Acute first-time hamstring strains during slow-speed stretching: clinical, magnetic resonance imaging, and recovery characteristics

Is there an association between high-speed running biomechanics and hamstring strain injury? A systematic review

Despite increased awareness of the multifactorial nature of Hamstring Strain Injury (HSI), the role of running biomechanics remains unclear. The aim of this systematic review was to investigate whether an association exists between running biomechanics and HSI. Five databases were searched from inception to January 2021. Eligibility criteria included epidemiological studies that provide data on running biomechanics in athletes who have sustained a HSI (retrospectively or prospectively) and compared to control data. Searches yielded 4,798 articles. Twelve met the selection criteria. Biomechanical analysis differed considerably across studies, thus meta-analyses was not possible. Studies largely found either no differences or contradicting findings between running biomechanics of athletes who have sustained a HSI (retrospectively or prospectively) and controls, with the exception of lateral trunk kinematics and horizontal propulsive forces. It is important to note some concern regarding the quality of included studies, particularly sample size, increasing the risk of bias associated with results. Further research utilising validated methods of biomechanical analysis, is needed to determine if an association exists between running biomechanics and HSI. Until then, definitive conclusions cannot be drawn as to whether specific biomechanical interventions should be included in injury prevention and/or rehabilitation programmes.

Outcomes of Activity-Related Lower Extremity Muscle Tears After Application of the British Athletics Muscle Injury Classification: A Systematic Review

CONTEXT

Muscle injury classification and grading systems have been reported for >100 years; yet it offer limited evidence relating the clinical or radiological qualities of a muscle injury to the pathology or clinical outcome. The British Athletics Muscle Injury Classification (BAMIC) incorporates recent predictive features of muscle injuries and provides a precise radiographic framework for clinical prediction and management.

OBJECTIVE

To investigate clinical outcomes, particularly time to return to play (RTP), reinjury rate (RIR), and prognostic value of specific magnetic resonance imaging (MRI) findings, of activity-related muscle injuries (tears) in athletes after application of the BAMIC.

DATA SOURCES

A search of PubMed (NLM), EMBASE (Ovid), Web of Science (Clarivate), Cochrane Library (Wiley), and ClinicalTrials.gov from the inception date of each database through August 31, 2022, was conducted. Keywords included the BAMIC.

STUDY SELECTION

All English language studies evaluating clinical outcomes of RTP and RIR after activity-related muscle injuries and where BAMIC was applied were included. A total of 136 articles were identified, and 11 studies met inclusion criteria.

STUDY DESIGN

Systematic review (PROSPERO: CRD42022353801).

LEVEL OF EVIDENCE

Level 2.

DATA EXTRACTION

Two reviewers independently screened studies for eligibility and extracted data. Methodological quality of included study was assessed independently by 2 reviewers with the Newcastle-Ottawa Quality Scale (NOS); 11 good quality studies (4 prospective cohort studies, 7 retrospective cohort studies) with 468 athletes (57 female) and 574 muscle injuries were included.

RESULTS

All studies reported a statistically significant relationship between BAMIC grade, BAMIC injury site, and/or combined BAMIC grade and injury site with RTP. A statistically significant increased RIR was reported by BAMIC grade and BAMIC injury site in 2 of 4 and 3 of 4 studies, respectively. The prognostic value of individual MRI criteria was limited.

CONCLUSION

Consistent evidence suggests that BAMIC offers prognostic and therapeutic guidance for clinical outcomes, particularly RTP and RIR, after activity-related muscle injuries in athletes that may be superior to previous muscle injury classification and grading systems.

The Cobra sign: A marker for overestimation of tendon retraction in proximal semimembranosus tendon avulsion

PURPOSE

To introduce a new magnetic resonance imaging (MRI) sign, termed the Cobra sign, and identify its diagnostic metrics. The secondary aim was to demonstrate that this sign can be a source of false evaluation of tendon retraction in patients with proximal hamstring avulsion injury.

METHOD

This retrospective cohort study targeted patients surgically treated for proximal hamstring avulsion injury from January 2019 to June 2023. The MRI Cobra sign was defined as a wavy curved T2-hypointense band with the free end folding distally over itself, resembling a cobra head. The primary outcome measure was the characterization of the Cobra sign in patients with proximal hamstring avulsion injury. The secondary outcome was the association of this sign with tendon retraction. The study included 81 proximal hamstring avulsion injury patients (mean age of 45.7, SD = 13.9), with 41 (50.6%) complete avulsions, 33 semimembranosus, and 7 conjoint tendons.

RESULTS

The MRI Cobra sign was found in 25 patients (17 semimembranosus and 8 complete). It was confirmed surgically only in semimembranosus cases. It demonstrated 51.5% sensitivity and 83.3% specificity for isolated semimembranosus avulsions, with a significant positive likelihood ratio of 3.0. MRI retraction was 10.05 cm (±3.0), reducing to 7.9 cm (±2.5) on surgical measurement (mean difference = 2.0 cm, p < 0.001). The regression analysis confirmed MRI retraction's influence on the Cobra sign, with a 1.4 odds increase per unit (p < 0.001). In linear regression analysis, each unit increase in MRI retraction corresponded to a 79% increase in surgical retraction (coefficient 0.7, t = 11.1, p < 0.001).

CONCLUSION

The Cobra sign demonstrated acceptable diagnostic accuracy for isolated semimembranosus avulsion, with a high specificity of 83.3%, a low sensitivity of 51.5%, and a positive likelihood ratio of 3.0. The presence of the Cobra sign indicates an overestimated MRI retraction by approximately 21%.

LEVEL OF EVIDENCE

Level III.

Anatomical Relationships of the Proximal Attachment of the Hamstring Muscles with Neighboring Structures: From Ultrasound, Anatomical and Histological Findings to Clinical Implications

BACKGROUND

Injuries of the proximal attachment of the hamstring muscles are common. The present study aimed to investigate the relationship of the proximal attachment of the hamstring muscles with neighboring structures comprehensively.

METHODS

A total of 97 hemipelvis from 66 cryopreserved specimens were evaluated via ultrasound, anatomical and histological samples.

RESULTS

The proximal attachment of the hamstring muscles presents a hyperechogenic line surrounding the origin of the semimembranosus and the long head of the biceps femoris muscles, as well as another hyperechogenic line covering the sciatic nerve. The anatomical and histological study confirms the ultrasound results and shows different layers forming the sacrotuberous ligament. Furthermore, it shows that the proximal attachment of the semimembranosus muscle has a more proximal origin than the rest of the hamstring muscles. Moreover, this muscle shares fibers with the long head of the biceps femoris muscle and expands to the adductor magnus muscle. The histological analysis also shows the dense connective tissue of the retinaculum covering the long head of the biceps femoris and semimembranosus muscles, as well as the expansion covering the sciatic nerve.

CONCLUSIONS

These anatomical relationships could explain injuries at the origin of the hamstring muscles.

Isolated spontaneous non-insertional tear of the iliopsoas tendon in an elderly patient: significance of ultrasound imaging

Isolated spontaneous tears in the non-insertional portion of the iliopsoas tendon without any underlying injury are uncommon, especially among elderly individuals. We describe the case of an 88-year-old man who experienced right groin pain caused by a spontaneous non-insertional tear in the iliopsoas tendon identified through ultrasound and confirmed via MRI. Ultrasound revealed hypoechogenicity in the non-insertional portion of the iliopsoas tendon, leading to quick identification and conservative treatment and resulting in positive functional outcomes. This case report emphasises the significance of considering spontaneous non-insertional iliopsoas tendon tears when evaluating cases of acute groin pain. This finding underscores the effectiveness of ultrasound as an initial diagnostic tool for the early cost-effective diagnosis of soft tissue injuries around the hip joint, especially in low-resource settings. Timely detection and management can help avoid unnecessary operative interventions and facilitate faster and better recovery.

Deciphering the Complexity: Addressing Recurrent Hamstring Injury in a Long-Distance Female Athlete

Hamstring muscle injuries are prevalent in sports, presenting substantial hurdles for athletes and teams due to their high recurrence rates and prolonged recovery periods. The biceps femoris (BF) muscle is frequently implicated in these injuries, with notably high recurrence rates, particularly at the distal musculotendinous T-junction (DMTJ), where half of BF reinjuries occur. This paper presents a case study of a 31-year-old female long-distance athlete with a history of DMTJ rupture, shedding light on the intricacies associated with hamstring injuries. The case underscores the challenges in accurately interpreting imaging findings, reinforcing the need for clinical-imaging correlation and exploration of lesion mechanisms to achieve an accurate diagnosis, optimize outcomes, and facilitate a safe return to sport.

Operative Repair of Hamstring Injuries From the Jackling Position in Rugby

Background

The jackling position within rugby has not been previously described as a mechanism for proximal hamstring injuries.

Hypothesis

Acute surgical repair of proximal hamstring avulsion injuries sustained from the jackling contact position enables a return to a previous level of sporting activity with low risk of recurrence.

Study Design

Case series; Level of evidence, 4.

Methods

This study included 54 professional rugby players (mean age, 26 ± 4.8 years) who underwent acute primary surgical repair of complete, proximal hamstring avulsion injuries. The mean follow-up time was 17 months (range, 12-24 months). Mean isometric hamstring strength and function testing was performed at 3 months and 1 year after repair.

Results

Of the 54 players, 51 (94.4%) returned to their preinjury level of sporting activity. The mean time from surgical repair to full sporting activity was 7 months (range, 4-12 months). No patients had recurrence of the primary injury. At 1 year postoperatively, patients had significantly restored mean isometric hamstring muscle strength when compared with the uninjured leg at 0° (98.4% ± 2.8%), 15° (95.9% ± 2.9%), and 45° (92.9% ± 4.1%); improved Lower Extremity Functional Score (78.0 ± 2.0); and improved Marx activity rating score (14.3 ± 1.5) (P < .001 for all).

Conclusion

Acute surgical repair of proximal hamstring avulsion injuries caused by the contact jackling position produced a high return to preinjury level of sporting activity, increased muscle strength, and improved functional outcome scores, with a low risk of recurrence at short-term follow-up.

