Calcaneal bone marrow oedema develops when the heel bone is subjected to more mechanical stress than it can safely tolerate. Rather than being a disease itself, bone marrow oedema represents the bone's biological response to excessive loading. Increased fluid accumulates within the bone marrow as part of the body's reaction to microscopic bone injury, often before a true stress fracture develops.
The most common cause is repetitive overload. Every step places force through the calcaneus, which acts as the primary weight-bearing bone of the heel. Under normal circumstances, healthy bone continually remodels itself by repairing tiny areas of microscopic damage. However, when loading exceeds the bone's ability to repair itself, these microscopic injuries accumulate faster than healing can occur. The result is a stress reaction within the bone, visible on MRI as bone marrow oedema.
One of the most frequent triggers is a sudden increase in activity. Beginning a new exercise programme, training for a marathon, increasing running distance too quickly or returning to sport after a period of inactivity can all overload the heel bone. Military recruits, athletes and people who suddenly spend much longer standing or walking at work are particularly susceptible because the increase in mechanical load often occurs before the bone has time to adapt.
Foot biomechanics also play an important role. Excessive pronation, cavus feet, altered gait patterns or reduced ankle mobility may change how forces pass through the calcaneus during walking and running. These biomechanical factors do not automatically cause bone marrow oedema, but they may increase local stress within particular regions of the heel bone, especially when combined with increased activity.
Body weight is another contributing factor. The heel absorbs forces several times greater than body weight during walking and substantially higher forces during running and jumping. An increase in body weight therefore increases the mechanical demands placed on the calcaneus with every step. However, it is important to recognise that bone marrow oedema also occurs in thin, highly active individuals, emphasising that the condition is related to load rather than weight alone.
Long-standing plantar fasciosis may also contribute. Chronic traction where the plantar fascia attaches to the calcaneus can increase stress within the underlying bone. MRI studies have demonstrated that bone marrow oedema commonly occurs adjacent to the plantar fascia insertion in patients with chronic plantar fasciosis. In these patients, the heel pain may arise from both the degenerative fascia and the underlying bone stress reaction.
Trauma is another recognised cause. A fall from height, awkward landing or direct blow to the heel may produce bone bruising or trabecular microfractures within the calcaneus without causing a complete fracture visible on X-ray. MRI is particularly sensitive for detecting these injuries during the early stages.
Less commonly, bone marrow oedema may occur in association with inflammatory arthritis, osteoporosis, metabolic bone disorders, infection or tumours. Although these conditions are much less frequent than mechanical overload, they must be considered when symptoms, examination findings or imaging appear atypical.
Age also influences the development of bone stress injuries. As people become older, changes in bone density, muscle strength and tissue recovery may reduce the skeleton's ability to tolerate repetitive loading. This partly explains why some patients develop bone marrow oedema despite activity levels that previously caused no difficulty.
Understanding the underlying cause is one of the most important aspects of treatment. Simply identifying bone marrow oedema on MRI is not enough. The clinician must determine why the bone has become overloaded. Without addressing the contributing factors—whether they relate to training errors, footwear, biomechanics, body weight or coexisting plantar fasciosis—the condition is more likely to persist or recur.
Successful management therefore extends beyond simply resting the heel. It requires identifying and correcting the mechanical factors responsible for the excessive stress so that the bone can heal and gradually tolerate normal loading again.