Relationships among patient-reported outcome measures, functional performances, and tendon properties in patients with mid-portion Achilles tendinopathy: A cross-sectional study

Abstract

Background

Achilles tendinopathy is a common overuse-related musculoskeletal disorder. The relationships among patient-reported outcome measures (PROMs), functional performance, and structural tendon changes remain poorly understood. This study aimed to clarify the relationships among these measures in patients with Achilles tendinopathy.

Methods

46 patients with mid-portion Achilles tendinopathy were included in the study. Evaluations included PROMs, functional performances, and tendon properties. Pearson correlation analysis and multiple linear regression were used to explore the relationships between measures.

Results

Only Victorian Institute of Sport Assessment-Achilles was found to have a significant association with Achilles tendon thickness (p = 0.038, β = 0.368), and tendon stiffness was found to have a significant association with maximal voluntary isometric contractions of ankle plantarflexion (p < 0.001, β = 0.598).

Conclusion

The relationships among PROMs, tendon properties, and functional performances are weak. Combining these outcomes is suggested for a comprehensive evaluation of patients with Achilles tendinopathy.

Levels of Evidence

Level Ⅳ

1

Introduction

The prevalence of Achilles tendinopathy has steadily increased in recent years as a result of more people participating in sports and physical activities . This condition affects approximately 6 % of the general population over their lifetime . Achilles tendinopathy is characterized by a degenerative process and impaired healing response , , including cellular degeneration, aberrant proliferation, disorganization of collagen fibers, and pathological neovascularization , . Based on the location of the symptoms, Achilles tendinopathy is classified into insertional and mid-portion types. Mid-portion Achilles tendinopathy, which is more prevalent (55–65 %) than the insertional type (20–25 %) , is defined as pain localized more than 2 cm proximal to the calcaneal insertion ,, . Clinical symptoms often include persistent pain, restricted activity, and diminished exercise capacity .

There is a wide variety of tools available to assist in evaluating the progression of mid-portion Achilles tendinopathy. However, no consensus has been reached on which of these tools is meaningful for use in clinical practice . Furthermore, previous research has demonstrated that an increase in patient-reported outcome measures (PROMs) does not always align with improvements in tendon structural properties or functional performances . This discrepancy raises questions about the relationship among different assessment measures and the value of incorporating multiple measures in clinical practice.

We hypothesized that only weak relationships exist among PROMs, tendon properties, and functional performances in patients with Achilles tendinopathy. Therefore, this study aims to evaluate the relationships among PROMs, tendon properties, and functional performances.

2

Methods

2.1

Participants

A total of 46 patients with mid-portion Achilles tendinopathy (33 males and 13 females) were recruited in this study. All participants provided informed consent for their participation and the use of their data. Both recruitment and data collection were completed at Sports Medicine and Rehabilitation Center of Beijing Sport University. The study was conducted in accordance with the Declaration of Helsinki, and approved by the Institutional Review Board of Sports Science Experiment Ethics Committee of Beijing Sports University (S202410043022).

The following inclusion criteria were used : 1) Over the age of 18; 2) Tenderness and swelling between 2 and 7 centimeters above the calcaneal insertion of the Achilles tendon; 3) Symptoms that had been present for at least two months; 4) Had detectable Doppler flow; The most affected tendon in bilateral cases was selected in the trial.

Exclusion criteria : 1) History of Achilles tendon rupture or surgery; 2) With sural neuropathy; 3) Use of medications (within 2 years) presumed to affect symptoms; 4) Insertional Achilles tendinopathy; 5) Pregnancy; 6) With inflammatory diseases such as rheumatoid arthritis and gouty arthritis; 7) Had received Achilles tendon-related conservative treatments (e.g., extracorporeal shock wave therapy, local block injection, night brace fixation, Achilles tendon stretching exercises) in the past 3 months.

2.2

Procedure

All the participants were recruited by online advertisements and posters. An experienced physical therapist conducted the enrollment of participants.

2.3

Measures

2.3.1

Patient-reported outcome measures

2.3.1.1

Victorian institute of sport assessment-achilles

The Victorian Institute of Sport Assessment-Achilles (VISA-A) questionnaire is a comprehensive tool to evaluate the dysfunction of patients with Achilles tendinopathy. Score of the VISA-A scale ranges from 0 to 100, with lower values indicating more severe functional impairment and greater limitations in physical capabilities . This questionnaire has excellent reliability and validity in evaluating patients with Achilles tendinopathy .

2.3.1.2

Lower extremity functional scale

The Lower Extremity Functional Scale (LEFS) is an instrument that covers three key domains: activities of daily living, balance, and motor function. It comprises 20 items, and each item ranges from 0 to 4. The total score ranges from 0 to 80, with lower scores indicating greater functional limitations , . This questionnaire has good test-retest reliability and content validity .