Validity and Reliability of Handheld Dynamometry to Assess Isometric Hamstrings and Quadriceps Strength at Varying Muscle Lengths

CONTEXT

The hamstrings are the most commonly injured muscle in sports and are especially injury prone in lengthened positions. Measuring knee muscle strength in such positions could be relevant to establish injury risk. Handheld dynamometry has been shown to be a valid, reliable, and practical tool to measure isometric muscle strength clinically. The aim of this study was to assess the validity and reliability of the assessment of isometric knee muscle strength with a handheld dynamometer (HHD) at various muscle lengths, by modifying the hip and knee angles during testing.

DESIGN

Concurrent validity and test-retest reliability.

METHODS

Thirty young healthy participants were recruited. Hamstring and quadriceps isometric strength was measured with a HHD and with an isokinetic dynamometer, over 2 testing sessions, in a randomized order. Isometric strength was measured on the right lower limb in 6 different positions, with the hip at either 0° or 80° of flexion and the knee at either 30°, 60°, or 90° of flexion. Pearson and Spearman correlations were used to assess the validity, and intraclass correlation coefficients were calculated to establish the test-retest reliability of the HHD.

RESULTS

Good to excellent reliability and moderate to high validity were found in all the tested muscle length positions, except for the hamstrings in a seated position with the knee extended at 30°.

CONCLUSIONS

The use of a HHD is supported in the clinical setting to measure knee muscle strength at varying muscle lengths in healthy adults, but not for the hamstrings in a lengthened position (hip flexed and knee extended). These results will have to be confirmed in sport-specific populations.

Eccentric Hamstring Strength Imbalance among Football and Soccer Athletes

OBJECTIVES

Hamstring strain injuries (HSI) are common among football and soccer athletes. Eccentric strength imbalance is considered a contributing factor for HSI. There is, however, a paucity of data on hamstring imbalances of soccer and American football athletes as they age and advance in skill level. High school athletes will display greater interlimb discrepancies compared with collegiate and professional athletes. In addition, soccer athletes will exhibit greater hamstring asymmetry than American football athletes.

METHODS

Hamstring testing was performed on soccer and American football athletes using the NordBord Hamstring Testing System (Vald Performance, Albion, Australia). Age, sex, weight, sport specialization, and sport level were recorded. Maximum hamstring forces (N), torque (N · m), and work (N · s) were measured. Hamstring imbalance (%) was calculated by dividing the absolute value of the difference in leg forces divided by their sum. One-way analysis of variance and independent sample t tests compared measurements between athlete groups.

RESULTS

A total of 631 athletes completed measurements, including 88 high school male soccer, 25 college male soccer, 23 professional male soccer, 83 high school female soccer, 28 college female soccer, 288 high school football, and 96 college football athletes. High school soccer players displayed significantly greater imbalances for torque (P = 0.03) and work (P < 0.01) than football athletes. Imbalances for maximum force (P = 0.035), torque (P = 0.018), and work (P = 0.033) were significantly higher for male soccer athletes in high school compared with college- and professional-level athletes. Female high school soccer players had significantly higher imbalance in torque (P = 0.045) and work (P = 0.001) compared with female collegiate soccer players. Football athletes did not experience significant changes in force imbalances between skill levels.

CONCLUSIONS

High school soccer athletes exhibit greater hamstring imbalances than football athletes. Higher levels of play in soccer, for both male and female athletes, correlate with less hamstring asymmetry.

Assessing site-specificity of the biomechanical properties of hamstring aponeuroses using MyotonPRO: A cadaveric study

BACKGROUND

Hamstring muscles are the most frequently reported sites of muscle strain injuries, especially near the bi-articular muscles' myotendinous junction, where aponeurosis provides a connective tissue network linking muscle fibers to the tendon. This study aimed to investigate the reliability and site-specific differences of hamstring aponeuroses under different conditions (formalin and urea) using MyotonPRO.

METHODS

Eight hamstring muscle groups were dissected from four human cadavers (two males and two females) aged 83-93 years. Measurements of the mechanical properties of the aponeuroses from the superficial and deep regions of biceps femoris long head, semitendinosus, and semimembranosus (after formalin solution immersion) were done using MyotonPRO (intra-rater reliability was examined within a 24-h interval), following which the hamstring aponeuroses were measured using a similar procedure after urea solution immersion.

FINDINGS

Test-retest (intra-rater) results revealed that the MyotonPRO measurement of tone, stiffness, relaxation, and creep of cadaveric aponeuroses presented good to excellent reliability (ICC: 0.86 to 0.98). There were no significant differences in tone, stiffness, elasticity, relaxation, and creep among the six sites of hamstring aponeuroses under both formalin and urea conditions. Significant differences between formalin and urea conditions were found in the tone, stiffness, relaxation, and creep of hamstring aponeuroses (P < 0.05).

INTERPRETATION

These results suggested that the biomechanical properties of hamstring aponeuroses showed homogeneity between the sites using MyotonPRO. Urea solution could potentially neutralize the effect of formalin on the biomechanical properties of cadaveric muscle-aponeurosis-tendon units. The present findings might influence the design of subsequent cadaveric studies on hamstring muscle strains.

Pathogenesis and Diagnosis of Proximal Hamstring Tendinopathies

The proximal hamstring complex is a highly vulnerable area that is especially prone to injury. Proximal hamstring tendinopathies (PHTs) remain challenging in diagnosis, treatment, rehabilitation, and prevention due to a large variety of different injuries, slow healing response, persistent symptoms, and functional impairments. PHTs are often misdiagnosed or underdiagnosed, leading to delayed treatment and therapy failure. In addition, many athletes are at a high risk of PHT recurrence, a leading cause of prolonged rehabilitation and impaired individual performance. Until now, there have been no clear criteria for the diagnosis and classification of PHT. Tendinopathies can be graded based on their symptoms and onset. Additionally, radiological characteristics exist that describe the severity of tendinopathies. The diagnosis usually includes a battery of pain provocation tests, functional tests, and imaging to ensure a proper classification. Understanding the specific tasks in the pathogenesis and diagnostic process of PHT requires knowledge of functional anatomy, injury pattern and pathophysiological mechanisms as well as examination and imaging techniques. This work provides a structured overview of the pathogenesis and diagnostic work-up of PHT, emphasizing structured examination and imaging to enable a reliable diagnosis and rapid treatment decisions.

Predictors of Early Return to Sport After Surgical Repair of Proximal Hamstring Complex Injuries in Professional Athletes: A Prospective Study

BACKGROUND

Proximal hamstring complex injury (PHCI) is a common injury among professional athletes, particularly those participating in pivot contact sports. Previous studies have suggested that surgery can be effective in restoring function and allowing athletes to return to sport (RTS), but the factors influencing successful RTS have been less clear.

PURPOSE

To assess RTS capabilities after surgical treatment of PHCI in professional athletes and to identify favorable predictors of RTS.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

This study (2002-2022) was conducted on professional athletes who underwent surgical treatment for PHCI at a sports surgery center. The primary outcome of the study was the RTS capability, evaluated based on the rate of athletes' return to their preinjury level of competition, time delay to RTS, and quality of RTS as measured using their level of performance and progression of scores on activity scales such as the Tegner Activity Scale (TAS) and University of California, Los Angeles (UCLA), scale. "Maintained performance" was defined as athletes returning to the same preinjury activity level (per the TAS and UCLA scale) and perceiving themselves to have maintained their performance. Secondary outcomes covered the potential RTS predictors and complication rate. The study distinguished 2 types of PHCI: proximal hamstring tendon avulsion injury (proximal rupture with empty footprint, or having a "positive dropped ice cream sign") and complete proximal hamstring free tendon rupture (PHTR; proximal rupture without empty footprint, or having a "negative dropped ice cream sign").

RESULTS

The study examined 64 professional athletes (mean age, 27.3 years; 82.8% male) undergoing surgery for PHCI. The RTS rate was 98.4%, with 78.1% of the athletes returning to their preinjury level of competition at 6.2 months (SD, 2.5 months). Twelve (19%) patients had returned to sport at an inferior level of competition, and 2 (3.1%) were unable to continue in their preinjury sport. Subgroup analysis revealed variation in RTS based on sport type, with the highest rate of return to preinjury performance found in athletes in handball and sports with splits (fencing, squash, and escalade; 100%) and soccer (95.2%). In the univariate analysis, male sex (hazard ratio [HR], 4.05; 95% CI, 1.45-11.3; P = .008), higher preinjury TAS score (HR, 1.27; 95% CI, 1.06-1.52; P = .011), injury involving the semimembranosus (HR, 4.84; 95% CI, 2.31-10.2; P < .001) or conjoint tendon (HR, 3.12; 95% CI, 1.55-6.25; P = .001), and PHTR (HR, 7.77; 95% CI, 3.54-17.0; P < .001) were significantly associated with a better postoperative level of competition. Multivariate analysis identified 3 favorable predictors of RTS with HRs of 2.91 (95% CI, 1.01-8.35; P = .047) for male sex, 3.86 (95% CI, 1.78-8.37; P < .001) for isolated semimembranosus injury, and 5.18 (95% CI, 2.24-12.0; P < .001) for PHTR. The complication rate was 4.7%.

CONCLUSION

Favorable predictors of early RTS were male sex, isolated semimembranosus injury, and PHTR injuries.

REGISTRATION

NCT02906865 (ClinicalTrials.gov identifier).

Hamstring Strain Ultrasound Case Series: Dominant Semitendinosus Injuries in National Collegiate Athletic Association Division I Athletes

Authors of previous studies of patients with acute hamstring strains have reported injury to the biceps femoris and semitendinosus (ST) in 50% to 100% and 0% to 30%, respectively. This retrospective case series of hamstring injuries in National Collegiate Athletic Association Division I collegiate athletes exhibited an injury pattern on ultrasound imaging that differed from what would be expected based on prior literature. We examined ultrasound images of 38 athletes with acute hamstring strains for injury location (proximal muscle, proximal myotendinous junction, midportion of muscle, distal muscle) and affected muscles (biceps femoris, ST, or semimembranosus). Twenty-six athletes (68.4%) injured the ST, and 9 athletes (23.7%) injured the biceps femoris long head. Most athletes (23, 60.5%) injured the proximal portion of the muscle or myotendinous junction. Though this study had many limitations, we demonstrated more frequent involvement of the ST and less frequent involvement of the biceps femoris than reported in the literature.

