Repair of osteochondral defects with recombinant human type II collagen gel and autologous chondrocytes in rabbit.

OBJECTIVE: Recombinant human type II collagen (rhCII) gels combined with autologous chondrocytes were tested as a scaffold for cartilage repair in rabbits in vivo. METHOD: Autologous chondrocytes were harvested, expanded and combined with rhCII-gel and further pre-cultivated for 2 weeks prior to transplantation into a 4 mm diameter lesion created into the rabbit's femoral trochlea (n = 8). Rabbits with similar untreated lesions (n = 7) served as a control group. RESULTS: Six months after the transplantation the repair tissue in both groups filled the lesion site, but in the rhCII-repair the filling was more complete. Both repair groups also had high proteoglycan and type II collagen contents, except in the fibrous superficial layer. However, the integration to the adjacent cartilage was incomplete. The O'Driscoll grading showed no significant differences between the rhCII-repair and spontaneous repair, both representing lower quality than intact cartilage. In the repair tissues the collagen fibers were abnormally organized and oriented. No dramatic changes were detected in the subchondral bone structure. The repair cartilage was mechanically softer than the intact tissue. Spontaneously repaired tissue showed lower values of equilibrium and dynamic modulus than the rhCII-repair. However, the differences in the mechanical properties between all three groups were insignificant. CONCLUSION: When rhCII was used to repair cartilage defects, the repair quality was histologically incomplete, but still the rhCII-repairs showed moderate mechanical characteristics and a slight improvement over those in spontaneous repair. Therefore, further studies using rhCII for cartilage repair with emphasis on improving integration and surface protection are required.

pQCT study on diffusion and equilibrium distribution of iodinated anionic contrast agent in human articular cartilage--associations to matrix composition and integrity.

OBJECTIVE: X-ray imaging of articular cartilage using anionic contrast agents has been introduced for quantification of tissue glycosaminoglycan (GAG) concentration. In this in vitro study we investigated diffusion and equilibrium distribution of an anionic contrast agent in human articular cartilage and related the results to tissue composition and integrity. METHODS: Osteochondral cylinders (d=4.0mm, n=24) were prepared from femoral medial condyles (FMCs, cartilage thickness 2.13+/-0.54 mm, mean+/-standard deviation [SD]), and tibial medial plateaus ([TMPs]1.99+/-0.38 mm) of human cadaver knees. Samples were immersed for 24h at room temperature in 21 mM concentration of anionic contrast agent Hexabrix. The X-ray absorption maps and profiles were measured before immersion, and after every 2h of immersion using clinical peripheral quantitative computed tomography (pQCT). RESULTS: An increase in X-ray attenuation along cartilage depth, indicating a characteristic density profile increasing from superficial to deep tissue, could be seen in pQCT images acquired without contrast agent. The complete diffusion of the contrast agent into cartilage took more than 12h. However, the uronic acid concentration correlated with the contrast agent concentration in femoral cartilage (r=-0.76, n=12, P=0.004) as early as after 2h of immersion, and the linear correlation was virtually unchanged during the remaining 22 h. Similarly, the histological tissue integrity (Mankin score) correlated positively with the contrast agent concentration in tibial cartilage (r=+0.75, P=0.005) after 2h of immersion. The X-ray absorption profiles before immersion, i.e., without the contrast agent, and after 24h of immersion were significantly correlated (r=-0.76+/-0.34, mean+/-SD). CONCLUSIONS: Although the complete contrast agent diffusion into human articular cartilage in vitro took more than 12h, significant apparent correlations were revealed between the spatial proteoglycan (PG) and contrast agent distributions already after 2h of immersion. At the stage of incomplete penetration, however, the spatial contrast agent concentration distribution cannot directly reflect the true PG distribution as the Donnan equilibrium has not been reached. However, in degenerated cartilage the diffusion rate increases. Obviously, this can lead to the reported correlation between the bulk PG content and the bulk contrast agent concentration already at the early stages of diffusion.

Contrast agent-enhanced computed tomography of articular cartilage: association with tissue composition and properties.

BACKGROUND: Contrast agent-enhanced computed tomography may enable the noninvasive quantification of glycosaminoglycan (GAG) content of articular cartilage. It has been reported that penetration of the negatively charged contrast agent ioxaglate (Hexabrix) increases significantly after enzymatic degradation of GAGs. However, it is not known whether spontaneous degradation of articular cartilage can be quantitatively detected with this technique. PURPOSE: To investigate the diagnostic potential of contrast agent-enhanced cartilage tomography (CECT) in quantification of GAG concentration in normal and spontaneously degenerated articular cartilage by means of clinical peripheral quantitative computed tomography (pQCT). MATERIAL AND METHODS: In this in vitro study, normal and spontaneously degenerated adult bovine cartilage (n=32) was used. Bovine patellar cartilage samples were immersed in 21 mM contrast agent (Hexabrix) solution for 24 hours at room temperature. After immersion, the samples were scanned with a clinical pQCT instrument. From pQCT images, the contrast agent concentration in superficial as well as in full-thickness cartilage was calculated. Histological and functional integrity of the samples was quantified with histochemical and mechanical reference measurements extracted from our earlier study. RESULTS: Full diffusion of contrast agent into the deep cartilage was found to take over 8 hours. As compared to normal cartilage, a significant increase (11%, P<0.05) in contrast agent concentration was seen in the superficial layer of spontaneously degenerated samples. Significant negative correlations were revealed between the contrast agent concentration and the superficial or full-thickness GAG content of tissue (|R| > 0.5, P<0.01). Further, pQCT could be used to measure the thickness of patellar cartilage. CONCLUSION: The present results suggest that CECT can be used to diagnose proteoglycan depletion in spontaneously degenerated articular cartilage with a clinical pQCT scanner. Possibly, the in vivo use of clinical pQCT for CECT arthrography of human joints is feasible.

T2, Carr-Purcell T2 and T1rho of fat and water as surrogate markers of trabecular bone structure.

Magnetic resonance imaging (MRI) techniques have been developed for non-invasive assessment of the structural properties of trabecular bone. These measurements, however, suffer from relatively long acquisition times and low resolution compared to the trabecular size. Spectroscopic measurement of relaxation times could be applied for more detailed and faster assessment of relaxation properties of bone marrow and also provide surrogate information on trabecular structure. In the present study, bovine trabecular bone was investigated with spectroscopic NMR (nuclear magnetic resonance) methods to determine the relationship between structural parameters as measured with micro-CT and T(2), Carr-Purcell T(2) and T(1rho) relaxation times of fat and water. To compare bone with a sample matrix with magnetic susceptibility interfaces, phantoms consisting of glass beads with different diameters in oil or water were used. The behavior of T(2) measured with different sequences and T(1rho) at different magnitudes of spin-lock fields were characterized, and relaxation times were correlated with structural parameters. T(2) and T(1rho) showed significant associations with structural bone parameters. Strongest linear correlations (r = 0.81, p < 0.01) were established between R(1rho) (1/T(1rho)) of fat component and structural model index. For glass beads, the behavior of T(2) and T(1rho) was similar to that of the water compartment of bone marrow. The present results suggest feasibility of spectroscopic NMR measurements to assess trabecular structure. However, further studies are required to determine the sensitivity of this approach to fat content of bone marrow and to lower the field strengths used in clinical devices.