Characterizing the Effects of Histotripsy for Osteosarcoma Treatment on Tendon Structure and Function

Abstract

Osteosarcoma (OS) is the most common malignant bone tumor in both humans and dogs. Current standards of care for OS consist of limb amputation, limb-salvage surgery, pre- and post-operative chemotherapy, and thermal ablation methods. While these methods are used to ablate and/or provide pain relief for OS in humans and dogs, there are risks and limitations associated with them, including potential deleterious effects to surrounding tissues. Histotripsy is a novel limb-salvage technique that can be used to treat OS. Histotripsy is a non-invasive, non-thermal, and non-ionizing focused ultrasound method that mechanically breaks down targeted tissue into subcellular components by generating acoustic cavitation bubble clouds. In order to establish the clinical safety of histotripsy for OS treatment in dogs, it is important to ensure that there is no damage to supporting structures, which include tumor-adjacent tendons, as tendons are important musculoskeletal structures that facilitate joint movement. The objective of this study is to evaluate the effects of histotripsy on tendon structure and function via biomechanical testing, ultrasound (US) image texture analysis, and histologic analysis. In this ex vivo model, canine extensor tendons collected from medium to large breed dogs are either left untreated (control) or treated indirectly (i.e. the focal point is located below the tendon) at a clinical dose of 1000 ppp or supraclinical dose of 4000 ppp, followed by quantification of bulk tensile properties, 1st and 2nd order ultrasound image texture parameters, and extracellular matrix integrity. A monotonic load to failure test (n = 8) was used to quantify biomechanical properties. 1st (mean, median, variance, skewness, kurtosis, and entropy) and 2nd (contrast, homogeneity, and energy) order statistics were used to analyze the images in each region (proximal, middle, and distal) of the tendon to observe the structural changes in tendons treated indirectly at different doses through texture parameters (n = 8). Collagen fiber and cell structure and arrangement were evaluated using Trichrome and Hematoxylin and Eosin (HandE) stains to investigate the histologic differences of tendons treated at different doses (n = 3). Results from biomechanical testing, US image texture analysis, and histological analysis showed mostly non-significant changes between untreated and treated tendons. Subtle dose-dependent, localized changes in the treatment region did not alter bulk tendon properties. This work establishes histotripsy as a safe and effective limb-salvage treatment for OS that preserves musculoskeletal function in dogs. The data from this study can be used to refine histotripsy treatment protocols for OS and establish a safety profile for tendons. Understanding how specific histotripsy parameters influence tendon tissue will facilitate the design of non-invasive, ablative treatments, such as debridement.