Histologic changes after meniscal repair using radiofrequency energy in rabbits

Radiofrequency ablation alters the microstructural organization of healthy and enzymatically digested porcine mitral valves

BACKGROUND

Myxomatous mitral valve degeneration is a common cause of mitral regurgitation and is often associated with mitral valve prolapse. With no known targets to pharmacologically treat mitral valve prolapse, surgery is often the only treatment option. Recently, radiofrequency ablation has been proposed as a percutaneous alternative to surgical resection for the reduction of mitral valve leaflet area.

OBJECTIVE

Using an in vitro model of porcine mitral valve anterior leaflet enlargement following enzymatic digestion, we sought to investigate mechanisms by which radiofrequency ablation alters the geometry, microstructural organization, and mechanical properties of healthy and digested leaflets.

METHODS

Paired measurements before and after ablation revealed the impact of radiofrequency ablation on leaflet properties. Multiphoton imaging was used to characterize changes in the structure and organization of the valvular extracellular matrix; planar biaxial mechanical testing and constitutive modeling were used to estimate mechanical properties of healthy and digested leaflets.

RESULTS

Enzymatic digestion increased leaflet area and thickness to a similar extent as clinical mitral valve disease. Radiofrequency ablation altered extracellular matrix alignment and reduced the area of digested leaflets to that of control. Additionally, enzymatic digestion resulted in fiber alignment and reorientation toward the radial direction, causing increased forces during ablation and a structural stiffening which was improved by radiofrequency ablation.

CONCLUSION

Radiofrequency ablation induces radial extracellular matrix alignment and effectively reduces the area of enlarged mitral valve leaflets. Hence, this technique may be a therapeutic approach for myxomatous mitral valve disease and is thus an avenue for future study.

Growth factor expression after lesion creation in the avascular zone of the meniscus: a quantitative PCR study in rabbits

PURPOSE

To define the variations in the expression of 5 growth factor genes in meniscal tissue after a lesion is created in the avascular zone of the medial meniscus of the rabbit.

METHODS

A longitudinal lesion was created in the avascular zone of the anterior horn of the medial meniscus in 42 rabbits. Six animals were killed at 0, 1, 3, 7, 14, 21, and 120 days after lesion creation. Meniscal tissue from the avascular and vascular zones was harvested. A quantitative polymerase chain reaction analysis was performed to evaluate the expression levels of 5 different growth factors: vascular endothelial growth factor A (VEGF-A), insulin-like growth factor 1 (IGF-1), transforming growth factor β1 (TGF-β1), platelet-derived growth factor β (PDGF-β), and interleukin 1β.

RESULTS

The basal expression levels of all the growth factors studied were similar in the avascular and vascular zones. There was an increase in VEGF-A expression in the avascular zone on the 14th day, an increase in IGF-1 expression in the vascular zone on the 14th day, a decrease in PDGF-β expression in both zones in the first week, an increase in interleukin 1β expression in both zones on the first day, and a decrease in TGF-β1 expression in the vascular zone in the first week. At 120 days, the expression levels of all 5 growth factors returned to basal levels.

CONCLUSIONS

There are significant variations in the expression of the growth factors studied during the first weeks after meniscal lesion creation. The preinjury expression levels are similar in the avascular and vascular zones and are not significantly different from the basal levels 4 months after injury.

CLINICAL RELEVANCE

This study identifies potential therapeutic molecular targets (VEGF-A, IGF-1, TGF-β1, and PDGF-β) that can be used in the treatment of meniscal tears.

Migration responses of outer and inner meniscus cells to applied direct current electric fields

Injuries to the inner regions of the knee meniscus do not heal and can result in degenerative changes to the articular surface, ultimately leading to osteoarthritis. A possible stimulus to enhance meniscus healing is to use electric fields that induce galvanotaxis. In this study, a novel characterization of the effects of direct current electric fields on migration characteristics of meniscus cells was performed. Primary and passaged inner and outer meniscus cells were exposed to varying electric field strengths from 0 to 6 V/cm. Cell migration was tracked using time lapse digital photography, and cell displacement and cathodal direct velocity were quantified. Cytoskeletal staining was performed to examine actin distribution and nuclear content. Cell adhesion strength was quantified as a function of wall shear stress. Meniscus cells exhibited cathodal migration and cell elongation perpendicular to the applied electric field accompanied by actin reorganization. Outer meniscus cells migrated quicker and exhibited lower adhesion strengths when compared to inner meniscus cells. Passaged cells exhibited higher migration characteristics when compared to primary cells. Overall, this study demonstrated that electric fields can significantly enhance and direct meniscus cell migration and suggests the potential for their incorporation in strategies of meniscus repair and tissue engineering.