Epidemiology of hamstring injuries in 538 cases from an FC Barcelona multi sports club

OBJECTIVES

Hamstring injuries are the most common muscle injuries in team sports. The aims of this study were to describe the epidemiology of hamstring muscle injuries in the professional and amateur sport sections of a multi-sport club Football Club Barcelona (FCB) and to determine any potential correlation between return-to-play (RTP) and injury location, severity of connective tissue damage, age, sex, and athlete's level of competition.

METHODS

This descriptive epidemiological study with data collected from September 2007 to September 2017 stored in the FCB database. The study included non-contact hamstring injuries sustained during training or competition.

RESULTS

A total of 538 hamstring injuries were reported in the club's database, of which 240 were structurally verified by imaging as hamstring injuries. The overall incidence for the 17 sports studied was 1.29 structurally verified hamstring injuries per 100 athletes per year. The muscle most commonly involved in hamstring injuries was the biceps femoris, and the connective tissue most frequently involved was the myofascial. There was no evidence of a statistically significant association between age and RTP after injury, and no statistically significant difference between sex and RTP. However, the time loss by professionals was shorter than for amateurs, and proximal hamstring injuries took longer RTP than distal ones.

CONCLUSION

In the 17 sports practiced at multi-sport club, the incidence of hamstring injury was 1.29 per 100 athletes per year. Players from sports in which high-speed sprinting and kicking are necessary, and amateurs, were at higher risk of suffering a hamstring injury. In addition, proximally located hamstring injuries involving tendinous connective tissue showed the longest RTP time. Age did not seem to have any influence on RTP. Documenting location and the exact tissue involved in hamstring injuries may be beneficial for determining the prognosis and RTP.

Epidemiology of quadriceps muscle strain injuries in elite male Australian football players

OBJECTIVE

To describe the epidemiology of quadriceps muscle strain injury (QMSI) in elite Australian Football League (AFL) players, explore recovery milestones and determine whether recovery is impacted by factors such as injury type (index vs. re-injury), the primary muscle injured and the mechanism of injury.

MEASURES

All QMSI data reported to the Soft Tissue Injury Registry of the AFL from the 2014 to 2020 seasons were evaluated. Player demographic data, circumstances of injury, MRI reports and recovery outcomes following injury were extracted. Descriptive statistics and frequency distributions are presented. Recovery outcomes for injury type, primary muscle injured and the mechanism of injury were compared using univariate analyses.

RESULTS

There were 164 QMSIs from 122 players reported (134 index; 30 re-injuries). Almost all (91.3%) QMSIs involved the rectus femoris. Half (48.4%) of the QMSIs occurred during kicking and most commonly affected the dominant kicking leg (72%). The majority occurred at training (64.6%). All re-injuries involved the rectus femoris, most occurred from kicking (63.0%) and within 6 months of the preceding injury (70%). The mean return to play (RTP) time was 25.4 days (95%CI = 22.6-28.2) and rectus femoris injuries took around 14 days longer to RTP than vastii injuries (p = 0.001). QMSIs with a kicking mechanism took the longest to RTP of all injury mechanisms.

CONCLUSION

In AFL players, QMSIs occur mostly in the dominant leg from a kicking mechanism. Rectus femoris injuries are more prevalent and result in longer RTP time frames. Re-injuries exclusively involved the rectus femoris, primarily from kicking.

Is there a relationship between isometric hamstrings-to-quadriceps torque ratio and athletes' plyometric performance?

BACKGROUND

The application of the modified reactive strength index (RSImod) and isometric hamstrings to quadriceps (H:Q) torque ratio to monitoring the athletes' performance is well established, but their relationship to each other still remains unknown. Therefore, the purpose of this investigation was to clarify whether there is a relationship between RSImod and the isometric H:Q torque ratio.

METHODS

Twenty-one male recreational athletes (age, 24.89 ± 4.46 years; weight, 74.11 ± 8.66 kg; height, 179.78 ± 6.76 cm) volunteered to participate in this research. Their isometric H:Q torque ratio via hand-held dynamometer and jumping performance variables during the stop jump (STJ), double leg-drop vertical jump (DL-DVJ), and single leg-drop vertical jump (SL-DVJ) tasks were measured. Also, the RSImod was calculated by dividing the vertical jump height by the time to take-off. Pearson correlation coefficients were used to determine the relationship between the RSImod and jumping performance variables.

RESULTS

The result showed a significant strong positive relationship between the H:Q torque ratio and STJ performance based on the RSImod (p = .027, r = .724). Although, there was a moderate positive relationship between the H:Q torque ratio and jumping height of the STJ task, but it wasn't statistically significant (p = .096, r = .588). Also, no significant relationship was found between the H:Q torque ratio and all jumping performance variables of the DL-DVJ and SL-DVJ tasks (p ≥ .05).

CONCLUSION

The current study exhibited that the isometric H:Q torque ratio correlates to STJ performance based on RSImod but not to SL-DVJ and DL-DVJ. Notably, the difference in results between jumping tasks can be attributed to the complexity of the movement, which means that the RSImod is probably related to other factors. Therefore, the isometric H:Q torque ratio used to monitor the athletes' performance couldn't independently represent the jumping performance that is determined by RSImod.

Intramuscular Tendon Injuries of the Hamstring Muscles: A More Severe Variant? A Narrative Review

Hamstring strain injuries (HSI) are one of the most common sport-related injuries. They have a high injury burden and a high recurrence rate. The development of novel muscle injury grading systems has provided new insights into the possible impact of injury location on the time to return to play (TTRTP) and re-injury following HSI. In particular, injuries to the intramuscular tendon (IMT) may be present in up to 41% of all HSI and have been described as a 'serious thigh muscle strain'. Re-injury rates as high as 60% have been described in elite track and field athletes, as well as prolonged TTRTP. A systematic search was carried out using appropriate keywords to identify articles reporting on HSI involving the IMT in athletes. The primary aim was to determine whether IMT injuries warrant being classified as a distinct clinical entity with different expected outcomes to other hamstring muscle injuries. This narrative review summarises the existing evidence on: (1) the anatomy of the IMT and its response to injury; (2) the role of MRI and novel grading scales in IMT injury management (3) clinical assessment of IMT injuries, (4) TTRTP and re-injury rates across sports following IMT, (5) conservative rehabilitation and the role of specific 'IMT-oriented' strategies, and (6) indications for and approaches to surgery. The review found that important clinical outcomes such as re-injury rates and TTRTP vary across populations, cohorts and sports which suggest that outcomes are specific to the sporting context. Bespoke rehabilitation, tailored to IMT injury, has been shown to significantly reduce re-injuries in elite track and field athletes, without compromising TTRTP. Continued prospective studies across other sports and cohorts, are warranted to further establish relevant clinical findings, indications for surgical intervention and outcomes across other sporting cohorts.

Relationship between shear elastic modulus and passive muscle force in human hamstring muscles using a Thiel soft-embalmed cadaver

PURPOSE

Assessing muscle flexibility and architecture is important for hamstring strain injury (HSI) prevention. We investigated the relationship between shear modulus and passive force in hamstring muscles at different sites and the effect of muscle architecture on the slope of the shear modulus-passive force using shear wave elastography (SWE).

METHODS

The biceps femoris long head (BFlh), semitendinosus (ST), and semimembranosus (SM) muscles were dissected from nine Thiel-embalmed cadavers and fixed to a custom-made mechanical testing machine. Calibrated weights (0-1800 g) were applied gradually in 150-g increments. The shear modulus and anatomical cross-sectional area (ACSA) were measured at proximal, central, and distal points using SWE. The muscle mass and length were measured before the loading test. The shear modulus-passive load relationship of each tested muscle region was analyzed by fitting a least-squares regression line. The increase in shear modulus slope per unit load was calculated and compared between the muscles before and after normalization by the muscle mass, length, and ACSA.

RESULTS

The shear modulus and passive force for all hamstring muscles in each region showed a statistically significant linear correlation. Furthermore, the increase in shear modulus slope was greater for BFlh and ST than for SM (P < 0.05), but after normalization by the muscle length and ACSA, there were no significant differences among the muscles.

CONCLUSION

The local mechanical properties of individual hamstring muscles can be indirectly estimated using SWE, and the slope of increase in shear modulus reflects characteristics of the muscle architecture.

Association Between Magnetic Resonance Imaging Findings and Time to Return to Sport After Muscle Injuries in High-Level Youth Athletes

OBJECTIVE

To describe the relationship between magnetic resonance imaging (MRI) findings and time to return to sport (RTS) from muscle injuries in youth athletes.

DESIGN

Prospective collection of injury surveillance data over 6 seasons (2014-2015 to 2019-2020) and reanalysis of MRIs by a radiologist blinded to RTS time after the data collection period.

SETTING

National sports academy and sports medicine hospital.

PARTICIPANTS

Male youth (11-19 years) athletes participating in the football (soccer) or athletics (track and field) programs with a muscle injury.

INDEPENDENT VARIABLES

Magnetic resonance imaging findings (eg, grade and location) in time-loss muscle injuries.

MAIN OUTCOME VARIABLES

Injury incidence, distributions, and RTS time.

RESULTS

In total, 353 time-loss muscle injuries were recorded for 1089 athlete-seasons, of which 85 satisfied our inclusion criteria (MRI within 14 days). Return to sport time was significantly longer for reinjuries compared with index injuries. Associations between MRI findings and RTS time were specific to the muscle group, with significant differences in RTS time observed between categories of structure, location, and grade. The largest number of injuries was to the hamstrings (n = 46), where injuries involving the tendon were more severe than those involving the myotendinous junction and muscle, proximal injuries were more severe than mid-portion and distal, and longer RTS time was observed for higher injury grade ( P < 0.05).

CONCLUSIONS

Muscle injuries in youth are diverse and cannot be treated as a single injury type. Specific injury durations can be expected depending on injury characteristics such as reinjury, location, structure, and grade.