2.3.1.3

12-Item short form health survey

The 12-item Short Form Health Survey (SF-12) is a modified form of the 36-item Short Form Health Survey. It consists of 12 questions with reduced completion time and comparable result accuracy and consistency . The SF-12 consists of the Physical Component Summary (PCS) and Mental Component Summary (MCS). As the focus of this study was on physical function, we only used the PCS score. The PCS scores were calculated using weighted formulas from the standard manual . Higher scores indicate superior health status, while lower scores imply more severe functional limitations and inferior health status.

2.3.2

Tests of functional performances

2.3.2.1

Maximal voluntary isometric contractions

Maximal voluntary isometric contraction (MVIC) of ankle plantarflexion was measured using an isokinetic dynamometer (Biodex-System 4, Biodex Medical Systems Inc., USA). During testing, the ankle joint was maintained in a neutral position (0°), the hip was flexed to 115°, and the lower leg was positioned parallel to the horizontal plane ( Fig. 1 ) . Participants first performed three submaximal warm-up contractions. Subsequently, they performed three maximal MVIC trials, each lasting 5 s. Participants were provided with a 60-second rest period between trials to prevent fatigue, and the highest torque value from the three trials was recorded for subsequent analysis.

Fig. 1

This is the body posture during the measures of MVIC and stiffness.

2.3.2.2

Countermovement jump

The height of the Countermovement jump (CMJ) of the affected limb was collected using a force plate (9280AA6, Kistler, Switzerland) at a sample rate of 1000 Hz. Participants were told to stand on a force plate with their hands on their hips to prevent arm swinging and supported by the affected foot ( Fig. 2 ). Participants were instructed to rapidly squat to a self-selected depth and then jump vertically for maximum height, landing on the starting foot , . Three practice jumps were permitted for familiarization. Following this, three maximal effort jumps were recorded, with 30 s of rest between attempts. Jump data were processed using a customized MATLAB code (R2023a, MathWorks, USA) to calculate jump height from the flight time of the force-time curve . The average peak height from the three jumps was used for subsequent analysis.

Fig. 2

The entire process of CMJ.

2.3.3

Evaluations of tendon properties

2.3.3.1

Thickness

All ultrasonographic assessments were performed by a single experienced investigator using a Doppler ultrasonography system (Apogee1000, Shantou Institute of Ultrasonic Instruments, China). The maximum thickness of the Achilles tendon was assessed in the longitudinal plane. A linear array transducer was positioned along the tendon’s longitudinal axis and scanned from its proximal segments to 2 cm above the insertion segments. The maximum thickness of the midportion was subsequently found and measured . All measures were taken three times, and the mean value was recorded.

2.3.3.2

Cross-sectional area

The Achilles tendon’s cross-sectional area (CSA) was measured in the transverse plane by positioning the transducer perpendicularly to the tendon at three locations: 20, 40, and 60 mm proximal to the distal tendon insertion . Images were analyzed using ImageJ software (v1.51, NIH, USA). The CSA at each location was measured three times, and the average of these measurements was calculated to represent the tendon’s CSA.

2.3.3.3

Tendon stiffness

The slope of the tendon force-elongation curve was used to calculate the stiffness of the tendon. To measure elongation, the ultrasound probe was fixed on the posterior lower leg using a custom-made rigid clamp to record displacement of the musculotendinous junction during MVIC ( Fig. 1 ) . The displacement of the Achilles tendon was determined by manually tracking the displacement of the musculotendinous junction. Plantar flexion torque (T) was obtained through the test of MVIC, and the tendon force (F) was determined via plantar flexor torque divided by the corresponding internal moment arm (MA) ( Eq. 1 ).

F = T MA

The internal moment arm (MA) was calculated using the method described by Maganaris and Paul . The MA was calculated using musculotendinous junction elongation (dx) during 20° passive ankle rotation (dθ) . And MA was equal to the ratio of dx / d θ where the angular displacement was converted to radians ( Eq. 2 ).

MA = dx / d θ

The force-elongation data from 50 % to 100 % of MVIC were used for linear regression analysis to derive stiffness , . The test was repeated three times, and the average stiffness value was used for subsequent analysis.

2.4

Data analysis

Data were analyzed using SPSS (Version 27.0 for Windows, SPSS Inc., USA). The significance level was set at α = 0.05. Normality of all continuous variables was confirmed using the Shapiro-Wilk test. Associations between outcomes were first assessed with Pearson’s correlation, with coefficients (r) interpreted based on the criteria established by Schober et al. . To further explore these relationships while controlling for confounders, we conducted a series of multiple linear regression analyses. Separate models were built to predict: (1) each functional performance outcome (MVIC, CMJ) using all PROMs or all tendon properties as predictors; and (2) each measurement of tendon property (stiffness, CSA, thickness) using all PROMs as predictors. All models were adjusted for age, sex, and body mass index and employed the enter method. In cases where regression results diverged from the correlation results, partial correlation coefficients were used to explain the contribution of the predictor.

3

Results

3.1

Participants

Table 1 presented the age, height, mass, BMI, training years, disease course, VISA-A, LEFS, PCS of SF-12, thickness, CSA, MVIC, CMJ, and stiffness of all participants. All values were expressed as mean ± standard deviation.

