This randomized clinical trial aims to compare the diagnostic performance, reproducibility, and agreement of several non-invasive instrumental methods for assessing plantar hyperkeratosis hardness in healthy subjects and patients with diabetes mellitus without active foot ulceration.

Participants will be evaluated in a single study session using plantar pressure platform analysis, durometer measurements, ultrasound elastography, and infrared thermography. The study seeks to identify the most reliable and discriminative methods for clinical and preventive assessment of plantar hyperkeratosis, particularly in populations at risk for diabetic foot complications.

This is a randomized, controlled, cross-sectional clinical trial with two parallel groups: healthy subjects and patients with diabetes mellitus without active or recent plantar ulceration.

All participants present at least one clinically identifiable plantar hyperkeratosis. Each subject undergoes a standardized assessment in a single session using four non-invasive instrumental techniques: plantar pressure platform, durometer, ultrasound elastography, and infrared thermography.

The order of application of the instrumental methods is randomized. Primary outcomes include superficial hardness, tissue stiffness, plantar pressure distribution, and plantar surface temperature. Secondary outcomes include demographic, anthropometric, and clinical variables.

The study aims to compare inter-group differences, method agreement, reproducibility, and discriminative capacity of each instrumental technique.

Inclusion Criteria:

• Age ≥ 18 years
• Presence of at least one clinically identifiable plantar hyperkeratosis
• Intact skin without ulceration
• Ability to maintain standing position for at least 30 seconds
• Signed informed consent

Additional Inclusion Criteria for Diabetes Mellitus Group:

• Medical diagnosis of type 1 or type 2 diabetes mellitus
• No active foot ulcer
• No history of foot ulcer within the previous 12 months

Exclusion Criteria:

• Active plantar ulcer, pre-ulcerative lesion, or recent ulcer scar
• Severe peripheral neuropathy (absence of protective sensation with 10 g monofilament)
• Severe peripheral arterial disease (Ankle-Brachial Index < 0.8)
• Foot surgery within the previous 6 months
• Active inflammatory, infectious, or dermatological condition at measurement site
• Use of keratolytic treatments or debridement within the previous 15 days
• Inability to complete the full assessment protocol

The statistical analyst assessing study outcomes will be blinded to participant group allocation. Due to the nature of the instrumental assessments, participant and investigator blinding was not feasible.