Concentrations of proteoglycan fragments in relation to maturation, sex and time of day: physiologic variations in knee joint fluid of rabbits

The effects of early or late treatment of osteochondral defects on joint homoeostasis: an experimental study in rabbits

A 3.5 x 4 mm tubular osteochondral defect was created on the right medial femoral condyles of 51 adult rabbits. In the control group (CG), defects were left untreated. In the early-(ETG) and late-(LTG) treatment groups, defects were treated by an osteoperiosteal graft 1 and 12 weeks, respectively, after the index procedure. Synovial fluid (SF) samples were collected regularly and proteoglycan fragments (PF), total collagen (TC) and collagenase (MMP-1) levels were measured. Rabbits were killed at 4 (early period), 12 (intermediate period), or 24 (late period) weeks postoperatively. Histological examination indicated a more successful healing in both grafting groups than in the CG, but without any difference at any time period between the grafting groups. In the CG, PF, and TC levels in SF increased continuously until the late period, indicating an ongoing degenerative activity in the joints. In contrast, SF marker levels in both grafting groups indicated that normalization in joint metabolism could be achieved-at least partially-after treatment. However, PF levels in the SF showed that the treatment of defects in earlier stages might result in better outcomes since the negative effects were more prominent in chronic stages, presumably due to the more prolonged period of disturbed homeostasis. Thus, histological values and SF marker levels indicated that treatment of osteochondral defects at any time of the disease had a positive effect on healing when compared to no treatment. Early treatment might better assist the recovery of joint homeostasis than late treatment.

The effects of age and sex on chondroitin sulfates in normal synovial fluid

OBJECTIVE

To examine how age and sex influence chondroitin sulfates (CS) in normal synovial fluid, we measured the concentrations of chondroitin 6-sulfate (C6S), chondroitin 4-sulfate (C4S), and hyaluronic acid (HA) in healthy subjects of different ages.

METHODS

Synovial fluid samples were obtained from 82 healthy volunteers, ages 20-79 years.

RESULTS

The concentrations of CS and HA and the C6S:C4S ratio varied with age. Their values were highest between 20 and 30 years of age, and thereafter they showed a tendency to decrease. Statistically, the C6S concentration and the C6S:C4S ratio at ages 60-70 years were significantly lower than those at 20-30 years of age. There was also a clear between-sex difference, in which the CS concentrations and the C6S:C4S ratio in women were significantly lower than those in men (P = 0.0003 for C6S, P = 0.02 for C4S, P = 0.002 for C6S:C4S ratio). In sharp contrast, little between-sex difference was found in the HA concentration. In multiple regression analysis, age correlated strongly with the C6S concentration and the C6S:C4S ratio (r = -0.521 and r = -0.617, respectively), weakly with the C4S concentration (r = -0.202), and moderately with the HA concentration (r = -0.483). Sex showed a weak correlation with the concentrations of C6S and C4S and the C6S:C4S ratio (r = 0.307, r = 0.225, and r = 0.237, respectively), and little correlation was seen between sex and the HA concentration.

CONCLUSION

The CS concentrations and the sulfation patterns in normal synovial fluid vary with age and sex, and these physiologic variations need to be taken into account when using synovial fluid CS as markers for arthritic conditions.

An immunohistochemical study of the rabbit suprapatella, a sesamoid fibrocartilage in the quadriceps tendon containing aggrecan

The rabbit suprapatella is a sesamoid fibrocartilage in the deep surface of the tendon of vastus intermedius and an integral part of the knee joint. We report the presence of a variety of proteoglycans (aggrecan and versican), glycosaminoglycans (chondroitin 4 and 6 sulfate, dermatan sulfate, keratan sulfate) and glycoproteins (tenascin) in its extracellular matrix and the intermediate filament vimentin in the fibrocartilage cells. The most significant finding is the presence of aggrecan in the extracellular matrix, along with its associated link protein and several of its integral glycosaminoglycans. Aggrecan probably enables the suprapatella to withstand compression. Although it can be assumed that aggrecan metabolites detected in synovial fluid from some human joints are predominantly associated with articular hyaline cartilage, the presence of aggrecan in the rabbit suprapatella means that this cannot be assumed for all animal knee joints. We conclude that it is important for orthopedic researchers who use animal models for arthritis research to check for the presence of a suprapatella when joint fluid analyses are interpreted.