The acute effects of higher versus lower load duration and intensity on morphological and mechanical properties of the healthy Achilles tendon: a randomized crossover trial.

The Achilles tendon (AT) exhibits volume changes related to fluid flow under acute load which may be linked to changes in stiffness. Fluid flow provides a mechanical signal for cellular activity and may be one mechanism that facilitates tendon adaptation. This study aimed to investigate whether isometric intervention involving a high level of load duration and intensity could maximize the immediate reduction in AT volume and stiffness compared with interventions involving a lower level of load duration and intensity. Sixteen healthy participants (12 males, 4 females; age 24.4±9.4 years, body mass 70.9±16.1 kg, height 1.7±0.1 m) performed three isometric interventions of varying levels of load duration (2 s and 8 s) and intensity (35% and 75% maximal voluntary isometric contraction) over a 3 week period. Freehand 3D ultrasound was used to measure free AT volume (at rest) and length (at 35%, 55% and 75% of maximum plantarflexion force) pre- and post-interventions. The slope of the force-elongation curve over these force levels represented individual stiffness (N mm-1). Large reductions in free AT volume and stiffness resulted in response to long-duration high-intensity loading whilst less reduction was produced with a lower load intensity. In contrast, no change in free AT volume and a small increase in AT stiffness occurred with lower load duration. These findings suggest that the applied load on the AT must be heavy and sustained for a long duration to maximize immediate volume reduction, which might be an acute response that enables optimal long-term tendon adaptation via mechanotransduction pathways.

3D Models Reveal the Influence of Achilles Subtendon Twist on Strain and Energy Storage.

The Achilles tendon (AT) has complex function in walking, exchanging energy due to loading by the triceps surae muscles. AT structure comprises three subtendons which exhibit variable twist among themselves and between individuals. Our goal was to create 3D finite element (FE) models to explore AT structure-function relationships. By simulating subtendon loading in FE models with different twisted geometries, we investigated how anatomical variation in twisted tendon geometry impacts fascicle lengths, strains, and energy storage. Three tendon FE models, built with elliptical cross sections based on average cadaver measurements, were divided into subtendons with varied geometric twist (low, medium, and high) and equal proportions. Tendon was modeled as transversely isotropic with fascicle directions defined using Laplacian flow simulations, producing fascicle twist. Prescribed forces, representing AT loading during walking, were applied to proximal subtendon ends, with distal ends fixed, and tuned to produce equal tendon elongation in each case, consistent with ultrasound measurements. Subtendon fascicle lengths were greater than free tendon lengths in all models by 1-3.2 mm, and were longer with greater subtendon twist with differences of 1.2-1.9 mm from low to high twist. Subtendon along-fiber strains were lower with greater twist with differences of 1.4-2.6%, and all were less than free tendon longitudinal strain by 2-5.5%. Energy stored in the AT was also lower with greater twist with differences of 1.8-2.4 J. With greater subtendon twist, similar elongation of the AT results in lower tissue strains and forces, so that longitudinal stiffness of the AT is effectively decreased, demonstrating how tendon structure influences mechanical behavior.

A new technique to determine the tension in extensor pollicis longus reconstruction.

We present an original technique for determining the tension of the extensor pollicis longus tendon after reconstruction. We treated 20 patients using this technique for an extensor pollicis longus tendon graft or extensor indicis tendon transfer and reviewed the results. The tension of the reconstructed extensor pollicis longus was adjusted so that the centre of the distal edge of the thumbnail was elevated 2 cm above the operation table. The mean retropositional distance of the treated thumbs was 1.2 cm less than the contralateral thumbs. The mean total active motion of the thumb was 90%. This technique resulted in satisfactory thumb function. Level of evidence: IV.

Indications of Lateral Ankle Ligament Reconstruction with a Free Tendon and Associated Evidence / 대한족부족관절학회지

Ankle sprain is one of the most common musculoskeletal injuries. Although most ankle sprains respond well to conservative measures, chronic instability following an acute sprain has been reported to occur in 20% to 40% of patients. Some individuals are eventually indicated for a lateral ankle ligament reconstruction due to persistent ankle instability. More than 80 surgical procedures have been described to address lateral ankle stability. These range from direct repair of the anterior talofibular ligament (ATFL) and of the calcaneofibular ligament (CFL) to reconstructions based on the use of autograft or allograft tissues. However, the best surgical option remains debatable. The modified Broström procedure is most widely used for direct ligament repair, but not always possible because of the poor ATFL or CFL quality or deficiency of these ligaments, which prevents effective shortening imbrication. Furthermore, the importance of a CFL reconstruction has been emphasized recently. On the other hand, it is difficult to achieve an efficient CFL reconstruction during the Broström procedure. Others have reported that an anatomic reconstruction of injured ligaments restores the normal resistance to anterior translation and inversion without restricting subtalar or ankle motion, and as a result, anatomic reconstructions for lateral ankle instability utilizing an autograft or allograft tendon have gained popularity.

The tendinopathic Achilles tendon does not remain iso-volumetric upon repeated loading: insights from 3D ultrasound.

