What is an Articular Cartilage Defect?

Articular Cartilage Defects of the Knee
Steve A. Mora, MD

Orange County Orthopedic Surgeon

Please see our Knee Injury Protocol for additional information on this topic.

Three bones meet within the knee joint: the femur (thighbone), the tibia, (shin), and the patella (kneecap). Like many other joints or "articulations," the surfaces of these bones are covered with a durable slick lining called articular cartilage.  Articular cartilage different than meniscus cartilage.  Articular cartilage serves as the slick pearly white lining of the joint in contrast to the 2 menisci  that lie on  the surface of the tibia and which serve as shock absorbers between the tibia and the femur.  Articular cartilage has unique biochemical and physical qualities which confer nearly frictionless characteristics. When functioning properly articular cartilage has less friction than 2 pieces of ice sliding on each other. 

Front_knee_Articular cartilage defects are common conditions affecting the knee. Articular cartilage resists wear quite well, but time and wear can eventually take their toll. When the joint surface extensively breaks down, the condition is known as degenerative arthritis or osteoarthrosis (OA). If a severe twisting or impact injury occurs, such as following an ACL rupture or fall, a focal area of cartilage injury may occur.  These traumatic lesions are referred to as an articular cartilage injury or chondral injury.   Since articular cartilage has such poor healing qualities, these injuries will rarely heal or regenerate spontaneously.   In addition to causing pain and restricted mobility, injuries to joint cartilage over time may lead to further deterioration.  A lesion which originated following trauma may take on a degenerative appearance over time. The symptoms of damaged articular cartilage may severely hinder normal activities and occupation, i.e. functional impairment.    The severity of the pain and dysfunction depends on the size and the depth of the injury.  Surgeons are able to "grade" the severity and complexity of articular cartilage defect based on the  depth of the injury.  Grade I- is very mild with softening, Grade II includes fissuring or crater depth less than half the full thickness, Grade III is a deep defect that is through most of the thickness of the cartilage, and the most severe, Grade IV is a full thickness defects with exposed bone.  The higher grade lesions such as the III or IV can have major negative impact on a person's function.

ACDGrade4They can be categorized into the following categories.  The categories are not rigid definitions in that some articular cartilage defects may fall into more than one category.  For example a 55 year old tennis player who falls onto their knee may have a new traumatic focal defect but the preexisting cartilage was degenerative.

  • Traumatic Focal Articular Cartilage Defects (aka traumatic arthropathy, chondral defects)
    An articular cartilage injury occurs when there is trauma to the joint surface.  This most often occurs when the bones are forced to slide across one another or impact each other with marked force. This can occur following a twisting mechanism, as happens at the time of an anterior cruciate ligament rupture. Articular cartilage defects of the patella frequently occur following a fall with direct impact to the front of the knee or a dislocation of the patella.  These injuries are difficult to see clearly on MRI but they should be suspected if swelling is visualized in the bone (bone edema).  An MRI with injected joint contrast is the best study to visualize these defects. 
  • Chondromalacia (localized wear and tear)
    Softening or fissuring of the articular cartilage usually a consequence of cumulative injury or degenerative joint disease. Very common in patients older than 50. 
  • Osteochondral fracture (joint cartilage and bone involvement)
    A hard blow to the knee may cause a piece of articular cartilage to break off and pull with it a piece of its underlying bone. The broken off fragment may end up free floating in the joint- "loose body".  A loose body may rub against the tissues within the knee, causing pain and locking. If large enough, the loose fragment of cartilage/bone may be re-attached into its original position, akin to a jigsaw puzzle, and secured with special anchors.  If the fragment is too small it is discarded and the remaining crater managed according to its size.  
  • Degenerative Joint Disease, a.k.a. osteoarthritis, arthrosis
    When the knee surface has most of its surface damaged or a large portion of a major weight bearing the knee is called arthritic.  The articular cartilage wear is extensive and severe and the knee function deteriorates. In some instances the cartilage degeneration is due to abnormal alignment causing more wear on one side than another of the knee.

Symptoms

Articular cartilage does not have pain fibers and as a result the pain symptom are not equally proportional to the amount of injury in some cases.  Therefore, it is possible for the articular cartilage lesion to be minimally painful in some cases.  Usually minor aches and stiffness may be the only warning of an articular cartilage injury. In general the larger and deeper the lesion the greater the pain.

  • Nonspecific swelling may signal a problem caused by fluid buildup
  • "Cracking" or "crunching" sounds as joint is moved through range of motion
  • Locking or catching sensation triggered by loose body or a jagged cartilage edge.
  • Pain and stiffness after sitting for a prolonged sitting period ("movie theater sign")
  • Poor athletic performance- speed and agility problems

Evaluation and Management

Each year, the ability of the MRI to visualize articular cartilage defects improves but is far from perfect.  The MRI is excellent for meniscus tears but not for articular cartilage.   A bone scan is sometimes necessary to identify difficult to see lesions. X-rays are helpful for advanced degenerative changes or osteochondral defects.

