Articular Cartilage Damage
Cartilage is a form of connective tissue that is more flexible than bone. Articular cartilage refers to the layer of cartilage covering the articulating ends of bones in a movable (synovial) joint.
How is Articular Cartilage damaged?
In a joint, the bone ends articulating with each other are protected by the articular cartilage cap. These cartilages bathe in a lubricating fluid that protects their surface from friction during joint movement and ensures smooth movement. Further, there are ligaments (bone-to-bone cordlike fibrous extensions) that hold the joining ends of the bone in the correct anatomical position during movement or in weight-bearing position so that no undue stresses accumulate at a specific point. This whole joint structure is enclosed in a capsule, which not only holds it in place, but is also the source of the lubricating fluid.
If this functional harmony is disrupted the whole joint suffers. Articular cartilage damage mostly occurs concomitantly with other joint problems, e.g.
- A torn or loose ligament
- Previous trauma/surgery altering joint mechanics
- Direct trauma to the cartilage during an accident or a sports injury
- Degenerative/ inflammatory joint disease such as rheumatoid arthritis, osteoarthritis, etc,
Cartilage serves as a shock absorber and protector of the underlying bone; although it lacks proper blood supply. It obtains nutrients from blood vessels lying nearby. This suffices for its needs during normal conditions, but it is unable to cope with undue stresses or trauma, and is slow to heal.
Articular cartilage damage is categorised as:
Grade I:cartilage becomes soft
Grade II:the surface becomes rough
Grade III: cartilage cracks
Grade IV: cartilage is disrupted, bone exposed
Furthermore, broken cartilage pieces may present as “loose bodies” in the joint space, causing pain and locking of the joint.
Articular cartilage has multiple functions:
- it provides a smooth gliding surface for ease of joint movement; it has one of the smoothest articulating surfaces, posing the least amount of friction
- it acts as a cushion between the articulating bone ends, absorbing the stresses and transferring the loads evenly to the underlying bone
- being more flexible than bone, it is better able to resist permanent deformation under mechanical loads
- Pain: localised and intermittent if only a small area of the cartilage is involved. It is more extensive and widespread when the damage is wider/deeper
- Swelling and stiffness of the joint
- Movement becomes difficult and painful
- Locking of the joint, or sometimes it may crumple
Symptoms are inconclusive as a stressed ligament or meniscus may cause the same disability.
X-rays provide little help, but help to rule out bone fractures or irregularities. MRI is an excellent tool for diagnosing cartilage and other soft tissue problems; however, it’s tedious and expensive.
Arthroscopy, although an invasive technique, is the method of choice for finding out articular cartilage damage. A small scope is inserted into the joint space through a cut in the skin, and the surface of cartilage is examined for any signs of wear.
Conservative treatment such as the RICE protocol, painkillers and physiotherapy provide relief in mild cases; nevertheless, surgery is often required.
Depending on the extent of damage, the surgical options include:
Debridement of the damaged surface::
Small roughened patches are shaved off until smooth; called “abrasion chondroplasty” and is performed arthroscopically.
Filling in the defects:
Radiofrequency ablation: another procedure to fill in deeper cracks. A special probe is introduced arthroscopically and the top layer is melted to smooth the surface and fill in the fissures.
Another way is to remove the damaged cartilage and fill the gap taking a cartilage/bone plug from another non-stressful area of the joint.
Stimulating new bone growth:
Autologus Chondrocyte Implantation:
This involves taking one’s own healthy cartilage cells, growing them in the lab and then implanting them back at the site of damaged cartilage. The damaged cartilage is first removed and the area cleaned for implantation. This leads to new cartilage growth.
It is a complicated procedure, requiring at least two operations; the operation for implantation is an open surgery. Many times there is overgrowth of the implanted tissue which may require another operation.
Microfracture is simple and can be performed in a single sitting right after diagnosing the cartilage condition. Small holes are made in the bone underneath the cartilage (remember cartilage lacks blood supply), the oozing blood from these holes accumulates in the defect and a clot is formed. Later on this clot solidifies into cartilage.
However, there are certain drawbacks with this procedure as well. The clot may not fill the gap completely, or the cartilage formed may not be as good in quality as the original one and may wear away in a few years.
In another technique, after performing the microfracture surgery, stem cells are injected at the site of the clot, which then aid in cartilage formation.
When the damage is extensive and repair unlikely, a part or whole of the cartilage may need to be replaced.
Knee Arthroplasty: Total replacement