Microstructure of the ligamentous apparatus of the fifth metatarsal bone

   Entheses are vulnerable to acute trauma under excessive loads, and are also the main target organ in a number of rheumatic conditions.

   Aim of the study was to investigate the features of the microscopic structure of the entheses of the fifth metatarsal bone in humans.

   Material and methods. The feet of 56 male cadavers aged 21–35 years were studied. On micropreparations of the fifth metatarsal bone with its ligamentous apparatus, the thickness of the fibrocartilaginous enthesis zones was measured, the location of collagen fibers was described, and their percentage content per unit area in the zones of calcified and mineralized fibrous cartilage of the enthesis was calculated, followed by a comparative analysis of the data obtained.

   Results and discussion. It was found that the connections of all four ligaments and the tendon to the V metatarsal bone are fibrocartilaginous entheses with four separate zones in their histological structure. A reliable predominance of the thickness of the calcified fibrous cartilage zone over the thickness of the mineralized fibrous cartilage zone of the entheses of the tendon of the short peroneus muscle, metatarsal plantar and collateral ligaments with a parallel arrangement of convoluted collagen fibers and single mature chondrocytes and their isogenic groups was revealed. The maximum thickness of the calcified fibrous cartilage zone is noted for the enthesis of the deep transverse metatarsal ligament with a direct arrangement of collagen fibers and multiple isogenic groups of chondrocytes, the minimum ‒ for the tarsometatarsal and long plantar ligaments with chaotically intertwined collagen fibers and many mature chondrocytes and their isogenic groups. The serrated basophilic line of enthesis of the tendon of the peroneus brevis muscle is characterized by the greatest thickness and amplitude of the serrations. A decrease in the proportion of collagen fibers from the calcified to the mineralized zone was revealed at the entheses of the tendon of the short peroneus muscle and the complex of the tarsometatarsal and long plantar ligaments; an increase in the proportion of collagen towards the mineralized zone at the enthesis of the deep transverse metatarsal ligament and its equal proportion at the entheses of the metatarsal plantar and collateral ligaments.

   Conclusions. The conducted study with the discovery of the features of the microstructure of the entheses of the fifth metatarsal bone testifies to the existence of age, sex, and possibly constitutional patterns of their structure and predisposition to mechanical injury.

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