With a global increasing in sporting activity there is a corresponding increasing in the incidence of joint trauma and consequently cartilage injuries. As patients get more demanding and want to return as quickly as possible to their pre-injury activity levels, it is imperative that techniques are discovered and developed to treat these injuries in an emergent way. Much progress has been made but the ultimate dream of cartilage self-induced regeneration has remained largely utopian.

Articular or hyaline cartilage is an extremely smooth, hard material, made up of the protein collagen, which lies on a bone's articulating surfaces. Its function is to allow for the smooth interaction between two bones in a joint and in spite of being only a few millimeters thick has an amazing resilience to compressive forces. Thus, if injured it can lead to impairment in the fluidity of joint movement. In addition articular cartilage is extravascular, meaning that it has no direct blood supply. This means that once injured it is extremely slow to heal.

Histology of Articular Cartilage

The mechanical and structural capacity of the articular cartilage is dependent on the integrity of its extracellular matrix. Chondrocytes sparsely distributed throughout a matrix of structural macromolecules work together with a hydrated extracellular glycosaminoglycans to attract and then sequentially extrude water. Water constitutes between 65-80% of the entire wet weight of articular cartilage and is about 15% more concentrated at the surface than in the deeper zones. Extracellular components of collagen, proteoglycans, non-collagenous proteins and water combine to provide the shear, compressive, and permeability characteristics of cartilage. It is the composition and highly complicated interaction of these components that makes regeneration and replacement techniques challenging.

Functions of the Articular cartilage

The functions of articular cartilage include load transmission and distribution, smooth articulation, and aid in lubrication. Load transmission and distribution is due to the ability of the structural matrix to deform, which leads to increased joint contact areas and distributed mechanical stresses. It also has the ability to respond to applied loads through fluid exudation and redistribution within the interstitial tissue. Some texts also mention about a proprioceptive function, which aids in recognizing and limiting joint-deforming forces and induce protection.

What is the Cartilage Crisis?

Most of the joints in the body are synovial joints, that is movable, lubricated joints which are able to provide normal pain-free movement because of the unique properties of the articular cartilage. The articular cartilage covers and protects the ends of the bones in joints. The knee is the largest synovial joint.

At the top of the knee are the massive quadriceps muscles, which cause the knee to extend. The hamstring muscles are at the back of the knee and cause it to flex. The knee joint has a synovial membrane, which is tissue that lines the noncontact surfaces within the joint capsule. The ends of the tibia, femur, and the patella are covered by articular cartilage. This is the structure that described to be in crisis.

Causes of Cartilage Damage

The common causes of cartilage damage are:

  1. Trauma and fractures
  2. Surgery
  3. Degenerative
  4. Disease and Obesity
  5. Regenerative

Diagnosis and Investigations

The articular cartilages are divided into 5 compartments including lateral and medial tibial, lateral and medial femoral and patellar compartments. The articular cartilages are graded using a modified Outerbridge classification. Grade 0 indicated intact cartilage, grade 1 chondral softening with normal contour, grade 2 superficial fraying, grade 3 surface irregularity and thinning and grade 4 full thickness cartilage loss. The grades of articular cartilage were compared with cartilage volume measurements.

MRI, by virtue of its superior soft-tissue contrast, lack of ionizing radiation and multiplanar capabilities, is superior to more conventional techniques for the evaluation of articular cartilage unlike radiography, MRI provides:

A. Provide direct visualization of the hyaline cartilage (as well as the meniscus and bone)
B. Accurate quantification with sensitivity to change
C. MRI is also less subject to positional change, which is a particular problem in the interpretation of small changes in radiological measures in longitudinal studies

Articular cartilage lesions may be categorized as degenerative or traumatic in cause. Early degenerative disease may be seen on MRI as fibrillation or surface irregularity, cartilage thinning or thickening or intrachondral alterations in signal intensity. Advanced degenerative chondral lesions manifest on MRI as multiple areas of cartilage thinning of varying depth and size, usually seen on opposing surfaces of an articulation. Other associated MRI findings of degenerative cartilage disease include central and marginal articular osteophytes, joint effusion, and synovitis. In contrast, traumatic chondral lesions generally manifest on routine clinical MRI as solitary focal cartilage defects with acutely angled margins. Traumatic chondral injuries are typically the result of shearing, rotational, or tangential impaction forces and often result in high-grade partial- or full-thickness cartilage tears or in osteochondral injuries of cartilage and the underlying subchondral bone. As a rule, recognition of a traumatic chondral defect should prompt careful inspection of the joint for a displaced intraarticular chondral body.

