Cartilage Injuries - Knee
Overview
Articular cartilage
plays an important role in joint load bearing and motion. The cartilage surface provides joints with a
smooth, lubricated surface that minimizes friction. Its biomechanical properties are directly related to its
composition. Articular cartilage is
composed mainly of water (65-80%), type II collagen (10-20%), and
proteoglycans.
Articular cartilage
injuries can either be from traumatic or atraumatic (inflammatory disease,
osteoarthritis) causes. When articular
cartilage is damaged, it has a limited ability to repair itself. Adult articular cartilage has difficulty
repairing itself due to its lack of undifferentiated cells and blood supply.
Classification
The Outerbridge
Classification system is often used to describe articular injuries. The following is a simplified description of
the classification of articular injuries.
Grade I: softening.
Grade II: fibrillation.
Grade III: fissuring.
Grade IV: erosion of the cartilage exposing subchondral bone.
History/Physical Exam
Cartilage injuries can
present in many different ways. Patients
may or may not cite a traumatic injury.
Degenerative lesions may present as intermittent pain that is localized
to the medial or lateral joint line. Patients with injuries to the cartilage
with loose bodies may complain of clicking, catching or locking. They may have crepitance with range of
motion.
Imaging
|
|
|
Full thickness cartilage defect |
Radiographs are important
in the work up of cartilage injuries. Chronic degenerative cartilage wear will show radiographic changes
including joint space narrowing, subchondral cysts, flattening and sclerosis
of the condyles, and osteophytic changes. An MRI may be helpful in determining the extent of the cartilage
lesion. It is not too helpful in the
workup of chronic degenerative changes but can be helpful in locating focal
cartilage injuries and identifying potential loose bodies.
Treatment
Treatment of focal
articular injuries depends on patient age as well as location, thickness, and
size of the defect. Symptomatic partial
thickness injuries may be treated with a conservative debridement with removal
of articular flaps and impending loose bodies.
There are numerous surgical procedures used to treat full thickness
cartilage injuries including procedures that stimulate healing, osteotomies,
and autogenous/allograft tissue transfers.
|
|
|
|
|
Microfracture
of full thickness cartilage defect |
Autologous osteoarticular transplantation:
schematic and intra-operative view |
|
Various techniques are
described to treat small full thickness cartilage injuries. These include debridement, drilling,
microfracture, and abrasion arthroplasty.
All of these techniques penetrate the subchondral bone and cause
bleeding. The bleeding stimulates
mesenchymal stem cells and promotes repair of the defect with
fibrocartilage. Fibrocartilage, which
is primarily type I collagen, has inferior wear characteristics compared to the
original hyaline cartilage.
If there is a notable
limb malalignment, an osteotomy may be performed to transfer the weight bearing
force away from the cartilage defect.
Osteotomies are used more frequently in patients with large
unicompartmental defects with an associated limb malalignment.
There are many procedures
described for the treatment of large full thickness cartilage defects.
Larger focal defects may be replaced with either autologous or allograft
tissue.
|
|
Autologous chondrocyte
implantation (ACI) is a surgical procedure used for the treatment of
full thickness articular injuries.
ACI is a two-stage procedure.
The first stage requires cartilage harvest from the patient. This cartilage specimen is then sent to the
laboratory and the chondrocytes are cultured and grown. In the second stage of the procedure, a periosteal
flap is sewn over the cartilage lesion and the cultured chondrocytes
are then injected under the flap. Early histologic studies have shown a hyaline type II collagen
like repair with ACI. |
Autologous
osteoarticular transplantation is a procedure that transfers normal cartilage
to the damaged area. The circular
osteoarticular plugs are harvested from a non weight-bearing region of the
knee and transplanted into the defect. The
benefits of this procedure are that there is no risk of disease transmission
and the defect is filled mainly with hyaline cartilage. However, the supply of autologous cartilage
is limited and there are concerns about donor site morbidity.
Allograft
cartilage may be used and is typically reserved for very large cartilage defects. Allograft specimens eliminate donor site morbidity
and graft size is typically not a problem. However, allograft tissue has less potential to heal compared to
autogenous tissue and there is also the small risk of disease transmission.
Osteochondritis Dessicans
|
|
|
OCD lesion of the medial femoral condyle |
Osteochondritis
dessicans (OCD) is a specific term that refers to a subchondral bone/cartilage
lesion. OCD lesions can be found in
any joint but is most common in the knee, elbow, patella, and talus. There are numerous potential etiologies including
traumatic, growth disorders, ischemia, and endocrine problems. In the knee, the OCD lesions are usually found
in the lateral aspect of the medial femoral condyle. Loose bodies may be associated with OCD lesions.
Patients often complain of knee pain, swelling, and may have catching
or locking if the OCD lesion separates. OCD lesions are seen on plain radiographs. CT or MRI scans can be helpful in determining the size and continuity
of the lesion.
OCD lesions are seen
in both children and adults. Most OCD
lesions in the skeletally immature heal spontaneously while adult onset OCD
lesions have a much higher probability of developing secondary degenerative
changes.
The
goals of treating OCD lesions are to promote healing of the bony lesion and
preserve the overlying cartilage. Intact
lesions in the skeletally immature patient are treated with activity modification. Operative management in the younger patient
is pursued if conservative management fails or if the OCD lesion is displaced. Treatment ranges from drilling to stimulate
subchondral bone healing to fixation of the fragment. Treatment of the skeletally mature is similar to children although
the results are less successful. Drilling
may be performed for intact lesions and displaced lesions may be reduced and
fixed. However, if lesions are irreparable,
options such as autologous osteochondral transplantation, allograft reconstruction,
or ACI may be necessary.
