Knee Problems: Articular Cartilage Damage

PROBLEMS Overview Overuse injuries Meniscal injuries Ligament injuries Articular cartilage damage Patellofemoral problems Other knee conditions Arthritis  SURGICAL PROCEDURES Arthroscopic surgery ACL reconstruction Partial knee replacement Total knee replacement   See Also: For more detailed information on articular cartilage problems please visit our cartilage web site: (under construction) www.cartilage.org.uk

What is Articular Cartilage?

Articular cartilage is a highly organized avascular tissue composed of chondrocytes embedded within an extracellular matrix of collagens, proteoglycans and noncollagenous proteins.

Its primary function is to enable the smooth articulation of joint surfaces, and to cushion compressive, tensile and shearing forces. Hyaline cartilage has one of the lowest coefficients of friction known for any surface to surface contact.

		Articular cartilage histology
Arthroscopic image of the small chondral defect of the femoral condyle

Why is articular cartilage repair necessary?

Cartilage is frequently injured, often as a result of sports related trauma, but due to its avascular nature, articular cartilage has very limited capacity for repair.

Partial-thickness defects in the articular cartilage do not heal spontaneously. Injuries of the articular cartilage that do not penetrate the subchondral bone do not heal and usually progress to the degeneration of the articular surface. Injuries that penetrate the subchondral bone undergo repair through the formation of fibrocartilage.

Deep osteochondral defect		Magnetic resonance image of the osteochondral defect of the femoral condyle

Although fibrocartilage fills and covers the defect, this is the wrong tissue from the biomechanical standpoint. The fibrocartilage is made to resist tension forces, while the hyaline cartilage is made to resist compression forces, to enable smooth articulation, and to withstand long-term variable cyclic load and shearing forces. Focal articular cartilage defects, often found in young adults, have been increasingly recognized as a cause of pain and functional problems.

There is more and more clinical evidence that full thickness articular cartilage defects continue to progress and deteriorate, although at a slow rate. Early diagnosis and treatment of these patients is recommended prior to the development of more advanced osteoarthritis.

In selecting methods of restoring the damaged articular surface, it is important to distinguish articular cartilage repair from articular cartilage regeneration. Repair refers to the healing of injured tissues or replacement of lost tissues by cell proliferation and synthesis of new extracellular matrix. Unfortunately, repaired articular cartilage generally fails to replicate the structure, composition, and function of normal articular cartilage. Regeneration in this context refers to the formation of an entirely new articulating surface that essentially duplicates the original articular cartilage. Therefore, the best we can do at present is to repair the chondral defect.

“It should be clear that cartilage does not yield its secrets easily and that inducing cartilage to heal is not simple. The tissue is difficult to work with, injuries to joint surface, whether traumatic or degenerative, are unforgiving, and the progression to osteoarthritis is sometimes so slow that we delude ourselves into thinking we are doing better than we are. It is important, however, to keep trying."
Dr Henry Mankin, Boston, USA.

Articular cartilage repair and reconstructive procedures:

Historically there have been many attempts to develop clinically useful procedures to repair damaged articular cartilage. However, most cartilage repair techniques have not proved entirely successful yet. At present, the treatment options are still limited and the long-term outcome is still uncertain.

The principal goals for surgical management of the symptomatic chondral and osteochondral defects are to reduce symptoms, improve joint congruence by restoring the joint surface with the best possible tissue, and to prevent additional cartilage deterioration. Although the need for surgical management is based on the patient's history, physical examination, and imaging studies, only knee arthroscopy will provide definitive information regarding the lesion's characteristics (ie, location, size and depth) and associated injuries (menisci and cruciate ligaments).

Based upon their anticipated outcome, it is helpful to define treatment options as being palliative, reparative, or restorative. First-line treatment for smaller injuries in lower-demand patients with limited symptoms can be treated effectively with palliative procedures such as Debridement and lavage. Relief, however, may be incomplete and short-lived. Mid-sized lesions in patients with moderate symptoms can be treated with a reparative procedure using a marrow-stimulating technique (Microfracture) in an effort to promote a fibrocartilage healing response.

