What is osteochondritis dissecans?
Osteochondritis dissecans, usually shortened to OCD, is a condition affecting a small area of bone sitting directly underneath the smooth cartilage lining of a joint. That area of bone loses part of its blood supply and softens. Because the cartilage above it depends on that bone for support, the joint surface itself can become unstable, and in more advanced cases a fragment of bone and cartilage can partially or completely separate.
It is quite different from the conditions most families have read about. Osgood-Schlatter, Sever's and Sinding-Larsen–Johansson are irritations of growth plates at the edges of the bone where tendons attach. OCD sits inside the joint, on the weight-bearing surface. That distinction drives everything about how it is managed.
In children and adolescents the knee is by far the most common site, typically the inner side of the end of the thigh bone, followed by the ankle and the elbow. Elbow lesions are strongly associated with throwing and gymnastics; knee lesions with running, jumping and pivoting sports.
Why does it happen?
The honest answer is that the cause is not fully settled. The most widely accepted picture is repetitive loading of a vulnerable area of growing bone rather than one traumatic event, which fits the typical story of a busy young athlete with months of grumbling joint discomfort and no memorable injury.
- Repetitive impact and shear through one small area of the joint surface, particularly in high-volume single-sport training.
- Sports with heavy repeated loading of one joint: football, basketball, gymnastics, throwing and racket sports.
- Local blood supply to that area of bone being relatively fragile during growth.
- Anatomy and alignment influencing where the load concentrates.
- A genetic or familial contribution in a minority of cases.
How does it differ from more common growing-athlete knee pain?
The single most useful trigger for a rethink is a young athlete who is doing the right rehab, doing it consistently, and simply not improving. Growth-plate conditions respond to well-judged loading. A joint-surface problem often does not, and continuing to push load into it is not neutral.
Growth-plate or load-related pain
- Pinpoint pain the child can point to
- Tender bump below or at the tip of the kneecap
- Clearly worse with impact, better with relative rest
- No true joint swelling
- Predictable improvement over weeks with a loading plan
Suggestive of OCD
- Deep, vague ache inside the joint
- Intermittent swelling after activity
- Occasional catching, locking or giving way
- Pain not clearly tied to one movement
- Little or no progress after 6–8 weeks of appropriate rehab
Typical patterns - helpful for triage, not a substitute for assessment.
How is it diagnosed?
Assessment starts with the history and examination - where the pain sits, whether the joint swells, whether there is any catching, and how movement and strength look. X-rays including specific views of the knee will often show the lesion, but they can look normal early on.
MRI is the investigation that answers the questions that matter: how large the lesion is, whether the overlying cartilage is intact, whether fluid is tracking behind the fragment, and therefore whether it is stable or unstable. That stability assessment, along with whether the growth plates are still open, determines the plan.
How is it treated, and what about sport?
For a stable lesion in a child whose growth plates are still open, the first line of treatment is a period of genuine offloading to give the bone a chance to heal, followed by a staged rebuild. Healing rates in this group are encouraging, considerably better than in skeletally mature athletes, which is exactly why the diagnosis is worth chasing early rather than late.
Where the fragment is unstable, has detached, or a well-run non-surgical period has not worked, surgery is considered. Options range from drilling to stimulate blood supply, through fixing the fragment, to cartilage restoration procedures in more advanced cases. Recovery timelines are measured in many months either way.
The conversation with a young athlete is rarely easy. Being told to come out of sport for three months when the knee only hurts sometimes feels disproportionate. It helps to frame it as protecting the joint surface they will need for the next fifty years, and to keep them physically engaged and in the squad environment through non-impact training rather than disappearing entirely.
Phase 1
Offload and protect
Impact, pivoting and deep loaded flexion come out. Often 6–12 weeks. Non-impact conditioning, hip and quadriceps strength and upper-body work continue.
Phase 2
Reassess and rebuild
Repeat imaging guides progress. Load is reintroduced gradually - walking, then jogging, then controlled jumping and landing, with strength progressing throughout.
Phase 3
Return to sport
Sport-specific volume, change of direction and match exposure are rebuilt stepwise, with symptoms and swelling reviewed at each increase.
A typical non-surgical pathway for a stable lesion with open growth plates.
What this means for parents and coaches
OCD is not common, and the overwhelming majority of aching knees, ankles and elbows in young athletes are load-related and will respond well to a sensible loading plan. But it is common enough that anyone working with growing athletes should know the pattern: deep joint ache, intermittent swelling, occasional catching, and rehab that is not working.
If that is the picture, ask for imaging rather than another six weeks of the same programme. Found early, while the growth plates are open and the cartilage is intact, this is a condition with genuinely good prospects. Found late, the options narrow considerably.