Abstract
BackgroundThe enthesis possesses morphological adaptations across the soft-hard tissue junction which are not fully restored during surgical avulsion repairs. This loss of anatomical structure, highly related to function, contributes to poor clinical outcomes. Investigating the native macro- and micro-structure of a specific enthesis can provide functional and biomechanical insights to develop specialised, novel tissue-engineered therapeutic options and potentially improve current surgical treatments for avulsion injuries.MethodsThis study examines the anatomy and histomorphology of the flexor digitorum profundus (FDP) enthesis in 96 fresh-frozen human cadaveric fingers, quantitatively and qualitatively analyzing the shape, size, angle of tendon fibres and histological architecture, and explores differences in sex, finger and distance along the enthesis using linear mixed effects models.ResultsMacroscopically, results showed a consistent trapezoidal insertion shape of 29.29 ± 2.35 mm2 mean surface area, but with significant morphometric size differences influenced primarily by the smaller dimensions of the little finger. Microscopically, a fibrocartilaginous enthesis was apparent with a 30.05 ± 0.72o mean angle of inserting tendon fibres, although regional variation in fibrocartilage and the angle change of tendon fibres before insertion existed.ConclusionsThe implication of these findings on native and specific FDP enthesis function is discussed whilst providing recommendations for optimal FDP enthesis recreation for interfacial tissue engineers and hand surgeons. The study emphasizes the importance of region-specific knowledge whilst also describing methods applicable to assessing any soft tissue insertion.
Highlights
The enthesis possesses morphological adaptations across the soft-hard tissue junction which are not fully restored during surgical avulsion repairs
The flexor digitorum profundus (FDP) tendon inserts into the base of the distal phalanx (DP) in the finger, functioning to provide a full fist for power grip and fingertip pinch required for everyday manual tasks
All 96 fingers from 12 donors were dissected for either footprint (3 male donors, 3 female; mean age 82.2, range 65–95) or histological (3 male, 3 female; mean age 79.3, range 73–91) investigation, selected as a sample of convenience but to provide equal sex balance. 3x magnification was used throughout dissection, and no gross pathology or previous surgery of the FDP insertion was observed
Summary
The enthesis possesses morphological adaptations across the soft-hard tissue junction which are not fully restored during surgical avulsion repairs. This loss of anatomical structure, highly related to function, contributes to poor clinical outcomes. Investigating the native macro- and micro-structure of a specific enthesis can provide functional and biomechanical insights to develop specialised, novel tissue-engineered therapeutic options and potentially improve current surgical treatments for avulsion injuries. The majority of entheses possess an interfacial fibrocartilage transition, providing a gradation in tissue properties [15, 16] Such entheses are categorized as ‘fibrocartilaginous’ and encompass 4 distinct tissue zones: dense fibrous connective tissue, uncalcified fibrocartilage (UF), calcified fibrocartilage (CF), and bone [17,18,19]; ‘fibrous’ entheses lack fibrocartilage. Surgical reattachment of an avulsed tendon does not recapitulate the fibrocartilaginous transition zone [20,21,22,23], leaving a biomechanically inferior interface [20, 22, 24] that promotes re-rupture risk and poor outcome
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