If the knee became swollen following the injury, an MRI will be valuable for characterizing the likely injury. 

If all the studies are normal and the patient continues to have knee pain that is characteristic of cartilage problems, a "diagnostic arthroscopy" may be done.

Treatment

Note the following discussion regarding treatment and surgery is not intended for arthritic or degenerative knees.   If surgery is necessary for a arthritic degenerative lesions, the best choice is usually a joint replacement type of surgery.

R.I.C.E (Rest, Ice, Compression and Elevation) is the best method for treating minor injuries in the first few days.  An ACE wrap may add support and comfort to the limb.   Early evaluation by a orthopaedic surgeon is important if the knee is symptomatic for more than one day.  If the injury occurred while playing sports and the swelling is severe, there is a high likelihood that a serious injury occurred.  If necessary, take over the counter NSAIDs (non-steroidal anti-inflammatory drugs, such as ibuprofen or acetaminophen) to manage swelling and pain.

For degenerative arthritis low impact exercises such as swimming, inclined stationary bike or elliptical machine will help maintain the knee motion and strength.  Activity modification is important to curtail painful activities.   A Physical Therapist (PT) may be helpful in teaching the proper ways of exercising and strengthening without overloading the joint and making the problem worse. Viscosupplementation injections (Synvisc®, Orthovisc®), steroid injections (cortisone) and anti-inflammatories (Naprosyn®, Celebrex®) serve as the foundation of the non-operative treatment. 

Arthroscopic Knee Surgery:  If the symptom are not satisfactory and there is persistent functional impairment, then arthroscopy may serve as the next viable option.  The risk and benefit profile needs to be balanced.  Most arthroscopies can be performed with local anesthesia and small amounts of intra-venous drugs.  The procedure is performed with the patient fully alert and awake (and comfortable!) as same day outpatient surgery.  The arthroscopic debridement procedure is used to wash out the cartilage debris, trim or smooth-out jagged pieces of cartilage, and attempt to heal or re-surface small denuded areas.  

Microfracture chondroplasty  is a arthroscopic procedure in which the surgeon creates multiple tiny puncture holes in the denuded areas (exposed bone) using a sharp surgical pick.  The punctures in the bone allow blood from the bone-marrow to escape and pool within the cartilage defect.  Eventually the pooled blood will solidify into a type of cartilage which can cover the denuded defect.   In approximately 80% of cases there is an acceptable degree of filling of the defect and symptom relief.  The major downside to microfracture chondroplasty is the necessity for  crutches and strict use of a motion machine (CPM) for 4-6 weeks.  There is also a question of long-term durability beyond 5 years after the surgery.  Nonetheless the arthroscopic debridement and the microfracture chondroplasty serve as the first-line surgical procedures before embarking onto much more complex options.

For larger  deeper articular cartilage defects or those defects which failed the above surgery, the treatment may be much more complex.  A handful of innovative procedures have been developed and studied in the last 15 years.  Treatment options are actually few and include:Autologous Chondrocyte Implantation (ACI, Genzyme, or Carticel)Osteochondral Plug Transfer ("OATS" or Mosaicplasty) using your own plugs or fresh cadaver plugsBulk Allograft Transfer (large "fresh" cadaver grafts, including hemi-condyles and plateau)

Small plugs of cartilage may be taken from a less critical part of the knee and inserted into the painful area, osteochondral autograft transfer (OATS).  These plugs look like dowels which can be tapped into the prepared cartilage defect.  Once the defect is pacted with the plugs the knee is protected with crutches until the plugs grow into the surrounding bone.  The surface of the plugs consist of cartilage which will form the new surface previously void of cartilage.  These plugs may be autograft (your own) or allograft (cadaver).   Autologous Chondrocyte Implantation (aka: ACI, Genzyme, Carticel) is a procedure in which the patient’s own cartilage cells are harvested from a less important site within the knee, grown in a laboratory, and then re-implanted into the cartilage lesion of the knee.  The procedure requires two surgeries, one for the harvest and the second for the implantation.  Lastly bulk fresh allograft transplant is used when the area of cartilage loss is large or massive.  The results have been good in selected cases of large osteochondral defects (OCD) and small avascular necrosis (AVN).  When performed properly each one of these surgical options may yield good results.  Keep in mind that the recovery from these procedure is about 1 year.  The time on crutches and the amount of PT could be up to 3 months.  It is also important to note that excellent results are not routinely achieved, therefore patient expectations have to be realistically tempered.

Summary

Treatment of articular cartilage defects, whether traumatic or degenerative, are highly challenging.  The greatest challenge is determining which treatment option is best suited for the individual case.  The surgical options may include highly complex procedures and therefore the decision to have surgery should be carefully made.  Although the recovery and rehabilitation period is long, good results are achievable in properly selected cases.