Osteochondritis dissecans of the talus is a particular form of osteochondra
l lesions of the talus. A trauma with subsequent osteochondral defect detec
ted immediately by radiology has to be differentiated from osteochondritis
dissecans of the talus.
Osteochondritis dissecans (o.d.) is primarily a disease of the subchondral
bone and can affect almost every joint in the human organism. After the kne
e and elbow, the talus is the third most common site of the disease account
ing for 4% of all cases. It mostly arises in the 2nd decade but can occur a
t almost any age.
Different etiological factors of osteochondritis dissecans (vascular, traum
atic, infectious, endogenous, genetic) are discussed in general and in part
icular for the talus. In the literature,the etiopathogenetic mechanism of t
rauma is favored. Several studies show an anamnestic coincidence of distors
ion and/or supination trauma prior to the onset of o.d. at the talus.
The most common localization of the o.d. lesion is the middle and posterior
third of the medial and less frequently anterior and middle third of the l
ateral talus. Biomechanical experiments demonstrated that these areas are t
hose with the highest load under varus/valgus and pronation/supination stre
ss.
Trauma is held responsible for both the more frequent medial, cup-shaped le
sion and the less frequent lateral, wafer-shaped lesion. Taking into consid
eration the complex motion patterns of the ankle joint, these conceptions s
hould be abandoned and the exact pathomorphogenetic mechanism assessed more
closely in future. Other possible etiological factors such as genetic, met
abolic or infectious causes are discussed but are not yet substantiated by
scientific and experimental evidence.
The different stages of o.d. do not differ from the stages in other joints
and from aseptic osteonecrosis. Theoretically, it seems that o.d. is initia
ted when an imaginary threshold value is reached so that a subchondral oste
onecrosis occurs (stage I). Repetitive mechanical forces possibly interfere
with the regeneration process of the lesions, resulting in the development
of a subchondral sclerosis (stage II). Further disturbance of the regenera
tive process may lead to a demarcation of the osteochondral area(stage III)
and eventually dissecation (stage IV) of the fragment with loose bodies in
the joint.
Clinical symptoms are nonspecific. Periarticular swelling, hydrarthrosis, r
educed range of motion and sometimes joint locking are the most common clin
ical signs. Differentiation of o.d. from posttraumatic osteochondral lesion
s of the talus is sometimes difficult or even impossible. In contrast, othe
r entities of the tibiotalar joint (such as talar necrosis or subchondral g
anglion) can be easily distinguished.