Intratendinous pressure of the Achilles tendon during exercise is related to the degree of tendon torsion

Loading Speed and Intensity in Eccentric Calf Training Impact Acute Changes in Achilles Tendon Thickness and Stiffness: A Randomized Crossover Trial

PURPOSE

Eccentric calf training for Achilles tendinopathy shows variable success in athletes. Recent insights suggest a role for tendon fluid flow (exudation or redistribution) during exercise, which explains post-exercise reductions in thickness and increases in stiffness of the tendon. This fluid flow is thought to be beneficial as it may promote tendon remodeling, reduce intratendinous pressure, and alleviate pain. In this perspective, slow, high-load exercises are promoted as they theoretically facilitate tendon fluid flow. However, evidence supporting this assumption is lacking. Therefore, this study aimed to investigate whether loading speed and intensity during eccentric calf training impact acute changes in midportion Achilles tendon thickness and stiffness, reflecting alterations in local tendon fluid content.

METHODS

A randomized, assessor-blinded, crossover trial was conducted with 34 healthy athletes (17 men, 17 women, age: 23.7 ± 6 yr). Participants underwent three single-leg eccentric heel-drop interventions with 20% additional bodyweight, varying in loading speed (fast: 1 s, slow: 3 s) and loading intensity (low: to plantigrade, high: to maximal dorsiflexion). Achilles tendon anteroposterior diameter, cross-sectional area, and shear wave velocity were assessed in the midportion region using ultrasonography and shear wave elastography pre- and immediately post-intervention.

RESULTS

The slow, high-load intervention produced greater immediate reductions in tendon anteroposterior diameter and cross-sectional area (8.9% and 10.1%), compared with the slow, low-load (3.8% and 4.7%) and fast, high-load (2.9% and 3.4%) interventions ( P < 0.001). Moreover, only the slow, high-load intervention increased tendon shear wave velocity (54.5%, P < 0.001).

CONCLUSIONS

These findings provide the first evidence that both loading speed and intensity during eccentric calf training impact acute changes in Achilles tendon thickness and stiffness, likely mediated by changes in fluid flow, which could be relevant for tendinopathy rehabilitation.

A Novel Method to Assess Subject-Specific Architecture of the Achilles Tendon In Vivo in Humans

The Achilles tendon (AT) comprises three subtendons whose relative locations, and respective lines of action, vary individually. This study was aimed to demonstrate the efficacy of a novel method, combining Ultrasound and electrical STIMulation (USTIM), to identify the in vivo location of individual subtendons in cross-sections of the AT. We individually stimulated the triceps surae muscle heads and imaged localized tissue movement on a transverse plane 1 cm proximal to the calcaneus using B-mode ultrasonography. Movement induced by muscle stimulation was presumed to arise from movement in the respective subtendon. Frame-by-frame changes in grayscale values were analyzed to detect localized tissue movement, establishing the three subtendon locations. From 12 successfully assessed legs, we found test-retest reliability to be excellent (ICC = 0.93, N = 3), and intra- and inter-rater reliability to be good for the subtendon centroid locations (ICC > 0.77, N = 12). Reliability for identifying the subtendon area was good for test-retest (ICC = 0.77) and intra-rater assessments (ICC > 0.70) but moderate between raters (ICC = 0.53). Subtendon centroid locations assessed using USTIM showed a strong association (N = 2; r2= 0.80, p < 0.001) with those identified via the high-field MRI method established by Cone et al. Fitting with prior literature, the majority of (83%) tendons were identified as low twist type I. The novel USTIM method can identify in vivo locations of the three subtendons within a cross-section of AT with moderate to excellent reliability. This method could be used to unravel the intricacies of structure-function relationships in the AT, with potential clinical benefits for treatment of patients with AT injuries.

Novel Insights Into the Intratendinous Pressure Behavior of the Achilles Tendon in Athletes

BACKGROUND

In contrast to other musculoskeletal tissues, the normal pressure behavior of the Achilles tendon is poorly understood. This study aimed to explore the normal intratendinous and perfusion pressures of the Achilles tendon at rest and during exercise, and investigate potential correlations with tendon load and morphology.

