Why is there a need for a total meniscus replacement?
A total meniscus replacement system is needed when the meniscus is severely damaged and undergoes irreparable and complex tears either due to trauma (acute tears) or because of degeneration associated with ageing (chronic tears). In such circumstances, the meniscus cannot be restored using contemporary methods involving sutures, partial scaffolds or meniscal spacers, leaving little alternative for the patient than to live with a partial meniscus or in some cases with no meniscus at all.
The meniscus plays a critical role in lubrication, load transmission and joint stability, however it is prone to wear and injury. Meniscal tears are well known to cause pain both at the time of and following injury. Some pain can be treated with anti-inflammatory drugs and will eventually disappear. Some tears can be repaired by suturing the damaged tissue, particularly if this is in an area where there is sufficient blood supply nearby1. Unfortunately, in many cases the tear occurs in an area which does not heal due to poor blood supply (the avascular zone) and the only relief from pain is more radical - irreparable lesions to the menisci are treated by surgery to remove all or part of the meniscal tissue, a procedure known as partial or total meniscectomy. However, reduction of menisci in this way has been shown to significantly increase the likelihood of developing osteoarthritis4. In recent years, as an alternative to removal, surgeons and engineers have developed methods for replacing part of the damaged meniscus using bio-degradable scaffolds, synthetic spacers or even entire meniscal transplants (allografts). However, in each case there are issues with the options currently available:
- Allografts, firstly, must be sourced from a suitable donor, and the supply is very limited. As about 100,000 people injure their menisci a year in the UK, such an approach is simply not viable and the procedure is therefore unsuitable for scale up to meet a growing demand. The results are also variable as allografts are difficult to attach and require complex surgery involving special surgical skills. These transplants also carry a risk of infection from donor material (meaning that post-operative patients have to be more closely supervised). A recent study on allografts has shown a high number of subsequent interventions with associated morbidity and socioeconomic costs6.
- Artificial spacer implants on the market today rely on a perfect fit within an intact outer rim so these can only be suitable if the outer meniscal rim is intact. As the rim is usually extruded, this is usually not suitable.
- The use of bio-degradable scaffolds have uncertain outcomes (according to NICE) given the difficulty for these to replicate the exact mechanical performance of the original tissue and they also rely on the ‘healing capability’ of the patient as well as the structural integrity of the remaining meniscal tissue following injury. Furthermore, partial meniscal scaffolds allow full weight bearing only after 8–10 weeks following surgery5.
What does the implant consist of?
The implant will be fitted into the knee using orthopaedic surgical tools and fittings. Our team has studied the structure of a natural meniscus and how it reacts to different forces to design a substitute that would function in exactly the same way. Orthonika’s product will comprise a durable implant that is self-contained, minimally invasive and maintains meniscal volume whilst withstanding the rigor of physical activity in the knee. It uses a keyhole surgical insertion procedure based on arthroscopic approach and related instruments to securely fix the replacement to the bone. This secure attachment is key - the meniscus has an extremely complex structure and is subject to high stresses so it needs to resist high tensile and compressive forces whilst at the same time being capable of adapting to an individual’s physiological movement.
How is the implant constructed?
The total meniscus replacement will be a fully synthetic, non-degradable meniscus implant based on proprietary high strength polymers and constructions that replicate not only the bulk macroscopic geometry of the meniscus, but also the underlying microstructure and anisotropic properties affiliated with natural tissue. Orthonika’s ground breaking implant design is unique in that it features an inherent attachment mechanism incorporated into the underlying microstructure that allows for optimal load transfer and recovery in the knee joint during mobility. The implant is able to replicate the ‘hoop stress mechanism’ occurring in the natural tissue – one of the key structure-function characteristics of the real tissue which preserves the underlying articular cartilage. The implant combines world class science, polymer processing and fibre engineering to develop the world’s first in class fully anatomical synthetic meniscus replacement. In its current form the implant is non-degradable and does not include bioactive agents to promote healing.
How steep is the learning curve for your surgical procedure to place the implant in the knee?
The surgical procedure is designed to minimise hurdles to adoption. We anticipate, the operation will be very similar to many other surgeries which orthopaedics currently perform on the knee such as meniscectomies or anterior cruciate ligament (ACL) reconstructions. Precise placement will be important, however this should be achieved using familiar equipment and fittings. Orthopaedic surgeons have been involved at every stage of the development. At this stage, we believe a referral-based adoption is likely to have the most potential for scalable market uptake.
Who would be the ideal patient to receive treatment with your product? How large is this segment of the patient population?
The ideal patient to receive treatment with a total meniscus repair system would be an adult with an injured or worn meniscus but intact articular cartilage. Injury or wear in the meniscus is a common problem and often leads to painful osteoarthritis. There are over 6m patients with osteoarthritis (OA) in the UK alone. By acting before the onset of OA we would expect to reduce the pain and suffering of patients, many of whom end up having knee replacements at a cost to the NHS of around £700m a year. We hope that replacement of an injured or worn meniscus with our implant will restore function to the knee and significantly delay or avoid the onset of osteoarthritis or the need for more radical surgical intervention. Over 1.5 million meniscus-related operations are performed in UK and US every year and we understand from speaking with a number of surgeons engaged in this field that at least 1/3rd of their patients would benefit from our implant.
From the literature3 we learn that approximately one third of the meniscal tears are acute tears associated with anterior cruciate ligament injuries with a peak incidence of in men aged 21–30 years and women aged 11–20 years. Also, degenerative types of meniscal tears commonly occur in patients aged between 40 and 60 years. The mean annual incidence of meniscal tears is about 60–70 per 100,000 and meniscal surgery is the most commonly performed knee procedure. Approximately 35% of all arthroscopic knee surgeries are meniscal repairs or meniscectomies followed by insertion of a partial replacement or allograft transplant2.
We have yet to finalise eligibility criteria for the implant but the criteria for a meniscal allograft transplant in UK include: Patient must be younger than 55 years and physically active; missing more than half of a meniscus as a result of previous surgery or injury, or having a meniscus tear that cannot be repaired; persistent activity-related pain; knee with stable ligaments and normal alignment; no or minimal knee arthritis; BMI <30. We also understand that many patients with an injured meniscus or meniscectomy have already developed signs of osteoarthritis. We plan to explore how this patient group may benefit from the implant in terms of delaying the progression of osteoarthritis.
- Brindle et al. 2001. The Meniscus: Review of Basic Principles With Application to Surgery and Rehabilitation. Journal of Athletic Training, v.36(2), pp.160-169
- Jameson et al. 2011. The burden of arthroscopy of the knee: a contemporary analysis of data from the English NHS. J Bone Joint Surg Br, v.93(10), pp.1327-33.
- Maffulli et al. 2010. Meniscal Tears. Open Access Journal of Sports Medicine, v.1, pp.45–54
- McDermott et al. 2006. The consequences of meniscectomy. The Journal of Bone & Joint Surgery. Br, v.88(12), pp.1549-1556.
- Spencer et al. 2012. Meniscal scaffolds: early experience and review of the literature. Knee Dec;19(6), pp. 760-5
- Van Der Straeten et al. 2015. Long-Term Follow Up of Meniscal Allograft Transplantation. Paper #252 presented at American Academy of Orthopaedic Surgeons Annual Meeting March 24-28, 2015; Las Vegas.