Cartilage Mapping
Using specialized image processing algorithms, individual structures, such as the articular cartilage, can be isolated from a MR image and quantified in a variety of ways, including total volume measurement and thickness mapping. The precision error for measuring cartilage volume is approximately 2 %, while that for cartilage thickness mapping is 0.3 mm.

Pressure Point Maps
Newer MRI machines and specialized sequences allow application of stress to the knee while the patient is in an MRI scanner. It has the ability to simulate squatting and stresses with the patient lying down. The result is a detailed picture of how the ligaments move and how the surfaces of the joint slide over each other during movement. Pressure points that appear and disappear transiently as the knee moves can be mapped and measured. Such points are potential sources of injury to the cartilage. This allows us to do quantitative measurements to evaluate how the repair and recovery are progressing. A more advanced MRI technique called MRI spectroscopy provides an even more accurate description of the health of tissues in the knee. While standard MRI essentially gives a picture of tissue density and water content, MRI spectroscopy offers a detailed picture of lipids, saturated and unsaturated fats, metabolic products and many other cellular markers.

New Techniques for the Objective Evaluation of Repair Tissue

Dr. J-K Suh and co-workers from the University of Pittsburgh are developing an ultrasonic indentation probe, which can be used arthroscopically to measure articular cartilage thickness and mechanical properties. Dr. Suh presented data supporting the accuracy and reproducibility of the technique. Dr. S. Treppo from MIT has described an electromechanical spectroscope probe that can detect cartilage degradation and may facilitate the evaluation of intrinsic material properties.

Scoring Cartilage Injuries

At the Symposium of the International Cartilage Repair Society (ICRS) in 1997, a working group presented The Cartilage Standard Evaluation Form, adapted from the International Knee Documentation Committee system. Patient data such as cause of injury, age at the occurrence of injury, onset of symptoms, sporting activities, knee pain, subjective knee function (percentage of function compared to the normal knee), previous surgery, and activity level were included. According to this system, the depth of cartilage defects is ranked on a 4-grade scale. The size and the anatomical localization further describe the defects. The defects are also outlined by the surgeon on standard grid maps including frontal and lateral views of the articular surfaces of the knee.

ICRS Grade I is superficial fissuring of the articular cartilage. Grade II is fissuring extending to less then half the normal cartilage depth. Grade III is fibrillations in the articular cartilage greater than half the normal cartilage depth and up to but not through the subchondral plate. Grade IV is significant lesions penetrating the subchondral bone.


Treatment of articular cartilage defects in the knee has been attempted in numerous studies and all with varying levels of success. Treatment can be directed at either treating the symptoms or trying to affect articular repair or regeneration Repair refers to the restoration of a damaged chondral surface with new tissue that resembles but does not duplicate the structure, biochemical makeup, function and durability of articular cartilage. Regeneration denotes the formation of new tissue indistinguishable from normal articular cartilage. There is also the component of other associated pathology in conjunction with focal articular cartilage damage. A few of the more common treatment methods are noted below.

Lavage: Lavage rids the knee of loose articular debris and inflammatory mediators that are known to be formed by damaged synovial joints. When arthroscopic lavage was performed in conjunction with mechanical debridement, there were improved results with about 88% short-term improvement. The results vary widely.

Bone marrow stimulation techniques: These procedures are theorized to stimulate and mobilize the mesenchymal stem cells to differentiate into cartilaginous repair tissue. Once disruption of the vascularized cancellous bone has occurred, a fibrin clot is formed and pluripotent cells are introduced into the area. These cells eventually differentiate into chondrocyte-like cells that secrete type I, II and other collagen types as well as cartilage specific proteoglycans after receiving mechanical and biological cues. The cells produce a fibroblastic repair tissue that on appearance and initial biopsy can have a hyaline-like quality. Unfortunately, over time the histological characteristics change into more predominantly fibrocartilaginous tissue.

