What is it about?
Skeletal muscles can attach to bone through a tendon or directly through a fleshy attachment, but the microscopic structure of these direct muscle–bone attachments has received little attention. This study examined seven human muscle–bone interfaces and compared fleshy attachments with classical tendinous entheses using histology and exploratory digital morphometry. Classical entheses showed the expected four-zone transition from tendon through uncalcified and calcified fibrocartilage to bone. In contrast, most fleshy attachments showed a distinct three-zone organization consisting of skeletal muscle, dense connective tissue and bone, without an intervening fibrocartilaginous layer. Collagen bundles approached the bone at acute angles and formed Sharpey-fiber-like interdigitations with the bone surface. One attachment, the external oblique at the iliac crest, showed both fibrous and fibrocartilaginous regions. These observations suggest that human muscle–bone attachments form a structural continuum rather than a single uniform type.
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Why is it important?
This study provides a systematic comparative histological framework for an anatomical interface that has been much less studied than the classical tendon-to-bone enthesis. The findings suggest that fleshy muscle attachments transmit force through a specialized periosteal connective-tissue continuum rather than through fibrocartilage. This distinction may be relevant to understanding how different muscle–bone interfaces respond to mechanical loading, injury and reconstruction. It also raises the testable possibility that direct reattachment of muscle to broad bony surfaces may require different biological and surgical considerations from conventional tendon-to-bone repair. The proposed three-pattern framework—fibrocartilaginous, fibrous and mixed—provides a basis for future histological, molecular and biomechanical studies.
Perspectives
As an anatomist, I was particularly interested in a simple but surprisingly underexplored question: how does skeletal muscle transmit force to bone when no macroscopic tendon is present? Classical entheses have been studied extensively, yet fleshy muscle–bone attachments are common throughout the human body and their microscopic organization remains comparatively poorly characterized. The most important observation for me was that these attachments are not merely simplified entheses. They appear to have their own structural solution—dense periosteal connective tissue, obliquely oriented collagen bundles and Sharpey-fiber-like interdigitations—without the fibrocartilaginous transition characteristic of a classical enthesis. I regard this study as a starting anatomical framework rather than a definitive classification, and I hope it encourages further molecular, biomechanical and clinical investigation of this neglected interface.
Prof. Dr. Hesham N. Mustafa
King Abdulaziz University
Read the Original
This page is a summary of: Human fleshy muscle–bone attachments are histologically distinct from classical entheses: A comparative exploratory study, Morphologie, December 2026, Elsevier,
DOI: 10.1016/j.morpho.2026.101145.
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