Are all hamstring injuries equal? A retrospective analysis of time to return to full training following BAMIC type 'c' and T-junction injuries in professional men's rugby union.

We aimed to determine whether the anatomical location (intramuscular tendon or T-Junction) of hamstring muscle injuries in professional men's rugby union associates with a prolonged time to return to full training and a higher rate of re-injury/subsequent injury. We reviewed the medical records of an Irish professional rugby union club to identify hamstring muscle injuries incurred across five seasons. Clinicians and players were not blinded to MRI results at the time of rehabilitation. A blinded musculoskeletal radiologist re-classified all included injuries (n = 91) according to the British Athletics Muscle Injury Classification framework. Players who sustained an injury with intramuscular tendon involvement required a longer time to return to full training compared to players who sustained an injury without intramuscular tendon involvement (78 days vs. 24 days). Players who sustained a biceps femoris injury with T-junction involvement did not require a longer time to return to full training compared to players who sustained a biceps femoris injury without T-junction involvement (29 days vs. 27 days). Injuries with either intramuscular tendon or T-junction involvement were not associated with an increased rate of re-injury/subsequent injury to the same limb (intramuscular tendon involvement - odds ratio = 0.96, T-junction involvement - odds ratio = 1.03). When a hamstring muscle injury involves the intramuscular tendon, the injured player and stakeholders should be made aware that a longer time to return to full training is likely required. T-junction involvement does not alter the expected clinical course of biceps femoris injuries.

MRI radiomics for hamstring strain injury identification and return to sport classification: a pilot study.

OBJECTIVE: To determine if MRI-based radiomics from hamstring muscles are related to injury and if the features could be used to perform a time to return to sport (RTS) classification. We hypothesize that radiomics from hamstring muscles, especially T2-weighted and diffusion tensor imaging-based features, are related to injury and can be used for RTS classification. SUBJECTS AND METHODS: MRI data from 32 athletes at the University of Wisconsin-Madison that sustained a hamstring strain injury were collected. Diffusion tensor imaging and T1- and T2-weighted images were processed, and diffusion maps were calculated. Radiomics features were extracted from the four hamstring muscles in each limb and for each MRI modality, individually. Feature selection was performed and multiple support vector classifiers were cross-validated to differentiate between involved and uninvolved limbs and perform binary (≤ or > 25 days) and multiclass (< 14 vs. 14-42 vs. > 42 days) classification of RTS. RESULT: The combination of radiomics features from all diffusion tensor imaging and T2-weighted images provided the most accurate differentiation between involved and uninvolved limbs (AUC ≈ 0.84 ± 0.16). For the binary RTS classification, the combination of all extracted radiomics offered the most accurate classification (AUC ≈ 0.95 ± 0.15). While for the multiclass RTS classification, the combination of features from all the diffusion tensor imaging maps provided the most accurate classification (weighted one vs. rest AUC ≈ 0.81 ± 0.16). CONCLUSION: This pilot study demonstrated that radiomics features from hamstring muscles are related to injury and have the potential to predict RTS.

The direct muscular origin of the semitendinosus: a pitfall in categorization of proximal hamstring tendon tears.

The ischial origin of the hamstring musculature is complex. While the conjoint tendon and semimembranosus are commonly discussed and understood by radiologists, there is a lesser-known origin of the semitendinosus along the inferior and medial surface of the ischium in the form of a broad direct muscular connection. This secondary origin is infrequently described in the radiology literature and is a potential pitfall during grading of semitendinosus injuries if the interpreting physician is unaware of its presence. In a proximal hamstring tendon tear, the direct muscular origin of the semitendinosus can be spared, torn along with the conjoint tendon, or remain intact and contribute to a vertical shearing injury of the semitendinosus myotendinous junction. Detailed knowledge of this anatomy and its imaging appearance in the setting of injury enables the reader to correctly diagnose these unique hamstring injuries.

Diffusion tensor imaging of hamstring muscles after acute strain injury and throughout recovery in collegiate athletes.

