Purpose

1) Introduce a novel expiremental model and design to study meniscal healing responses to a variety of treatment options, and 2) to present biomechanical and histological baseline data of the model.

Methods and Materials

Human meniscus tissue was obtained from patients undergoing total knee arthroplasty, according to IRB approved protocols. Standardized human menisci with a central defect filled with autologous meniscus tissue were cultured for up to eight weeks without stimulation. Specimens were cut using biopsy punches, the outer ring with an 8 mm biopsy punch, the inner plug with a 4 mm biopsy punch. Meniscus formation and integrity were analyzed at the defect site through 1) biomechanical testing and 2) histology (Safranin O with Haematoxylin counterstain, Picro Sirius Red) and collagen autofluorescence using confocal microscopy. The biomechanical testing was carried out using a static universal test system. The maximal force required to push out the implant from the meniscus rings (Fmax(insert)) was determined using a cylindrical indenter (diameter 3.8 mm).

Results

A total of 92 samples were tested biomechanically and 21 samples histologically. Both biomechanical maximal push out force, as well as histological analysis showed no significant difference between all time points. No significant healing response was visible in the histological images. These results reflect the limited intrinsic healing properties of the human meniscus.

Figure 1. Force graph of push-out test of a specimen. Force abruptly drops, as soon as inner cylinder is pushed out.

Figure 2. Collagen autofluoresence image of the punch interface of a simulated 7 days old meniscus tear

Conclusion

The present human meniscus punch model represents a robust, reproducible and highly suitable tool for the long-term culture of meniscus tissue, maintaining matrix integrity and homoeostasis. As an alternative to animal studies, this model may closely reflect early stages of meniscus regeneration/healing, allowing the evaluation of promising regenerative treatment regimes.