Table 2.

Characteristics of studies included in the systematic review on therapeutic ultrasound used for musculoskeletal conditions in horses and donkeys. TU, therapeutic ultrasound; US, ultrasound; HQW, hind quarter weakness; NI, no information.

Main Author [Ref.] Publication Year Country	Study Design	Study Population	Therapeutic Ultrasound: No. of Sessions and Duration Mode TU Frequency Intensity	Controls	Outcome Variables	Main Results	Study Risk of Bias
Muscle and tendon temperature
Adair [37] 2019 USA	Experimental, before-after design	10 healthy mares	One 10-min session Mode NI 1 MHz 1–2 W/cm2	Baseline temperature	Temperature measured by a thermistor at different depths in epaxial muscles	Muscle temperature rise at the end of treatment 1.2–2.5 °C, highest at 1 and 5 cm depth	Low
Montgomery [38] 2011 USA	Experimental, before-after design	10 healthy horses	Tendons: One 10-min session Continuous mode 3.3 MHz Comparing 1.0 with 1.5 W/cm2 Epaxial muscles: One 20-min session Continuous mode 3.3 MHz 1.5 W/cm2	Baseline temperature	Temperature monitored by a thermistor in the superficial and deep flexor tendons of the thoracic limb and in epaxial muscles	The temperature rises at the end of treatment 2.5–5.2 °C in tendons (therapeutic temperature rise according to authors) and 0.7–1.3 °C in epaxial muscles (non-therapeutic temperature rise)	Low
Tendon and ligament injury and bursitis
Lang [16] 1980 USA	Clinical cohort without controls	10 horses with synovitis and bursitis	1–8 sessions, duration and intervals not specified. Pulsed mode TU frequency NI Intensity 3 W/cm2	None	Clinical examinations with an assessment of swelling, pain, activity, and function at an unspecified time point. Radiography as needed	5/10 horses fully resolved at end of treatment	High (heterogeneous cohort, follow-up not systematic)
Fernandes [39] 2003 Brazil	Experimental, randomized controlled trial	18 horses with collagen-induced injuries of superficial digital flexor tendon	8 sessions 2 intervention groups, one with continuous and one with pulsed mode 3 MHz 1 W/cm2	Device switched off	40 days’ follow-up Clinical examinations UltrasonographyHistology	Regression of clinical signs was detected on average in 9 days in horses receiving continuous US, 12 days in horses receiving pulsed mode US, and 21 days in controls. Decreases in clinical severity by ultrasonography after 40 days were 42.5%, 57.7%, and 34.1% in the three groups, respectively. Intense neovascularization and fibroblastic activity in US-treated groups compared with controls	Low
Sharifi [40] 2007 Iran	Experimental, non-randomized controls	8 castrated horses with experimentally induced lacerations of the superficial digital flexor tendon of the right hind limb	Daily 10-min sessions for 14 days 3 MHz Intensity 1 W/Esq	Non-treated horses	Clinical assessment and hydroxyproline content in the lacerated tendon at 60 days	Local tenderness and swelling were reported as less severe in treated limbs. Significantly less decline in tendon hydroxyproline tendon content in the treated limb, indicating improved tendon regeneration	Moderate
Carrozzo [41] 2019 Italy	Clinical cohort without controls	23 client-owned sport horses with injuries to the suspensory ligament	6 sessions 1st week, thereafter 3–6 sessions per week for 2–3 weeks 6 min 38 kHz Intensity NI	None	Clinical evaluation Time to healing by diagnostic ultrasound Return to competition status	20/23 horses showed healing by diagnostic ultrasound and returned to competition status	High
Acute aseptic arthritis
Singh [19] 1996 Singh [20] 1997 India	Experimental, randomized controlled trial	8 donkeys with aseptic arthritis induced in the left carpal joint	Daily 10-min sessions for 7 days Pulsed mode 1 MHz 1.0–1.5 W/cm2	Untreated donkeys	30-day follow-up Rectal temperature, respiratory rate, pulse rate, and joint circumference. Synovial biopsies. Clinical assessments Histopathology and histochemistry	Earlier improvement of lameness, faster reduction of joint swelling, and less pain on flexion in TU-treated donkeys than in non-treated donkeys. Synovial cytological and biochemical parameters indicate less inflammation in the TU group. Histomorphology: Improved healing and fewer signs of cartilage degeneration in TU-treated donkeys	Moderate (only four donkeys in each group)
Back muscle pain [myositis]
Mercado [42] 2002 Argentina	Clinical cohort, non-randomized controls	63 showjumpers with back pain (longissimus dorsi muscle)	Daily 20-min sessions for 30 days Pulsed mode TU frequency NI 3.5 W/cm2	TU alone compared with (a) TENS and (b) TU plus TENS	Weekly clinical assessments and ultrasonography, 28-day follow-up	Nearly total recovery at 28 days in the TU alone group, faster than with TENS treatment alone, but slower than in the group with TU combined with TENS	Moderate (no non-treated controls)
Spinal and other bone and joint lesions
Lang [16] 1980 USA	Clinical cohort without controls	30 horses with various types and locations of spinal and other bone and joint lesions	1–8 sessions, duration and intervals not specified. Pulsed mode TU frequency NI 3 W/cm2	None	Clinical examinations with an assessment of swelling, pain, activity, and function at an unspecified time point. Radiography as needed	24/30 horses fully resolved at end of treatment (unspecified time point)	High (heterogeneous cohort, follow-up not systematic, no controls)