Is hamstrings-to-quadriceps torque ratio useful for predicting anterior cruciate ligament and hamstring injuries? A systematic and critical review

BACKGROUND

For the past 30 years, the hamstring (H)-to-quadriceps (Q) (H:Q) torque ratio has been considered an important index of muscle strength imbalance around the knee joint. The purpose of this systematic review was to examine the value of H:Q torque ratio as an independent risk factor for hamstring and anterior cruciate ligament (ACL) injuries.

METHODS

Database searches were performed to identify all relevant articles in PubMed, MEDLINE, Cochrane Library, and Scopus. Prospective studies evaluating the conventional (concentric H:Q), functional (eccentric H: concentric Q), and mixed (eccentric H at 30°/s: concentric Q at 240°/s) H:Q ratios as risk factors for occurrence of hamstring muscle strain or ACL injury were considered. Risk of bias was assessed using the Quality In Prognosis Studies tool.

RESULTS

Eighteen included studies reported 585 hamstrings injuries in 2945 participants, and 5 studies documented 128 ACL injuries in 2772 participants. Best evidence synthesis analysis indicated that there is very limited evidence that H:Q strength ratio is an independent risk factor for hamstring and ACL injury, and this was not different between various ratio types. Methodological limitations and limited evidence for ACL injuries and some ratio types might have influenced these results.

CONCLUSION

The H:Q ratio has limited value for the prediction of ACL and hamstring injuries. Monitoring strength imbalances along with other modifiable factors during the entire competitive season may provide a better understanding of the association between H:Q ratio and injury.

Mechanisms of Hamstring Injury in Professional Soccer Players: Video Analysis and Magnetic Resonance Imaging Findings

OBJECTIVE

To describe the injury mechanisms and magnetic resonance imaging (MRI) findings in acute hamstring injuries of male soccer players using a systematic video analysis.

DESIGN

Descriptive case series study of consecutive acute hamstring injuries from September 2017 to January 2022.

SETTING

Two specialized sports medicine hospitals.

PARTICIPANTS

Professional male soccer players aged between 18 and 40 years, referred for injury assessment within 7 days after an acute hamstring injury, with an available video footage of the injury and positive finding on MRI.

INDEPENDENT VARIABLES

Hamstring injury mechanisms (specific scoring based on standardized models) in relation to hamstring muscle injury MRI findings.

MAIN OUTCOME MEASURES

Hamstring injury mechanism (playing situation, player/opponent behavior, movement, and biomechanical body positions) and MRI injury location.

RESULTS

Fourteen videos of acute hamstring injuries in 13 professional male soccer players were analyzed. Three different injury mechanisms were seen: mixed-type (both sprint-related and stretch-related, 43%), stretch-type (36%), and sprint-type (21%). Most common actions during injury moments were change of direction (29%), kicking (29%), and running (21%). Most injuries occurred at high or very high horizontal speed (71%) and affected isolated proximal biceps femoris (BF) (36%). Most frequent body positions at defined injury moments were neutral trunk (43%), hip flexion 45-90 degrees (57%), and knee flexion <45 degrees (93%). Magnetic resonance imaging findings showed that 79% were isolated single-tendon injuries.

CONCLUSIONS

According to a video analysis, most hamstring injuries in soccer occur during high-speed movements. Physicians should suspect proximal and isolated single-tendon-most often BF-hamstring injury, if represented injury mechanisms are seen during game play. In addition to sprinting and stretching, also mixed-type injury mechanisms occur.

Unique morphological architecture of the hamstring muscles and its functional relevance revealed by analysis of isolated muscle specimens and quantification of structural parameters

The structural and functional differences of individual hamstrings have not been sufficiently evaluated. This study aimed to clarify the morphological architecture of the hamstrings including the superficial tendons in detail using isolated muscle specimens, together with quantification of structural parameters of the muscle. Sixteen lower limbs of human cadavers were used in this study. The semimembranosus (SM), semitendinosus (ST), biceps femoris long head (BFlh), and biceps femoris short head (BFsh) were dissected from cadavers to prepare isolated muscle specimens. Structural parameters, including muscle volume, muscle length, fiber length, sarcomere length, pennation angle, and physiological cross-sectional area (PCSA) were measured. In addition, the proximal and distal attachment areas of the muscle fibers were measured, and the proximal/distal area ratio was calculated. The SM, ST, and BFlh were spindle-shaped with the superficial origin and insertion tendons on the muscle surface, and the BFsh was quadrate with direct attachment to the skeleton and BFlh tendon. The muscle architecture was pennate in the four muscles. The four hamstrings possessed either of two types of structural parameters, one with shorter fiber length and larger PCSA, as in the SM and BFlh, and the other with longer fiber length and smaller PCSA, as in the ST and BFsh. Sarcomere length was unique in each of the four hamstrings, and thus the fiber length was suitably normalized using the average sarcomere length for each, instead of uniform length of 2.7 μm. The proximal/distal area ratio was even in the SM, large in the ST, and small in the BFsh and BFlh. This study clarified that the superficial origin and insertion tendons are critical determinants of the unique internal structure and structural parameters representing the functional properties of the hamstring muscles.

London International Consensus and Delphi study on hamstring injuries part 1: classification

Muscle injury classification systems for hamstring injuries have evolved to use anatomy and imaging information to aid management and prognosis. However, classification systems lack reliability and validity data and are not specific to individual hamstring muscles, potentially missing parameters vital for sport-specific and activity-specific decision making. A narrative evidence review was conducted followed by a modified Delphi study to build an international consensus on best-practice decision-making for the classification of hamstring injuries. This comprised a digital information gathering survey to a cohort of 46 international hamstring experts (sports medicine physicians, physiotherapists, surgeons, trainers and sports scientists) who were also invited to a face-to-face consensus group meeting in London . Fifteen of these expert clinicians attended to synthesise and refine statements around the management of hamstring injury. A second digital survey was sent to a wider group of 112 international experts. Acceptance was set at 70% agreement. Rounds 1 and 2 survey response rates were 35/46 (76%) and 99/112 (88.4%) of experts responding. Most commonly, experts used the British Athletics Muscle Injury Classification (BAMIC) (58%), Munich (12%) and Barcelona (6%) classification systems for hamstring injury. Issues identified to advance imaging classifications systems include: detailing individual hamstring muscles, establishing optimal use of imaging in diagnosis and classification, and testing the validity and reliability of classification systems. The most used hamstring injury classification system is the BAMIC. This consensus panel recommends hamstring injury classification systems evolve to integrate imaging and clinical parameters around: individual muscles, injury mechanism, sporting demand, functional criteria and patient-reported outcome measures. More research is needed on surgical referral and effectiveness criteria, and validity and reliability of classification systems to guide management.

London International Consensus and Delphi study on hamstring injuries part 3: rehabilitation, running and return to sport

Hamstring injuries (HSIs) are the most common athletic injury in running and pivoting sports, but despite large amounts of research, injury rates have not declined in the last 2 decades. HSI often recur and many areas are lacking evidence and guidance for optimal rehabilitation. This study aimed to develop an international expert consensus for the management of HSI. A modified Delphi methodology and consensus process was used with an international expert panel, involving two rounds of online questionnaires and an intermediate round involving a consensus meeting. The initial information gathering round questionnaire was sent to 46 international experts, which comprised open-ended questions covering decision-making domains in HSI. Thematic analysis of responses outlined key domains, which were evaluated by a smaller international subgroup (n=15), comprising clinical academic sports medicine physicians, physiotherapists and orthopaedic surgeons in a consensus meeting. After group discussion around each domain, a series of consensus statements were prepared, debated and refined. A round 2 questionnaire was sent to 112 international hamstring experts to vote on these statements and determine level of agreement. Consensus threshold was set a priori at 70%. Expert response rates were 35/46 (76%) (first round), 15/35 (attendees/invitees to meeting day) and 99/112 (88.2%) for final survey round. Statements on rehabilitation reaching consensus centred around: exercise selection and dosage (78.8%-96.3% agreement), impact of the kinetic chain (95%), criteria to progress exercise (73%-92.7%), running and sprinting (83%-100%) in rehabilitation and criteria for return to sport (RTS) (78.3%-98.3%). Benchmarks for flexibility (40%) and strength (66.1%) and adjuncts to rehabilitation (68.9%) did not reach agreement. This consensus panel recommends individualised rehabilitation based on the athlete, sporting demands, involved muscle(s) and injury type and severity (89.8%). Early-stage rehab should avoid high strain loads and rates. Loading is important but with less consensus on optimum progression and dosage. This panel recommends rehabilitation progress based on capacity and symptoms, with pain thresholds dependent on activity, except pain-free criteria supported for sprinting (85.5%). Experts focus on the demands and capacity required for match play when deciding the rehabilitation end goal and timing of RTS (89.8%). The expert panellists in this study followed evidence on aspects of rehabilitation after HSI, suggesting rehabilitation prescription should be individualised, but clarified areas where evidence was lacking. Additional research is required to determine the optimal load dose, timing and criteria for HSI rehabilitation and the monitoring and testing metrics to determine safe rapid progression in rehabilitation and safe RTS. Further research would benefit optimising: prescription of running and sprinting, the application of adjuncts in rehabilitation and treatment of kinetic chain HSI factors.

London International Consensus and Delphi study on hamstring injuries part 2: operative management

The key indications for surgical repair of hamstring injuries (HSIs) remain unclear in the literature due to a lack of high-level evidence and expert knowledge. The 2020 London International Hamstring Consensus meeting aimed to highlight clear surgical indications and to create a foundation for future research. A literature review was conducted followed by a modified Delphi process, with an international expert panel. Purposive sampling was used with two rounds of online questionnaires and an intermediate round involving a consensus meeting. The initial information gathering (round 1) questionnaire was sent to 46 international experts, which comprised open-ended questions covering decision-making domains in HSI. Thematic analysis of responses outlined key domains, which were evaluated by a smaller international subgroup (n=15) comprising clinical academic sports medicine physicians, physiotherapists and orthopaedic surgeons in a consensus meeting. After group discussion of each domain, a series of consensus statements were prepared, debated and refined. A round 2 questionnaire was sent to 112 international hamstring experts to vote on these statements and determine level of agreement. The consensus threshold was set a priori at 70% agreement. Rounds 1 and 2 survey respondents were 35/46 (76%) and 99/112 (88.4%), respectively. The consensus group agreed that the indications for operative intervention included: gapping at the zone of tendinous injury (87.2% agreement) and loss of tension (70.7%); symptomatic displaced bony avulsions (72.8%); and proximal free tendon injuries with functional compromise refractory to non-operative treatment (72.2%). Other important considerations for operative intervention included: the demands of the athlete/patient and the expected functional outcome (87.1%) based on the anatomy of the injury; the risk of functional loss/performance deficit with non-operative management (72.2%); and the capacity to restore anatomy and function (87.1%). Further research is needed to determine whether surgery can reduce the risk of reinjury as consensus was not reached within the whole group (48.2%) but was agreed by surgeons (70%) in the cohort. The consensus group did not support the use of corticosteroids or endoscopic surgery without further evidence. These guidelines will help standardise treatment of HSIs, specifically the indications and decision-making for surgical intervention.

