FIGURE 9-1. Cross-sectional, schematic diagram of the cellular organization of healthy articular cartilage.
cartilage functioning as a one-way valve. The valve allows the flow of fluid from the joint space into the subchondral bone but not in the opposite direction. During weight bearing, similar contact pressures in the talus and tibial cartilage forces fluid into the damaged subchondral bone, which is the path of least resistance. Unloading of the joint allows fluid to re-enter the articular cartilage, but as the cycle of fluid shift continues, cyst formation slowly ensues16 (Fig. 9-2A-D).
males slightly predominant and medial dome lesions more common than lateral. A recent report by Hermanson and Ferkel15 found the incidence of bilateral lesions to be 10% in a population of 526 patients with OLT.
impaction. With the lateral lesions, as the foot is dorsiflexed and strongly inverted, the lateral talar margin is impacted and compressed against the medial articular surface of the fibula, causing a shearing and compressing component that could potentially displace the osteochondral fragment. Conversely, in medial talar dome lesions, when the foot was inverted and plantar flexed with the tibia in external rotation, the posteromedial edge of the talar dome impacted against the posteromedial tip of the tibia, causing increased shear stress.
FIGURE 9-3. Location of osteochondral lesions of the talus. Most lesions are central to posteromedial or anterior to midlateral, as seen on the axial view of the talus. (Illustration by Susan Brust.)
FIGURE 9-4. The size of the osteochondral lesion varies by location. Lateral lesions tend to be shallower and wafer shaped, and medial lesions deeper and cup shaped. (Illustration by Susan Brust.)
particularly on the medial side, occur without preceding known trauma.
CT scan is often necessary to more accurately define the borders of the lesion.
FIGURE 9-8. Hindfoot CT scan in two planes. (A) Coronal plane demonstrates stage III lesion with lucency under the fragment. (B) Axial view shows that the lesion extends from the central to the posterior aspect of the medial talus.
32 patients with osteochondritis dissecans of the talar dome and also found CT scans to be superior to x-rays for both diagnosis and follow-up.
Table 9-1. CT Classification
They classified lesions in three grades: intact, firm, and shiny articular cartilage; intact, but soft cartilage; and frayed cartilage (Fig. 9-14). Several lesions were noted to progress from grade 1 to grade 3 during the course of treatment. In addition, there was a poor correlation between x-ray appearance and arthroscopic findings. Therefore, they concluded that the arthroscopic appearance was considered the most important determinant of treatment.26
FIGURE 9-12. CT scan classification. See also Table 9-1. (Modified after J. Daugherty and Richard Ferkel.) (Illustration by Susan Brust.)
Table 9-2. MRI Classification
FIGURE 9-13. Anderson MRI classification. (Illustration by Susan Brust.) See also Table 9-2.
and no one surgical technique reliably produces zonal hyaline cartilage. Although our current treatment options have produced encouraging results, not all patients will achieve a successful outcome. Therefore, it is essential to have an informed discussion with the patient to develop a treatment plan with realistic expectations.
Table 9-3. Surgical Grade Based on Articular Cartilage
Table 9-4. Comparison of Arthrotomy Treatment Results
Table 9-5. Treatment of Acute OLT
blood vessels. This leads to the formation of a fibrin clot, and a fibrocartilaginous repair tissue often forms over the surface if it is protected from excessive loading. It has been shown experimentally that the cells responsible for the new fibrocartilaginous articular surface enter the fibrin clot from the marrow. These cells start as undifferentiated mesenchymal cells and then differentiate into chondroblasts and chondrocytes.
FIGURE 9-17. Transmalleolar and transtalar drilling, both laterally and medially. (Copyright, Richard D. Ferkel.)
Table 9-6. Treatment of Chronic OLT
(Refer to Fig. 9-16.) The Orthosorb pin (Biomet, Warsaw, IN), an absorbable pin, is made of polyglycolic acid and takes 6 months to absorb. Usually two or three pins are necessary for stable fixation. If drilling is difficult from the anterolateral portal, the MicroVector drill guide can be inserted through the anterolateral portal, and drilling can be done from the medial portion of the talus across into the lateral talar dome lesion. Alternatively, the arthroscope can be inserted anterolaterally, and the MicroVector can be inserted anteromedially to drill into the anterolateral lesion. Postoperative x-rays at 4 months demonstrate excellent healing (Fig. 9-20A-F).