Results in larger lesions in higher-demand patients, however, are generally less favorable and shorter-lived, independent of any prior treatments rendered. Larger defects, especially in higher-demand patients with significant symptoms who have failed less aggressive primary treatment options, are most effectively treated with a restorative treatment option such as Osteochondral Autologous Graft Transplantation (OATS) and Autologous Chondrocyte Implantation (ACI).

See also:
Chester Knee Clinic Articular Cartilage Patient Information

Debridement and lavage

Lavage (arthroscopic washout) is one of the most basic of traditional arthroscopic techniques. Dr Robert Jackson, the pioneer of arthroscopy in North America, observed that in the course of performing diagnostic arthroscopies patients with intra-articular knee problems had significant pain relief following joint lavage.

Exactly how arthroscopic lavage and debridement may help the early symptoms of osteoarthritis is still not entirely clear. Joint lavage removes loose intra-articular tissue debris and inflammatory mediators known to be generated by the synovial lining. In early stages, removing these degradative enzymes from the joint may allow chondrocyes to increase their biosynthetic activity.

Another mechanism by which lavage may relieve the symptoms and increase the resiliency and stiffness of articular cartilage is through changing the ionic environment within the synovial fluid. Lavage may provide some patients with advanced degenerative disease of the knee, which may last as long as 3 years.

However, the lavage provides only short-term symptomatic relief without correction of underlying pathology. If predisposing malalignment is not corrected, the beneficial effects seem to be minimised. The outcome of this simple procedure is generally insufficient for the active population, and benefits are short-lived.

Microfracture

This technique was developed and popularised by Dr Richard Stedman, from Vail, Colorado, USA. The treatment involves a disruption of subchondral bone in an attempt to induce bleeding (fibrin clot formation) and to initiate primitive stem cell migration from the bone marrow into the cartilage defect site.

Arthroscopic microfracture

These techniques utilise primitive stem cells, which are capable of differentiating into bone and cartilage under the influence of various biologic and mechanical intraarticular factors. The subchondral bone is penetrated in order to reach a zone of vascularisation, stimulating the formation of a fibrin clot containing pluripotential stem cells.

This clot differentiates and remodels, resulting in a fibrocartilaginous repair tissue. Although fibrocartilage often appears to offer the patient significant pain relief, this tissue lacks several key structural components to perform the mechanical functions, as a wear-resistant and as a weight-bearing surface. The fibrocartilage repair tissue does not produce a proper compressive stiffness against applied mechanical load and thus is subjected to an excessive deformation under physiological loading. This in turn causes a mechanical failure of the repaired tissue and eventually leads to a recurrence of degeneration of the repaired cartilage.

For more information on Microfracture see
Dr Steadman's website.

Osteochondral Autologous Transplantation (OATS)

	Osteochondral autograft transplantation

This technique was developed simultaneously by Dr L Hangody in Hungary and Mr V Bobic in the UK approximately 10 years ago.

Osteochondral autograft transplantation seems to be the only surgical technique that can restore the height and the shape of articulating surface in focal osteochondral defects, with composite autologous material that contains all necessary ingredients: hyaline articular cartilage, intact tidemark and a firm bone carrier.

However, like many other orthopaedic procedures that require the use of autologous tissues, osteochondral autograft transfer (or MosaicPlasty) is the "rob Peter to pay Paul" situation.

The main problem with this reconstructive technique is the limited availability of autografts, which significantly reduces the choice of treatable defects down to a small focal chondral defect, and a long-term donor morbidity in multiple donor sites.

Deep and large, crater-like osteochondral defects are not suitable for osteochondral autograft transplantation, mainly because of the limited availability of autologous osteochondral grafts. Also, it is difficult to reconstruct the subchondral bone and restore the contour of the defect area, and to cover the entire defect area with hyaline articular cartilage. The dead spaces between circular grafts, the lack of integration of donor and recipient hyaline cartilage, different orientation, thickness and mechanical properties of donor and recipient hyaline cartilage are further sources of clinical concern.