HYPOTHESIS

Intratendinous and perfusion pressures of the Achilles tendon exhibit similarities to other musculoskeletal tissues and depend on tendon load and morphology.

STUDY DESIGN

Observational study.

LEVEL OF EVIDENCE

Level 3.

METHODS

A total of 22 recreational athletes were enrolled. Demographics, activity level, and blood pressures were recorded. Achilles tendon thickness and echogenicity were assessed 25 mm proximal to the posterosuperior calcaneal border. In this region, intratendinous and perfusion pressures of the Achilles tendon were measured at rest and during isometric plantarflexion up to 50 N, using the microcapillary infusion technique. Linear mixed models were used to investigate the effects of plantarflexion force, tendon thickness, and echogenicity on intratendinous and perfusion pressures.

RESULTS

At rest, intratendinous and perfusion pressures of the Achilles tendon were 43.8 ± 15.2 and 48.7 ± 18.4 mmHg, respectively. Intratendinous pressure increased linearly with plantarflexion force, reaching 101.3 ± 25.5 mmHg at 50 N (P < 0.01). Perfusion pressure showed an inverse relationship, dropping below 0 mmHg at 50 N (P < 0.01). Neither intratendinous nor perfusion pressures of the Achilles tendon correlated with tendon thickness or echogenicity.

CONCLUSION

The normal intratendinous resting pressure of the Achilles tendon is higher than other musculoskeletal tissues, making it more susceptible to ischemia. During exercise, intratendinous pressure increases significantly to a level that lowers perfusion pressure, thereby compromising blood supply at already low plantarflexion forces.

CLINICAL RELEVANCE

Given the potential role of ischemia in Achilles tendinopathy, our findings caution against intratendinous injections, as they may exacerbate high intratendinous resting pressure, and against prolonged postexercise tendon stretching, as the associated rise in intratendinous pressure may impair the required hyperemic response.

Estimation of the Achilles tendon twist in vivo by individual triceps surae muscle stimulation

The Achilles tendon (AT) is composed of three distinct subtendons, each arising from one of the three heads of the triceps surae muscles: gastrocnemius medialis (GM), gastrocnemius lateralis (GL), and soleus (SOL). These subtendons exhibit a twisted structure, classified as low (Type I), medium (Type II), and high (Type III) twist, based on cadaveric studies. Nevertheless, the in vivo investigation of AT twist is notably scarce, resulting in a limited understanding of its functional significance. The aim of this study was to give insights into the complex 3D AT structure in vivo. A total of 30 healthy participants underwent individual stimulation of each of the triceps surae muscles at rest with the foot attached to the pedal of an isokinetic dynamometer. Ultrasound images were captured to concomitantly examine the displacement of the superficial, middle and deep AT layers. SOL stimulation resulted in the highest AT displacement followed by GM and GL stimulation. Independent of the muscle stimulated, non-uniformity within the AT was observed with the deep layer exhibiting more displacement compared to the middle and superficial layers, hence important inter-individual differences in AT displacement were noticeable. By comparing these individual displacement patterns during targeted stimulations with insights from cadaveric twist classifications on each subtendon area, our classification identified 19 subjects with a 'low' twist and 11 subjects with a 'high' twist. These findings enable us to move beyond cadaveric studies and relate the twisted microstructure of the AT in vivo to its dynamic behaviour.

Elevated fluid and glycosaminoglycan content in the Achilles tendon contribute to higher intratendinous pressures: Implications for Achilles tendinopathy

BACKGROUND

Tendinopathy alters the compositional properties of the Achilles tendon by increasing fluid and glycosaminoglycan content. It has been speculated that these changes may affect intratendinous pressure, but the extent of this relationship remains unclear. Therefore, we aimed to investigate the impact of elevated fluid and glycosaminoglycan content on Achilles tendon intratendinous pressure and to determine whether hyaluronidase (HYAL) therapy can intervene in this potential relationship.

