Microscopic Structural Features of Fifth Metatarsal Bone Entheses in Men During the First Mature Age Period

The aim was to investigate the microscopic structural features of the entheses of the fifth metatarsal bone in men of the first mature age period. Material and methods. The study examined the microscopic features of the entheses of the fifth metatarsal bones bilaterally in 56 cadaveric specimens from males aged 21–35 years. Tissue specimens from the typical ligament and tendon attachment sites at the head and base of the fifth metatarsal bone were histologically analyzed using Masson’s trichrome staining. The thickness of enthesis zones was measured, and the organization of collagen fibers was analyzed with quantification of their percentage content in relation to adjacent structures using light microscopy of scanned histotopograms. Results. The study revealed that all four ligamentous and tendinous connections of the fifth metatarsal demonstrate fibrocartilaginous entheses comprising four distinct zones that structurally form a continuous transition from soft connective tissue to osseous tissue. Results showed greater thickness of the calcified versus mineralized fibrocartilage zones in the peroneus brevis tendon, plantar metatarsal, and collateral ligament entheses, featuring parallel wavy collagen fibers with scattered mature chondrocytes and isogenous groups. The maximal thickness of the calcified fibrocartilage zone was identified in the deep transverse metatarsal ligament enthesis, characterized by linearly oriented collagen fibers and abundant chondrocyte isogenous groups. The study determined the minimal thickness of the calcified fibrocartilage zone in the tarsometatarsal and long plantar ligament enthesis complex, exhibiting a disordered arrangement of collagen fibers and numerous mature chondrocytes organized in isogenous groups. Basophilic demarcation lines with serrated morphology in virtually all enthuses was documented. The most pronounced serrations (in both thickness and amplitude) were registered at the peroneus brevis tendon attachment site, while the deep transverse metatarsal ligament exhibited a characteristically attenuated and flattened basophilic line. A decreasing collagen gradient from calcified to mineralized zones was established in the peroneus brevis tendon and tarsometatarsal-long plantar ligament entheses, while the deep transverse metatarsal ligament exhibited an inverse pattern. The plantar metatarsal and collateral ligament entheses maintained equivalent collagen proportions across zones. Conclusion. The investigation of microarchitectural characteristics in fifth metatarsal entheses provides evidence supporting the probable existence of distinct structural patterns influenced by age, sex, and body constitution, which may correlate with differential susceptibility to mechanical trauma.

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