Biomechanical properties of the forefoot plantar soft tissue as measured by an optical coherence tomography-based air-jet indentation system and tissue ultrasound palpation system

BackgroundThe forefoot medial plantar area withstand high plantar pressure during locomotion, and is a common site that develops foot lesion problems among elderly people. The aims of the present study were to (1) determine the correlation between the biomechanical properties of forefoot medial plantar soft tissue measured by a newly developed optical coherence tomography-based air-jet indentation system and by tissue ultrasound palpation system, and (2) to compare the biomechanical properties of plantar soft tissues of medial forefoot between a young and old adult group.MethodsThirty healthy subjects were classified as the young or older group. The biomechanical properties of plantar soft tissues measured at the forefoot by the air-jet indentation system and tissue ultrasound palpation system were performed, and the correlation of the findings obtained in the two systems were compared.FindingsA strong positive correlation was obtained from the findings in the two systems (r = 0.88, P < 0.001). The forefoot plantar soft tissue of the older group was significantly stiffer at the second metatarsal head and thinner at both metatarsal heads than that of the young group (all P < 0.05). The stiffness coefficient at the second metatarsal head was 28% greater than that at the first metatarsal head in both study groups.InterpretationOlder subjects showed a loss of elasticity and reduced thickness in their forefoot plantar soft tissue, with the second metatarsal head displaying stiffer and thicker plantar tissue than the first metatarsal head. The air-jet indentation system is a useful instrument for characterizing the biomechanical properties of soft tissue.