Abrasion arthroplasty consists of debriding the articular defect to a normal tissue edge so that fresh collagen can be produced in the fibrin clot. The surface of the subchondral bone is exposed and penetrated to a depth of about 1 mm. Various reports show 12-53% reduced pain post-operatively. One of the potential problems with abrasion arthroplasty is the cell death produced by the heat of the abrasion burr and thus the destruction of the normal subchondral anatomy may impede any future repair or regeneration efforts.

Subchondral drilling consists of drilling through the defect to penetrate the subchondral bone. The technique was first popularized in the late 1950's by Pridie and subsequent findings suggest the repair tissue introduced into the area can look like grossly like hyaline cartilage but histologically resembles fibrocartilage. Drilling also increases the possibility of cell death through heat necrosis.

Microfracture is another such technique in which the lesion is exposed, debrided, and a series of small fractures about 3 to 4 mm in depth are produced with a sharp instrument. Adjacent cartilage is debrided to a stable cartilaginous rim, and any loose fragments and fibrous tissue are removed. In microfracturing, there is no heat necrosis and the structural integrity of the subchondral bone is maintained. Fibrocartilage is produced and the clinical results remain mixed.

Soft tissue and osteochondral grafts: Utilizing either autologous tissue or allografts, these procedures are designed to provide a suitable environment for stimulation of the mesenchymal cells to produce type II collagen fibers. The success of such approaches is at least in part related to the severity of the abnormalities, the graft quality and technique utilized, age of the patient and correction of associated pathology. Attempts to provide the damaged articular cartilage with a viable durable surface has led to the introduction of soft-tissue grafts consisting of periosteum, perichondrium, fascia, joint capsule and tendinous structures into the defect. A critical component for success with these techniques is that the cambium layer must be placed facing into the joint and the surface must be secured adequately to avoid being knocked loose with joint motion. The potential benefits include the introduction of a new cell population along with an organic matrix, a decrease in the possibility of degeneration of the tissue before a new articular surface can be produced, and an increased protection of the graft from damage due to excessive loading.

Mosaicplasty: This technique consists of harvesting a bone-cartilage graft harvested from the posterior aspect of the femoral condyle and transplanted into the defect. The technique is also referred to as “mosaic-plasty” because of the mosaic fashion in which the grafts are implanted into the defect. Several authors have reported good to excellent results with 70-92% reduction of symptoms and improvement of function in short term observations. This technique has also been shown to restore subchondral bone, improve joint incongruity and actually restore an articular surface.

Osteochondral allograft: The small number of available graft sites and donor site morbidity could be avoided by the use of fresh or cryopreserved allografts. However, there are additional problems of allograft rejection, disease transmission, mismatch in sizes and congruity, and sparse supply. Those suffering from primary degenerative arthrosis or those with patella defects do not seem to benefit. Some investigators have found a 63-77% good result from 2-10 years.

Autologous chondrocyte cell transplantation (Auologous Cartilage Implantation ) or ACI: The limited ability of chondrocyte cells to effectively differentiate, proliferate, and regenerate hyaline cartilage has increased the interest in of transplanting live cells into chondral defects. This technique requires that no penetration of the subchondral bone occur in order to prevent the introduction of blood and the circulating fibrocytes. Short term follow-up reveals newly formed cartilage-like tissue covering about 70% of the transplanted area in animals. However, the results deteriorate significantly by one year. Two years after transplantation, about 66 % have good to excellent results with histological examination showing appearance of hyaline-like cartilage. Subsequent research has shown encouraging results regarding the use and efficacy of this technique for focal chondral defects but not for osteoarthritic joints. It is thought that the degradative enzymatic synovial fluid of the arthritic knee is not conducive to cell transfer by this technique.