Table 1

Measurement of patients’ demographic characteristics, PROMs, tendon properties, and tests of functional performances.

Characteristics Total (46) Male (33) Female (13)
Mean±SD Mean±SD Mean±SD
Age (years) 20.22 ± 1.92 19.94 ± 1.90 20.92 ± 1.85
Height (cm) 177.25 ± 7.89 177.32 ± 7.35 177.08 ± 9.45
Mass (kg) 71.47 ± 9.92 71.53 ± 9.96 71.31 ± 10.27
BMI (kg/m 2) 22.67 ± 2.26 22.69 ± 2.40 22.63 ± 1.93
Training years (year) 6.74 ± 2.41 6.55 ± 2.20 7.23 ± 2.92
Disease course (month) 7.20 ± 1.95 7.42 ± 2.15 6.62 ± 1.19
VISA-A (score) 64.57 ± 10.51 64.70 ± 9.59 64.23 ± 12.99
LEFS (score) 74.13 ± 3.64 73.24 ± 3.61 76.38 ± 2.725
PCS of SF-12 (score) 49.20 ± 0.93 49.20 ± 0.92 49.22 ± 1.01
Thickness (mm) 10.80 ± 1.73 11.00 ± 1.58 10.28 ± 2.04
CSA (cm 2) 0.59 ± 0.12 0.59 ± 0.11 0.59 ± 0.14
MVIC (Nm) 125.20 ± 44.22 123.19 ± 36.98 130.32 ± 60.39
Stiffness (N/mm) 280.79 ± 90.48 277.13 ± 85.21 290.10 ± 105.86
CMJ (cm) 15.40 ± 5.39 14.79 ± 4.84 16.96 ± 6.55

BMI, Body Mass Index; VISA-A, Victorian Institute of Sport Assessment-Achilles; LEFS, Lower Extremity Functional Scale; PCS of SF-12, Physical Component Summary of 12-item Short Form Health Survey; CSA, Cross-sectional area; MVIC, Maximal voluntary isometric contraction; CMJ, Countermovement jump.

3.2

PROMs and tendon properties

Pearson correlation analysis revealed no significant correlations between PROMs and stiffness, CSA (p ranged from 0.422 to 0.956). Subsequent linear regression analyses, adjusted for covariates, further confirmed these relationships. For stiffness, it was not a significant predictor of any PROM (β ranged from −0.055–0.270; p ranged from 0.156 to 0.767). Similarly, the addition of CSA to the models resulted in a slight decrease in R² (from 0.219 to 0.192), and CSA was not a significant predictor (β ranged from −0.178–0.166; p ranged from 0.270 to 0.530). In contrast, while Pearson correlation also showed no significant association between PROMs and tendon thickness (p from 0.300 to 0.792), linear regression revealed that thickness was a significant positive predictor of the VISA-A score (β = 0.368, p = 0.038), though it did not predict other PROMs. According to Cohen’s criteria, this significant association corresponded to a small effect size (f² = 0.146) ( Table 3 ).

3.3

PROMs and functional performances

.Our analyses revealed a lack of significant association between patient-reported outcome measures (PROMs) and outcomes of functional performance. Pearson correlation analysis demonstrated no significant correlation between PROMs and either MVIC or CMJ (all p-values > 0.05). Subsequent multivariate linear regression modeling revealed that the inclusion of PROMs did not improve the explanatory power of either model compared to covariates alone (ΔR² = 0.001 for MVIC; ΔR² = −0.035 for CMJ). In the adjusted models, no PROMs emerged as significant predictors of MVIC (β ranged from −0.284–0.285; p ranged from 0.079 to 0.911) or CMJ performance (β ranged from −0.076–0.024; p ranged from 0.588 to 0.867).

3.4

Tendon properties and functional performances

As shown in Table 2 , tendon stiffness demonstrated a moderate correlation with MVIC (r = 0.650, p < 0.001) and a weak correlation with CMJ height (r = 0.390, p = 0.007). Similarly, CSA was weakly correlated with both CMJ and MVIC (r = 0.321, p = 0.030 and r = 0.306, p = 0.039, respectively), while tendon thickness was weakly inversely correlated with CMJ performance (r =-0.326, p = 0.027). In the regression models of tendon properties and functional performances, the inclusion of tendon properties increased the explanatory power for MVIC and CMJ by 15.9 % and 34.9 % respectively, compared to models containing covariates alone. As detailed in Table 4 , stiffness emerged as a significant independent predictor of MVIC (β = 0.598, p < 0.001) after adjusting for covariates. In contrast, none of the tendon properties were significantly associated with CMJ performance after adjustment (all p > 0.05, β ranged from −0.081–0.205). The effect sizes for these associations, as quantified by Cohen’s f², ranged from 0.087 to 0.270, indicating small to medium practical effects.

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Sep 5, 2026 | Posted by in ORTHOPEDIC | Comments Off on Relationships among patient-reported outcome measures, functional performances, and tendon properties in patients with mid-portion Achilles tendinopathy: A cross-sectional study

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