The purpose of the current study was to determine whether stress fractures and shin splints could be discriminated with MRI in the early phase. Twenty-two athletes, who had pain in the middle or distal part of their leg during or after sports activity, were evaluated with radiographs and MRI scans. Stress fractures were diagnosed when consecutive radiographs showed local periosteal reaction or a fracture line, and shin splints were diagnosed in all the other cases. In all eight patients with stress fractures, an abnormally wide high signal in the localized bone marrow was the most detectable in the coronal fat-suppressed MRI scan. In 11 patients with shin splints, the coronal fat-suppressed MRI scans showed a linear abnormally high signal along the medial posterior surface of the tibia, and in seven patients with shin splints, the MRI scans showed a linear abnormally high signal along the medial bone marrow. No MRI scans of shin splints showed an abnormally wide high signal in the bone marrow as observed on MRI scans of stress fractures. This study showed that fat-suppressed MRI is useful for discrimination between stress fracture and shin splints before radiographs show a detectable periosteal reaction in the tibia.Athletes frequently experience chronic pain induced by exercise in the medial aspect of the lower leg. Because the pain disturbs their sports activities, it is necessary for a patient with chronic leg pain to be diagnosed correctly as early as possible. Stress fractures and shin splints are wellknown as causes of chronic leg pain. Although shin splints and tibial stress fracture are involved in overuse injuries, they are different diseases. 14,15,19 According to the standard nomenclature of the American Medical Association as reported by Slocum, 19 shin splints are defined as pain and discomfort in the leg from repetitive running on hard surfaces or excessive use of foot flexors. The diagnosis should be limited to musculotendinous inflammation excluding fractures and ischemic disorders. However, stress fractures are recognized as the continuum of changes from microfracture to frank fracture under excess stress. However, patients with stress fractures or shin splints have similar symptoms and they have similar clinical signs, at least during the early phase of each disease. Because treatment of these diseases is different, early discrimination between shin splints and stress fractures is important for athletes. Athletes with shin splints do not need a long rest time, but all athletes with stress fractures of the tibia should cease sports activity for at least 4 or 6 weeks. Early discrimination between shin splints and stress fractures can allow athletes a return to sports activity as early as possible.The differential diagnosis between these two diseases is difficult in the early phase as determined from the physical examination and the radiographs. Radiographs are not useful in the early phase of stress fractures, although they are useful in the late phase because they show periosteal reaction, callus...

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Ligament healing is composed of several phases, including acute inflammation and reaction phase, repair and regeneration phase, and remodeling phase. At the molecular level, these phases are regulated by a complex interplay among inflammatory cells, fibroblasts, and the molecules, such as inflammatory cytokines, proteinases, extracellular matrices, and etc, which are produced by these cells. Macrophage migration inhibitory factor (MIF), which was discovered in 1966 as the first lymphokine, has been recognized as a pivotal mediator of inflammation in various pathological conditions including sepsis, arthritis, ARDS, and etc. Recent studies have shown that MIF plays an important role in proliferation and differentiation of cells, generation of organs, and wound healing 1-3. However, a role of MIF on the ligament healing process has not been elucidated as of yet. Based on the abovedescribed knowledge, we have hypothesized that MIF may enhance healing of the injured medial collateral ligament (MCL). Recently, a murine MCL injury model has attracted much notice because it is useful to clarify the effect of specific factor ablation on MCL healing by using genetically altered mice 4. A specific hypothesis to be tested in this study using MIF gene-deficient (MIF KO) mice is that the genetic ablation of MIF may inhibit natural improvement of the structural and mechanical properties of the injured MCL.