Sprains, strains, fractures, and other trauma to the ankle can result in a condition known as osteochondral lesions of the talus or OLT. The talus is the bone located below the tibia (lower leg bone) and above the calcaneus (heel). The lesion or defect can affect just the cartilage lining the bone (called a chondral lesion) or the hole can go all the way down to the bone (an osteochondral defect).
Cysts that form under the cartilage are referred to as subchondral cysts and are seen more often in chondral type of osteochondral lesions of the talus (OLT). Cyst formation may be an indication that the reparative process got started but was interrupted and did not complete itself. Or it may be a signal of a degenerative process going on.
The cyst formation occurs more often in older adults without a history of trauma but can certainly develop in cases of sports trauma such as you report. Chondral lesions take longer to heal. This may contribute to the start of a degenerative process and subsequent formation of cysts.
Patients with osteochondral lesions have a better chance of self-healing compared with those who have the chondral type. This is because bone marrow cells (inside the bone) can move or migrate from inside the bone to the defect and stimulate healing. Chondral lesions don’t have that direct connection to bone marrow cells and must rely on far fewer bone marrow cells reaching the lesion. The cells come from the joint synovial membrane (lining around the joint containing fluid).
The size of the lesion (not just the depth) is the most important factor in healing osteochondral (or chondral) lesions. Larger defects tend to need surgical intervention to bring about healing. Your surgeon is the best one to review the significance of these findings for you. Your age, size (body mass index), activity level, and symptoms (along with characteristics of the lesion) will all be factors to consider when planning the appropriate treatment.