For more information on OATS please visit the ISAKOS website:

V Bobic: The Utilisation of Osteochondral Autografts
in the Treatment of Articular Cartilage Lesions

For more information on OATS instrumentation/surgical technique please see:

OATS Surgical Technique Video

For further information please visit this website:

The OATS Procedure. John Hopkins University, Baltimore, USA.

Autologous Chondrocyte Implantation (ACI)

This advanced FDA-approved technology allows cartilage cells, know as chondrocytes, to be harvested from your knee and cultured and multiplied. The fresh chondrocytes are then re-implanted in your knee and cause hyaline-like cartilage to repair the defect in articulating surface.

Chondral biopsy		ACI graft hypertrophy

The ACI restores the articular surface with your own hyaline-like cartilage without compromising the integrity of healthy tissue or the subchondral bone. This technology has demonstrated significant benefits in patients with a femoral focal lesion, in terms of diminished pain and improved function.

If you have this type of lesion, then ACI may be an appropriate treatment option. However, this expensive tissue engineering technology is not available in most NHS hospitals, following the recommendation of the NHS NICE (www.nice.org.uk).

Graft hypertrophy is relatively frequent problem and it may require further arthroscopic surgery. The procedure consists of two steps:

1. The first is the harvesting of some healthy cartilage from you knee, which is done arthroscopically. This sample of cartilage is sent to special tissue-engineering laboratory, and it is used to grow new chondrocytes, which are sent back to us after 4 to 6 weeks.
2. The second step is the re-implantation of the cultured chondrocytes. This procedure is done through an arthrotomy (open knee surgery). Basically, the surgeon debrides the cartilage defect down to the subchondral bone plate and prepares the recipient site. The defect area is covered with autologous periosteal or tissue-engineered collagen membrane, which is stitched in place and sealed with fibrin glue. The chondrocyte suspension is injected into this ”bioactive chamber”. The next step is final closure by suturing and applying fibrin adhesive. Within this chamber the cells will undergo re-differentiation and will be stimulated by growth factors to proliferate and to regenerate their specific cartilage matrix.

For more information on ACI surgery and rehabilitation please see this article:

Tom Minas, MD.
Autologous Chondrocyte Implantation for Chondral Defects of the Knee.
Department of Orthopaedic Surgery and Cartilage Repair Center, Brigham & Women's Hospital, Boston, Massachusetts, USA.

and visit the website: www.cartilagerepaircenter.org

Downloads:

For further information on ACI surgery please download: Chester Knee Clinic ACI Patient and GP Information Stanmore ACI vs. MACI Patient and GP Information Sheet ACI rehabilitation information: To get maximum benefit from ACI surgery, you should adhere to specific rehabilitation programme. This may include weight-bearing restrictions, limited range of motion, and numerous muscle strengthening exercises which will progress very slowly initially. However, when you successfully complete your rehabilitation, you should be able to resume normal activities, including most sports. The original Gothenburg program Carticell ACI rehabilitation guide TGX ChondroCelect Rehabilitation Program Chester Knee Clinic Femoral and Tibial ACI Rehabilitation Guide Chester Knee Clinic Patellar and Trochlear ACI Rehabilitation Guide

More Information on ACI:

For more information on Autologous Chondrocyte Implantation (ACI) visit:

TiGenix ChondroCelect™ Geistlich Chondro-Gide® ACI     Genzyme Biosurgery Carticell® ACI Verigen ACI and MACI

Further Information on Cartilage Repair:

Randall R. Wroble, MD: "Articular Cartilage Injury and Autologous Chondrocyte Implantation - Which Patients Might Benefit?" www.physsportsmed.com/issues/2000/11_00/wroble.htm

Site last updated on: 20 June 2008

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