METHODS

Twenty paired fresh-frozen cadaveric Achilles tendons were mounted in a tensile-testing machine and loaded up to 5% strain. Intratendinous resting (at 0% strain) and dynamic pressure (at 5% strain) were assessed using the microcapillary infusion technique. First, intratendinous pressure was measured under native conditions before and after infusion of 2 mL physiological saline. Next, 80 mg of glycosaminoglycans were administered bilaterally to the paired tendons. The right tendons were additionally treated with 1500 units of HYAL. Finally, both groups were retested, and the glycosaminoglycan content was analyzed.

RESULTS

It was found that both elevated fluid and glycosaminoglycan content resulted in higher intratendinous resting and dynamic pressures (p < 0.001). HYAL treatment induced a 2.3-fold reduction in glycosaminoglycan content (p = 0.002) and restored intratendinous pressures.

CONCLUSION

The results of this study demonstrated that elevated fluid and glycosaminoglycan content in Achilles tendinopathy contribute to increased intratendinous resting and dynamic pressures, which can be explained by the associated increased volume and reduced permeability of the tendon matrix, respectively. HYAL degrades glycosaminoglycans sufficiently to lower intratendinous pressures and may, therefore, serve as a promising treatment.

Degree of twist in the Achilles tendon interacts with its length and thickness in affecting local strain magnitude: a finite element analysis

Introduction

The relationship between the twisting of the three subtendons of the Achilles tendon (AT) and local strain has received attention in recent years. The present study aimed to elucidate how the degree of twist in the AT affects strain using finite element (FE) analysis, while also considering other geometries (e.g., length, thickness, and width) and their combinations.

Methods

A total of 59 FE models with different degrees of twist and geometries were created. A lengthening force (z-axis) of 1,000 N was applied to each subtendon (total: 3,000 N). The average value of the first principal Lagrange strain was calculated for the middle third of the total length of the model.

Results

Statistical (stepwise) analysis revealed the effects of the degree of twist, other geometries, and their combinations on AT strain. The main findings were as follows: (1) a greater degree of twist resulted in higher average strains (t = 9.28, p < 0.0001) and (2) the effect of the degree of twist on the strain depended on dimensions of thickness of the most distal part of the AT (t = -4.49, p < 0.0001) and the length of the AT (t = -3.82, p = 0.0005). Specifically, when the thickness of the most distal part and length were large, the degree of twist had a small effect on the first principal Lagrange strain; however, when the thickness of the most distal part and length were small, a greater degree of twist results in higher first principal Lagrange strain.

Conclusion

These results indicate that the relationship between the degree of twist and local strain is complex and may not be accurately assessed by FE simulation using a single geometry.

Clinical anatomy of the human Achilles subtendons twist - meta-analysis

PURPOSE

This study aimed to provide a comprehensive and current overview of the anatomy of the Achilles tendon (AT) twisted structure, as there is a discrepancy in the literature regarding its rotating morphology.

METHODS

An extensive literature search was conducted across multiple databases to identify all studies that reported relevant data on the AT torsion, with no date or language restrictions applied. Data was extracted and assessed for this meta-analysis following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The quality of the included articles was examined using the anatomical quality assessment (AQUA) tool.

RESULTS

Seven articles (n=690 limbs) were pooled into this meta-analysis. The prevalence of Achilles tendon torsion types was as follows: type II was the most common (46.7%, 95% CI: 31.6-60.9%), followed by type I (44.7%, 95% CI: 29.8-59.0%), and least commonly, type III (8.6%, 95% CI: 1.8-18.8%). Additionally, morphometric analysis, utilizing the method described by van Gils et al., revealed a mean Achilles tendon torsion of 46.5° (95% CI: 25.1-67.9°).

CONCLUSIONS

This meta-analysis underscores the prominent and variable twist within the Achilles tendon among individuals, emphasizing the inherent diversity in AT morphology. Furthermore, the study highlights the importance of considering torsion angle as a potential factor influencing AT pathologies and biomechanical function.