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Competing Interests: Competing interests: None declared.

Background and Objective: Muscle injuries are one of the main daily problems in sports medicine, football in particular. However, we do not have a reliable means to predict the outcome, i.e. return to play from severe injury. The aim of the present study was to evaluate the capability of the MLG-R classification system to grade hamstring muscle injuries by severity, offer a prognosis for the return to play, and identify injuries with a higher risk of re-injury. Furthermore, we aimed to assess the consistency of our proposed system by investigating its intra-observer and inter-observer reliability., Methods: All male professional football players from FC Barcelona, senior A and B and the two U-19 teams, with injuries that occurred between February 2010 and February 2020 were reviewed. Only players with a clinical presentation of a hamstring muscle injury, with complete clinic information and magnetic resonance images, were included. Three different statistical and machine learning approaches (linear regression, random forest, and eXtreme Gradient Boosting) were used to assess the importance of each factor of the MLG-R classification system in determining the return to play, as well as to offer a prediction of the expected return to play. We used the Cohen's kappa and the intra-class correlation coefficient to assess the intra-observer and inter-observer reliability., Results: Between 2010 and 2020, 76 hamstring injuries corresponding to 42 different players were identified, of which 50 (65.8%) were grade 3 r , 54 (71.1%) affected the biceps femoris long head, and 33 of the 76 (43.4%) were located at the proximal myotendinous junction. The mean return to play for grades 2, 3, and 3 r injuries were 14.3, 12.4, and 37 days, respectively. Injuries affecting the proximal myotendinous junction had a mean return to play of 31.7 days while those affecting the distal part of the myotendinous junction had a mean return to play of 23.9 days. The analysis of the grade 3 r biceps femoris long head injuries located at the free tendon showed a median return to play time of 56 days while the injuries located at the central tendon had a shorter return to play of 24 days (p = 0.038). The statistical analysis showed an excellent predictive power of the MLG-R classification system with a mean absolute error of 9.8 days and an R-squared of 0.48. The most important factors to determine the return to play were if the injury was at the free tendon of the biceps femoris long head or if it was a grade 3 r injury. For all the items of the MLG-R classification, the intra-observer and inter-observer reliability was excellent (k > 0.93) except for fibres blurring (κ = 0.68)., Conclusions: The main determinant for a long return to play after a hamstring injury is the injury affecting the connective tissue structures of the hamstring. We developed a reliable hamstring muscle injury classification system based on magnetic resonance imaging that showed excellent results in terms of reliability, prognosis capability and objectivity. It is easy to use in clinical daily practice, and can be further adapted to future knowledge. The adoption of this system by the medical community would allow a uniform diagnosis leading to better injury management., (© 2022. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Despite the recent publication and subsequent clinical application of several muscle injury classification systems, none has been able to address the varying and often unique/complex types of injuries that occur in different muscles. Although there are advantages of using a unified classification, there are significant differences between certain muscles and muscle groups. These differences may complicate the clinical effectiveness of using a unified injury classification. This narrative explores the difficulties in using a single classification to describe the heterogeneous nature of muscle injuries. Within that context, the possibility of viewing muscles and muscle injuries in the same manner as other biological tissues, structures, organs, and systems is discussed. Perhaps, in addition to a unified classification, subclassifications or muscle specific classifications should be considered for certain muscles. Having a more specific (granular) approach to some of the more commonly injured muscles may prove beneficial for more accurately and effectively diagnosing and treating muscle injuries. Ideally, this will also lead to more accurate determination of the prognosis of specific muscle injuries.

