Cartilage Injury and Repair

Author: Dr C. Benjamin Ma University of California San Francisco 2008-07-28
Cartilage Injury and repair: Current treatment of cartilage injuries Cartilage Injuries are common joint injuries and can lead to significant pain and suffering. We will go over the signs and symptoms of cartilage injuries and also some of the common and latest treatment available.

Overview

            Articular cartilage is the white shiny covering over the ends of the bone.  Articular cartilage has a very unique feature as it is smooth yet tough, and serves well as the bearing surfaces of the joint. Over time, however, cartilage degeneration can lead to osteoarthritis, pain, and disability of the joint.

            Articular cartilage is produced by chondrocytes, which are cells that divide or multiply very slowly.  This is one of the reasons that articular cartilage injuries do not repair well and can lead to continued degeneration and deterioration of joint condition.  Skin, on the other hand, is formed by fibroblasts, which have a high turnover rate and thus has a great potential to heal. 

            Articular cartilage injuries can be focal, which is localized and contained, or global, which can lead to joint osteoarthritis.  Osteoarthritis is a general term used to describe the wearing out of the articular cartilage.  End-stage osteoarthritis, also known as bone-on-bone arthritis, describes the condition when all of the articular cartilage has worn off.  When this happens, the bone that is covered by the cartilage is exposed.  Nerve endings are not present in articular cartilage but are present in the underlying bone.  When bone is exposed, to the patient may begin to experience pain and joint disability.  Unstable cartilage can also lead to swelling of the joint. 

            In this KNOL, we will outline some of the signs and symptoms of articular cartilage injuries and current repair options.

Cartilage Injury

Causes

            There are a variety of reasons that cartilage may be injured.  Most of the injuries are traumatic:

·        Joint dislocation

·        Ligament tear

·        Meniscus tear

·        Fall/impact

·        Infection

·        Inflammation (Gout attack, rheumatoid arthritis)

Most cartilage injuries will lead to swelling and pain in the joint.  The swelling can persist with the presence of unstable cartilage.  Unstable cartilage can lead to irritation of the synovium, which is the covering around the joint, causing excessive secretion of synovial fluid (joint fluid), which causes swelling.

The most common joint with symptomatic cartilage injuries are knee, shoulder, elbow, hip and knee.  All synovial joints can have cartilage injuries, however, the management of smaller joint cartilage injuries are most limited.

Recognition of worrisome joint swelling

            Joint swelling that is present for more than 1 day following injury is concerning.  The injured joint should be evaluated by a clinician to rule out fracture, ligament and meniscus injury, or cartilage injury.  The diagnosis of fracture can be established using plain radiographs, or X-rays.  Ligament and meniscus injuries can be diagnosed with clinical examination or magnetic resonance imaging (MRI) scan.  The best diagnostic tool for cartilage injury is MRI scan.  Advanced MRI scans are very accurate in diagnosing full thickness or partial thickness cartilage injuries. These are helpful to determine the significance of the cartilage injuries. Significant research has also focused on quantifying the amount of cartilage left, using quantitative MRI.

            The onset of joint swelling provides clues as to the type of joint injury that has been sustained, as displayed in the following table:

Onset of joint swelling	Causes
Immediate (less than 1 hour)	Fracture, anterior cruciate ligament, or posterior cruciate ligament tear, joint dislocation
Subacute (2-6 hours)	Meniscus, cartilage
Chronic	Osteoarthritis, unstable cartilage, infection

Treatment

Medical treatment

            Anti-inflammatory medication or systemic steroids can be taken to decrease inflammation. Common medications include ibuprofen, motrin, naproxyn and methylprednisolone.  These systemic treatments can affect the entire body, not just the involved joint.  They are helpful when the patient has generalized inflammation, such as inflammatory arthritis (rheumatoid arthritis) or multiple joint aches.  Ice or cryotherapy can also be used to decrease swelling of the joint.  Cool temperature leads to decreased inflammation and lower cellular activity and can decrease symptoms.  When icing the joint, it is important to keep the put a layer of cooling device or ice

Injection

            Corticosteroid injection directly into the joint can be used to suppress inflammation and thus, decrease pain.  Other injections, such as hyaluronic acid, can also be used.  The latter are also known as artificial joint fluid injections, which are products that have similar composition to human synovial  fluid.  These can act as lubricants for the knee and decrease swelling or irritation.  However, the injection itself does not treat the underlying condition.  Unstable cartilage or loose cartilage fragment can still lead to persistent swelling after the effect of the injections has worn off. The effect of injections is dependent on the severity of the problem.  It normally takes 2-3 days to come into effect and may last up to weeks and months.

Surgery

Cartilage injuries or unstable cartilage can be treated surgically.  Most surgical procedures are recommended for high grade cartilage injuries that require resurfacing or debridement.  For debridement, the unstable cartilage is removed using an arthroscopic shaver, after which resurfacing can be performed in a variety of ways.

