Teaching Case

An amateur runner suffered from a pain localised along the posteromedial border of the tibia. The pain, lasting for three months, was exercise-related and disappeared with stopping exercise. On physical examination a hard and painful lump was appreciable along the medial aspect of the middle third of the tibia.

Plain radiography evidenced a focal bone resorption along with periosteal reaction along the medial aspect of the tibial diaphysis (Fig. 1).

T1-weighted and T2-weighted MRI showed oedema of bone marrow and periosteum, and bone resorption (Fig. 2a-e). Enhancement of periosteum and bone marrow were evidenced on post-contrast MRI; subtle enhancement of bone cavities were also appreciable (Fig. 2f, g).

CT confirmed focal resorption and periosteal reaction along the posteromedial aspect of the tibial diaphysis (Fig. 3).

Medial tibial stress syndrome (MTSS) is a frequent overuse injury in athletes, accounting up to 17% of all running injuries. [1] Aetiology comprises two hypotheses: an overload bone microdamage or a periosteal traction at the origin of the tibialis posterior, flexor digitorum longus, or soleus muscles. [2] The chronic overload causes a bone weakening from imbalance of initial osteoclastic activity and repairing osteoblastic activity. [3, 4] It is noteworthy that a tibial stress reaction may be asymptomatic and not evolving to a MTSS or a stress fractures. [5] Relationship between MTSS and tibial stress fracture remains uncertain as they can be considered the spectrum of a continuous entity or two distinct pathologies. [2, 6] Plain radiography is useless in the early stage because negative; a bone callus along the posteromedial aspect of the tibial diaphysis can be appreciable in an advanced stage [7]. MRI is the golden standard for imaging of stress injuries, because very sensitive in depicting soft tissue abnormalities and in identifying other injuries, which share similar symptoms. [4, 8, 9]

MTTSs can be graded on the basis of MRI findings. [2]:

- Grade 0: No abnormality
- Grade 1: Isolated periosteal oedema
- Grade 2: Periosteal oedema and bone marrow oedema detectable on T2-weighted
imaging only
- Grade 3: Periosteal oedema and bone marrow oedema detectable on both T1-weighted
and T2-weighted MRI
- Grade 4a: Intracortical foci of abnormal signal and marrow oedema detectable on both
T1-weighted and T2-weighted MRI
- Grade 4b: Intracortical linear of abnormal signal and marrow oedema detectable on both
T1-weighted and T2-weighted MRI.

A simplified classification was proposed by Kijowski et al., which grouped grades 2, 3 and 4a, which share similar MRI features and prognosis. [4]
CT is useful and specific when a fracture line exists, but this occurs at the late stage of a stress bone injury; it can reveal a mild osteopenia of the tibial diaphysis in the early stage of cortical overload. [2, 3, 8]
Diagnosis of a MTSS is clinical and imaging is indicated only when symptoms are not relieved with conservative treatment; MRI can provide diagnosis and grading of a MTSS as well as differential diagnosis with other chronic injury of the leg. [6, 10] Despite lack of evidence of therapeutic options, a prompt diagnosis of a MTSS is essential for a rapid return to sport activities. [6]