Steps in ACI

  1. Harvesting normal articular cartilage from non- weightbearing sites of the knee by arthroscopy (Diagram A)
  2. Extraction of chondrocytes in the laboratory and in-vitro cultivation for 2-6 weeks.
  3. Debridement of the articular cartilage defect and harvesting of the periosteum from the tibia. (Diagram B)
  4. Suturing of the periosteum over the defect or sealing it using fibrin glue. (Diagram B)
  5. Injection of 1 x 106 cultivated dedifferentiated chondrocytes per cubic centimeter under the perisoteum (Diagram B)
Diagram A
Diagram B

Meniscus implantation/replacement: Due to the complexity of the the tissue, meniscus shape and function has never been able to be modeled or reproduced effectively. It is this inherent intricacy that has eluded practitioners' ability to provide effective treatment for this condition. The most common and relatively successful technique to date is the use of allograft meniscal transplantation surgery using a frozen meniscus. Over 1600 such implants have been performed nationwide with only fair follow-up studies conducted on their use and efficacy. The most common problem post-implantation is shrinkage of the meniscal tissue, yet the results are currently moderately encouraging. Research has shown no reported benefit to using cryopreserved meniscal cartilages. Fresh frozen menisci is currently used. The use of a continuous passive motion machine and a good strengthening program are also critical for success following this procedure.

Carbon Fiber Matrix Implant

Dr. G. Bentley reported 8 year follow-up of carbon fiber matrix implants, noting satisfactory results in 77% of patients overall, with 93% satisfactory results in the treatment of medial femoral condyle lesions.

Unconventional Therapies

Role of Prolotherapy in Cartilage Growth
Prolotherapy involves the injection of substances, such as hypertonic dextrose various minerals, Sarapin (extract of the pitcher plant), and various other substances including growth hormone which act by stimulating the structures to repair. The current theory of cartilage regeneration is that this irritation acts in the same mechanism as above in inducing the chondrocytes into the chondroblastic stage of development capable of proliferation and repair. It is impossible to do a double-blind study on Prolotherapy because even an injection of sterile water under the skin has a beneficial therapeutic effect. The jury is still out on the efficacy and the possible safety of these procedures.

Rehabilitation after surgery:
The objectives of rehabilitation are:

  1. Protecting the joint in the early stages from further mechanical injury via the appropriate use of braces, crutches or sticks.
  2. Reducing swelling and inflammation as soon as possible to allow full mobilisation
  3. Identifying infection early before it has a chance to spread
  4. Restoring range of motion (ROM) to prevent later permanent limitation of flexion or extension. This also rebuilds muscle strength and prevents adhesions.
  5. Restoring priprioception and restoring normal gait patterns.

Cartilage Repair Registry

The Cartilage Repair Registry is an international, multi-center, prospective, outcomes assessment database. It is a program that longitudinally assesses clinical outcomes in cartilage repair patients. The Registry uses standardized data collection forms to track treatment outcomes in specific cohorts of patients undergoing implantation with autologous cartilage or CARTICEL and who have consented to participate in the registry. The Registry includes data on grade, location, and size of defects, concomitant procedures, previous surgeries and the Modified Cincinnati Knee Rating Score. The Registry hopes to provide valuable data to help address clinicians concerns regarding appropriate treatments and prognostic information for articular cartilage injuries. This data is adding to the orthopaedic community's knowledge about cartilage injury and can help improve clinical decision-making.


Cartilage repair techniques have now evolved to make cartilage autotransplant and chondrocyte culture a viable and option for cartilage defects in the athlete. Obviously, patient selection remains the single most important factor for the results in cartilage repair studies. As seen in various trials and studies, patients with cartilage defects are not a uniform group, and this should be taken into consideration. Cartilage injuries in the athlete are commonly associated with other pathological conditions of the joint such as ACL ruptures and meniscal injuries and they need to be addressed primarily for improving outcomes.

Recommended Reading

  1. Recht MP, Resnick D. MR imaging of articular cartilage: current status and future directions. AJR 1994;163 : 283-290
  2. Xia Y, Farquhar T, Burton-Wurster N, Lust G. Origin of cartilage laminae in MRI. J Magn Reson Imaging1997; 7:887 -894
  3. Lehner KB, Rechl HP, Gmeinwieser JK, Heuck AF, Lukas HP, Kohl HP. Structure, function, and degeneration of bovine hyaline cartilage: assessment with MR imaging in vitro. Radiology 1989;170 : 495-499 International Cartilage Repair Society.
  4. Rehabilitation following microfracture/ abrasive chondroplasty or mosaicplasty to femoral condyle, 2003 RJ&AH Orthop & District NHS Trust Oswestry.
  5. New techniques for cartilage repair and replacement , Kevin R. Stone, M.D. , Michael J. Mullin, ATC, PTA , The Stone Clinic, 3727 Buchanan Street