Chondroitin sulphate glycosaminoglycans contribute to widespread inferior biomechanics in tendon after focal injury.

Both mechanical and structural properties of tendon change after injury however the causal relationship between these properties is presently unclear. This study aimed to determine the extent of biomechanical change in post-injury tendon pathology and whether the sulphated glycosaminoglycans (glycosaminoglycans) present are a causal factor in these changes. Equine superficial digital flexor tendons (SDF tendons) were surgically-injured in vivo (n=6 injured, n=6 control). Six weeks later they were harvested and regionally dissected into twelve regions around the lesion (equal medial/lateral, proximal/distal). Glycosaminoglycans were removed by enzymatic (chondroitinase) treatment. Elastic modulus (modulus) and ultimate tensile strength (UTS) were measured under uniaxial tension to failure, and tendon glycosaminoglycan content was measured by spectrophotometry. Compared to healthy tendons, pathology induced by the injury decreased modulus (-38%; 95%CI -49% to -28%; P<0.001) and UTS (-38%; 95%CI -48% to -28%; P<0.001) and increased glycosaminoglycan content (+52%; 95%CI 39% - 64%; P<0.001) throughout the tendon. Chondroitinase-mediated glycosaminoglycan removal (50%; 95%CI 21-79%; P<0.001) in surgically-injured pathological tendons caused a significant increase in modulus (5.6MPa/µg removed; 95%CI 0.31-11; P=0.038) and UTS (1.0MPa per µg removed; 95%CI 0.043-2; P=0.041). These results demonstrate that the chondroitin/dermatan sulphate glycosaminoglycans that accumulate in pathological tendon post-injury are partly responsible for the altered biomechanical properties.

Passive mechanical properties of the gastrocnemius after spinal cord injury.

INTRODUCTION: In this study we compared passive mechanical properties of gastrocnemius muscle-tendon units, muscle fascicles, and tendons in control subjects and people with ankle contractures after spinal cord injury. METHODS: Passive gastrocnemius length-tension curves were derived from passive ankle torque-angle data obtained from 20 spinal cord injured subjects with ankle contractures and 30 control subjects. Ultrasound images of muscle fascicles were used to partition length-tension curves into fascicular and tendinous components. RESULTS: Spinal cord injured subjects had stiffer gastrocnemius muscle-tendon units (stiffness index: 74.8 ± 27.0 m(-1) ) than control subjects (54.4 ± 17.7 m(-1) ) (P = 0.004). Muscle-tendon slack lengths, as well as slack lengths and changes in length of fascicles and tendons, were similar in the two groups. CONCLUSIONS: People with ankle contractures after spinal cord injury have stiff gastrocnemius muscle-tendon units. It is not clear whether this reflects changes in properties of muscle fascicles or tendons.

Passive mechanical properties of gastrocnemius muscles of people with ankle contracture after stroke.

OBJECTIVE: To investigate the mechanisms of contracture after stroke by comparing passive mechanical properties of gastrocnemius muscle-tendon units, muscle fascicles, and tendons in people with ankle contracture after stroke with control participants. DESIGN: Cross-sectional study. SETTING: Laboratory in a research institution. PARTICIPANTS: A convenience sample of people with ankle contracture after stroke (n=20) and able-bodied control subjects (n=30). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Stiffness and lengths of gastrocnemius muscle-tendon units, lengths of muscle fascicles, and tendons at specific tensions. RESULTS: At a tension of 100N, the gastrocnemius muscle-tendon unit was significantly shorter in participants with stroke (mean, 436mm) than in able-bodied control participants (mean, 444mm; difference, 8mm; 95% confidence interval [CI], 0.2-15mm; P=.04). Muscle fascicles were also shorter in the stroke group (mean, 44mm) than in the control group (mean, 50mm; difference, 6mm; 95% CI, 1-12mm; P=.03). There were no significant differences between groups in the mean stiffness or length of the muscle-tendon units and fascicles at low tension, or in the mean length of the tendons at any tension. CONCLUSIONS: People with ankle contracture after stroke have shorter gastrocnemius muscle-tendon units and muscle fascicles than control participants at high tension. This difference is not apparent at low tension.