Establishment of an ultrasound protocol for monitoring the morphometric and analgesic effects of photobiomodulation on the iliopsoas muscle of dogs undergoing rehabilitation

Introduction Musculoskeletal ultrasound is a non-invasive emerging clinical tool for diagnosis and longitudinal monitoring of musculoskeletal disorders. In humans, morphological alterations of iliopsoas muscle have been associated with chronic low back pain. In dogs, we found no reports regarding morphometric evaluation, nor the therapeutic effect of photobiomodulation on this muscle. This study aimed to describe a repeatable ultrasonographic protocol for morphometric assessment of the canine iliopsoas muscle and to characterize clinical and ultrasonographic changes following photobiomodulation therapy in dogs with chronic bilateral muscle pain on physical examination. Methods Seventeen client-owned small- to medium-sized dogs (13 females, 4 males; mostly Dachshunds, n = 8), presenting concurrent neurological, orthopedic and/or overweight conditions, with mean ± standard deviation of 7.7 ± 3.5 years and 8.5 ± 5.1 kg were included. Each animal underwent ultrasonographic examination (Mindray Vetus E7) (three repeated measurements R1, R2 and R3) before (T0) and after treatment with therapeutic laser sessions (LaserFlex LT16 Class IV) over 3 months (T1). Images were acquired at muscle origin, belly, and insertion on the lesser trochanter of the femur. Statistical analysis was performed considering each side individually. Iliac wings distance and thigh girth measurement were acquired to calculate ratios. Results Repeatability of measurements was statistically adequate, with lower limits of 95% confidence intervals for intraclass correlation coefficients ≥0.75, and good agreement between repeated measurements in Bland–Altman analysis. Between T0 and T1, significant reductions were observed in both orthogonal linear dimensions of iliopsoas muscle, at origin ( p ≤ 0.003) and belly ( p ≤ 0.014). These differences remained significant after normalization to iliac wings distance and thigh girth ( p ≤ 0.041). Significant reductions in pain scores ( p < 0.001) and ultrasonographic injury grades at origin ( p < 0.001) and insertion ( p < 0.001), with increased hip extension ( p = 0.003), occurred. Concurrent reduction in muscle dimensions and injury severity was compatible with improvement in pathological tissue changes, including possible reduction in inflammation and intramuscular oedema. Discussion/conclusion The proposed protocol provided repeatable quantitative assessment of canine iliopsoas muscle and allowed longitudinal characterization of ultrasonographic changes following photobiomodulation. To the authors’ knowledge, this is the first study to describe a standardized approach for serial morphometric assessment. Results highlight clinical utility of musculoskeletal ultrasound for early diagnostic of muscle injury and monitoring treatment.