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Articular Cartilage Lesions

Articular cartilage wraps the end of the bones and has a smooth, slick surface that allows the bones to slide over one another without friction or direct contact - minimizing pressure during movement. While cartilage tissue is void of nerves, worn or torn areas on the cartilage may result in inflammation of the joint and cause pain. Injuries to the articular cartilage often present as tears or holes in the surface of the cartilage. Lesions can vary in thickness of injury. Most superficial injuries, or partial thickness injuries, are not serious. If the lesion is large, full thickness, and exposes the bone below, it could result in arthritis.

Articular cartilage is injured when the knee joint is compressed under heavy load or when angular or shear forces are applied to the surface. The result is one of several possible lesions...softening, fissuring, fragmenting or complete removal of the cartilage covering. Symptoms include pain, swelling and subsequent loss of joint function.

Adult articular cartilage does not repair itself. The reason is that the chondrocytes have little mobility and there is no blood supply to the matrix to provide healing elements. The above mentioned lesions then, are more or less permanent. Worse yet, they progress from softening to complete destruction of the joint if left untreated.

The symptoms of an articular cartilage injury is not as obvious as a torn meniscus or ligament.

1. Intermittent Swelling: Sometimes the only symptom. The loose fragments of cartilage floating in the knee can cause swelling.

2. Pain: Pain may occur with prolonged walking or climbing stairs.

3. Loss of stability: The knee may become unstable when walking.

4. Block: loose cartilage fragments floating within the knee can be trapped when the knee is flexed causing the blockage of this.

5. Noise: The knee may crackle or make noise during movement, especially if it is the cartilage of the patella which is damaged.

It can be difficult to diagnose articular cartilage injury. Physical examination may show swelling of the knee, but the test may be normal.

X-rays may be normal in most cases because only the bone is visible on X-rays. When the loss of cartilage is advanced there is a decrease in space between two bone surfaces. Loose bone fragments can be detected in a condition called osteochondritis dissecans (OCD), in which a piece of bone between the articular cartilage.

MRI can reveal the different changes in the cartilage, from early stages of cartilage disease, such as softening, to complete loss of this or osteochondral loose fragments.

Diagnosing articular cartilage damage is more reliable with an arthroscopic exam. In this procedure, a tiny fiberoptic lens inserted into the joint with fully observed inside the knee.

Cartilage injuries are described and classified based on the location of injury, size of the injury, and the depth of the injury. The type of surgery necessary largely depends on the aforementioned factors.

There are four grades of lesions to take into account when considering surgery.

Grade 1: Softening
Grade 2: Fibrillation
Grade 3: Partial thickness
Grade 4: Full thickness with exposed bone

In addition to the characteristics of the articular cartilage lesion in the knee, the following factors are considered when planning a surgery for articular cartilage:

STABILITY: Instability of the knee can be a precipitating factor for cartilage injury and must be treated in conjunction with appropriate surgery for the cartilage lesion. For example, an ACL deficient knee is treated with an ACL reconstruction at the time of the cartilage restoration surgery to restore stability to the knee and protect the articular cartilage repair.

ALIGNMENT: Malalignment can be a risk factor for articular cartilage injury. Malalignment off the knee causes weight to be distributed unevenly across the inner (medial) or outer (lateral) aspect of the knee. If the cartilage lesion is in the knee compartment bearing a disproportionate amount of body weight, the knee is treated with a knee alignment correcting procedure (knee osteotomy) in conjunction with cartilage restoration procedure.

MENISCUS: Meniscus injuries can coexist with articular cartilage injuries. Removal of small pieces of torn meniscus, meniscal repair, and even meniscal transplantation are performed if necessary during articular cartilage restoration surgery.

KNEE ARTHROSCOPY/DEBRIDEMENT

Small articular cartilage lesions that do not involve the full thickness of the cartilage (grade 2 or 3) can cause mechanical symptoms and swelling. Knee arthroscopy with debridement of the lesion removes unstable flaps of cartilage and loose bodies and can result in symptomatic improvement in the knee, especially when surrounding cartilage is normal. Weight bearing is allowed with crutches immediately and return to sports can be expected after physical therapy for 6-8 weeks.

MICROFRACTURE

When an articular lesion extends down to bone, it is termed full thickness or grade 4. Microfracture is considered by many sports medicine knee surgeons as a first line cartilage restoration procedure, particularly for small lesions less than 2cm. This surgery is performed arthroscopically and involves the following steps:

1. Removal of loose cartilage flaps to create a lesion that is well shouldered

2. Removing the calcified cartilage layer to expose the subchondral bone

3. Penetration of the bone with a specialized instrument to access the bone marrow

4. The bone marrow forms a clot which fills in the defect in the articular cartilage with scar cartilage.

Osteochondral autografts have been examined as an alternative to allografts for the treatment of osteochondral defects. Two related procedures have been investigated: (i) mosaicplasty, and (ii) the osteochondral autograft transfer system (OATS). Mosaicplasty is a relatively new, reconstructive bone grafting procedure for the treatment of articular defects of the knee, ankle and hip. In general, treatment of articular defect of the knee by mosaicplasty entails transplantation of small cylindrical osteochondral grafts (4 to 10 mm in diameter, 15 to 20 mm deep) from the less weight-bearing periphery of the femoral condyles at the level of the patello-femoral joint, and transplanting them in a mosaic-like fashion into a prepared defect site on the weight-bearing surfaces of the same knee. Its goal is to produce a smooth gliding articular surface of hyaline or hyaline-like cartilage in weight-bearing surfaces of the knee. Mosaicplasty is carried out either by an open approach or arthroscopically if the defect/lesion is small and not more than 4 to 6 grafts are needed. Both open and arthroscopic mosaicplasty require a relatively short rehabilitation period - normal daily activity can be allowed after 5 to 8 weeks.

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