Radiographs and a CT tomogram are shown from five different patients with the same disease. What is the most likely diagnosis?
PROBLEM:
Radiographs and a CT tomogram are shown from five different
patients with the same disease. What is the most likely
diagnosis?
DISCUSSION:
Osteochondritis dissecans represents a localized injury of
subchondral bone and adjacent cartilage at an articular surface. In
this disorder, it is commonly believed that the bone undergoes
avascular necrosis, with the overlying cartilage exhibiting
degenerative changes. This can lead to the separation of the dead
bone and damaged cartilage from its adjacent healthy tissue,
resulting in the formation of an osteochondral body.1 As seen in
the preceding radiographs, the knee, ankle, and elbow are the most
common sites of osteochondritis dissecans. It also occurs less
commonly at the hip, shoulder, and other joints.
This disease affects two distinct groups of patients. The
juvenile form of the disease involves patients between the ages of
five and fifteen years of age in whom the physes remain open. The
adult form of the disease affects older adolescents and adults
whose physes are closed.
The exact etiology of osteochondritis dissecans remains
controversial. Theories implicating trauma, ischemia, abnormal
ossification, and genetic predisposition have been proposed, but
none of these has been universally accepted.1,2,3 The precipitating
cause is most likely multifactorial, though some mechanisms may
have stronger associations with certain joints. Accordingly,
treatment of this disease is also not uniformly agreed upon,
remaining dependent on the skeletal age of the patient, the
specific joint involved, and the exact location within the joint.
Clinical symptoms, etiology, radiographic findings, and treatment
options for the knee, ankle, and elbow joints are discussed
below.
Osteochondritis dissecans of the knee afflicts men twice as
often as women, and it is seen most frequently in adolescents. This
disease is relatively rare in those who are younger than 10 years
or older than 50 years of age. Early symptoms are non-specific,
usually consisting of complaints of a dull ache in the knee.
Catching, clicking, popping, locking, or the feeling of a loose
body in the joint can all manifest as late symptoms when the defect
has undergone a complete or partial separation.1 A history of
trauma to the knee is common, but not universal. The medial condyle
of the femur is affected approximately 85% of the time. On routine
anteroposterior and lateral radiographs the bony lesion can be seen
as a well defined area of sclerotic subchondral bone that is
separated from the normal areas of the femur by a radiolucent zone
(figure 1).2 A third view, the notch or tunnel view, can best
delineate the lesion in the non-weight-bearing portion, or inner
aspect, of the medial femoral condyle (figure 2).1 Purely chondral
lesions, however, call for arthrography, CT arthrography, MRI, or
arthroscopy for proper diagnosis. These latter studies can also
better characterize loose fragments, degree of displacement, and
orientation of major fragments.3 Those patients who are skeletally
immature should also have the opposite knee examined
radiographically.
Although there is no standard classification system, Cahill and
Berg have described a system for use with AP and lateral
radiographs.4 In their technique, the AP radiograph is divided into
five segments: the medial compartment is divided into segments 1
and 2; the notch is segment 3; and the lateral compartment is
divided into segments 4 and 5. The lateral radiograph is separated
into three sections: section A is anterior to the Blumensaat line;
section B lies between the Blumensaat line and a median extended
from the posterior femoral cortex; and section C describes the area
posterior to a line extended along the posterior femoral
cortex.
For osteochondritis dissecans of the knee, the major
differential diagnosis to consider is spontaneous osteonecrosis of
the knee. This entity generally is seen in older patients who
present with a sudden onset of symptoms. This defect usually
involves the weight-bearing portion of the medial femoral condyle
and may be a true osteonecrosis, though its etiology also remains
uncertain.2
Treatment varies markedly for the juvenile and adult forms of
osteochondritis dissecans of the knee. Patients with the juvenile
form (with open physes) usually can be successfully managed
non-operatively with protected weight-bearing and limitation of
activity.3 A knee immobilizer or splint may be used, and careful
follow-up with serial radiographs is needed to assess the patient's
progress.