OBJECTIVE: To identify the region of interest (ROI) to represent injury and observe between-limb diffusion tensor imaging (DTI) microstructural differences in muscle following hamstring strain injury. MATERIALS AND METHODS: Participants who sustained a hamstring strain injury prospectively underwent 3T-MRI of bilateral thighs using T1, T2, and diffusion-weighted imaging at time of injury (TOI), return to sport (RTS), and 12 weeks after RTS (12wks). ROIs were using the hyperintense region on a T2-weighted sequence: edema, focused edema, and primary muscle injured excluding edema (no edema). Linear mixed-effects models were used to compare diffusion parameters between ROIs and timepoints and limbs and timepoints. RESULTS: Twenty-four participants (29 injuries) were included. A significant ROI-by-timepoint interaction was detected for all diffusivity measures. The edema and focused edema ROIs demonstrated increased diffusion at TOI compared to RTS for all diffusivity measures (p-values < 0.006), except λ1 (p-values = 0.058-0.12), and compared to 12wks (p-values < 0.02). In the no edema ROI, differences in diffusivity measures were not observed (p-values > 0.82). At TOI, no edema ROI diffusivity measures were lower than the edema ROI (p-values < 0.001) but not at RTS or 12wks (p-values > 0.69). A significant limb-by-timepoint interaction was detected for all diffusivity measures with increased diffusion in the involved limb at TOI (p-values < 0.001) but not at RTS or 12wks (p-values > 0.42). Significant differences in fractional anisotropy over time or between limbs were not detected. CONCLUSION: Hyperintensity on T2-weighted imaging used to define the injured region holds promise in describing muscle microstructure following hamstring strain injury by demonstrating between-limb differences at TOI but not at follow-up timepoints.

The 11+ injury prevention programme decreases rate of hamstring strain injuries in male collegiate soccer players.

OBJECTIVES: To investigate if the 11+ injury prevention programme decreases the risk of hamstring injury and improves recovery time and determine whether compliance with the 11+ affects hamstring injury risk. METHODS: This study is a secondary analysis from a prospective cluster randomised controlled trial that included 65 National Collegiate Athletic Association (NCAA) division I and II men's soccer teams over the fall 2012 season. Thirty-one teams were randomised to the intervention group that were using the 11+ as their warm-up and 35 teams to the control group that continued to use their traditional warm-up. Each certified athletic trainer (ATC) collected data on demographics, hamstring injury (HSI), mechanism of injury, position, playing surface, time lost due to injury and compliance to the 11+ programme. RESULTS: The 11+ decreased the risk of HSI by 63% compared with the control group (RR=0.37, 95% CI 0.21 to 0.63). Difference in return to play after HSI between the control (9.4±11.2 days) and intervention groups (10.2±11.3 days) was not significant (p=0.8). High compliance (>2 or more doses on average per week) reduced the risk of HSI by 78% (RR=0.22, 95% CI 0.06 to 0.87) compared with low compliance (<1 dose on average per week), and moderate compliance (1 to <2 doses on average per week) decreased the risk of HSI by 67% (RR=0.33, 95% CI 0.11 to 0.97) compared with low compliance. There was no significant difference between high and moderate compliance. CONCLUSION: The 11+ decreased the risk of HSI by 63% but did not improve recovery time. High to moderate compliance is essential and makes the programme more effective at reducing HSI.

Baseline clinical and MRI risk factors for hamstring reinjury showing the value of performing baseline MRI and delaying return to play: a multicentre, prospective cohort of 330 acute hamstring injuries.

