Injuries to soft tissue, such as cartilage, skin, muscle, bone, tendon and ligament, where the tissue has been injured or traumatized frequently require surgical intervention to repair the damage and facilitate healing. Such surgical repairs can include suturing or otherwise repairing the damaged tissue with known medical devices, augmenting the damaged tissue with other tissue, using an implant, a graft or any combination of these techniques.
One common example of cartilage injury is damage to the menisci of a knee joint. There are two menisci of the knee joint, a medial and a lateral meniscus. Each meniscus is a biconcave, fibrocartilage tissue that is interposed between the femur and tibia of the leg. In addition to the menisci of the knee joint, meniscal cartilage can also be found in the acromioclavicular joint, i.e., the joint between the clavicle and the acromion of the scapula, in the stemoclavicular joint, i.e., the joint between the clavicle and the sternum, and in the temporomandibular joint, i.e., the joint of the lower jaw. The primary functions of meniscal cartilage are to bear loads, to absorb shock and to stabilize a joint. If not treated properly, an injury to the meniscus, such as a “bucket-handle tear” in the knee joint, may lead to the development of osteoarthritis. Current conventional treatment modalities for damaged meniscal cartilage include the removal and/or surgical repair of the damaged cartilage.
One common type of tissue injury at the knee joint involves damage to articular cartilage, a non-vascular, resilient, and flexible connective tissue. Cartilage typically acts as a “shock-absorber” at articulating joints, but some types of cartilage provide support to tubular structures, such as for example, the larynx, air passages, and the ears. In general, cartilage tissue is comprised of cartilage cells, known as chondrocytes, located in an extracellular matrix, which contains collagen, a structural scaffold, and aggrecan, a space-filling proteoglycan. Several types of cartilage can be found in the body, including hyaline cartilage, fibrocartilage and elastic cartilage. Hyaline cartilage can appear in the body as distinct pieces, or alternatively, this type of cartilage can be found fused to the articular ends of bones. Hyaline cartilage is generally found in the body as articular cartilage, costal cartilage, and temporary cartilage (i.e., cartilage that is ultimately converted to bone through the process of ossification). Fibrocartilage is a transitional tissue that is typically located between tendon and bone, bone and bone, and/or hyaline cartilage and hyaline cartilage. Elastic cartilage, which contains elastic fibers distributed throughout the extracellular matrix, is typically found in the epliglottis, the ears and the nose.
One common example of hyaline cartilage injury is a traumatic focal articular cartilage defect to the knee. A strong mechanical or loading impact to the joint can result in the complete or partial detachment or removal of a cartilage fragment of various size and shape. Damaged articular cartilage can severely restrict joint function, cause debilitating pain and may result in long term chronic diseases such as osteoarthritis, which gradually destroys the cartilage and underlying bone of the joint. Injuries to the articular cartilage tissue will not heal spontaneously and require surgical intervention if symptomatic. The current modality of treatment consists of lavage, removal of partially or completely unattached tissue fragments. In addition, the surgeon will often use a variety of methods such as abrasion, drilling or microfractures, to induce bleeding into the cartilage defect and formation of a clot. It is believed that the cells coming from the marrow will form a scar-like tissue called fibrocartilage that can provide temporary relief to some symptoms. Unfortunately, the fibrocartilage tissue does not have the same mechanical properties as hyaline cartilage and degrades faster over time as a consequence of wear. Patients typically have to undergo repeated surgical procedures to relieve reoccurring symptoms, though this type of surgery does not delay or prevent further deterioration of the cartilage surface.
More recently, experimental approaches involving the implantation of autologous chondrocytes have been used with increasing frequency. The process involves the harvest of a small biopsy of articular cartilage in a first surgical procedure, which is then transported to a laboratory specialized in cell culture for amplification. The tissue biopsy is treated with enzymes that will release the chondrocyte cells from the matrix, and the isolated cells will be grown for a period of 3 to 4 weeks using standard tissue culture techniques. Once the cell population has reached a target number, the cells are sent back to the surgeon for implantation during a second surgical procedure. This manual labor-intense process is extremely costly and time consuming. Although, the clinical data suggest long term benefit for the patient, the prohibitive cost of the procedure combined with the traumatic impact of two surgical procedures to the knee, has hampered reasonable acceptance of this technique among patients and doctors.
Other known surgical techniques for the surgical treatment of damaged tissue (e.g., cartilage, meniscal cartilage, ligaments, tendons and skin) include the use of surgical implants. Various surgical implants are known and have been used in surgical procedures to help achieve these benefits. For example, it is known to use various devices and techniques for creating implants having isolated cells loaded onto a delivery vehicle. Such cell-seeded implants are used in an in vitro method of making and/or repairing cartilage by growing cartilaginous structures that consist of chondrocytes seeded onto biodegradable, biocompatible fibrous polymeric matrices. Such methods also require the initial isolation of chondrocytes from cartilaginous tissue prior to the chondrocytes being seeded onto the polymeric matrices. Other techniques for repairing damaged tissue employ implants having stem or progenitor cells that are used to produce the desired tissue. For example, it is known to use stem or progenitor cells, such as the cells within fatty tissue, muscle, or bone marrow, to regenerate bone and/or cartilage in a patient. The stem cells are removed from the patient and placed in an environment favorable to cartilage formation, thereby inducing the fatty tissue cells to proliferate and to create a different type of cell, such as for example, cartilage cells.
While these current treatments address focal point defects, they are not tailored for treating large surface areas of diseased or damaged tissue (e.g., cartilage) that occur with the progression of degenerative joint diseases such as osteoarthritis. Osteoarthritis is a long term degenerative joint disease that results from the breakdown of the joint's cartilage. In patients suffering from osteoarthritis, as the cartilage wears down, the bones rub against each other, damaging the bones and causing pain and limited movement of the joint. Swelling and stiffness of the joint can also occur, along with the creation of bony spurs that can decrease the flexibility in the affected joint. If the disease is advanced or severe enough, the bones of the joint may grow into each other, or fuse together, and result in complete loss of movement.
At the present time, there is no cure for osteoarthritis. Current treatment options focus on slowing down the progression of the disease, pain management and/or improving joint movement. Corticosteroids, glucocorticosteroids, aspirin, ibuprofen, or acetaminophen can be administered, as well as heat/cold therapy for the temporary relief of pain. A typical treatment regimen can include, in addition to the administration of therapeutic agents listed above, physical therapy and regular exercise to keep the joints flexible and improve muscle strength. Weight loss can also reduce excess stress on weight-bearing joints, while splints can be used to protect the joint and prevent further stress or strain. If all attempted treatments fail, surgery may be necessary to fuse, replace or stop deformation in the joints and relieve chronic pain.
Since osteoarthritis is a chronic disease that has a fairly long progression window before a total knee replacement surgery can be recommended, there exists a need for a way to provide early surgical or medical intervention to arrest the progression, and possibly enable the prevention, of the joint's destruction. Furthermore, because current surgical devices and methods of treatment involving osteochondral transplantation and chondrocyte transplantation suffer from setbacks such as incomplete tissue integration and tedious implant manufacturing process and prolonged rehabilitation time, there exists a need for a surgical solution for repairing a cartilage defect spanning a large surface area which overcomes the aforementioned problems.