The normal meniscus in the knee are two crescent discs that consist of cartilage-like tissue. The menisci are positioned between the thighbone (femur) and shinbone (tibia). On cross-section, perpendicular to the surface, they are wedge-shaped. The menisci play a role in evenly distribution and transmission of your body load over the joint and have a shock-absorbing (cushioning) function. Stabilization and lubrication of the knee joint are other functions of the meniscus. Each knee has two menisci, a medial (inner) meniscus and a lateral (outside) meniscus . The medial and lateral menisci are different. The lateral meniscus covers a larger area of the tibia plateau, is wider and more important for weight transfer (approximately 70%). The medial meniscus provides approximately 50% weight transfer, is c-shaped, located towards the inside of the knee and is more rigidly fixed and more important for stability. This makes the medial meniscus less mobile than the lateral meniscus. This disparity in motion explains why medial meniscus injuries occur three times more frequently than lateral, which was the primary reason for ATRO Medical to first start development of a medial meniscus replacement.
Meniscus tears are among the most common knee injuries. These can be acute, when the tear is due to trauma (forced movement or rotation) or chronic (degenerative), which usually occur in older patients when the meniscus has gradually weakened and has become degenerative, losing its mechanical properties and shock absorbing function .
When a tear in the meniscus is diagnosed, the first question to be asked is whether this tear can be sutured. The meniscus lesion type, size and location determine whether the surgeon can repair the tear by suturing. If the meniscus cannot be sutured, the torn parts of the meniscus are often removed by meniscectomy (partial or total removal of the meniscus). Although a meniscectomy in general reduces pain and restores knee function immediately after surgery, the underlying problem is the deficient meniscus tissue that increases the local pressure on the cartilage of the tibia and femur, which leads to cartilage degeneration and increased risk to knee osteoarthritis and future total knee replacement .
Knee osteoarthritis is a chronic joint disease that results from breakdown and wear of joint cartilage and ultimately the underlying bone. This decreases the natural cushioning in the knee joint, resulting in chronic joint pain, stiffness and swelling of the knee. These disease symptoms seriously affect the ability to move and people’s daily life activities overall.
Currently the treatment options for knee pain after meniscectomy are limited to replacement with allograft (donor meniscus) tissue, bone realignment surgery (High Tibial Osteotomy) and total knee replacement surgery. Allografts have shown to successfully reduce pain and improve knee function in patients with meniscectomy. However, their availability is limited, and meniscal allograft transplantation is generally restricted to patients younger than 50 years [4, 5] .Total knee replacement surgeries, where a full metal knee joint replaces the native knee joint, are only possible for patients with severe articular cartilage damage. Due to its limited durability total knee joint replacement are more suitable for older patients as younger patients will require revision surgery later on, which is a more complex procedure with a high rate of complications . A meniscus implant that is able to preserve the patient’s knee and delay total knee replacement as long as possible may serve as an alternative to meniscal allografts.
The Trammpolin® meniscus prosthesis system is an implant system for the medial meniscus compartment and consists of a meniscus implant (Trammpolin® meniscus prosthesis), two fixation screws to attach the horns of the meniscus prosthesis to the tibia plateau in the knee and accessory surgical instruments to facilitate the operation and to determine the correct implant size and fixation screws positioning.
The Trammpolin® meniscus prosthesis is an anatomically shaped, non-biodegradable polymer meniscus implant designed to mimic the function of the natural meniscus and functions as a shock absorber by adequate load distribution within the knee joint. The Trammpolin® meniscus prosthesis with the two fixation screws are implanted during an arthroscopic procedure.
The Trammpolin® meniscus prosthesis is made from a medical grade polymer with excellent mechanical and friction properties, thereby evenly distributing loads over the joint cartilage and having a shock-absorbing (cushioning) function. This polymer polycarbonate urethane (PCU) has been extensive history of safe use as orthopedic, spine and cardiac implants. After implantation and rehabilitation, the Trammpolin® meniscusprosthesis is intended to provide relieve of the chronic pain and full functionality of the knee. The treatment of meniscus defects with a meniscus implant can provide an additional treatment option next to meniscus tear surgical repair and the donor meniscus and delays the need for a total knee replacement for patients with persistent knee pain following medial meniscus surgery.
Trammpolin® meniscus prosthesis is a potential solution for patients suffering from knee joint pain associated with loss of medial meniscus function when this is caused by meniscectomy. Biomechanical models, computer simulations and animal experiments showed similar biomechanical performance as a meniscus allograft [7-12].