What is articular cartilage?
Articular Cartilage is the smooth shiny white tissue lining the end of bones where these bones connect to form joints. It ranges from a millimetre in thickness to several millimetres thick depending on the on the load across the joint. It acts as a cushioning material and allows the ends of the femur (thighbone), tibia (shinbone) and patella (kneecap) to move freely with minimal friction. It is a highly specialised tissue and does not receive a direct blood supply thereby relying on the synovial fluid (joint fluid) to receive its nutrition and oxygen. As a result, if damaged or worn, it tends not to heal on its own.
What causes damage to articular cartilage?
Articular cartilage can degenerate with increasing age, wear and tear, or trauma such as a fall or twist. Occasionally it may degenerate with its underlying bone spontaneously. This results in the joints rubbing during movement and a lack of cushioning with weight causing pain, inflammation and swelling. Pain may be localised, and patients may also complain of the knee catching with occasional giving way and locking.
How is articular cartilage damage diagnosed?
The diagnosis is made according to symptoms, mechanism of injury if applicable and a physical examination. An MRI scan is particularly accurate in quantifying the size and depth and location of the articular cartilage lesion.
How is articular cartilage damage treated or repaired?
Cartilage repair refers to surgical procedures where orthopaedic surgeons stimulate the growth of new cartilage to restore normal or near normal function. Degenerate conditions can be delayed or potentially prevented with this type of procedure. The aim of cartilage replacement therapies is to stimulate growth of new ‘hyaline-like’ cartilage. Various arthroscopic procedures which can have an active role in cartilage replacement include:
Arthroscopic Abrasion or Radiofrequency Chondroplasty. This involves the use of a high speed shaver or a special radiofrequency probe to either shave damaged and frayed articular cartilage flaps or superheat them to produce a smooth stable surface.
Microfracture surgery (pick chondroplasty) uses fine tipped picks to make multiple small “pepperpot” holes that breach the subchondral plate and produce channels between the deeper underlying bone and the articular surface. This is a form of a marrow stimulation technique and induces bleeding and therefore a healing response. This generates a fibrocartilage cap over the defect.
Subchondral Drilling uses a very narrow drill to achieve the same as microfracture. It allows for deeper penetration into the bone to produce a fibrocartilage cap.
Autologous Chondrocyte Implantation (ACI) In this method, healthy cartilage cells are removed using an arthroscopic technique and are cultured in a laboratory. Cultured cells can then be implanted in the damaged area with an open surgical technique involving a second surgical procedure. The cells are covered with a collagen matrix/membrane. If the cultured cells are impregnated into the matrix before application to the chondral (articular cartilage) defect this is referred to as MACI (Matrix Autologous Chondrocyte Implantation).
Bioabsorbable Matrix/Scaffold. These are scaffold or matrices that are applied to the cartilage defect often after preparation of the lesion with a marrow stimulation technique such as subchondral drilling or microfracture. The matrix is then applied often after mixing with aspirate (fluid taken) from the bone marrow or PRP (Platelet Rich Plasma) and fixed to cover the defect with an absorbable fibrin glue as a sealant. The matrix then captures and contains the mesenchymal cells (often referred to as Stem or Stromal Cells) from the bone marrow to remain in the defect and mature into new cartilage tissue.
Recovery from any of these procedures requires a period of time non-weight bearing, mobilising with crutches and wearing a range of motion knee brace before progressing onto a full course of physiotherapy rehabilitation.