Abstract
Statement of Purpose
Meniscal tears are common knee injuries that subsequently lead to degenerative arthritis, attributed to changes in stress distribution in the knee. In such cases there is need to protect the articular cartilage by repairing or replacing the menisci. While traditionally, meniscal replacement involves implantation of allografts, problems related to availability, size matching, cost and risk of disease transmission limit their use. Another optional treatment is that of biodegradable scaffolds which are based principally on tissue engineering concepts. The variability in body response to biodegradable implants and the quality of the tissue formed still pose a problem in this respect, under intense knee loading conditions. Moreover, biological solutions are mostly limited to younger patients <40 years old. Therefore, the goal of this study was, to develop a synthetic meniscal implant which can replace the injured meniscus, restore its function, and relieve pain.
Methods
A composite, non-fixed self-centering discoid-shaped meniscus implant (NUsurafce®, AIC, Memphis, TN), composed of polycarbonate-urethane (PCU) and reinforced circumferentially with UHMWPE fibers is proposed (Fig. 1). The implant geometry was based on an extensive MRI study of over 100 knee scans [1]. The proposed structure aims to mimic the circumferential collagen reinforcement of the natural meniscus. Biomechanical evaluation of the implant was focused on in-vitro measurements of contact pressure under the implant in cadaver knees and computational finite element (FE) analyses [2,3]. Pressure distribution on the tibial plateau (under the meniscus implant) was measured by pressure sensitive films (Tekscan, MA) and quantified with respect to the natural meniscus. FE analyses were used to evaluate internal stress and strains, and to support the selection of optimal implant configuration. The last pre-clinical step was a large-animal (sheep) study in which the cartilage condition was evaluated microscopically over six months [4].
Results
Contact pressure distributions on the tibia, were in good agreement with those measured under the natural meniscus (Fig. 2). Specifically, peak and average pressures developed under the implant were found to similar to those of the natural meniscus. The contact area measured under the implant (658±135mm2) was also restored when compared to the natural meniscus (642±96mm2). FE models confirmed that internal strains/stresses within the device components remained within the materials' allowed limits. The evaluation of an implant adapted to sheep showed no signs of wear or degradation of the materials. Histology showed relatively mild cartilage degeneration that was dominated by loss of proteoglycan content and cartilage structure. First clinical results for the implant, with up to 2 years follow-up, demonstrate encouraging prospects for this concept in terms of pain relief.
Conclusions
In the current study, we presented the development of a novel PCU meniscal implant for the medial compartment of the knee, along with an overview of essential tests. It was found that (a) the implant is able to reduce the overall cartilage load associated with meniscectomy by effectively distributing joint loads, and (b) the implant completely prevents contact between opposing cartilage surfaces. The results of implantation in sheep can be considered favourable in arresting joint degeneration, and first implantations have shown that arthroscopic implantation of the device is short and uncomplicated.
Results
Contact pressure distributions on the tibia, were in good agreement with those measured under the natural meniscus (Fig. 2). Specifically, peak and average pressures developed under the implant were found to similar to those of the natural meniscus. The contact area measured under the implant (658±135mm2) was also restored when compared to the natural meniscus (642±96mm2). FE models confirmed that internal strains/stresses within the device components remained within the materials' allowed limits. The evaluation of an implant adapted to sheep showed no signs of wear or degradation of the materials. Histology showed relatively mild cartilage degeneration that was dominated by loss of proteoglycan content and cartilage structure. First clinical results for the implant, with up to 2 years follow-up, demonstrate encouraging prospects for this concept in terms of pain relief.
Conclusions
In the current study, we presented the development of a novel PCU meniscal implant for the medial compartment of the knee, along with an overview of essential tests. It was found that (a) the implant is able to reduce the overall cartilage load associated with meniscectomy by effectively distributing joint loads, and (b) the implant completely prevents contact between opposing cartilage surfaces. The results of implantation in sheep can be considered favourable in arresting joint degeneration, and first implantations have shown that arthroscopic implantation of the device is short and uncomplicated.
