Asymptomatic Runners With MRI Abnormalities

Several studies scanned healthy, pain-free marathoners and found surprisingly high rates of structural findings that had no clinical correlation.

A 2024 study of amateur marathon runners found a 42.3% prevalence of knee cartilage lesions (mostly mild grade 1–2), and when combined with meniscus lesions and bone marrow edema, the overall prevalence of some knee abnormality reached 45.7% for cartilage, 72.4% for meniscus lesions, and 49.5% for bone marrow edema — with the patellofemoral cartilage and posterior horn of the medial meniscus most commonly affected. Many of these runners had no knee complaints at all.[pmc.ncbi.nlm.nih][journals.plos]

A UK-based longitudinal study (the "London Marathon" cohort) scanned 82 healthy, sedentary novice runners with 3T MRI six months before they started training and again shortly after they completed their first marathon. Even at baseline — before any training — the majority of these asymptomatic volunteers already had signs of damage in various knee structures; one companion analysis found 97% of knees had some abnormality, with the patellofemoral compartment most affected. This shows that "abnormal" MRI findings are common in the general population even without running.[discovery.ucl.ac][bmjopensem.bmj]

An older but frequently cited study scanned 23 asymptomatic ultra-distance/marathon runners (some running 26, 50, or even 100-mile races, averaging 41 miles per week in training) and found a meniscal tear prevalence of just 9% — actually lower than rates reported in sedentary, asymptomatic nonathletes (16%) and asymptomatic non-runner athletes (20%). The authors concluded that heavy running mileage does not increase meniscal degeneration compared to the general population.[ajronline]

A 3.0T MRI study compared 10 marathon runners to 12 physically active (non-runner) controls, all asymptomatic. Eight of the ten runners and 7 of the 12 controls showed some knee abnormality on MRI — a high rate in both groups — and running a single marathon didn't significantly change the MRI findings before versus after the race.[pubmed.ncbi.nlm.nih]

Pain or Symptoms Without Matching MRI Findings

The flip side you mentioned — people reporting knee pain or injury complaints where MRI shows nothing definitive, or where imaging changes don't track with symptoms — also shows up clearly in this literature.

The same London Marathon cohort found that after finishing the marathon, several MRI changes appeared or worsened (increased cartilage signal changes in the lateral patella, semimembranosus tendon, iliotibial band, and prepatellar bursa) despite the runners remaining largely asymptomatic. Meanwhile, pre-existing subchondral bone marrow edema in the tibia and femur actually improved after marathon training and completion — the opposite of what you'd expect if pain and imaging findings moved together. A six-month follow-up on the same runners found these improvements in bone marrow and cartilage condition were sustained long-term, again largely disconnected from symptom reports.[bmjopensem.bmj][link.springer]

A Chinese study of 50 asymptomatic amateur runners looked specifically at bone marrow edema-like signal before and immediately after a half marathon. They found a 62% incidence of this edema signal in runners (significantly higher than in 20 non-running controls), but critically, there was no significant change in the group-level incidence before versus after the race — even though individually, 3 runners developed new lesions, 8 showed progression, and 4 actually showed improvement. All of this occurred in runners who reported no pain.[pubmed.ncbi.nlm.nih][sciencedirect]

A University of Miami study using advanced T2 relaxation mapping (a technique sensitive enough to detect biochemical cartilage changes before structural damage appears) scanned female runners before and after a half marathon. They detected significant localized cartilage changes on the medial knee that wouldn't show up on conventional MRI, but found no significant changes in the patella, medial femoral condyle, or lateral tibial surfaces — illustrating how imaging findings can be highly technique-dependent and don't map cleanly onto pain patterns.[news.med.miami]

The Bigger Picture

A systematic review in the American Journal of Sports Medicine specifically examined acute MRI changes after running and their reversibility, concluding that many post-run MRI changes (like bone marrow edema or fluid signal) are transient and resolve on their own, reinforcing that isolated MRI findings — positive or negative — often don't reliably predict or explain symptoms.[journals.sagepub]

Taken together, this body of research is part of why many sports medicine physicians are cautious about ordering knee MRIs for runners with mild pain, or about over-interpreting incidental findings: structural "abnormalities" are extremely common in symptom-free knees (running or not), and the relationship between what MRI shows and what a patient actually feels is often weak or inconsistent, especially for common findings like mild cartilage signal changes, small meniscal degeneration, or bone marrow edema.