Basic research on intrameniscal injection as a direct treatment for knee meniscal pathology

The meniscus is an essential structure of the knee joint, performing functions such as load transmission, shock absorption, joint stability, and joint lubrication. The deterioration of meniscal function due to trauma or degenerative changes causes meniscal-related symptoms and leads to cartilage damage and osteoarthritis. Current treatments target not the meniscus itself, but the entire knee joint or intra-articular tissues, and non-surgical treatments that directly access the meniscal tissues are not widely used. This study aimed to evaluate the effects of the intrameniscal injection technique on meniscal tissue and cells.

Four healthy porcine menisci and 10 human menisci from patients after total knee arthroplasty were injected with different solutions to investigate the required injection force, intrameniscal distribution of the injected solution, and biological effects on the meniscal cells. The initial force exerted by the syringe piston was measured by a pressure gauge. After the injection of Fast Green FCF solution, the distribution was observed, measured, and analyzed in 3 indicators: Width, Stained Area, and Calculated Volume. Other meniscal tissues were injected with recombinant interleukin-1 beta (rIL-1β), dexamethasone or papain, cultured and harvested for qRT-PCR or histology analysis.

Statistically significantly greater force was required for the intrameniscal (24.9 ± 4.3 N) versus adipose (1.1 ± 0.2N) or muscle tissue (0.8 [interquartile range 0.6-1.1] N) using a 1 mL syringe (p < 0.01), while less force was required when using a microsyringe (0.5 [interquartile range 0.4-0.5] N) versus 1 mL syringe (p < 0.0001). When different injection volumes were compared, the indicators were significantly higher after a 10-μL versus 5-μL injection (p < 0.05). When the same amount of Fast Green FCF solution was injected, the indicators were larger in the degenerative human versus healthy porcine menisci. The injection of rIL-1β promoted inflammatory factor and matrix proteinase transcription in meniscal cells. In contrast, the injection of dexamethasone into meniscal tissue cultured in rIL-1β-containing medium suppressed this transcription. The injection of papain resulted in decreased Safranin O staining and a changed picrosirius red staining pattern.

These results provide new insights that may serve as a basis for the more useful clinical application of intrameniscal injections.

V, Mechanism-based reasoning/Lab Studies.