Osteochondral refers to the area where bone meets cartilage inside a joint. The term combines “osteo” (bone) and “chondral” (cartilage) to describe a layered structure that lines the ends of bones in joints like the knee, ankle, and elbow. When doctors use this word, they’re usually talking about damage or a defect that affects both the smooth cartilage surface and the bone underneath it, not just one or the other.
The Osteochondral Unit
Inside every major joint, the ends of your bones are covered by a structure called the osteochondral unit. It has three distinct layers that work together to absorb shock and allow smooth movement. The outermost layer is articular cartilage, the slippery white tissue you’d recognize if you’ve ever looked at the end of a chicken bone. Beneath that sits a thin zone of calcified cartilage, which acts as a transition between the soft cartilage above and the hard bone below. The deepest layer is subchondral bone, which itself has two parts: a thin, porous bone plate and a spongy bone layer underneath.
This layered design matters because each layer has a different job. The cartilage handles friction and distributes force across the joint. The calcified zone anchors the cartilage to the bone. The subchondral bone provides structural support and channels nutrients upward. When an injury or disease disrupts any one of these layers, it tends to affect the others, which is why doctors think of them as a single functional unit rather than separate structures.
What Osteochondral Defects Are
An osteochondral defect is a specific type of joint injury where both the cartilage and the bone beneath it are damaged. This distinguishes it from a purely chondral defect, which involves only the cartilage layer. Osteochondral defects can range from a softened area of cartilage with a bone bruise underneath to a full crack where a fragment of cartilage and bone breaks partially or completely away from the joint surface.
Trauma is by far the most common cause. In the ankle, for example, 93% to 98% of defects on the outer side of the talus (the bone that sits inside the ankle joint) are linked to a specific injury, usually an ankle sprain. When the talus twists inside the ankle during a sprain, the cartilage can bruise, soften, crack, or peel away from the bone. High-impact forces can also drive straight through the cartilage and contuse the bone underneath.
Not every osteochondral defect has a clear traumatic cause. On the inner side of the talus, only 61% to 70% of defects are tied to a known injury. The rest may develop from reduced blood supply to the bone (ischemia), which can cause a small area of bone to die and the cartilage above it to collapse. Genetics may also play a role in these nontraumatic cases.
Osteochondritis Dissecans
Osteochondritis dissecans is a condition where a segment of bone just beneath the cartilage loses its blood supply and begins to separate from the surrounding bone. It most commonly affects the knee, specifically the inner side of the thighbone where it meets the shinbone. The elbow and ankle are the next most frequent locations.
Doctors classify the severity using a four-grade system. Grade 1 means the area is softened but the cartilage surface is still intact. Grade 2 involves a partial crack but the fragment is still stable. Grade 3 means the fragment has fully separated from the surrounding bone but hasn’t moved. Grade 4 is the most severe: the fragment has broken loose and is floating freely in the joint. Each grade is further divided based on depth, with lesions shallower or deeper than 10 mm.
Symptoms range widely depending on the stage. Early lesions may cause no symptoms at all or only mild, vague joint pain. More advanced cases, particularly those with a loose fragment, tend to cause noticeable joint pain, swelling, locking (where the joint catches or gets stuck mid-motion), and a feeling of instability. On exam, you might have tenderness when the area is pressed, reduced range of motion, or visible swelling from fluid buildup in the joint.
How Osteochondral Lesions Are Diagnosed
MRI is the gold standard for detecting osteochondral problems. It picks up lesions with a sensitivity of up to 96% and a specificity between 96% and 100%, meaning it rarely misses a defect and almost never flags one that isn’t there. MRI is especially good at catching early-stage damage that’s limited to the cartilage layer, and it can identify unstable lesions with 97% sensitivity and 100% specificity. It also shows bone marrow swelling, which is often the earliest sign that something is wrong beneath the cartilage surface.
CT scans are highly specific (99%) but less sensitive overall, catching about 81% of lesions. The gap comes from low-grade defects that involve only the cartilage, which CT simply cannot see. For this reason, MRI is typically the first imaging choice when an osteochondral problem is suspected, while CT may be added later to get a more detailed look at the bone architecture before surgery.
What Happens if It Goes Untreated
Leaving an osteochondral defect alone doesn’t guarantee rapid joint destruction, but the damage does tend to progress. Patients with untreated cartilage defects in the knee are more likely to develop additional cartilage damage over time. One long-term study following young, active patients with a single defect on the weight-bearing surface of the knee found that 39% had developed osteoarthritis at an average of 15 years later. In another study with 12 years of follow-up, degenerative changes appeared in 13 out of 21 knees, whether or not the defect had been repaired.
The risk of further cartilage breakdown roughly doubles once a defect is present. One large study found that people with moderate cartilage damage had about twice the odds of developing new cartilage loss elsewhere in the same joint over a 30-month period compared to people with healthy cartilage. The progression doesn’t always show up on standard X-rays within the first couple of years, which can create a false sense of security. The damage is often visible on MRI well before it appears on X-ray.
Surgical Treatment Options
When conservative measures like rest, bracing, and physical therapy don’t resolve symptoms, surgery aims to restore the damaged cartilage and bone. The main approaches fall into two categories: transplanting cartilage and bone as a unit, or growing new cartilage cells to fill the defect.
Osteochondral autograft transfer takes a small plug of healthy cartilage and bone from a non-weight-bearing area of your own joint and moves it into the defect. This works well for smaller lesions but creates a secondary wound at the donor site. Osteochondral allograft transplantation uses donor tissue from a tissue bank instead, avoiding that donor-site problem and allowing treatment of larger defects. It also restores the subchondral bone layer, which makes it particularly useful when bone loss is significant.
Autologous chondrocyte implantation takes a different approach. Surgeons first harvest a small sample of your own cartilage cells, grow them in a lab over several weeks, then implant the expanded cells back into the defect. A newer version of this technique seeds the cells into a membrane before implantation, which simplifies the surgery. When comparing outcomes, chondrocyte implantation and allograft transplantation produce similar functional results, but allografts have shown a higher revision rate in some studies (21% versus 4% for chondrocyte implantation). When the subchondral bone is intact and only the cartilage needs repair, both options work well.
Recovery After Surgery
Recovery from osteochondral surgery is slow compared to many orthopedic procedures, largely because cartilage heals much more slowly than bone or muscle. The first two weeks after surgery typically involve a rigid splint and no weight on the affected joint. After that, the splint comes off and you transition to a removable walking boot while starting physical therapy focused on range of motion.
The most common rehabilitation protocols keep you non-weight-bearing for six to eight weeks total. Some surgeons allow earlier weight bearing starting at two weeks, and early research suggests this may not harm outcomes. Either way, expect to spend several weeks on crutches or a scooter before gradually returning to full weight bearing. Return to sport or high-impact activity takes considerably longer, often six months to a year depending on the size and location of the defect and the type of repair performed.