Mid-portion Achilles tendinopathy (MAT) alters the normal three-dimensional (3D) morphology of the Achilles tendon (AT) at rest and under a single tensile load. However, how MAT changes the 3D morphology of the AT during repeated loading remains unclear. This study compared the AT longitudinal, transverse and volume strains during repeated loading of the tendinopathic AT with those of the contralateral tendon in people with unilateral MAT. Ten adults with unilateral MAT performed 10 successive 25 s submaximal (50%) voluntary isometric plantarflexion contractions with both legs. Freehand 3D ultrasound scans were recorded and used to measure whole AT, free AT and proximal AT longitudinal strains and free AT cross-sectional area (CSA) and volume strains. The free AT experienced higher longitudinal and CSA strain and reached steady state following a greater number of contractions (five contractions) in the tendinopathic AT compared with the contralateral tendon (three contractions). Further, free tendon CSA and volume strain were greater in the tendinopathic AT than in the contralateral tendon from the first contraction, whereas free AT longitudinal strain was not greater than that of the contralateral tendon until the fourth contraction. Volume loss from the tendon core therefore preceded the greater longitudinal strain in the tendinopathic AT. Overall, these findings suggest that the tendinopathic free AT experiences an exaggerated longitudinal and transverse strain response under repeated loading that is underpinned by an altered interaction between solid and fluid tendon matrix components. These alterations are indicative of accentuated poroelasticity and an altered local stress-strain environment within the tendinopathic free tendon matrix, which could affect tendon remodelling via mechanobiological pathways.

Regional three-dimensional deformation of human Achilles tendon during conditioning.

Our understanding of in vivo Achilles tendon (AT) conditioning is limited to two-dimensional ultrasound measures of longitudinal deformation of the whole tendon. This study investigated the regional three-dimensional (3D) deformation of the AT during conditioning. Eighteen ATs were scanned using 3D freehand ultrasound during 10 successive 25 s submaximal (50%) voluntary isometric plantarflexion contractions. Longitudinal strain was assessed for the whole AT, aponeurosis, and free AT and transverse strain was assessed for the proximal-, mid-, and distal-portions of the free AT. Longitudinal conditioning of the whole AT was primarily driven by creep response of the free AT and transverse conditioning was greatest for the mid-portion of the free AT. Whole and free AT longitudinal strain increased up to the third contraction and were accompanied by a corresponding reduction in free AT cross-sectional area (CSA) strain in proximal-, mid-, and distal-portions. No significant changes in aponeurosis strain or tendon volume were detected between contractions. These findings suggest that conditioning alters free AT shape, with increased tendon length attained at the expense of reduction in free AT CSA. Although AT experiences different amounts of strain in different regions, the number of contractions required to reach steady-state strain during conditioning is uniform throughout the tendon.

Changes in Achilles tendon mechanical properties following eccentric heel drop exercise are specific to the free tendon.

Mechanical loading of the Achilles tendon during isolated eccentric contractions could induce immediate and region-dependent changes in mechanical properties. Three-dimensional ultrasound was used to examine the immediate effect of isolated eccentric exercise on the mechanical properties of the distal (free tendon) and proximal (gastrocnemii) regions of the Achilles tendon. Participants (n = 14) underwent two testing sessions in which tendon measurements were made at rest and during a 30% and 70% isometric plantar flexion contractions immediately before and after either: (a) 3 × 15 eccentric heel drops or (b) 10-min rest. There was a significant time-by-session interaction for free tendon length and strain for all loading conditions (P < 0.05). Pairwise comparisons revealed a significant increase in free tendon length and strain at all contraction intensities after eccentric exercise (P < 0.05). There was no significant time-by-session interaction for the gastrocnemii (medial or lateral) aponeurosis or tendon for any of the measured parameters. Immediate changes in Achilles tendon mechanical properties were specific to the free tendon and consistent with changes due to mechanical creep. These findings suggest that the mechanical properties of the free tendon may be more vulnerable to change with exercise compared with the gastrocnemii aponeurosis or tendon.

Comparison of results after surgical repair of acute and chronic ulnar collateral ligament injury of the thumb.

This study sought to demonstrate that successful outcomes can be achieved with the new technique presented here for chronic ulnar collateral ligament (UCL) injury of the thumb metacarpophalangeal (MCP) joint, as well as with K-wire pinning for acute UCL injury. We followed 19 patients who suffered an UCL rupture (mean follow-up: 14.26±4.65 months) and 32 patients who presented with UCL avulsion fracture (mean follow-up: 16.81±7.54 months). We used a free tendon graft for UCL reconstruction in the UCL rupture group. Both ends of the graft were stabilized with bioabsorbable suture anchors, which were used as biotenodesis interference screws. Closed reduction and K-wire fixation was used in UCL avulsion fracture group. There were no statistically significant differences between operated and contralateral healthy thumb MCP joint in both groups in the grip strength, tip pinch strength, flexion, extension, ulnar deviation, and radial deviation movements at final follow-up. Grip strength, tip pinch strength, ulnar deviation and radial deviation were significantly better in the avulsion group than the rupture group. All patients regained full stability at the MCP joint in avulsion group; 16 patients regained full stability and 3 patients presented with mild laxity (less than 10° laxity) in rupture group. Glickel grading scale used as a functional score was excellent for 30 patients and good for 2 patients in avulsion group; it was excellent for 17 patients and good for 2 patients in rupture group. Our study shows that closed reduction and percutaneous K-wire fixation of acute displaced large UCL avulsion fracture is a simple technique and achieves adequate stability of UCL. For UCL rupture, free tendon reconstruction with bioabsorbable suture anchors provides adequate stability and stable fixation within the tunnels.