Use of Weight-Bearing Computed Tomography (WBCT) Imaging in the Assessment of the Achilles Tendinopathy: A Prospective Comparative and Controlled Study

Abstract

Category: Hindfoot; Sports Introduction/Purpose: Insertional and non-insertional Achilles tendinopathy (AT) are prevalent diseases in the active, working-age population. Ultrasound (US) and magnetic resonance imaging (MRI) are frequently utilized in the assessment and grading of AT. Use of these imaging modalities are limited by operator interpretation/variability and costs, respectively. Also, these assessments are performed in the non-weight bearing positioning of the lower extremity, thus poorly evaluating the functional position of the loaded tendon. Validation of weight-bearing computed tomography (WBCT) for Achilles tendon imaging could provide a novel and functional means of quantifying tendon pathology. The study’s purposes were to: 1) Correlate Achilles tendon tissue structural findings when assessed by WBCT and US imaging, and 2) Compare WBCT Achilles tendon tissue changes between AT patients and controls. Methods: This was a prospective-comparative IRB-approved cohort study including 10 adults with AT (Age = 54.7 ± 10.3 years, BMI = 40.65 ± 10.07 kg/m2, 8F/2M), 10 age-matched controls (Age = 54.6 ± 11.33 years, BMI = 37.9 ± 9.55 kg/m2, 8F/2M), and 4 younger controls (Age = 32.25 ± 8.3 years, BMI = 24.32 ± 5.14 kg/m2, 2F/2M). WBCT scans (Curvebeam HiRise/PedCAT) and US imaging (Butterfly iQ+) of the Achilles tendon were collected. Tendons were manually segmented in WBCT images (3D Slicer software) and tendon thickness was measured at the maximum anterior-posterior (AP) diameter of the tendon (insertion and midportion regions). Radiodensity was quantified by the average Hounsfield Units (HU) of each tendon region and normalized to the radiodensity of each participant’s talus (segmented using Disior Bonelogic). US measures of the tendon thickness were similarly completed by independent observers who were blinded to the WBCT measurement. Intraclass correlation coefficient (ICC) assessed correlation between WBCT and US findings. Paired T-tests compared WBCT HU between patients and controls. P-values < 0.05 were considered significant. Results: There was excellent correlation (ICC= 0.83-0.94, Table 1) between WBCT and US imaging regarding tendon thickness, with WBCT overestimating thickness by only 0.27-0.55mm (4-9% of total tendon thickness). These findings could be explained by decreased US tendon thickness measurements secondary to the tendon’s compression by the US probe. WBCT imaging demonstrated a higher radiodensity (HU) within the Achilles tendon (for both insertion and midportion regions) in AT patients when compared to controls (Table 2), with p-values of 0.009 and 0.001 for insertional and midportion regions, respectively. Findings are consistent with tendinopathic differentiation of the Achilles tendon substance in the AT patients. Color-coded maps demonstrating HU distributions across the Achilles tendon were created to facilitate interpretation of tissue characteristics (Fig. 1). Conclusion: In this prospective, comparative, and controlled study, we observed a high correlation between US and WBCT imaging in the assessment of Achilles tendon thickness in AT patients and controls. We also found that WBCT HU distribution in the Achilles tendon was significantly increased in the AT patients when compared to controls. Findings are likely explained by tendinopathic tissue changes in the diseased tendons, potentially related to the well-known chondroid metaplasia observed in Achilles tendinopathy pathological process. WBCT imaging and color-coded maps can represent a promising tool in the assessment of AT patients.