Resurfacing procedures

1.      Marrow stimulating techniques – arthroscopic surgeries can be performed to resurface the injured cartilage.

Chondroplasty  – an arthroscopic shaver can be used to remove the unstable cartilage and stimulate the underlying bone to bleed and form a blood clot over the exposed area.  The blood clot can mature and form fibrocartilage.  Fibrocartilage is not articular cartilage; however, it can cover the exposed bone and can decrease symptoms.

Microfracture  – microfracture is an arthroscopic procedure where small holes are made on the underlying bone to allow bleeding directly from the bone marrow.  This can lead to access to bone marrow cells which can form a blood clot over the exposed area.  Very similar to chondroplasty, the blood clot can mature and form into fibrocartilage, which covers the exposed area.

2.      Replacement – Besides stimulation techniques, the degenerated cartilage can also be replaced by existing cartilage from other parts of the joint or from a cadaver (allograft).

Mosaicplasty – this procedure can be performed either arthroscopically (surgeries performed using an arthroscope, a specialized camera and surgical tools passed through a small incision) or via an open surgical approach.  The damaged cartilage or exposed bone can be replaced by small cylinders of cartilage and bone obtained from other parts of the joint.  Most of the cartilage and bone are taken from areas that are not weight-bearing, or are less important, to cover weightbearing or more important and painful areas of the joint.

               

Allograft –If the damaged cartilage is over a large area, cartilage can be taken from a cadaver to replace the injured segment.  Cadaveric tissue, or allograft, can be used.  Allograft cartilage replacements are usually fresh osteochondral transplants.  The patient does not need to be on immunosuppressive medications to suppress rejection, however. The tissue used is fresh and the procurement from the cadaver must be sterile and disease-free to avoid infection.  This is different from allograft ligament reconstructions where cadaveric ligaments are used for ligament reconstruction.  For allograft ligaments, the tissue can be processed and cleaned, hence, the rate of infection is lower.

3.      Chondrocyte Transplantation – chondrocytes are very slow growing cells.  With the improvement in cell biology and culture, we are finally able to culture and grow human chondrocytes, or cartilage cells.

Autologous chondrocyte implantation (ACI) – this is the first step to culture human chondrocytes and re-implant them to treat cartilage injuries.  In 1994, Brittberg and Peterson first reported the use of cultured human chondrocytes to replace damaged cartilage in the knee.  
Articular cartilage is biopsied or taken from the patient’s knee during arthroscopic surgery. The chondrocytes from the cartilage are then isolated and grown in the laboratory over a 6-8 week period.  After a sufficient number of chondrocytes has been cultured, they are injected back into the defect of the knee, where a periosteal flap covers the defect.  This technique is the first cell-based type treatment of cartilage injuries.  The initial advancement has led to significant amount of interest, however, the long-term results of ACI are still unknown?.  Nonetheless, this technique has opened doors for significant development and hopefully, better methods of implanting cultured cells.

Advanced ACI – since the first report of ACI in 1994, other investigators have studied different methods to improve the success rate of chondrocyte implantation.  While some investigations have focused on the use of scaffolds to hold and deliver the cells, others have studied the use of mechanical pressure to improve the quality of tissue being implanted.  All these exciting investigations are currently under clinical trials and we hope to put it into clinical use in the very near future.

4.      Joint Replacements – for significant cartilage injuries, the joint can be partially or completely replaced.  Knee, hip, and shoulder replacements are fairly common replacement procedures.  All three of these replacements have shown long term success, with higher than 85% success rates after 10-15 years of follow-up.  Other replacements, such as finger, wrist, elbow, ankle, and toe have lower success rate but can be very effective for treatment of end-stage cartilage damage in the involved joint.  Partial joint replacements have also become available when only parts of the joint are damaged; only a selective portion of the joint is replaced.  Unicompartmental knee replacement, or shoulder hemiarthroplasty are commonly performed partial joint replacements for cartilage injuries. 

      In general, joint replacements are reserved for end-stage cartilage injuries and older patients.  Newer designs and improved bearing surfaces will likely lead to longer durability of the implants, and may improve long-term success rates.

Future Treatment

            Cartilage injuries and repair have made significant improvements over the past 20-30 years.  There are a few exciting development that may improve our ability to treat these painful and disabling conditions.

·        Understanding the mechanism of cartilage degeneration – when articular cartilage gets damaged, other surrounding cartilage may also deteriorate.  Improvement in controlling the deteriorating pathway of cartilage is the next target for the treatment of cartilage degeneration.  Disease Modifying OsteoArthritic Drugs, also known as DMOADs, are currently being developed to slow down cartilage degeneration or control damage after the initial trauma.

·        Early detection and monitoring of disease progression – significant improvement in detection and monitoring cartilage injuries using imaging techniques have been made. Quantitative MR imaging scans may allow us to monitor cartilage health and degeneration in a more accurate and efficient manner.  Better detection and monitoring can lead to better assessment of the severity of injury and choice of medical treatments.

·        Cartilage replacement – improvement in cartilage resurfacing procedures can lead to less pain and disability to the patient.  Advanced cartilage implantation techniques and more durable joint replacements can lead to better long-term outcome following surgical treatment of cartilage injuries.

References

1. American Academy of Orthopaedic Surgeon
2. Cartilage Repair and Regeneration Center