Effects of Functional Magnetic Stimulation on Pain, Function, and MRI-Derived Outcomes in Athletes with Tibial Bone Stress Injury: A Randomized Controlled Trial

Background: Tibial bone stress injury (TBSI) with associated bone marrow edema (BME) is a common and clinically challenging condition in athletes, often requiring prolonged load restriction and delayed return to sport. Evidence for adjunctive interventions that improve both symptoms and MRI‐derived recovery remains limited. The aim of this study was to investigate whether adding Functional Magnetic Stimulation (FMS) to standardized rehabilitation improves pain, function, and MRI‐derived outcomes over 16 weeks in athletes with MRI‐confirmed TBSI. Materials and Methods: Forty athletes with Fredericson grade 2‐3 TBSI were randomized to FMS plus rehabilitation (n = 20) or rehabilitation alone (n = 20). Both groups completed a 4‐week load‐based rehabilitation program, while the FMS group additionally received eight 30 min FMS sessions at 40 Hz. Outcomes were assessed at baseline, 4 weeks, and 16 weeks. The primary outcome was activity‐related pain (NPRS), while secondary outcomes included lower‐limb function (LEFS‐GR), BME extent, and Fredericson grade. Continuous outcomes were analyzed using two‐way mixed ANOVA, whereas Fredericson grade was analyzed using an ordinal generalized estimating equation model. The level of statistical significance was set at p < 0.05. Results: Groups were comparable at baseline. Significant group × time interactions favored FMS for NPRS, F(2, 76) = 12.46, p < 0.001, η2p = 0.247; LEFS‐GR, F(1.08, 41.09) = 81.56, p < 0.001, η2p = 0.682; and BME extent, F(1.44, 54.85) = 49.33, p < 0.001, η2p = 0.565. At 16 weeks, the FMS group showed lower NPRS scores, higher LEFS‐GR scores, and lower BME extent than controls. Fredericson grade also showed a significant group × time effect, Wald χ2(2) = 20.38, p < 0.001. The FMS group had significantly lower cumulative odds of classification in a higher Fredericson grade at 4 weeks (OR = 0.045, 95% CI: 0.012‐0.163, p < 0.001), whereas the corresponding difference at 16 weeks remained directionally favorable but did not reach statistical significance (OR = 0.033, 95% CI: 0.001‐1.029, p = 0.052). Conclusions: The addition of FMS to load‐based rehabilitation was associated with greater clinical and functional improvements, greater reductions in BME extent, and a more favorable longitudinal trajectory in MRI severity classification than rehabilitation alone in athletes with TBSI. However, because the study did not include a sham‐FMS condition and participants could not be blinded, the self‐reported pain and functional outcomes should be interpreted cautiously. FMS may represent a useful adjunct to structured rehabilitation, although sham‐controlled and longer‐term studies should determine its effects on return‐to‐sport progression and recurrence risk.