Histological study of the Achilles tendon in diabetic and non-diabetic individuals: a comprehensive comparison

The Achilles tendon (AT) is crucial for locomotion but is vulnerable to diabetes mellitus (DM)-associated pathologies. Comprehensive human histological comparisons between diabetic and non-diabetic ATs are scarce. This study provides a detailed histological comparison and addresses a significant knowledge gap.

Achilles tendons from four individuals with diabetes (undergoing amputation for diabetic foot syndrome) and four non-diabetic donors were analyzed. Samples from three anatomical levels (Level 1: calcaneal insertion; Level 2: midportion; Level 3: myotendinous junction) underwent histological processing, including hematoxylin and eosin and Sirius Red staining. Key features were scored semi-quantitatively.

Diabetic ATs showed a tendency toward increased adipose tissue at Level 1 and a higher frequency of blood vessels across all levels. Control (non-diabetic) ATs showed a higher prevalence of cells located in lacunae (Levels 1 and 2). At Level 1, non-diabetic cases also presented more developed cartilage than the traces observed in diabetic cases, and ossification was observed exclusively in the non-diabetic group.

Diabetes mellitus is associated with distinct histological alterations in the human Achilles tendon, affecting adipose tissue, vascularity, cellular components, and entheseal features, such as cartilage development and ossification. This study provides novel human histological evidence of the impact of DM on AT structure, suggesting impaired adaptive and regenerative capacity in individuals with diabetes.