Articular cartilage defects rarely heal spontaneously. Although some patients initially may not have clinically significant problems, most will ultimately develop degenerative changes associated with cartilage damage.

There are many ways in which articular cartilage can be damaged. Treatment of cartilage lesions aims to relieve pain, reduce effusions and inflammation, restore function, reduce disability and postpone or alleviate the need for prosthetic replacement.

There appears to have been a sudden regeneration of interest in chondral defects (defects in the cartilages). Many techniques have been used and include spongialization, abrasions, drilling, tissue autografts, allografts and cell transplantation.

Arthroscopic abrasion arthroplasty
Arthroscopic abrasion arthroplasty, introduced approximately 20 years ago, was an alternative to open debridement procedures. It was suitable for older patients with degenerative arthritis of the knee.

Microfracture technique
This technique was developed to enhance chondral resurfacing by providing a suitable environment for new tissue formation and taking advantage of the body's own healing potential.

The microfracture technique offers many advantages over concentrated drilling procedures. It is more biological and is an attempt to produce articular cartilage.

Mosaicplasty
Autogenous osteochondral grafting (bone and cartilage graft) represents an innovative and promising treatment for chondral and osteochondral articular cartilage defects of the weight bearing surfaces.

A multicentric comparative, prospective evaluation of 413 arthroscopic resurfacing procedures revealed that mosaicplasty offered the most favourable long term clinical outcome. Intermediate term evaluation of femoral condyle implantation (3 to 6 years follow-up) and talar mosaicplasties (3 to 7 years follow-up) confirmed the durability of the early results.

The role of periosteum in cartilage repair
Periosteum (dense layer of connective tissue around a bone) has been used alone for biological resurfacing in humans for more than a decade.

Successful results were first reported in four out of four patients with osteochondritis dissecans (painful condition where pieces of articular cartilage become detached from the joint surface) and one patient with avascular necrosis (condition where tissue cells die because their supply of blood has been cut) after 1 year follow-up. Four patients had no pain and one experienced a dull aching.

Periosteal grafts have also been used to resurface patellar defects in some patients.

Periosteal grafting is now indicated for patients younger than 35 years with isolated chondral or osteochondral defects attributable to trauma or osteochondritis dissecans who have not responded to arthroscopic microfracture.

The advantages of periosteal arthroplasty over mosaicplasty and autologous chondrocyte transplantation are that it causes minimal donor site morbidity and can be done in one operation without the additional expense of culturing the cells.

Autologous chondrocytes used for articular cartilage repair
Articular chondrocytes are responsible for unique features of articular cartilage; therefore, it seems rational to use committed chondrocytes to repair a cartilaginous defect. From arthroscopically harvested cartilage, chondrocytes can be isolated by enzymatic digestion and expanded in culture 20 to 50 times the initial number of cells.

Cultured autologous chondrocytes covered with a periosteal membrane were first used 5 years ago to treat patients with chronic disabling symptoms of articular cartilage lesions of the knee.

This technique seemed most successful in patients who had injuries on the femoral surfaces that produced one localised deep cartilage lesion.

In the future, one can expect the use of chondrocytes or other chondrogenic cells for induced cartilage repair to take two directions:

1. Continuous use of implantation of in-vitro cultured cells with sutured top membrane consisting of a reabsorbable material with cells sealed in the membrane (sandwich technique); or

2. In-vitro construction of an osteochondral plug (composite graft with cartilaginous and osseous parts).

Current research is focusing on in-vitro regeneration of a three dimensional cartilage matrix from articular chondrocytes, sealed on a bioreabsorbable polymeric scaffold. These scaffolds can be manufactured in an injectable form for a minimally invasive procedure or in a preformed state to treat large irreparable lesions, including those due to arthritis.

The ultimate goal of tissue engineering is to recapitulate normal chondrogenesis to create histologically and functionally normal tissue.

Summary
Cartilage repair knowledge continues to expand at a rapid rate.

Options available to surgeons for treating articular cartilage defects are:

• Marrow stimulating treatment
• Abrasive arthroplasty
• Microfracture
• Autologous osteochondral transplant
• Periosteal patches with or without autologous condrocyte cell implantation
• Osteochondral allograft

Marrow stimulation techniques are indicated for small lesions between 2 to 4 cm2 as a primary treatment. They are cost effective and provide good short term results.

An alternative for patients who do not respond to marrow stimulation may be autologous osteochondral transplantation.

For lesions greater than 2 to 4.5 cm2 there appears to be a gradual deterioration of the results of marrow stimulation and autologous osteochondral plug transfer. For these lesions, either periosteal patches with or without autologous chondrocyte cell implantation or osteochondral allografts should be used.

Conclusion
Cartilage restoration is a rapidly evolving field and management options must be continually reassessed.

Current research has demonstrated the ability to form hyaline cartilage in-vitro. This cartilage then with an appropriate scaffold and growth factor, would then be available for transfer directly to articular cartilage defects. It is important for orthopaedic surgeons to be aware of the latest developments so that they can provide the best and most cost effective treatment.

Professor Kamal Bose is a Consultant Orthopaedic Surgeon of Mount Elizabeth Medical Centre and Director of Research in the Department of Orthopaedic Surgery, Singapore General Hospital, Singapore and Professor of Research & Development, Mechanical and Production Engineering, Nanyang Technological University.

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