April 2022

LONGER FASCICLE LENGTH MAY CAUSE DEFICIT IN NON-SURGICAL HEALING OF ACHILLES

Figure. Ultrasonographic images of muscle-tendon unit structural properties 1-year post-rupture in both limbs. A) images of MG muscle where pennation angle and fascicle length were analyzed. B) Images where AT thickness was measured 1 cm away from the calcaneal insertion. Injured limb AT was longer and thicker than the uninjured AT. At rest, MG had a smaller CSA with longer and more pennate fascicles.

Achilles tendon rupture appears to alter stiffness and length of the tendon. These alterations may affect the function of tendon in force transmission and in energy storage and recovery. We studied the mechanical properties of the Achilles’ tendon post-rupture and their association with function.

Methods Twenty-four (20 males, 4 females) participants (mean age: 43 y, 176 cm, 81 kg) were recruited. Ultrasonography and dynamometry were used to assess the muscle-tendon unit morphological and mechanical properties of non-surgically treated patients 1-year post rupture.

Findings Injured tendons were longer with difference of 1.8 cm (95%CI: 0.5-1.9 cm; P<0.001), and thicker by 0.2 mm (0.2-0.3 mm; P<0.01). Medial gastrocnemius cross-sectional area was 1.0 cm² smaller (0.8-1.1 cm²; P<0.001), fascicles were 0.6 cm shorter (0.5-0.7 cm; P<0.001) and pennation angle was 2.5-degree higher (1.3-3.6 degrees; P<0.001) when compared to the uninjured limb. We found no differences between injured and uninjured tendon stiffness 1-year post-rupture (mean difference: 29.8 N/mm, -7.7–67.3 N/mm; P=0.170). The injured tendon showed 1.8 mm (1.2–2.4 mm; P<0.01) lower elongation during maximal voluntary isometric contractions. Patient reported functional outcome was related to the tendon resting length (β=0.68, r(10)=4.079, P=0.002). Inter-limb differences in the medial gastrocnemius fascicle length were related to inter-limb differences in maximum contractions (β=1.17, r(14)=2.808, P=0.014).

Interpretation Longer Achilles tendon resting length was associated with poorer self-evaluated functional outcome. Although the stiffness of non-surgically treated and uninjured tendons was similar 1-year post rupture, plantar flexion strength deficit was still present, possibly due to shorter medial gastrocnemius fascicle length.

Source: Khair RM, Stenroth L, Cronin NJ, Reito A, Paloneva J, Finni T. Muscle-tendon morphomechanical properties of non-surgically treated Achilles tendon 1-year post-rupture. Clin Biomech (Bristol, Avon). 2022;92:105568. Use per Creative Commons CC BY.

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