The superficial zone (SFZ) of articular cartilage has unique structural and biomechanical features, and is important for joint long-term function. Previous studies have shown that TGF-β/Alk5 signaling upregulating PRG4 expression maintains articular cartilage homeostasis. However, the exact role and molecular mechanism of TGF-β signaling in SFZ of articular cartilage homeostasis are still lacking. In this study, a combination of in vitro and in vivo approaches were used to elucidate the role of Alk5 signaling in maintaining the SFZ of articular cartilage and preventing osteoarthritis initiation. Mice with inducible cartilage SFZ-specific deletion of Alk5 were generated to assess the role of Alk5 in OA development. Alterations in cartilage structure were evaluated histologically. The chondrocyte apoptosis and cell cycle were detected by TUNEL and Edu staining, respectively. Isolation, culture and treatment of SFZ cells, the expressions of genes associated with articular cartilage homeostasis and TGF-β signaling were analyzed by qRT-PCR. The effects of TGF-β/Alk5 signaling on proliferation and differentiation of SFZ cells were explored by cells count and alcian blue staining. In addition, SFZ cells isolated from C57 mice were cultured in presence of TGF-β1 or SB505124 for 7 days and transplanted subcutaneously in athymic mice. Postnatal cartilage SFZ-specific deletion of Alk5 induced an OA-like phenotype with degradation of articular cartilage, synovial hyperplasia as well as enhanced chondrocyte apoptosis, overproduction of catabolic factors, and decreased expressions of anabolic factors in chondrocytes. qRT-PCR and IHC results confirmed that Alk5 gene was effectively deleted in articular cartilage SFZ cells. Next, the PRG4-positive cells in articular cartilage SFZ were significantly decreased in Alk5 cKO mice compared with those in Cre-negative control mice. The mRNA expression of Aggrecan and Col2 were decreased, meanwhile, expression of Mmp13 and Adamts5 were significantly increased in articular cartilage SFZ cells of Alk5 cKO mice. In addition, Edu and TUNEL staining results revealed that slow-cell cycle cell number and increase the apoptosis positive cell in articular cartilage SFZ of Alk5 cKO mice compared with Cre-negative mice, respectively. Furthermore, all groups of SFZ cells formed ectopic solid tissue masses 1 week after transplantation. Histological examination revealed that the TGF-β1-pretreated tissues was composed of small and round cells and was positive for alcian blue staining, while the SB505124-pretreated tissue contained more hypertrophic cells though it did stain with alcian blue. TGF-β/alk5 signaling is an essential regulator of the superficial layer of articular cartilage by maintaining chondrocyte number, its differentiation properties, and lubrication function. Furthermore, it plays a critical role in protecting cartilage from OA initiation

This study investigated confocal laser scanning microscopy (CLSM) as a novel method of imaging of chondrocytes on a collagen membrane used for articular cartilage repair. Cell viability and the effects of surgery on the cells were assessed. Cell images were acquired under four conditions: 1, Pre-operative 2, After handling 3, Heavily grasped with forceps 4, Cut around the edge. Live and dead cell stains were used. Images were obtained for cell counting and morphology. Mean cell density was 1.12–1.68 ± 0.22 × 10. 6. cells/cm. 2. in specimens without significant trauma (n=25 images), this decreased to 0.253 × 10. 6. cells/cm. 2. in the specimens that had been grasped with forceps (p <0.001) (5 images). Cell viability on delivery grade membrane was 86.8±2.1%. The viability dropped to 76.3 ± 1.6% after handling and 35.1 ± 1.7% after crushing with forceps. Where the membrane was cut with scissors, there was a band of cell death where the viability dropped to 17.3 ± 2.0% compared to 73.4 ± 1.9% in the adjacent area (p <0.001). Higher magnification revealed cells did not have the rounded appearance of chondrocytes. CLSM can quantify and image the fine morphology of cells on a MACI membrane. Careful handling of the membrane is essential to minimise chondrocyte death during surgery

In 1823 J. White excised the head. In 1887 a German surgeon replaced the head with ivory. Interposition arthroplasties were common after WW1. Short-stemmed head replacing prosthesis were developed after WW2. Moores and Thompson designed a more stable intramedullary stem. Acetabular erosion was troublesome—and so replacing both surfaces started in the late 1950s using Teflon cup and metal femur. Unfortunately, these quickly became loose due to wear or sepsis. In 1960, Charnley used a polyethylene cup and stainless-steel femur and fixed both with dental cement. This ‘low friction arthroplast’ became a routine procedure after 1961. In the 1970s there were many ‘Charnley look-alike’ prosthesis with similar problems of poly-wear, granulomas and cysts causing bone loss, loosening, breakages and infection. Resurfacing with two thin shells was developed to reduce the foreign material, the bone resection and the cement used. Unfortunately, neck fractures, avascular necrosis and excessive wear of the poly shell were common. Despite operating theatres with laminar flow of sterile air, space suits and improved cementing techniques, the same problems occurred. To avoid poly and cement, Mittelmayer developed a ceramic screw cup, which did not require cement. Although some screws migrated, they did not wear. Because the un-cemented metal stem remained fixed solid to the femur, un-cemented metal cups and stems were developed. To avoid the poly-wear, ceramic liners became popular. To provide the active patients with a stable joint that requires no restriction in physical activity, a large head in a large cup is desirable. Unfortunately, the large metal-on-metal resurfacing prosthesis produce metal wear ions and nanoparticles which can form hypersensitivities, cysts and pseudotumours. Computer assisted navigation to ensure correct positioning of the prosthetic components is obviously useful for surgeons that use incisions too small to see enough to be certain of the cups position. Presently, articular cartilage research is progressing rapidly and by 2020 most arthritic hip joints will be arthroscopically debrided and resurfaced by an injection of genetically engineered articular cartilage stem cells