Osteochondritis dissicans generally indicates fragmentation
and probable separation of a portion of the articular surface.
The age of onset is variable but adolescence is most frequent.
Patients may be entirely asymptomatic, however, pain, limited
range of motion, soft tissue swelling, and the locking of
the knee may be apparent.
The most typical location for osteochondritis dissicans
is the lateral aspect of the medial femoral condyle affecting
approximately 70 percent of cases. Men are typically more
affected than women and the average age at the onset of symptoms
is approximately 15 to 20 years although this is variable.
Unilateral changes predominate over bilateral changes and
there is a history of knee trauma and about 50 percent of
The pathogenesis of osteochondritis dissicans of the femoral
condyles has not been completely agreed upon. Most doctors
agree that trauma initiates this condition, probably related
to rotatory forces acting on a fixed weight bearing knee.
Shearing forces and direct blows could also produce osteochondral
Radiographically, a purely chondral lesion requires advanced
imaging for diagnosis. If an osseous component of an osteochondral
lesion is present, routine radiography is very helpful. Sometimes
a small osseous lesion is separated from the sclerotic base
of the femoral defect by radiolucent crescent zone. It is
also possible for the osteochondral fragment to produce a
loose intraarticular osseous body which can cause joint locking
clinically. Over time, the site of origin on the femur can
be remodeled although a slightly flattened or at least irregular
surface frequently lasts for a long period of time. Secondary
degenerative joint disease also occurs in patients with osteochondritis
dissicans much earlier in life than the usual osteoarthritis
of the knee and is frequently associated with loose bodies.
The major differential diagnosis of osteochondritis dissicans
is spontaneous osteonecrosis of the knee. Typically this lesion
occurs in older persons with a sudden onset of clinical manifestations
and almost always involves the weight bearing portion of the
medial femoral condyle.
PATELLA - INFERIOR POLE
Sinding-Larson in 1921 and Johansson in 1922
independently described a syndrome which occurred most commonly
in adolescence between 10 and 14 years of age consisting of
tenderness and soft tissue swelling over the lower pole of
the patella, accompanied by radiographic evidence of osseous
fragmentation. Initially it was suggested that this was an
"epiphysitis" or "apophysitis" but is now recognized that
it is traumatic in origin. Its pathogenesis is very similar
to that of Osgood-Schlatter's disease and is probably related
to a traction phenomenon in which contusion or tendinitis
in the proximal attachment of the patellar tendon is followed
by calcification and ossification. In Sinding-Larson-Johansson
disease, pain and tenderness are typically aggravated by activity.
The small bony fragments may subsequently coalesce and become
incorporated into the patella. The natural duration of the
disease is approximately 3 to 12 months.
Osgood-Schlatter's disease was described in 1903
as a disorder of the developing tibial tuberosity which each
of the developers believed to be a manifestation of trauma.
Other case studies were presented incorrectly emphasizing
the possibility of "apophysitis" or osteonecrosis as the etiology
of this condition. Osgood-Schlatter's disease typically occurs
in adolescence boys between the ages of 11 and 15 years of
age with the history of participation in sports and the rapid
growth spurt prior to the onset of symptoms.
Clinically, there is typically local pain and tenderness
which is aggravated with activity and relieved with rest.
This disease is generally unilateral, however, bilateral alterations
are detected on approximately 25 percent of cases.
Radiographic abnormalities in Osgood's Schlatter's disease
are difficult to detect and because subtle soft tissue changes
may be missed if the lateral knee films are over penetrated,
a low kV technique is ideal. Initial radiographic abnormalities
include subtle soft tissue swelling in front of the tuberosity
with an indistinct margin of the patellar tendon and often
times increased radiodensity of the infrapatellar fat pad.
Multiple ossific irregularities in the region of the tibial
tuberosity are also present, similar to the fragmentation
of the inferior pole of the patella which occurs in Sinding-Larson-Johansson
disease. Eventually the radiographic appearance can return
to normal, however, it is not uncommon for ossific fragment
to persist. MR imaging reveals evidence of patellar tendinitis
and bursitis, however, again, this is not typically indicated.
To complicate things a little, it needs to be known that
it's normal for one or more osseous centers to be present
just anterior to the tibial tuberosity in children between
the ages of approximately 8 and 14 years. Therefore, the most
accurate way to diagnose Osgood-Schlatter's disease is based
on both radiographic and clinical findings. If there is pain
in the region of the tibial tuberosity in the right age group,
especially with the history of repetitive stress, and the
radiograph demonstrates soft tissue swelling, the diagnosis
can confidently be made. Sometimes comparison views of the
opposite, uninvolved side may be helpful.