This randomized controlled trial evaluates whether Functional Magnetic Stimulation (FMS) can provide additional benefits when combined with a structured physiotherapy rehabilitation program in athletes with MRI-confirmed tibial bone stress injury and associated bone marrow edema. A total of 40 athletes with Fredericson grade 2 or 3 lesions are allocated to either a combined intervention group receiving FMS plus rehabilitation or a control group receiving rehabilitation alone. The intervention period lasts four weeks. Participants in both groups follow the same load-based rehabilitation program, while those in the FMS group also receive eight 30-minute FMS sessions. Assessments are performed at baseline, after the four-week intervention, and at 16 weeks. The evaluated outcomes include activity-related tibial pain, lower-limb functional ability, MRI-measured bone marrow edema extent, and Fredericson MRI grade. The purpose of the study is to examine whether adding FMS to standardized rehabilitation leads to greater clinical, functional, and MRI-derived improvement compared with rehabilitation alone.

Background: Tibial bone stress injury is a clinically relevant overuse condition in athletes and is commonly associated with bone marrow edema on magnetic resonance imaging. It typically presents with localized tibial pain during weight-bearing or sport-related loading and may interfere with training participation and return to activity. MRI is used to confirm the diagnosis, determine injury severity, and monitor structural recovery. Fredericson grades 2 and 3 represent tibial bone stress injuries with bone marrow edema but without a visible fracture line, and are usually treated conservatively through activity modification, graded loading, therapeutic exercise, and progressive rehabilitation. Functional Magnetic Stimulation (FMS) is a non-invasive electromagnetic intervention that can induce deep neuromuscular activation and may contribute to pain modulation, improved load tolerance, and local tissue responses. However, its role as an adjunctive intervention in athletes with MRI-confirmed tibial bone stress injury remains insufficiently investigated.

Aim: The aim of this randomized controlled clinical trial is to evaluate whether adding Functional Magnetic Stimulation to a standardized physiotherapy rehabilitation program provides additional benefits in athletes with MRI-confirmed tibial bone stress injury associated with bone marrow edema. The study examines whether the combined intervention leads to greater improvement in activity-related pain, lower-limb functional ability, and MRI-derived indicators of recovery compared with standardized rehabilitation alone.

Method: Forty athletes with MRI-confirmed tibial bone stress injury classified as Fredericson grade 2 or 3 are randomly allocated to two groups. The intervention group receives Functional Magnetic Stimulation in addition to a structured four-week physiotherapy rehabilitation program, while the control group receives the same rehabilitation program without FMS. The rehabilitation program is based on symptom-guided activity modification, progressive lower-limb loading, strengthening, mobility exercises, neuromuscular control, and gradual return to impact-based activity. FMS is applied twice weekly for four weeks, for a total of eight 30-minute sessions, over the symptomatic tibial region. Assessments are performed at baseline, at the end of the four-week intervention period, and at 16-week follow-up. Outcomes include activity-related tibial pain assessed with the Numerical Pain Rating Scale, lower-limb functional ability assessed with the Greek version of the Lower Extremity Functional Scale, MRI-derived bone marrow edema extent, and Fredericson MRI grade. Continuous outcomes are analyzed using repeated-measures mixed analysis of variance, while Fredericson grade is analyzed as an ordinal repeated-measures outcome.

Expected Results: It is expected that athletes receiving Functional Magnetic Stimulation in addition to standardized physiotherapy rehabilitation will demonstrate greater reductions in activity-related tibial pain, greater improvements in lower-limb functional ability, and more favorable MRI-derived recovery compared with athletes receiving rehabilitation alone. The findings are expected to clarify whether FMS may serve as a useful adjunctive modality within a structured rehabilitation approach for athletes with tibial bone stress injury.

Inclusion Criteria:

• Age between 18 and 45 years.
• Regular participation in sports training at least three times per week during the previous six months.
• MRI-confirmed tibial bone stress injury classified as Fredericson grade 2 or grade 3.
• Localized tibial pain provoked by loading activity.
• Activity-related pain intensity of at least 3/10 on the Numeric Pain Rating Scale.
• Written informed consent provided before participation.

Exclusion Criteria:

• Fredericson grade 4 injury or visible fracture line on MRI.
• Bone marrow edema related to infection, tumor, systemic inflammatory disease, or another non-mechanical cause.
• History of fracture, surgery, or intra-articular/peri-osseous injection in the affected lower limb within the previous 12 weeks.
• Previous Functional Magnetic Stimulation or Extracorporeal Shockwave Therapy within the previous 8 weeks.
• Contraindications to magnetic stimulation, including pacemaker, implanted neurostimulator, cochlear implant, or significant metallic implant in or near the treatment area.
• Pregnancy or breastfeeding.
• Any neurological, metabolic, cardiovascular, or systemic condition that could affect safe participation or interpretation of study outcomes.

A masked assessor will conduct the measurements