Indications for operative intervention in this population
include presence of loose bodies, persistence of symptoms for 6 to
12 months, lack of evidence of healing, or approach of skeletal
maturity.1 Adult forms of the disease do not fare well with
non-operative repair techniques and, therefore, surgical treatment
is preferable for optimal results in adult patients. Such
techniques include retrograde drilling of the intact articular
cartilage; curettage and drilling of the defect; fixation of
fragments with compression screws, bone pegs, or pins; and bone
grafting to restore articular surface congruity.3 Strict
postoperative instructions for non-weight bearing are essential to
optimize the chances of healing, although early range-of-motion
exercises are allowed. Patients who are older than 60 years of age
with a large osteochondral defect may be candidates for knee
arthroplasty. Younger patients with large defects, however, may
experience significant trouble with advanced degenerative joint
disease, although recent work with osteochondral allografts has
shown promising results.1
Patients with osteochondritis dissecans of the ankle have
lesions in either a posteromedial or anterolateral location on the
talus. This occurs more often in young adults, and men are affected
more often than women. Patients with posteromedial lesions may
present with no symptoms and no history of trauma; the lesions
frequently heal spontaneously, and the patients usually do not
develop extensive arthritis.1 Those patients with anterolateral
lesions, however, can present with pain, swelling, catching with
walking, and a history of trauma. These lesions are strongly
associated with trauma, they rarely heal without intervention, and
patients often develop early arthritis.1
The traumatic etiology of osteochondritis of the ankle is
clearer than that for the knee. Lateral lesions most likely result
from impaction of the talus against the fibular articular surface
by inversion and dorsiflexion, whereas medial lesions may arise
from inversion and plantar flexion with lateral rotation against
the tibia.3 These lesions may, in fact, be osteochondral fractures.
Similar to the knee, radiographs reveal a well defined area of
subchondral bone separated from the normal bone by a radiolucent
line (figure 3).2 Berndt and Harty have developed a radiographic
classification system divided into four stages: stage 1 is a small
area of compression of subchondral bone; stage 2 describes a
partially detached osteochondral fragment; stage 3 is a completely
detached osteochondral fragment remaining in the underlying crater;
and stage 4 describes an osteochondral fragment that is displaced.5
CT can be helpful for accurate determination of the size and
orientation of the lesion before surgery (figure 4). MRI also has
been shown to correlate well with findings from arthroscopy.2
Berndt and Harty's stages are used as treatment guidelines.1,3
Stage 1 and 2 lesions may best be treated non-operatively. Medial
stage 3 lesions also fare better when treated non-operatively with
immobilization of the limb and non-weight-bearing for up to 6
months. However, stage 3 lateral lesions and all stage 4 lesions
are best treated operatively. This involves excision of the
fragment, and curettage and drilling of the crater. If the fragment
is in good condition, it may be pinned after débridement and
preparation of the crater. Lateral lesions usually can be
approached anteriorly because the lateral malleolus is posterior to
the tibia. Medial lesions have been approached without the use of
osteotomy of the medial malleolus by "grooving" the anteromedial
surface of the distal tibia to allow improved exposure.1 These
techniques are utilized to prevent or slow degenerative changes in
the ankle, and they have generally produced good results.
Osteochondritis dissecans of the elbow usually occurs as a
result of overuse injuries. Symptoms may include swelling, pain,
and limited motion, with intermittent locking occurring if loose
bodies are present. Such patients are usually adolescents and young
adults who are involved in throwing activities. Repetitive
microtrauma from throwing results from the increased valgus stress
placed on the elbow, with compressive forces placed on the radial
head and capitellum.3 Plain radiographs will show a radiolucency of
the lateral or central portion of the capitellum (figure 5). MRI
can be useful for evaluating the presence and stage of the
lesion.
The major differential diagnosis to consider is Panner disease
("little leaguer's elbow"). This entity involves rarefaction and
fragmentation of the entire capitellum, but is seen in children
between four and eight years of age, is self-limiting, and improves
with rest. Panner disease should be suspected if, on radiography,
the entire capitellum is found to be involved.2
Again, younger patients have better results with non-operative
treatment. Operative treatment includes débridement of loose
bodies, as well as curettage and drilling to stimulate vascular
growth.3 Unlike osteochondritis dissecans of the knee and ankle,
results of treatment for osteochondritis dissecans of the elbow
have not been as favorable. Degenerative changes and limitation of
motion are expected results.
In summary, the radiographic findings of osteochondritis
dissecans of various joints are similar. However, each different
joint involved is unique, with different etiologies proposed for
the lesion, as well as different treatment strategies. It may be
best to consider osteochondritis dissecans of the knee, ankle, and
elbow as three distinct entities sharing the same name in order to
find the best method of treatment.
References
1. Crenshaw AH (ed): Campbell's Operative Orthopaedics, ed 8.
St. Louis, Mosby, 1992.
2. Resnick D (ed): Diagnosis of Bone and Joint Disorders, ed 3.
Philadelphia, WB Saunders, 1994.
3. Schenck RC Jr., Goodnight JM: Osteochondritis dissecans. J
Bone and Joint Surg 78-A (3):439-456, 1996.
4. Cahill BR: Osteochondritis dissecans of the knee: Treatment
of juvenile and adult forms. J Am Acad Orthop Surg 3:237-247,
1995.
5. Berndt AL, Harty M: Transcondylar fractures (osteochondritis
dissecans) of the talus. J Bone Joint Surg 41-A(9):988-1020,
1959.
This series of diagnostic challenges is prepared by David J.
Sartoris, MD,Professor, Department of Radiology, University of
California School of Medicine,
San Diego, CA.