High-resolution ultrasound (US) has helped to characterize the "tennis leg injury" (TL). However, no specific classifications with prognostic value exist. This study proposes a medial head of the gastrocnemius injury classification based on sonographic findings and relates this to the time to return to work (RTW) and return to sports (RTS) to evaluate the prognostic value of the classification. 115 subjects (64 athletes and 51 workers) were retrospectively reviewed to asses specific injury location according to medial head of the gastrocnemius anatomy (myoaponeurotic junction; gastrocnemius aponeurosis (GA), free gastrocnemius aponeurosis (FGA)), presence of intermuscular hematoma, and presence of gastrocnemius-soleus asynchronous movement. Return to play (RTP; athletes) and return to work (RTW; occupational) days were recorded by the treating physician. This study proposes 5 injury types with a significant relation to RTP and RTW (P < .001): Type 1 (myoaponeurotic injury), type 2A (gastrocnemius aponeurosis injury with a <50% affected GA width), type 2B (gastrocnemius aponeurosis with >50% affected GA width), type 3 (free gastrocnemius aponeurosis (FGA) tendinous injury), and type 4 (mixed GA and FGA injury). The longest RTP/RTW periods were associated with injuries with FGA involvement. Intermuscular hematoma and Gastrocnemius-soleus asynchronous motion during dorsiflexion and plantarflexion were observed when the injury affected >50% of the GA width, with or without associated FGA involvement, and this correlated with a worse prognosis. The proposed classification can be readily applied in the clinical setting although further studies on treatment options are required., (© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Chronic exertional compartment syndrome is characterized by exertional pain and elevated intracompartmental pressures affecting the leg in physically active young people. In patients who have failed conservative measures, fasciotomy is the treatment of choice. This study presents a new method for performing fasciotomy using high-resolution ultrasound (US) guidance and reports on the clinical outcomes in a group of these patients. Over a 3-year period, 7 consecutive patients with a total of 9 involved legs presented clinically with anterior compartment chronic exertional compartment syndrome, which was confirmed by intracompartmental pressure measurements before and after exercise. After a US examination, fasciotomy under US guidance was performed. Preoperative and postoperative pain and activity levels were assessed as well as number of days needed to "return to play." All patients had a decrease in pain, and all except 1 returned to presymptomatic exercise levels with a median return to play of 35 days., (© 2016 by the American Institute of Ultrasound in Medicine.)

Objective: To assess the sensitivity of ultrasound in detecting soleus muscle lesions diagnosed on magnetic resonance imaging (MRI) and to characterize their location, ultrasound pattern, and evolution., Materials and Methods: Ultrasound and MRI studies were performed between May 2009 and February 2013 on all patients who presented to the Medical Services Clinic of the Catalan Sport Council with the initial onset of sharp pain in the calf compatible with injury of the soleus muscle. An inter-observer ultrasound reliability study was also performed., Results: A total of 55 cases of soleus injury were studied prospectively (22 with right leg involvement, 33 left) by ultrasound and MRI, which was utilized as the "gold standard." In MRI studies, 24 cases (43.7%) had myofascial injuries that were localized in the posterior aponeurosis (PMF) in 15 cases (27.3%) and in the anterior aponeurosis (AMF) in 9 (16.4%). Thirty-one cases (56.3%) were musculotendinous injuries, with 9 cases (16.4%) in the medial aponeurosis (MMT), 11 cases (20%) in the lateral aponeurosis (LMT), and 11 cases (20%) in the central tendon (CMT). In comparison to MRI, ultrasound was able to detect injury to the soleus in 27.2% of cases. No injuries were detected by ultrasound alone. Posterior myofascial injuries were more likely to be detected by ultrasound than anterior myofascial injuries or all types of musculotendinous injuries. Ultrasound patterns for each type of injury were described., Conclusion: Ultrasound is not a sensitive technique for detecting and assessing soleus traumatic tears compared with MRI, although the sensitivity is enhanced by a thorough anatomically based ultrasound examination. Timing of the ultrasound examination may be of importance. Each type of soleus injury appears to have a characteristic ultrasound pattern based on a defect of connective expansions, the existence of small myofascial filiform collections, and the rarefaction of the fibrillar area.

Background: Although posterior thigh muscle strains are common in athletes, there are no reports regarding isolated gracilis muscle injuries. The authors present a case series of 7 elite athletes with isolated gracilis muscle ruptures., Purpose: To present the injury pattern, clinical presentation, diagnosis, and outcome of gracilis muscle ruptures., Study Design: Case series; Level of evidence, 4., Methods: This is a retrospective review of 7 elite athletes with posterior thigh pain (3 dancers, 2 soccer players, 1 tae kwon do player, 1 tennis player). In all athletes, the injury occurred during thigh adduction with the hip internally rotated, as clearly evident at ultrasound scans performed 1 to 20 days after the injury. Management included an initial rest period, followed by physiotherapy and gradual return to sports activities., Results: According to the ultrasound scans, the lesions were in the proximal-middle third junction of the thigh, at the muscle-tendon junction. The lesions were classified as grade 2 (partial discontinuity). The muscle injury area was, on average, 17.1 × 23.7 mm (range, 10-31 × 9-46 mm). The average length of the lesions was 40.14 mm (range, 20-52 mm). All athletes recovered and returned to full performance within 6 weeks of the injury (average, 35.6 days)., Conclusion: Medial thigh pain after eccentric contraction during hip adduction should raise suspicion of a gracilis muscle tear. Ultrasound is useful, and full recovery occurs within 6 weeks from the injury.