Do Repeated Sprints Affect the Biceps Femoris Long Head Architecture in Football Players with and without an Injury History?-A Retrospective Study

The aim of this study was to compare the biceps femoris long head (BFlh) architecture between football players with (twelve) and without (twenty) history of BFlh injury before and after a repeated sprint task. Fascicle length (FL), pennation angle (PA) and muscle thickness (MT) were assessed at rest and in the active condition before and after the repeated sprint protocol. Athletes with previous BFlh injury showed shorter FL at rest (p = 0.014; η2p = 0.196) and active state (p < 0.001; η2p = 0.413), and greater PA at rest (p = 0.002; η2p = 0.307) and active state (p < 0.001; η2p = 0.368) before and after the task. Intra-individual comparisons showed that injured limbs have shorter FL at rest (p = 0.012; η2p = 0.519) and in the active state (p = 0.039; η2p = 0.332), and greater PA in passive (p < 0.001; η2p = 0.732) and active conditions (p = 0.018; η2p = 0.412), when compared with contralateral limbs. Injured players, at rest and in the active condition, display shorter BFlh FL and greater PA than contralateral and healthy controls after repeated sprints. Moreover, the BFlh of injured players presented a different architectural response to the protocol compared with the healthy controls.

Associations of time to return to performance following acute posterior thigh injuries with running biomechanics, hamstring function, and structure in collegiate sprinters: A prospective cohort design

BACKGROUND

The time to return to sport from acute hamstring strain injuries is associated with several functional and structural impairments. However, not all previous studies assessed the preinjury level before acute hamstring strain injuries directly. The purpose of this study was to examine the associations of the time to return to performance following acute hamstring strain injuries with deficits in running biomechanics, hamstring function and structure in collegiate sprinters by a prospective study.

METHODS

Using a prospective cohort design, 72 participants were recruited from a collegiate track and field team. At the preinjury assessment, a 60-m running-specific test, passive straight leg raise test and isometric knee flexion strength test were assessed at the beginning of the competitive season for three consecutive years (2017-2019). Afterwards, postinjury examinations were performed only in sprinters with acute hamstring strain injuries.

FINDINGS

Twelve sprinters strained their hamstring muscle (incidence rate of hamstring strain injuries: 16.7%); the majority (n = 10) were classified as grades 0-2. The running speed deficit of the running-specific test was associated with the time to return to performance as well as the passive straight leg raise test deficit. In the running-specific test, lower-limb kinetic deficits were more strongly associated with the time to return to performance compared to lower-limb kinematic deficits.

INTERPRETATION

A running-specific test may be considered one of the most convenient and valid tests for assessing rehabilitation progress after acute hamstring strain injuries.

Association Between Injury Mechanisms and Magnetic Resonance Imaging Findings in Rectus Femoris Injuries in 105 Professional Football Players

OBJECTIVE

To describe the injury mechanism and its association with magnetic resonance imaging (MRI) injury findings in acute rectus femoris injuries.

DESIGN

Combined retrospective and prospective descriptive injury study. Retrospective cohort from January 2010 to October 2013 and prospective cohort from October 2013 to January 2019.

SETTING

Specialized sports medicine hospital.

PARTICIPANTS

Male professional football players older than 18 years playing in a national football league, referred for injury assessment within 7 days after an acute rectus femoris injury, with a positive finding on MRI.

INDEPENDENT VARIABLES

Rectus femoris muscle injury MRI findings in relation to injury mechanism in male football players.

MAIN OUTCOME MEASURES

Rectus femoris injury mechanism (kicking, sprinting, and others), MRI injury location, and grade.

RESULTS

There were 105 injuries in total, with 60 (57.1%) and 45 (42.8%) injuries from the retrospective and prospective cohorts, respectively. Kicking was the injury mechanism in 57 (54.3%) of all acute rectus femoris injuries, sprinting represented 32 (30.4%), and 16 (15.2%) were classified as others. There were 20 (19.05%) free tendon, 67 (63.8%) myotendinous junction and/or intramuscular tendon, and 18 (17.1%) peripheral myofascial located injuries. All free tendon injuries were related to kicking and graded as a complete tear of at least one of the tendons in 15/20 (75.0%) cases.

CONCLUSIONS

Kicking seems to be an important mechanism related to complete ruptures and injuries occurring at the proximal free tendon. Sprinting was the other most common mechanism but was never associated with injury to the proximal free tendon.

Evidence-Based Hamstring Injury Prevention and Risk Factor Management: A Systematic Review and Meta-analysis of Randomized Controlled Trials

BACKGROUND

Hamstring injuries are common among athletes. Considering the potentially prolonged recovery and high rate of recurrence, effective methods of prevention and risk factor management are of great interest to athletes, trainers, coaches, and therapists, with substantial competitive and financial implications.

PURPOSE

To systematically review the literature concerning evidence-based hamstring training and quantitatively assess the effectiveness of training programs in (1) reducing injury incidence and (2) managing injury risk factors.

STUDY DESIGN

Systematic review and meta-analysis; Level of evidence, 1.

METHODS

A computerized search of MEDLINE, CINAHL, Cochrane Central Register of Controlled Trials, and SPORTDiscus with manual screening of selected reference lists was performed in October 2020. Randomized controlled trials investigating methods of hamstring injury prevention and risk factor management in recreational, semiprofessional, and professional adult athletes were included.

RESULTS

Of 2602 articles identified, 108 were included. Eccentric training reduced the incidence of hamstring injury by 56.8% to 70.0%. Concentric hamstring strength increased with eccentric (mean difference [MD], 14.29 N·m; 95% CI, 8.53-20.05 N·m), concentric, blood flow-restricted, whole-body vibration, heavy back squat, FIFA 11+ (Fédération Internationale de Football Association), and plyometric training methods, whereas eccentric strength benefited from eccentric (MD, 26.94 N·m; 95% CI, 15.59-38.30 N·m), concentric, and plyometric training. Static stretching produced greater flexibility gains (MD, 10.89°; 95% CI, 8.92°-12.86°) than proprioceptive neuromuscular facilitation (MD, 9.73°; 95% CI, 6.53°-12.93°) and dynamic stretching (MD, 6.25°; 95% CI, 2.84°-9.66°), although the effects of static techniques were more transient. Fascicle length increased with eccentric (MD, 0.90 cm; 95% CI, 0.53-1.27 cm) and sprint training and decreased with concentric training. Although the conventional hamstring/quadriceps (H/Q) ratio was unchanged (MD, 0.03; 95% CI, -0.01 to 0.06), the functional H/Q ratio significantly improved with eccentric training (MD, 0.10; 95% CI, 0.03-0.16). In addition, eccentric training reduced limb strength asymmetry, while H/Q ratio and flexibility imbalances were normalized via resistance training and static stretching.

CONCLUSION

Several strategies exist to prevent hamstring injury and address known risk factors. Eccentric strengthening reduces injury incidence and improves hamstring strength, fascicle length, H/Q ratio, and limb asymmetry, while stretching-based interventions can be implemented to improve flexibility. These results provide valuable insights to athletes, trainers, coaches, and therapists seeking to optimize hamstring training and prevent injury.

Location of Hamstring Injuries Based on Magnetic Resonance Imaging: A Systematic Review

CONTEXT

Hamstring muscle injury location using magnetic resonance imaging (MRI) is not so well described in the literature.

OBJECTIVE

To describe the location of hamstring injuries using MRI.

DATA SOURCES

PubMed, Web of Science, Scopus, SPORTDiscus, Cochrane Library.

STUDY SELECTION

The full text of studies, in English, had to be available. Case reports and reviews were excluded. Included studies must report the location of hamstring injuries using MRI within 8 days of the acute injury.

STUDY DESIGN

Systematic review.

LEVEL OF EVIDENCE

Level 4.

DATA EXTRACTION

A first screening was conducted based on title and abstract of the articles. In the second screening, the full text of the remaining articles was evaluated for the fulfillment of the inclusion criteria.

RESULTS

From the 2788 references initially found in 5 databases, we included 34 studies, reporting a total of 2761 acute hamstring injuries. The most frequent muscle head involved was the long head of the biceps femoris (BFLH) (70%), followed by the semitendinosus (ST) (15%), generally associated with BFLH. The most frequent tissue affected was the myotendinous junction (MTJ) accounting for half the cases (52%). Among all lesions, the distribution between proximal, central, and distal lesions looked homogenous, with 34.0%, 33.4% and 32.6%, respectively. The stretching mechanism, while only reported in 2 articles, represented 3% of all reported mechanisms, appears responsible for a specific lesion involving the proximal tendon of the semimembranosus (SM), and leading to a longer time out from sport.

CONCLUSION

BFLH was the most often affected hamstring injuries and MTJ was the most affected tissue. In addition, the distal, central, and proximal locations were homogeneously distributed. We also noted that MRI descriptions of hamstring injuries are often poor and did not take full advantage of the MRI strengths.

SYSTEMATIC REVIEW REGISTRATION

Before study initiation, the study was registered in the PROSPERO International prospective register of systematic reviews (registration number CRD42018107580).

