A Prospective, Randomized, Double-blind, Placebo Controlled Single Centre Trial to Assess the Efficacy and Safety of rESWT Combined With a Specific Rehabilitation Program for Acute Hamstring Muscle Complex Injury Type 3b in Athletes

Acute injuries of the hamstring muscle complex (HMC) are frequently observed in various sports disciplines both in elite and recreational sport, and are the most common injury in soccer. Despite intensive research into prevention and management of acute HMC injury during the last decade epidemiological data show no decline in injury and re-injury rates. In this regard a recent study prospectively observed 374 Danish elite soccer players during a 12-month period and registered 46 first-time and eight recurrent HMC injuries (incidence rates: 12.3% [first-time injuries] and 2% [recurrent injuries]). Statistically significantly more players experienced a first-time acute HMC injury during a match than during training. Moreover, among 32 players who suffered from acute HMC injury in a period of 12 months before the study, eight players incurred an injury that fulfilled the criteria for a recurrent injury (incidence: 25%). Approximately two thirds of the first-time injuries were categorized as moderate, with time to return to play between 8 to 28 days.

Anatomical and functional aspects of the HMC predispose it to injury, including the fact that the muscles cross two joints and undergo eccentric contraction during the gait and running cycle.

Acute HMC injury typically occurs through an eccentric mechanism at the terminal stages of the swing phase of running. The long head of the biceps femoris (LHBF) muscle is most commonly affected, and within the LHBF muscle, the proximal myotendinous junction and proximal locations are most commonly affected.

The diagnosis of acute HMC injury is based on the presence of acute-onset pain in the posterior thigh, and presence of the triad of pain on contraction, stretching and palpation. Imaging has a role in confirming the site of injury and characterizing its extent, providing some prognostic information and helping plan treatment. In this regard both magnetic resonance imaging (MRI) and ultrasonography (US) have been shown to be effective for identification of hamstring strains and tendinopathy. Both MRI and US provide detailed information about the HMC with respect to localization and characterization of injury. Several clinical, MRI and US determinants were established that are associated with a longer recovery time in nonoperative management of acute HMC injury. However, it is important to realize that for an individual HMC injury none of these MRI and US determinants show a direct correlation with the time to return to play. Accordingly, the prognosis of HMC injuries should not be guided by imaging findings alone.

Precise classification of acute HMC injury has important implications for treatment and prognosis (i.e., time to return to play), as outlined in detail below. There are anatomical differences between a Type 3a injury (minor partial muscle tear ≤ 5 mm; intrafascicle/bundle-tear) and a Type 3b injury (moderate partial muscle tear > 5 mm; interfascicle/bundle-tear).