Patellar tendinopathy (PT) is one of the most common injuries in sports involving jumping (Lian et al., 2005). Clinically, patients complain of pain localized at the proximal insertion of the patellar tendon, particularly during squatting and landing after jumping (Cook et al., 2000). Its prevalence has been reported to be as high as 32% to 45% in athletes involved in jumping sports, (Lian et al., 2005) and the incidence rate is higher in males than females (de Vries et al., 2015). Most importantly, the condition is often prolonged and causes an early cessation of an athletic career (Kettunen et al., 2002).
Extracorporeal shockwave therapy (ESWT) is one of the modalities for reducing pain and improving function in individuals with PT (van Leeuwen et al., 2009; Everhart et al., 2017). Extracorporeal shockwaves are acoustic waves characterized by a high positive peak pressure of short duration followed by a lower-magnitude tensile wave (Rompe et al., 1998). The energy flux density represents the amount of acoustic energy passing through a 1[mm.sup.2] area per impulse, ranging from
The pain mechanism of tendinopathy is unclear. Pathophysiological changes such as an ncrease in substance P and in-growth of nerves near the neo-vessels; as well as pathomechanical changes such as mal-function in collagen slidings are being proposed as the source of pain associated with tendinopathy (Vasta et al., 2016; Zhang et al., 2011). Recent studies has demonstrated an increase in patella tendon shear modulus (an index of tendon stiffness) in patients with chronic PT than control (Coombes and Tucker, 2018; Zhang et al., 2014) with the amplitude of tendon shear modulus associated with the intensity of activity-related pain in tendinopathic tendon (Coombes and Tucker, 2018). In this connection, the therapeutic effects of ESWT on nerve conduction and vascularization have been reported. ESWT was found to induce an improvement of nerve conduction and a faster rate of axonal regeneration on peripheral nerve in rat. (Hausner et al., 2012); as well as an upregulation in vascularization in the Achilles tendon-bone junction on healthy dogs and rabbits (Wang et al., 2002; Wang et al., 2003), and a down-regulation in vascularity in patients with supraspinatus tendinopathy (Notarnicola et al., 2011). ESWT-induced modulation on the mechanical properties of tendinopathic tendon has not been established (Zhang et al., 2014; Wang et al., 2003).
In a recent study, Lee et al. reported a greater decrease in patellar tendon stiffness when ESWT was applied in the initial 6 weeks of an eccentric exercise program (by 29%) than exercise alone (by 12%) (Lee et al., 2020). The group difference, however, was not statistically significant. In this study, tendon stiffness was measured using ultrasound and a dynamometer and such a measurement method could not record localized or regional measurement of tendon properties. Pathology in patellar tendinopathy commonly occurs in the proximal region of the patellar tendon. (Kulig et al., 2013) A question therefore arises whether ESWT could modulate regional tendon stiffness and whether regional modulation on tendon stiffness would be related to symptomatic changes. Such findings would help to explore the mechanical effects of ESWT on the tendon of individuals with tendinopathy.
The primary aim of the present study was to examine the immediate effect of 1-session of ESWT on tendon shear modulus. The second aim was to explore whether the change in tendon shear modulus would associate with the change in the intensity of pain during pressure- and single-legged declined-squat tests. We hypothesized that 1-session of ESWT could reduce tendon shear modulus at the proximal portion of the patellar tendon and the changes in tendon shear modulus would be positively associated with reduction in the intensity of pain in patients with patellar tendinopathy.
Thirty-four male athletes aged 22.2 [+ or -] 3.8 with PT were recruited from the local university and community basketball and volleyball teams. Only males were recruited, because PT is more prevalent in male athletes (de Vries et al., 2015). The sample size was calculated based on the first 5 participants receiving ESWT. The G-power was calculated using pre-ESWT and post-ESWT values of the mean and standard deviation of tendon elastic modulus. Taking alpha at 5% and power at 80%, the estimated sample size per group should be 24. The inclusion criteria were as follows: 1) between 18 and 35 years of age; 2) persistent pain for at least 3 months; 3) maximum intensity of pain in the previous week [greater than or equal to] 3 using a visual analogue scale (VAS) with 0 as no pain and 10 as the worst pain; 4) Victorian Institute of Sport Assessment-patellar score (VISA-p) less than 80; 5) pain and tenderness on palpation in the inferior pole of the patella or during a loading test using single-leg squatting or jumping (Zwerver et al., 2010); and 6) thickening of the proximal part of the patellar tendon with areas of hypoechoic signals (Kulig et al., 2013). Exclusion criteria were history of corticosteroid injection and previous surgery to the lower limb. All recruited patients were physically screened by an experienced sports physical therapist with 13 years of clinical experience. Ultrasound imaging was captured by a second physical therapist with 3 years of experience of ultrasound scanning after attending a certified musculoskeletal ultrasound course. The present study was approved by the Human Subjects Ethics Sub-committee of the administrating institution, and all participants gave their written informed consent before the study. All procedures adhered to the Declaration of Helsinki.
Figure 1 shows the study flow diagram. After collection of demographic information such as age, weight, height as well as sports-related information on training hours per week. Participants were randomized into treatment and sham groups. A simple randomization procedure was performed using sealed identical non-opaque envelopes marked inside with "ESWT" or "sham". After picking up an envelope, the subject handed it to the physiotherapist providing the intervention. The patient did not know the type of intervention. He was informed that the shockwave machine would cause some noise and pain might or might not be provoked. Tendon stiffness before and immediately after the intervention by another physiotherapist who did not know the type of intervention. The test was conducted in a room with room temperature controlled at 25[degrees]C.
Supersonic Shearwave Imaging (SSI) was conducted using an Aixplorer[R] ultrasound unit (Supersonic Imaging, Aix-en-Provence, France) in conjunction with a 50 mm linear-array transducer at 4-15 MHz frequency to measure patellar tendon shear modulus (an index of tissue stiffness) (Zhang and Fu, 2013). The musculoskeletal acquisition mode was used with the temporal averaging (persistence) and...