Mechanical and Material Tendon Properties in Patients With Proximal Patellar Tendinopathy

Abstract

Introduction: The effect of chronic patellar tendinopathy on tissue function and integrity is currently unclear and underinvestigated. The aim of this cohort comparison was to examine morphological, material, and mechanical properties of the patellar tendon and to extend earlier findings by measuring the ability to store and return elastic energy in symptomatic tendons. Methods: Seventeen patients with chronic (>3 months, VISA-P < 80), inferior pole patellar tendinopathy (24 ± 4 years; male = 12, female = 5) were carefully matched to controls (25 ± 3 years) for training status, pattern, and history of loading of the patellar tendon. Individual knee extension force, patellar tendon stiffness, stress, strain, Young's modulus, hysteresis, and energy storage capacity, were obtained with combined dynamometry, ultrasonography, magnetic resonance imaging, and electromyography. Results: Anthropometric parameters did not differ between groups. VISA-P scores ranged from 28 to 78 points, and symptoms had lasted from 10 to 120 months before testing. Tendon proximal cross-sectional area was 61% larger in the patellar tendinopathy group than in the control group. There were no differences between groups in maximal voluntary isometric knee extension torque (p = 0.216; d < −0.31) nor in tensile tendon force produced during isometric ramp contractions (p = 0.185; d < −0.34). Similarly, tendon strain (p = 0.634; d < 0.12), hysteresis (p = 0.461; d < 0.18), and strain energy storage (p = 0.656; d < 0.36) did not differ between groups. However, patellar tendon stiffness (−19%; p = 0.007; d < −0.74), stress (−27%; p< 0.002; d < −0.90) and Young's modulus (−32%; p = 0.001; d < −0.94) were significantly lower in tendinopathic patients compared to healthy controls. Discussion: In this study, we observed lower stiffness in affected tendons. However, despite the substantial structural and histological changes occurring with tendinopathy, the tendon capacity to store and dissipate energy did not differ significantly.

Mechanical properties and UTE‐T2* in Patellar tendinopathy: The effect of load magnitude in exercise‐based treatment

“…This support that the changes in the tendinopathic tendon may be related to increased water content more than immediate alteration in the tensile bearing components. In contrast, some studies 7,8 have shown decreased mechanical stiffness in tendinopathic tendons compared to healthy controls. Reduction in loading and pain or a combination might have led to the between‐studies variation in stiffness.…”

“…Tendinopathic tendons typically display disorganization of the extracellular matrix (increased cellularity; increased proteoglycans, glycosaminoglycans, and water); hypervascularization; and disorganized collagen 5 . Concomitantly, mechanical properties have been reported to both decrease 7,8 or remain unchanged 9‐11 in tendinopathic tendons, although the reason for this discrepancy remains unknown. Therefore, additional investigation on how to restore the mechanical properties of tendon in management of patellar tendinopathy is warranted.…”

Changes in Physiological Tendon Substrate Stiffness Have Moderate Effects on Tendon-Derived Cell Growth and Immune Cell Activation

“…The tensile modulus of tendon tissue, however, has been well characterised by elastography or ex-vivo tensile testing ( Coombes et al, 2018 ; Finnamore et al, 2019 ). In tendinopathy the tensile modulus of tendon is reduced, resulting in a less stiff tendon ( Wiesinger et al, 2020 ). Higher stiffness characteristic of scar tissue is also relevant to tendinopathy, but our current knowledge is mostly based on measurements of scar formation in other tissues ( Liu et al, 2010 ).…”

The patellar ligament: A comprehensive review

“…This compensatory increase in CSA is supported by similar changes in PL stiffness and overall collagen content (Cristi‐Sánchez et al, 2019; Young et al, 2018; Zhou et al, 2014). A larger CSA allows dissipation of mechanical force loading across a greater area, protecting against strain‐related injuries (Wiesinger et al, 2020). Tendinopathy of the PL often occurs at the posterior proximal attachment, which has a smaller CSA (Basso et al, 2001; Pearson & Hussain, 2014; Wiesinger et al, 2020).…”

“…However, a study showed no difference between men and women, or between young boys and girls, in the measures of tendon stiffness or Young's modulus (O'Brien et al, 2010). Likewise, previous studies showed that while the tendon's mechanical properties were predictive of strain injuries, the sex difference was not (Wiesinger et al, 2020). Given these mixed findings, the definitive causes of increased strain-type injuries in the female human PL are not fully understood.…”