This randomized, double-blind clinical trial aims to compare the clinical and imaging effects of autologous bone marrow aspirate versus platelet-rich fibrin injections in patients with chronic plantar fasciitis. The procedures are performed under ultrasound guidance to ensure precision and safety. The study evaluates pain reduction, foot function, and ultrasonographic changes in the plantar fascia at follow-up intervals.

Chronic plantar fasciitis is a common cause of heel pain that may persist despite standard conservative measures such as physical therapy, stretching, orthoses, and corticosteroid injections. Regenerative medicine techniques, including autologous platelet concentrates and bone marrow-derived products, have emerged as potential alternatives to promote tissue healing and long-term symptom improvement.

This randomized controlled trial investigates and compares two minimally invasive orthobiologic interventions:

Bone Marrow Aspirate (BMA) - obtained from the posterior iliac crest under local anesthesia and injected into the most symptomatic region of the plantar fascia under ultrasound guidance.

Platelet-Rich Fibrin (PRF) - prepared from autologous venous blood by centrifugation without anticoagulants, forming a fibrin matrix injected into the plantar fascia under ultrasound guidance.

All procedures are performed under sterile conditions and tibial nerve regional anesthesia.

Pain and safety will be monitored using the Visual Analog Scale (VAS) and by recording adverse events at the following time points: baseline (0), 30 minutes, 1, 6, 12, and 24 months after the procedure.

Functional outcomes will be collected with Modified AOFAS Score at baseline, 1, 6, 12, and 24 months. Ultrasonography will measure plantar fascia thickness immediately before the intervention and at 12 months.

This research contributes to the growing evidence supporting orthobiologic therapies as viable, minimally invasive options for chronic plantar fasciitis management.

Inclusion Criteria:

• Adults aged 18 to 75 years.
• Clinical diagnosis of chronic plantar fasciitis for more than 6 months, confirmed by ultrasonography (increased plantar fascia thickness and hypoechogenicity).
• Persistent heel pain refractory to conventional conservative treatment (stretching, orthotics, physical therapy, or corticosteroid injections).
• Visual Analog Scale (VAS) pain score ≥ 4 at baseline.
• Ability and willingness to comply with study procedures and follow-up assessments.
• Signed informed consent.

Exclusion Criteria:

• Previous foot or ankle surgery on the affected limb.
• Acute trauma, infection, or ulceration in the region of the plantar fascia.
• Systemic inflammatory diseases (e.g., rheumatoid arthritis, lupus, psoriatic arthritis).
• Metabolic or endocrine disorders interfering with healing (e.g., diabetes mellitus with poor glycemic control, thyroid disorders).
• Current use of systemic corticosteroids, immunosuppressants, or anticoagulants.
• Active neoplasia or hematologic disorders.
• Pregnancy or breastfeeding.
• Peripheral vascular disease or neuropathy affecting the lower limbs.
• Contraindications to local anesthesia or venipuncture.

De-identified individual participant data (IPD) that support the findings of this study will be made available upon reasonable request after publication of the main results. Data will be shared with qualified researchers for academic purposes only, upon approval by the principal investigator and the ethics committee.

The IPD will be available beginning 6 months after publication and for up to 3 years thereafter.

Researchers must provide a methodologically sound proposal and obtain approval from the study's principal investigator (Lucas Fonseca, MD). Data access will be granted through a secure data transfer agreement.

Double-blind design: both participants and investigators performing follow-up assessments are blinded to group allocation. The injectate is prepared in a separate room by a technician not involved in patient assessment.