Its not all about sprinting: mechanisms of acute hamstring strain injuries in professional male rugby union—a systematic visual video analysis

Objectives

The mechanisms of hamstring strain injuries (HSIs) in professional Rugby Union are not well understood. The aim of this study was to describe the mechanisms of HSIs in male professional Rugby Union players using video analysis.

Methods

All time-loss acute HSIs identified via retrospective analysis of the Leinster Rugby injury surveillance database across the 2015/2016 to 2017/2018 seasons were considered as potentially eligible for inclusion. Three chartered physiotherapists (analysts) independently assessed all videos with a consensus meeting convened to describe the injury mechanisms. The determination of the injury mechanisms was based on an inductive process informed by a critical review of HSI mechanism literature (including kinematics, kinetics and muscle activity). One of the analysts also developed a qualitative description of each injury mechanism.

Results

Seventeen acute HSIs were included in this study. Twelve per cent of the injuries were sustained during training with the remainder sustained during match-play. One HSI occurred due to direct contact to the injured muscle. The remainder were classified as indirect contact (ie, contact to another body region) or non-contact. These HSIs were sustained during five distinct actions—‘running’ (47%), ‘decelerating’ (18%), ‘kicking’ (6%), during a ‘tackle’ (6%) and ‘rucking’ (18%). The most common biomechanical presentation of the injured limb was characterised by trunk flexion with concomitant active knee extension (76%). Fifty per cent of cases also involved ipsilateral trunk rotation.

Conclusion

HSIs in this study of Rugby Union were sustained during a number of playing situations and not just during sprinting. We identified a number of injury mechanisms including: ‘running’, ‘decelerating’, ‘kicking’, ‘tackle’, ‘rucking’ and ‘direct trauma’. Hamstring muscle lengthening, characterised by trunk flexion and relative knee extension, appears to be a fundamental characteristic of the mechanisms of acute HSIs in Rugby Union.

Evidence-Based Management and Factors Associated With Return to Play After Acute Hamstring Injury in Athletes: A Systematic Review

Background:

Considering the lengthy recovery and high recurrence risk after a hamstring injury, effective rehabilitation and accurate prognosis are fundamental to timely and safe return to play (RTP) for athletes.

Purpose:

To analyze methods of rehabilitation for acute proximal and muscular hamstring injuries and summarize prognostic factors associated with RTP.

Study Design:

Systematic review; Level of evidence, 4.

Methods:

In August 2020, MEDLINE, CINAHL, Cochrane Central Register of Controlled Trials, and SPORTDiscus were queried for studies examining management and factors affecting RTP after acute hamstring injury. Included were randomized controlled trials, cohort studies, case-control studies, and case series appraising treatment effects on RTP, reinjury rate, strength, flexibility, hamstrings-to-quadriceps ratio, or functional assessment, as well as studies associating clinical and magnetic resonance imaging factors with RTP. Risk of bias was assessed using the Cochrane Risk-of-Bias Tool for Randomized Trials or the Methodological Index for Non-Randomized Studies (MINORS).

Results:

Of 1289 identified articles, 75 were included. The comparative and noncomparative studies earned MINORS scores of 18.8 ± 1.3 and 11.4 ± 3.4, respectively, and 12 of the 17 randomized controlled trials exhibited low risk of bias. Collectively, studies of muscular injury included younger patients and a greater proportion of male athletes compared with studies of proximal injury. Surgery for proximal hamstring ruptures achieved superior outcomes to nonoperative treatment, whereas physiotherapy incorporating eccentric training, progressive agility, and trunk stabilization restored function and hastened RTP after muscular injuries. Platelet-rich plasma injection for muscular injury yielded inconsistent results. The following initial clinical findings were associated with delayed RTP: greater passive knee extension of the uninjured leg, greater knee extension peak torque angle, biceps femoris injury, greater pain at injury and initial examination, “popping” sound, bruising, and pain on resisted knee flexion. Imaging factors associated with delayed RTP included magnetic resonance imaging-positive injury, longer lesion relative to patient height, greater muscle/tendon involvement, complete central tendon or myotendinous junction rupture, and greater number of muscles injured.

Conclusion:

Surgery enabled earlier RTP and improved strength and flexibility for proximal hamstring injuries, while muscular injuries were effectively managed nonoperatively. Rehabilitation and athlete expectations may be managed by considering several suitable prognostic factors derived from initial clinical and imaging examination.

Muscle- and Region-Specific Associations Between Muscle Size and Muscular Strength During Hip Extension and Knee Flexion in the Hamstrings

CONTEXT

Strength deficits of the hamstrings following sports injuries decrease athletic performance and increase the risk of injury recurrence. Previous studies have shown a high correlation between the muscular strength during hip-extension and knee-flexion and total muscle size of the hamstrings. However, it remains unclear which region of the individual hamstring muscles is closely associated with muscular strength.

OBJECTIVE

To investigate the relationship between the size of each region of the individual hamstring muscles and muscular strength during hip extension and knee flexion.

DESIGN

Within-subject repeated measures.

SETTING

University laboratory.

PARTICIPANTS

Twenty healthy young male volunteers who regularly engaged in sports activities.

OUTCOME MEASURES

Anatomical cross-sectional areas were acquired from the proximal, middle, and distal regions of the biceps femoris long head, biceps femoris short head, semitendinosus, and semimembranosus. Hip-extension and knee-flexion strength were measured during maximal voluntary isometric and concentric contractions (angular velocities of 60°/s and 180°/s).

RESULTS

The anatomical cross-sectional area of the distal regions in biceps femoris long head (r = .525-.642) and semitendinosus (r = .567) were significantly correlated with hip-extension strength under all conditions and only at an angular velocity of 180°/s, respectively. Meanwhile, anatomical cross-sectional areas of the distal regions in biceps femoris short head (r = .587-.684) and semimembranosus (r = .569-.576) were closely associated with knee-flexion strength under all conditions.

CONCLUSION

These results suggest that muscle size in the distal regions of biceps femoris long head and semitendinosus greatly contributes to the production of hip-extension strength, whereas that of biceps femoris short head and semimembranosus significantly contributes to the generation of knee-flexion strength. These findings could be useful for designing training and rehabilitation programs to efficiently improve strength deficits following sports injuries such as strain injury and anterior cruciate ligament tears.

Return to Play After a Hamstring Strain Injury: It is Time to Consider Natural Healing

Return to play (RTP) criteria after hamstring strain injuries (HSIs) help clinicians in deciding whether an athlete is ready to safely resume previous sport activities. Today, functional and sport-specific training tests are the gold standard in the decision-making process. These criteria lead to an average RTP time between 11 and 25 days after a grade 1 or 2 HSI. However, the high re-injury rates indicate a possible inadequacy of the current RTP criteria. A possible explanation for this could be the neglect of biological healing time. The present review shows that studies indicating time as a possible factor within the RTP-decision are very scarce. However, studies on biological muscle healing showed immature scar tissue and incomplete muscle healing at the average moment of RTP. Twenty-five percent of the re-injuries occur in the first week after RTP and at the exact same location as the index injury. This review supports the statement that functional recovery precedes the biological healing of the muscle. Based on basic science studies on biological muscle healing, we recommend a minimum period of 4 weeks before RTP after a grade 1 or 2 HSI. In conclusion, we advise a comprehensive RTP functional test battery with respect for the natural healing process. Before deciding RTP readiness, clinicians should reflect whether or not it is biologically possible for the injured tissue to have regained enough strength to withstand the sport-specific forces. In an attempt to reduce the detrimental injury-reinjury cycle, it is time to start considering (biological healing) time.

A 4-year study of hamstring injury outcomes in elite track and field using the British Athletics rehabilitation approach

OBJECTIVES

The British Athletics Muscle Injury Classification (BAMIC) correlates with return to play in muscle injury. The aim of this study was to examine hamstring injury diagnoses and outcomes within elite track and field athletes following implementation of the British Athletics hamstring rehabilitation approach.

METHODS

All hamstring injuries sustained by elite track and field athletes on the British Athletics World Class Programme between December 2015 and November 2019 that underwent an MRI and had British Athletics medical team prescribed rehabilitation were included. Athlete demographics and specific injury details, including mechanism of injury, self-reported gait phase, MRI characteristics and time to return to full training (TRFT) were contemporaneously recorded.

RESULTS

70 hamstring injuries in 46 athletes (24 women and 22 men, 24.6±3.7 years) were included. BAMIC grade and the intratendon c classification correlated with increased TRFT. Mean TRFT was 18.6 days for the entire cohort. Mean TRFT for intratendon classifications was 34±7 days (2c) and 48±17 days (3c). The overall reinjury rate was 2.9% and no reinjuries were sustained in the intratendon classifications. MRI variables of length and cross-sectional (CSA) area of muscle oedema, CSA of tendon injury and loss of tendon tension were associated with TRFT. Longitudinal length of tendon injury, in the intratendon classes, was not associated with TRFT.

CONCLUSION

The application of BAMIC to inform hamstring rehabilitation in British Athletics results in low reinjury rates and favourable TRFT following hamstring injury. The key MRI variables associated with longer recovery are length and CSA of muscle oedema, CSA of tendon injury and loss of tendon tension.

[Analysis of muscle injuries and return-to-training in elite Taekwondo athletes: results of a prospective cohort study over a period of five years]

BACKGROUND

 Muscle injuries frequently occur in sports involving explosive movement patterns, and they can cause considerable downtime. There is a lack of detailed data on muscle injuries in Olympic elite Taekwondo.

METHODS

 All injuries sustained by 76 elite Taekwondo athletes from a national Olympic training centre during training and competition were prospectively recorded over a period of five years. Data on muscle injuries, including location and time elapsed until return-to-training, were extracted from medical records. Injuries were diagnosed by means of MRI and were classified according to the British Athletes Muscle Injury System. The relationship between MRI classification subgroups and time elapsed until return-to-training was assessed.

RESULTS

 Mean age of athletes was 22.5 ± 3.2 (16-27) years with an average Taekwondo experience of 12.1 ± 4.0 (7-20) years. Hamstring muscles were most commonly injured (48.4 %), followed by quadriceps muscles (32.3 %) and calf muscles (9.6 %). The analysis of MRI injury subgroups showed grade 1 (32.2 %) and grade 2 (41.9 %) injuries in most cases. A positive correlation was found between injury groups and return-to-training (r = 0.56). The comparison between different injury groups and time elapsed until return-to-training also revealed significant differences (p < 0.0001).

