pay more attention to the calcified zone and subchondral bonechanges in the process of OA, which contributing to comprehensive and profoundunderstanding of the pathogenesis of OA, and providing new insights into the prevention andtreatment of osteoarthritis. This study selected the most representative knee osteoarthritis as the experimentalobject. After gross observation, the decalcified sections were stained with different dyes toinvestigate the pathologic characteristics of the hyaline cartilage, calcified zone andsubchondral bone. The osteochondral structural parameters were measured by bonehistomorphometry, in order to compare the difference of hyline cartilage, calcified zone andsubchondral bone between the medial and lateral plateau. The study will provide experimentalbasis for in-depth study of the pathogenesis of knee osteoarthritis.Materials and Methods:1. Source of specimen: Thirty patients who suffering from knee osteoarthritis wereselected in center for joint surgery, southwest hospital. Before surgery, rheumatoid arthritis,trama, infection, tumor and other diseases of the knee were excluded. The specimens werevoluntarily donated by the patients, including19femals and11males with an average age of65.1years (range,55-78). The mean disease duration was16.6years (range,10-25years) andthe mean varus angle of the diseased knee was9.3°(range,1-23°).2. Gross obserbation: Thirty tibial plateaus were taken form patients during TKA. Thecolor, appearance, malacia, ulcers, fissures and pannus-like tissue of the cartilage wereobserved by naked eye. Subchondral bone exposure, eburnation and osteophytes formationwere observed by the same way. After that,60bone-cartilage samples were taken out fromthe most weight-bearing regions in the internal areas of the medial and lateral plateaus toavoid regional difference, then the samples were observed by stereomicroscope.3.Histological observation: The paraffin-embedded sections were prepared after fixationand decalcification, and were stained with HE, safranin O/fast green, toluidine blue, sirius redand collagen type Ⅱ immunohistochemical staining, in order to explore the pathologiccharacteristics of the hyaline cartilage, calcified zone and subchondral bone. By means ofsafranin O/fast green staining, the degree of cartilage degeneration was staged and graded byMankin score and OARSI scoring system with double-blind method, then compare thedifference of Mankin score between medial and lateral plateau.4.Bone histomorphometry: By means of safranin O/fast green staining, the osteochondralstructural parameters were measured by Image-Pro Plus6.0imaging system, in order tocompare the structural difference of hyaline cartilage, calcified zone and subchondral bonebetween the medial and lateral plateau. 5. Statistical analysis: The data were analyzed by SPSS13.0, measurement data wereexpressed as mean±standard deviation. Paired-t test was used in paired samples, inspectionlevel α=0.05.Results:1. Gross obserbation: Cartilage degeneration was more severe in the medial plateau thanthat of the lateral plateau by naked eye. Macroscopic observation of the longitudinal sectionshowed that the cartilage thickness reduced, the interface between calcified zone andsubchondral bone was obscure, and the subchondral bone was obviously thickened.2.Histological observation:(1) Hyaline cartilage: The course of knee osteoarthritis could be divided into three stages.Among the60samples,14samples were at stageⅠ(early stage), characterized by fissuresformation within the superficial zone;19samples were at stage Ⅱ (middle stage),characterized by longitudinal fissures extending into the deep zone and clustering chondrocyts;27samples were at stage Ⅲ (advanced stage), characterized by total chondral defects andpannus-like tissue.The degree of cartiage denegeration could be divided into0to6gradesaccording to OARSI grading system. Mankin score of the medial plateau (12.4±1.1) wassignificantly higher than that of the lateral plateau (8.3±1.6).(2) Calcified zone: duplicated tidemarks and multiple microcracks were observed instageⅠ; thickened calcified zone and invading vessels were observed in stageⅡ; calcifiedzone thickness was reduced and endochondral ossification phenomenon was common in stageⅢ.(3) Subchondarl bone: subchondral bone thickness increased in stageⅠ; subchondralbone thickness obviously increased and local subchondral bone exposue appeared in stageⅡ;extensively eburnated subchondral bone, pannus-like tissues, subchondral bone cysts andcartilaginous deposits emerged in stageⅢ.3.Bone histomorphometry: The TAC and Tb.Sp of the medial plateau were significantlylower than those of the lateral plateau (P<0.05). The ACC/TAC, SCP, BV/TV, Tb.Th andTb.N of the medial plateau were significantly higher than those of the lateral plateau(P<0.05).However, there was no significant change in the ACC between the medial and lateralplateau(P>0.05). Conclusions:1. The hyaline cartilage, calcified zone and subchondral bone have particular pathologicchanges in the pathogenesis of knee osteoarthritis.2. In the development of knee osteoarthritis, the hyaline cartilage thickness is obviouslyreduced, the subchondral bone plate is obviously thickened, and the thickness of calcifiedzone may be increased in stageⅠand reduced in stageⅡand Ⅲ. The increased BV/TV iscomposed of increased Tb.Th and Tb.N, but reduced Tb.Sp.3. The calcified zone and subchondral bone may play an important role in the initiationand progression of knee osteoarthritis. |
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