Gastrocnemius fascicles are shorter and more pennate throughout the first month following acute Achilles tendon rupture

Abstract

1The purpose of this study was to characterize the short-term effects of Achilles tendon 2 ruptures on medial gastrocnemius. We hypothesized that the fascicles of the medial 3 gastrocnemius muscle of the injured Achilles tendon would be shorter and more pennate 4 immediately following the injury and would persist throughout 4 weeks post-injury. B-mode 5 longitudinal ultrasound images of the medial gastrocnemius were acquired in 10 adults who 6 suffered acute Achilles tendon ruptures and were treated non-operatively. Ultrasound images 7 were acquired during the initial clinical visit following injury as well as two and four weeks 8 following this initial clinical visit. Resting muscle structure was characterized by measuring 9 fascicle length, pennation angle, muscle thickness, and muscle echo intensity in both the injured 1 0 and contralateral (control) limbs. Fascicle length was 15% shorter (P < 0.001) and pennation 1 1 angle was 21% greater (P < 0.001) in the injured muscle compared to the uninjured (control) 1 2 muscle at the presentation of injury (week 0). These differences in fascicle length and pennation 1 3 angle persisted throughout the 4 weeks after the injury (P < 0.008). Muscle thickness changes 1 4were not detected at any of the post-injury visits (difference < 4%, P > 0.04). Echo intensity of 1 5 the injured limb was 8% lower at the presentation of the injury and 11% lower (P = 0.008) than 1 6 the contralateral muscle at 2 weeks following injury (P < 0.001) but returned to within 1% by 4 1 7 weeks (P = 0.393). Our results suggest that Achilles tendon ruptures elicit rapid changes in the

Changes in Tendon Elongation and Muscle Atrophy Over Time After Achilles Tendon Rupture Repair: A Prospective Cohort Study on the Effects of Early Functional Mobilization

“…35 The mechanical properties of the MG undergo atrophic remodeling early after ATR, leading to reduced force generation and impaired functional outcome. 4,5,22,43,53 This study found that the MG CSA seems to recover to some degree over time but with persistent atrophy as compared with the healthy side, which is consistent with previous studies. 20,35,53…”

“…35 The mechanical properties of the MG undergo atrophic remodeling early after ATR, leading to reduced force generation and impaired functional outcome. 4,5,22,43,53 This study found that the MG CSA seems to recover to some degree over time but with persistent atrophy as compared with the healthy side, which is consistent with previous studies. 20,35,53 The observation that the soleus muscle atrophied later than the MG and LG is in accordance with an earlier study by Eliasson et al 15 Animal studies have shown that when muscles are immobilized in a position shorter than their resting length, the degree of atrophy is greater and begins faster than if the muscle is immobilized in a stretched position.…”

Muscle Fascicles Exhibit Limited Passive Elongation Throughout the Rehabilitation of Achilles Tendon Rupture After Percutaneous Repair

“…This was accompanied by limited MTJ displacement throughout the same ROM ( Figure 3B ). These results are comparable to previous short-term measurements that found consistently shorter fascicle lengths and lower muscle thickness up to 4 weeks post-ATR when held in plantarflexion ( Hullfish et al, 2019 ). This appears to be consistent throughout the rehabilitation of gait, suggesting that current post-operative rehabilitative exercise do not appear to induce muscle adaptations on fascicle length in the affected MTU.…”

“…In particular, muscle remodeling following ATR injury is rapid compared to the rate of tendon healing, which can last as long as 1 year ( Sharma and Maffulli, 2005 ). Side-to-side differences in muscle morphology are apparent soon after ATR, as Hullfish and colleagues have recently reported that medial gastrocnemius fascicles on the ATR-injured side remain both shorter and more pennate within 1 month post-injury ( Hullfish et al, 2019 ). Recent findings suggest that further muscle remodeling occurs after this time, with increases in medial gastrocnemius volume found between 6 and 26 weeks after ATR ( Eliasson et al, 2018 ).…”

Age and Tightness of Repair Are Predictors of Heel-Rise Height After Achilles Tendon Rupture

“…The ATRA could be considered to be a quantification of the overall tension in the musculotendinous unit. The influence of muscle fiber pennation and fiber length has been considered, 20 which is also likely to influence the ATRA.…”