Tibial Nerve Imaging Enters the Chronic Plantar Fasciitis Workup
Chronic plantar fasciitis is usually framed as a fascia problem, but this protocol treats it as a broader neuromuscular pain disorder. Investigators at Sultan Abdülhamid Han Training and Research Hospital in Istanbul are planning a cross-sectional case-control study to examine whether tibial nerve morphology at the tarsal tunnel tracks with plantar fascia thickness, pressure pain threshold, foot posture, and functional status.
The study focuses on a question that matters at the bedside: why do some patients report pain and disability out of proportion to the apparent thickness of the fascia? If plantar fascia pathology alone explained the syndrome, ultrasound measurements and symptoms would line up more neatly. Instead, this protocol is built around the possibility that nerve involvement, altered pain sensitivity, and postural mechanics are all feeding the clinical picture.
Why a Tibial Nerve Measure Could Change the Frame
The central biological premise is straightforward. The tibial nerve runs through the tarsal tunnel under the flexor retinaculum, close enough to become clinically relevant when local tissue stress, chronic inflammation, or repetitive mechanical loading alters the region. Measuring its cross-sectional area could help determine whether a nerve-level abnormality accompanies persistent heel pain, especially in patients whose symptoms seem too severe for the plantar fascia findings alone.
A single sentence captures the potential clinical shift: heel pain may not be confined to the fascia. If tibial nerve enlargement or altered morphology is associated with lower pressure pain thresholds, poorer posture scores, or worse function, chronic plantar fasciitis may need to be assessed as a mixed structural and sensitization problem rather than as isolated enthesopathy.
The protocol does not claim causation, and it does not try to. Its value lies in mapping relationships that could justify future prospective studies and, eventually, more targeted treatment pathways.
What the Investigators Will Measure at Baseline
The study will enroll an estimated 102 participants and uses a non-probability sample drawn from people presenting to the clinic, along with healthy volunteers. Adults 18 to 65 years old are eligible, and both sexes can participate. The plantar fasciitis group must have heel pain lasting at least six months, morning first-step pain, and tenderness at the medial calcaneal tubercle. Healthy controls must be free of acute or chronic disease.
Measurements will be made at baseline only. Three ultrasound-based and clinical components anchor the protocol: tibial nerve cross-sectional area within the tarsal tunnel, plantar fascia thickness, and pressure pain threshold at the calcaneus. The protocol also includes the Numeric Pain Rating Scale, Foot Posture Index, Short Form-12, and Foot Function Index.
That combination is clinically sensible. Pain threshold gives a direct read on sensitivity, ultrasound captures structural change, and function scales show whether the disorder is merely painful or actually disabling in daily life.
How the Ultrasound and Pain Testing Are Structured
The ultrasound component is more than a cursory look at the heel. For the tibial nerve, images will be obtained from within the tarsal tunnel, next to the medial malleolus, under the flexor retinaculum, alongside the artery-venous bundle. Three measurements will be taken, and the mean will be calculated. An independent researcher will code and record the images, which will be analyzed using ImageJ offline DICOM software.
Plantar fascia thickness will also be assessed ultrasonographically, with participants in a prone position. Although the protocol excerpt truncates the exact positioning details, the intent is clear: standardize the measurement of a structure that is often used as a proxy for chronic heel pathology.
Pressure pain threshold testing adds another layer. Using a Wagner manual pressure algometer with a 1 cm² probe, investigators will apply pressure to the calcaneus, the plantar fascia attachment point, until pain is perceived. The test will be repeated twice with a one-minute interval, and the average will be recorded. In practical terms, this measures the local threshold at which tissue loading becomes painful, a useful marker when chronic pain may involve peripheral sensitization.
Eligibility Criteria Draw a Narrow Clinical Lane
The exclusion criteria are extensive and clinically important. Recent physical therapy, injection, radiation, or surgery involving the plantar fascia or tibial nerve are excluded, as are calcaneal fracture, tumor, cyst, lumbosacral radiculopathy, polyneuropathy, inflammatory rheumatic disease, foot and ankle osteoarthritis, osteomyelitis, skin infection, kidney or liver failure, diabetes, peripheral arterial disease, and pregnancy.
This is not just administrative caution. Each of those conditions could distort nerve morphology, pain sensitivity, gait, or functional scores. Removing them helps isolate the relationship between chronic plantar fasciitis and the tibial nerve, even though the design remains observational and cannot prove a directional effect.
Functional Scores Will Tell the Story Beyond Anatomy
Ultrasound alone will not answer the clinical question. Foot posture and function matter because heel pain becomes meaningful only when it changes how patients stand, walk, and tolerate daily activity. The Foot Posture Index may reveal whether mechanical alignment contributes to ongoing strain at the plantar fascia origin or the tarsal tunnel region. The Foot Function Index and SF-12 will show whether local symptoms spill into broader physical and mental health burden.
Pain is measured in two ways for a reason. Morning first-step pain is a classic plantar fasciitis hallmark, while average weekly pain captures the broader pain experience. If those scores correlate more closely with tibial nerve size than with fascia thickness, the anatomy of chronic heel pain may be more complex than routine clinical labeling suggests.
What This Study Can and Cannot Deliver
This protocol is built to generate associations, not answers about cause and effect. Cross-sectional data cannot determine whether tibial nerve enlargement precedes pain, results from it, or simply travels alongside it. Even so, the planned measurements could help identify which patients warrant a closer look at nerve involvement rather than repeated focus on plantar fascia thickness alone.
The practical consequence would be in future hypothesis generation, not immediate treatment change. If the tarsal tunnel proves relevant, clinicians may eventually think more carefully about neuropathic contributors, mechanosensitivity, and the possibility that some chronic plantar fasciitis cases are better understood through a mixed musculoskeletal and nerve-based model.
For now, the study offers a precise observational framework. Its real strength lies in asking whether a common heel pain syndrome is being under-read by ultrasound that stops at the fascia and does not continue to the nerve traveling beside it.