CONCLUSION

 Hamstring muscles are the most injured muscles in Taekwondo besides the quadriceps femoris muscle. Most injuries were mild to moderate (grade 1-2). The time needed for return-to-training increased significantly with the severity of injuries diagnosed by MRI.

Effect of Knee Joint Angle on Regional Hamstrings Activation During Isometric Knee-Flexion Exercise

CONTEXT

Each hamstring muscle is subdivided into several regions by multiple motor nerve branches, which implies each region has different muscle activation properties. However, little is known about the muscle activation of each region with a change in the knee joint angle. Understanding of regional activation of the hamstrings could be helpful for designing rehabilitation and training programs targeted at strengthening a specific region.

OBJECTIVE

To investigate the effect of knee joint angle on the activity level of several regions within the individual hamstring muscles during isometric knee-flexion exercise with maximal effort (MVCKF).

DESIGN

Within-subjects repeated measures.

SETTING

University laboratory.

PARTICIPANTS

Sixteen young males with previous participation in sports competition and resistance training experience.

INTERVENTION

The participants performed 2 MVCKF trials at each knee joint angle of 30°, 60°, and 90°.

OUTCOME MEASURES

Surface electromyography was used to measure muscle activity in the proximal, middle, and distal regions of the biceps femoris long head (BFlh), semitendinosus, and semimembranosus of hamstrings at 30°, 60°, and 90° of knee flexion during MVCKF.

RESULTS

Muscle activity levels in the proximal and middle regions of the BFlh were higher at 30° and 60° of knee flexion than at 90° during MVCKF (all: P < .05). Meanwhile, the activity levels in the distal region of the BFlh were not different among all of the evaluated knee joint angles. In semitendinosus and semimembranosus, the activity levels were higher at 30° and 60° than at 90°, regardless of region (all: P < .05).

CONCLUSION

These findings suggest that the effect of knee joint angle on muscle activity level differs between regions of the BFlh, whereas that is similar among regions of semitendinosus and semimembranosus during MVCKF.

Managing the return to sport of the elite footballer following semimembranosus reconstruction

Hamstring strains are the most common injury in elite football and typically occur during high-speed running. Despite its important contribution to power production in the late swing phase, injury to the semimembranosus (SM) is less common than to the biceps femoris, but may involve the free tendon and depending on the degree of retraction, warrant surgical repair. Few case reports detail clinical reasoning, supported by objective data during rehabilitation in elite footballers, and none have described the return to sport (RTS) process following this type of hamstring injury. In this article, we outline the management and RTS of an English Premier League (EPL) footballer who suffered a high-grade SM proximal tendon tear during training. Due to the degree of retraction of the free tendon, the player underwent surgical reconstruction at the recommendation of an orthopaedic surgeon. Early physiotherapy care, nutritional support, on- and off-pitch injury-specific reconditioning and global athletic development are outlined, alongside strength and power diagnostic and global positioning systems data, assessment of pain, player feedback and MRI informed clinical reasoning and shared decision-making during the RTS process. 18 weeks post-surgery the player returned to team training, transferring to a new club 3 weeks later. 2.5 years post RTS, the player remains free of re-injury playing regularly in the EPL.

Management of hamstring injuries: current concepts review

Injuries to the hamstring muscle complex are common in athletes, accounting for between 12% and 26% of all injuries sustained during sporting activities. Acute hamstring injuries often occur during sports that involve repetitive kicking or high-speed sprinting, such as American football, soccer, rugby, and athletics. They are also common in watersports, including waterskiing and surfing. Hamstring injuries can be career-threatening in elite athletes and are associated with an estimated risk of recurrence in between 14% and 63% of patients. The variability in prognosis and treatment of the different injury patterns highlights the importance of prompt diagnosis with magnetic resonance imaging (MRI) in order to classify injuries accurately and plan the appropriate management. Low-grade hamstring injuries may be treated with nonoperative measures including pain relief, eccentric lengthening exercises, and a graduated return to sport-specific activities. Nonoperative management is associated with highly variable times for convalescence and return to a pre-injury level of sporting function. Nonoperative management of high-grade hamstring injuries is associated with poor return to baseline function, residual muscle weakness and a high-risk of recurrence. Proximal hamstring avulsion injuries, high-grade musculotendinous tears, and chronic injuries with persistent weakness or functional compromise require surgical repair to enable return to a pre-injury level of sporting function and minimize the risk of recurrent injury. This article reviews the optimal diagnostic imaging methods and common classification systems used to guide the treatment of hamstring injuries. In addition, the indications and outcomes for both nonoperative and operative treatment are analyzed to provide an evidence-based management framework for these patients. Cite this article: Bone Joint J 2020;102-B(10):1281-1288.

The mechanism of hamstring injuries - a systematic review

Background

Injuries to the hamstring muscles are among the most common in sports and account for significant time loss. Despite being so common, the injury mechanism of hamstring injuries remains to be determined.

Purpose

To investigate the hamstring injury mechanism by conducting a systematic review.

Study design

A systematic review following the PRISMA statement.

Methods

A systematic search was conducted using PubMed, EMBASE and the Cochrane Library. Studies 1) written in English and 2) deciding on the mechanism of hamstring injury were eligible for inclusion. Literature reviews, systematic reviews, meta-analyses, conference abstracts, book chapters and editorials were excluded, as well as studies where the full text could not be obtained.

Results

Twenty-six of 2372 screened original studies were included and stratified to the mechanism or methods used to determine hamstring injury: stretch-related injuries, kinematic analysis, electromyography-based kinematic analysis and strength-related injuries. All studies that reported the stretch-type injury mechanism concluded that injury occurs due to extensive hip flexion with a hyperextended knee. The vast majority of studies on injuries during running proposed that these injuries occur during the late swing phase of the running gait cycle.

Conclusion

A stretch-type injury to the hamstrings is caused by extensive hip flexion with an extended knee. Hamstring injuries during sprinting are most likely to occur due to excessive muscle strain caused by eccentric contraction during the late swing phase of the running gait cycle.

Level of evidence

Level IV

Acute Surgical Repair of Complete, Nonavulsion Proximal Semimembranosus Injuries in Professional Athletes

BACKGROUND

Nonoperative management of proximal semimembranosus injuries is associated with prolonged periods of convalescence and high risk of recurrence. To our knowledge, the outcomes of acute surgical repair for complete, nonavulsion proximal semimembranosus injuries have not been previously reported.

HYPOTHESIS

Acute surgical repair of complete, nonavulsion proximal semimembranosus injuries enables early return to sporting activity with low risk of recurrence.

STUDY DESIGN

Case series: Level of evidence, 4.

METHODS

This prospective single-surgeon study included 20 professional athletes undergoing acute primary surgical repair of complete, nonavulsion proximal semimembranosus injuries confirmed on preoperative magnetic resonance imaging. All study patients underwent a standardized postoperative rehabilitation program. Predefined outcomes were recorded at regular intervals after surgery. Mean follow-up time was 27.6 months (range, 24.0-34.6 months) from date of surgery.

RESULTS

Of the 20 patients, 19 (95%) returned to their preinjury level of sporting activity. Mean ± SD time from surgical repair to full sporting activity was 11.9 ± 5.7 weeks. No patients had recurrence of the primary injury. At 3 months after surgery, patients had improved mean passive straight leg raise (71.5° ± 5.9° vs 31.1° ± 7.2°; P < .001); increased mean isometric hamstring muscle strength at 0° (83.8% ± 5.9% vs 48.4% ± 8.3%; P < .001), 15° (77.6% ± 6.0% vs 52.3% ± 14.7%; P < .001), and 45° (88.6% ± 5.4% vs 66.7% ± 13.1%; P < .001); higher mean lower extremity functional scores (64.8 ± 4.6 vs 34.4 ± 5.1; P < .001); and improved Marx activity rating scores (10.7 ± 1.6 vs 5.5 ± 2.0; P < .001) as compared with preoperative values. High patient satisfaction and functional outcome scores were maintained at 1 and 2 years after surgery.

CONCLUSION

Acute surgical repair of complete, nonavulsion proximal semimembranosus injuries is associated with high patient satisfaction, increased muscle strength, improved functional outcome scores, and high return to preinjury level of sporting activity with low risk of recurrence at short-term follow-up.

Musculotendinous Junction Injuries of the Proximal Biceps Femoris: A Prospective Study of 64 Patients Treated Surgically

BACKGROUND

Injuries to the hamstring complex most commonly involve the proximal musculotendinous junction of the long head of the biceps femoris (MTJ-BFlh). Nonoperative management of these injuries is associated with prolonged rehabilitation and high risk of recurrence. To our knowledge, the surgical management of acute MTJ-BFlh injuries has not been previously reported.

HYPOTHESIS

Surgical repair of acute MTJ-BFlh injuries enables return to sporting activity with low risk of recurrence.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

A total of 64 patients (42 male and 22 female) undergoing surgical repair of acute MTJ-BFlh injuries were included. Predefined outcomes were recorded at regular intervals after surgery. Mean follow-up time after surgery was 29.2 months (range, 24.0-37.1 months).

RESULTS

All study patients returned to their preinjury levels of sporting activity. Mean ± SD time from surgical intervention to return to sporting activity was 13.4 ± 5.1 weeks. Three patients had reinjury at the operative site: 1 (1.6%) with MTJ-BFlh injury and 2 (3.2%) with myofascial tears. At 3 months after surgery, patients had improved mean passive straight-leg raise (72.0° ± 11.4° vs 24.1° ± 6.8°; P < .001); increased mean isometric hamstring muscle strength at 0° (84.5 % ± 10.4% vs 25.9% ± 8.9%; P < .001), 15° (89.5% ± 7.3% vs 41.2% ± 9.7%; P < .001), and 45° (93.9% ± 5.1% vs 63.4% ± 7.6%; P < .001); higher mean Lower Extremity Functional Scale scores (71.5 ± 5.0 vs 29.8 ± 6.3; P < .001); and improved mean Marx activity rating scores (9.8 ± 2.2 vs 3.8 ± 1.9; P < .001), as compared with preoperative scores. High patient satisfaction and functional outcome scores were maintained at 1 and 2 years after surgery.

