What is articular cartilage?
Articular cartilage is the shiny, white surface that covers the ends of most bones. Articular cartilage protects bones during movement by dispersing the force applied to a joint and allowing the joint surfaces to glide smoothly with less friction. This covering is only a few millimeters thick, and has no blood supply to facilitate the healing process. Therefore, if it gets damaged, there is very little capacity for healing.
What is an articular cartilage defect in the knee?
An articular cartilage injury (also known as a chondral injury) may occur as a result of a pivot or twist on a bent knee, a direct blow to the knee, or wear and tear as a patient gets older. Cartilage defects may accompany an injury to a ligament, such as the anterior cruciate ligament (ACL). Small pieces of the articular cartilage can break off and float around in the knee as loose bodies, causing locking, catching, and/or swelling. For the majority of patients, there is no clear history of a specific causative injury. Articular cartilage injury can actually result from a series of minor injuries that have occurred over time.
What are the symptoms of a cartilage defect?
The symptoms of an articular cartilage injury are not as obvious as those of a meniscus tear or ligament injury, and swelling is often the only symptom. Other symptoms might include:
- Pain – difficulty with prolonged walking or climbing stairs can occur
- Giving way – The knee may occasionally buckle or give way when weight is placed upon it
- Locking or catching – The loose, floating pieces of cartilage may block the joint as it bends, causing the knee to lock
- Noise – The knee may make noise during motion, especially if the cartilage on the back of the kneecap is damaged
How is articular cartilage damage diagnosed?
Articular cartilage injuries can be difficult to diagnose. Physical examination may show a swollen knee, but typically the exam is normal. X-ray may show a decrease in joint space, indicating advanced cartilage loss, and MRI imaging may reveal thinning or softened cartilage. Articular cartilage damage is most reliably diagnosed with a knee arthroscopy where a camera is used to visually assess the damage.
Chondral damage is graded from mild to severe, and all grades can have characteristics of osteoarthritis.
- Grade 1 – The cartilage becomes soft in the earliest form of damage
- Grades 2 and 3 – As the condition worsens, the cartilage may become fibrillated with a shredded appearance. The grade of injury depends on the size and thickness of the defect
- Grade 4 – The cartilage may wear away completely, leaving the underlying bone exposed. When the involved areas are large, pain usually becomes more severe and causes limitations in activity
What is the treatment for articular cartilage defects?
The treatment of chondral damage in the knee typically depends on the specific location and size of the defect. In some instances, the area of articular cartilage damage may be small enough to trial a period of conservation measures and rehabilitation. These patients may benefit from activity modification, anti-inflammatories, strengthening in physical therapy, and joint injections.
For patients with large or advanced cartilage defects, surgical intervention may be necessary to prevent further joint damage. The procedure chosen varies greatly on the location and overall size of the defect. Articular cartilage defect surgeries include:
- Microfracture – Creating small holes in the subchondral bone to allow for healing cells to flow into the defect and stimulate fibrocartilage formation
- Autologous Chondrocyte Implantation (ACI) – This is a two-step procedure where articular cartilage is biopsied from the patient’s knee during the initial arthroscopy and sent to a lab where the chondrocytes (cartilage cells) are processed and grown. When ready, the cells are re-implanted into the cartilage defect under a special patch to facilitate healing
- Osteochondral autograft/allograft transfer (OATS) – Replaces the defect with a plug of bone and cartilage from a donor (allograft). This procedure is ideal for large defects and in situations where the underlying bone is damaged along with the cartilage