Abstract
Highly regular aligned trabeculae are found in the superficial posterior and inferior calcaneus appearing to connect the Achilles tendon (AT) to the plantar fascia (PF) in a bridge-like manner. This provides a morphological basis for the stretching-based heel pain treatment. However, the continuity of collagen fibres between the AT and the PF remains debated controversially to date. The given study morphologically investigated the AT-calcaneus-PF complex using histology and plastination. Moreover, the AT-calcaneus-PF complex was biomechanically mapped based on 13 sub-regions with a total of 76 tested samples. Regular calcaneal trabeculae were surrounded by tendon-like collagen fibre bundles and adipocytes. The orientation of calcaneal trabeculae was further closely related to the course of the PF collagen fibre bundles. The pooled biomechanical analysis revealed low elastic moduli (minimum = 4 MPa) and ultimate tensile strengths of the decalcified calcaneal samples (minimum = 0.4 MPa) and the calcaneal periostea (minimum = 2 MPa) and high respective values (elastic modulus maximum of 144 MPa; ultimate tensile strength maximum of 29 MPa) for the PF samples compared to the other sub-regions. This study provides structural evidence for a morphological connection between the AT and PF via the highly aligned calcaneal trabeculae of the posterior calcaneus. The AT-calcaneus-PF complex was biomechanically mapped to allow for an assessment of its site-dependent mechanical characteristics.
Highlights
Plantar fasciitis is the most frequent cause of inferior heel pain and affects approximately one percent of the adult population[1]
Low elastic moduli were noted in the decalcified calcaneal samples (MB: 4 MPa; lateral decalcified bone sample (LB): 7 MPa) and the lateral calcaneal periosteum sample (LCP: 16 MPa)
The ultimate tensile strength (UTS) was low for the decalcified calcaneal samples (MB: 0.4 MPa; LB: 0.6 MPa) and the medial calcaneal periosteum sample (MCP: 2 MPa)
Summary
Plantar fasciitis is the most frequent cause of inferior heel pain and affects approximately one percent of the adult population[1]. Highly regular aligned trabeculae were noted in the calcaneus that seemed to anatomically connect AT and PF in a bridge-like manner[6] These published findings raised the question whether the AT and PF are two structurally different tissues, inserting separately into the calcaneus from two ends, or if the AT and PF resemble one continuing collagenous structure, which is secondarily divided by the calcaneal ossification during life[6]. To shed light on the structural connection between the AT and the PF via the calcaneus this study followed two aims: Firstly, the proximal–distal transition of the AT-calcaneus-PF complex should be morphologically investigated continuously between the formation of the AT starting at the distal calf and ending at the insertion of the PF at the heads of the metatarsal bones It aimed at establishing a biomechanical testing setup for this heterogenous complex, which allows for a uniform investigation of the structural organization by means of a materials testing approach to subsequently enable the structural analysis of the same from a materials testing perspective
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