CONCLUSION

Surgical repair of acute MTJ-BFlh injuries enables return to preinjury level of sporting function with low risk of recurrence at short-term follow-up.

Regional differences in hamstring muscle damage after a marathon

Previous studies suggest that marathon running induces lower extremity muscle damage. This study aimed to examine inter- and intramuscular differences in hamstring muscle damage after a marathon using transverse relaxation time (T₂)–weighted magnetic resonance images (MRI). 20 healthy collegiate marathon runners (15 males) were recruited for this study. T₂-MRI was performed before (PRE) and at 1 (D1), 3 (D3), and 8 days (D8) after marathon, and the T₂ values of each hamstring muscle at the distal, middle, and proximal sites were calculated. Results indicated that no significant intermuscular differences in T₂ changes were observed and that, regardless of muscle, the T₂ values of the distal and middle sites increased significantly at D1 and D3 and recovered at D8, although those values of the proximal site remained constant. T₂ significantly increased at distal and middle sites of the biceps femoris long head on D1 (p = 0.030 and p = 0.004, respectively) and D3 (p = 0.007 and p = 0.041, respectively), distal biceps femoris short head on D1 (p = 0.036), distal semitendinosus on D1 (p = 0.047) and D3 (p = 0.010), middle semitendinosus on D1 (p = 0.005), and distal and middle sites of the semimembranosus on D1 (p = 0.008 and p = 0.040, respectively) and D3 (p = 0.002 and p = 0.018, respectively). These results suggest that the distal and middle sites of the hamstring muscles are more susceptible to damage induced by running a full marathon. Conditioning that focuses on the distal and middle sites of the hamstring muscles may be more useful in improving recovery strategies after prolonged running.

High-grade intramuscular tendon disruption in acute hamstring injury and return to play in Australian Football players

BACKGROUND

Recent literature has reported intramuscular tendon (IT) disruption is associated with longer return to play (RTP) following acute hamstring injury.

OBJECTIVES

Investigate whether an increase in hamstring injury severity involving high-grade IT disruption and proximal injury location is associated with longer RTP times in elite Australian Rules Football (AFL) players.

METHODS

Hamstring injury records and RTP times from one professional AFL club were obtained over six seasons. MRI of injuries was retrospectively reviewed by a musculo-skeletal radiologist blinded to RTP information. A simplified four-grade classification of acute hamstring injuries was developed based on IT disruption severity and proximodistal injury location. MR0 had no observable MRI tissue damage; MR1 involved muscle-tendon junction, myofascial and low-grade IT injuries; MR2 involved distal and/or single muscle high-grade IT injuries, and MR3 involved high-grade IT injuries of the proximal biceps femoris (BF) IT with concomitant injury to BF+ semitendinosus muscles.

RESULTS

Forty-one injuries were available for analysis. Median RTP times were as follows: MR0, 14 days; MR1, 21 days; MR2, 35 days; and MR3, 88 days. For MRI-positive injuries (MR1, MR2, MR3), there was a significant difference in the distributions of RTP, with increased injury severity associated with increased RTP times (P < .001). The distributions of RTP were significantly different between MR1 vs MR2 (P = .008), MR1 vs MR3 (P = .002), and MR2 vs MR3 (P = .012).

CONCLUSION

In elite AFL players, acute hamstring injuries with high-grade IT disruption identified on MRI were associated with increased times to RTP compared to injuries with low-grade or no IT disruption.

Hamstring Injuries Prevention in Soccer: A Narrative Review of Current Literature

Hamstring injuries and reinjuries are one of the most important sport lesions in several sport activities including soccer, Australian football, track and field, rugby, and in general in all sport activities requiring sprinting and acceleration. However, it is important to distinguish between the lesions of the biceps femoris and semitendinosus and semimembranosus. Indeed, three muscles representing the hamstring complex have a very different injury etiology and consequently require different prevention strategies. This fact may explain, at least in part, the high incidence of reinjuries. In soccer, hamstring injuries cause an important rate of time loss (i.e., in average 15–21 matches missed per club per season). The hamstring injury risk factors may be subdivided in three categories: “primary injury risk factors” (i.e., the risk factors mainly causing a first lesion), “recurrent injury risk factors” (i.e., the risk that can cause a reinjury), and bivalent injury risk factors” (i.e., the risk factors that can cause both primary injuries and reinjuries). The high incidence of hamstring lesions caused consequently an important increase in hamstring injury research. However, although the prevention has increased paradoxically, epidemiological data do not show a loss in injuries and/or reinjuries but, on the contrary, they show an increase in hamstring injuries. This apparent paradox highlights the importance both of the improvement in the prevention programs quality and the criteria for return to play after hamstring injury.

Mechanisms of Hamstring Strain Injury: Interactions between Fatigue, Muscle Activation and Function

Isolated injury to the long head of biceps femoris is the most common type of acute hamstring strain injury (HSI). However, the precise hamstring injury mechanism (i.e., sprint-type) is still not well understood, and research is inconclusive as to which phase in the running cycle HSI risk is the greatest. Since detailed information relating to hamstring muscle function during sprint running cannot be obtained in vivo in humans, the findings of studies investigating HSI mechanisms are based on modeling that requires assumptions to be made based on extrapolations from anatomical and biomechanical investigations. As it is extremely difficult to account for all aspects of muscle-tendon tissues that influence function during high-intensity running actions, much of this complexity is not included in these models. Furthermore, the majority of analyses do not consider the influence of prior activity or muscular fatigue on kinematics, kinetics and muscle activation during sprinting. Yet, it has been shown that fatigue can lead to alterations in neuromuscular coordination patterns that could potentially increase injury risk. The present critical review will evaluate the current evidence on hamstring injury mechanism(s) during high-intensity running and discuss the interactions between fatigue and hamstring muscle activation and function.

Calf muscle strain injuries in elite Australian Football players: A descriptive epidemiological evaluation

BACKGROUND

Calf muscle strain injuries (CMSI) show consistent rates of prevalence and re-injury in elite Australian Football players. An epidemiological evaluation is warranted to better understand the clinical presentation and recovery of CMSI.

PURPOSE

First, to describe the epidemiology of CMSI in elite Australian Football players. Second, to determine if recovery following injury is different according to: (a) injury type (index vs re-injury); (b) muscle injured (soleus vs gastrocnemius); and (c) mechanism of injury (running-related activity vs non running-related activity).

STUDY DESIGN

Descriptive epidemiological.

METHODS

Data retrieved from the Soft Tissue injury Registry of the Australian Football League were analyzed. Sixteen clubs submitted data on CMSI from 2014 to 2017. Data included: player characteristics, training and match history at the time of injury, MRI, and the time to reach recovery milestones.

RESULTS

One hundred and eighty-four CMSI were included (149 index injuries; 35 re-injuries). Soleus injuries were most prevalent (84.6%). Soleus injuries took 25.4 ± 16.2 days to return to play, whereas gastrocnemius injuries took 19.1 ± 14.1 days (P = .097). CMSI sustained during running-related activities took approximately 12 days longer to recover than injuries sustained during non running-related activities (P = .001). Compared to index injuries, re-injuries involved older players (P = .03) and significantly more time was taken to run at >90% of maximum speed, return to full training, and return to play (P ≤ .001). Almost all of the observed re-injuries involved soleus (91.4%).

CONCLUSION

Soleus injuries are more prevalent than gastrocnemius injuries in elite Australian Football players. Prognosis appears to be influenced by clinical factors, with CMSI sustained during running-related activities and re-injuries needing more time to recover.

Exercise interventions to prevent hamstring injuries in athletes: A systematic review and meta-analysis

The aim of this meta-analysis was to assess the effectiveness of exercise-based interventions for prevention of hamstring injuries in sport. PubMed, Cochrane Central Register of Controlled Trials, Web of Science, ResearchGate, CINAHL, PEDro, ScienceDirect and Google Scholar databases were searched for randomized controlled trials and prospective cohort studies exploring the effects of exercise interventions on hamstring injury incidence. Subgroup analyses were performed to determine effects of several independent variables related to the interventions. Altogether, 17 studies were included. Exercise interventions decreased hamstring injury risk (RR = 0.49; 95%CI = 0.40-0.59; p < 0.001). There were similar effects found for interventions performed ≤2 times per week (RR = 0.35; 95%CI = 0.15-0.82) and the interventions performed >2 times per week (RR = 0.44; 95%CI = 0.31-0.61). Similarly, there were similar effects found for the interventions with progressive increase in load (RR = 0.53; 95%CI = 0.37-0.74) and the interventions with constant loads (RR = 0.46; 95%CI = 0.36-0.58). Other subgroup analyses (intervention supervision, sport type, inclusion of Nordic hamstring exercise and type of the trial) also showed no indications on specific characteristics of the interventions, that increase the preventive effects. Our findings showed that hamstring injury incidence can be decreased with exercise-based interventions, and that weekly frequency and load progression are not among the most important variables to consider in prevention programmes design.

Contact-Related Strain of Quadratus Femoris, Obturator Externus, and Inferior Gemellus in an Australian Football Player: A Case Report

CONTEXT

Muscle injuries of the hip stabilizers are considered rare in sport.

OBJECTIVE

This report presents a previously unreported case of a contact injury resulting in acute strain of quadratus femoris, obturator externus, and inferior gemellus in an amateur Australian rules football player.

DESIGN

Level 4-case report.

CASE PRESENTATION

A player was tackled ipsilateral to the injured leg, while in hip flexion in a lunged position. The case describes the diagnostic process, initial management, and return to play for this athlete.

RESULTS

Following rehabilitation, the player was able to return to sport at 8 weeks without ongoing issues.

CONCLUSIONS

A literature search for sports-related contact injuries to either muscle returned only one result. All other documented cases of injury to these muscle groups are confined to noncontact mechanisms or delayed presentations. Despite conventional teaching, the action of the deep external rotators of the hip appears to be positionally dependent. Knowledge of this type of injury and mechanism may be useful for future clinical reasoning and differential diagnosis in patients with this type of presentation.