OBJECTIVES: Studies identifying clinical and MRI reinjury risk factors are limited by relatively small sample sizes. This study aimed to examine the association between baseline clinical and MRI findings with the incidence of hamstring reinjuries using a large multicentre dataset. METHODS: We merged data from four prospective studies (three randomised controlled trials and one ongoing prospective case series) from Qatar and the Netherlands. Inclusion criteria included patients with MRI-confirmed acute hamstring injuries (<7 days). We performed multivariable modified Poisson regression analysis to assess the association of baseline clinical and MRI data with hamstring reinjury incidence within 2 months and 12 months of follow-up. RESULTS: 330 and 308 patients were included in 2 months (31 (9%) reinjuries) and 12 months (52 (17%) reinjuries) analyses, respectively. In the 2-month analysis, the presence of discomfort during the active knee extension test was associated with reinjury risk (adjusted risk ratio (ARR) 3.38; 95% CI 1.19 to 9.64). In the 12 months analysis, the time to return to play (RTP) (ARR 0.99; 95% CI 0.97 to 1.00), straight leg raise angle on the injured leg (ARR 0.98; 95% CI 0.96 to 1.00), the presence of discomfort during active knee extension test (ARR 2.52; 95% CI 1.10 to 5.78), the extent of oedema anteroposterior on MRI (ARR 0.74; 95% CI 0.57 to 0.96) and myotendinous junction (MTJ) involvement on MRI (ARR 3.10; 95% CI 1.39 to 6.93) were independently associated with hamstring reinjury. CONCLUSIONS: Two clinical findings (the presence of discomfort during active knee extension test, lower straight leg raise angle on the injured leg), two MRI findings (less anteroposterior oedema, MTJ involvement) and shorter time to RTP were independently associated with increased hamstring reinjury risk. These findings may assist the clinician to identify patients at increased reinjury risk following acute hamstring injury. TRIAL REGISTRATION NUMBERS: NCT01812564; NCT02104258; NL2643; NL55671.018.16.

Epidemiology of Hamstring Tears in National Collegiate Athletic Association Athletes: Findings From the National Collegiate Athletic Association Injury Surveillance Program Between 2014/2015 and 2018/2019.

OBJECTIVE: To describe the epidemiology of hamstring tears in National Collegiate Athletic Association (NCAA) sports. DESIGN: Descriptive epidemiology study. Athletic trainers from NCAA schools reported injuries to the NCAA Injury Surveillance Program. SETTING: A convenience sample of NCAA hamstring tear injuries during the 2014/2015 through 2018/2019 academic years. PATIENTS OR PARTICIPANTS: NCAA student-athletes. INDEPENDENT VARIABLES: Sport, sex, event type, season segment, injury history, and activity at the time of injury. MAIN OUTCOME MEASURES: Injury counts, rates, and proportions were used. RESULTS: Two thousand ninety-six hamstring tears from 8 474 400 athlete-exposures (AEs) were reported (2.47 per 10 000 AEs). Rates were highest in Men's Soccer (5.97 per 10 000 AEs) and Women's Soccer (3.13 per 10 000 AEs), among all Men's and Women's sports, respectively. Competition-related rates in Men's and Women's sports were highest in 2015 to 2016 then followed a decreasing pattern across the remainder of the study period. Among sex-comparable sports, rates were higher in men's (compared with women's) Baseball/Softball, Soccer, and Track and Field. The prevalence of recurrent injuries was comparable among men's (14.8%) and women's (11.5%) sports. Time loss hamstring tears were more prevalent in Men's sports than Women's sports [injury proportion ratio = 1.33; 95% confidence interval, (1.21, 1.47)]. CONCLUSIONS: Overall, hamstring tear rates were higher across all Men's sports compared with Women's sports. Rates across event type were comparable in several sports; and so, adjustments to practice are needed considering that practice environments are more modifiable than competitions. Indeed, improving hamstring tear prevention programs to reduce the burden of this injury in NCAA athletes remains critical.

Prognosticating Return-To-Play Time Following a Hamstring Strain Injury Using Early Flexibility Asymmetry and Musculoskeletal Ultrasound Imaging Outcomes: An Exploratory Study Among Canadian University Football Players.

OBJECTIVE: Identify key flexibility and point-of-care musculoskeletal ultrasound (POCUS) measures for prognosticating return-to-play (RTP) following a first hamstring strain injury (HSI) and informing the clinical decision-making process. DESIGN: Exploratory prospective cohort study. SETTING: Sport medicine and rehabilitation clinic of a Canadian university. PARTICIPANTS: One hundred and sixty-seven elite Canadian university football athletes followed over 5 seasons. INTERVENTIONS: Clinical and POCUS measures collected within 7 days after HSI and preseason clinical measures. MAIN OUTCOME MEASURES: Active knee extension (AKE) and Straight Leg Raise (SLR) to quantify hamstring flexibility, POCUS-related outcomes to characterize tissue alteration, and RTP until full sport resumption were documented (categorized as Early [1-40 days] or Late [>40 days] RTP). RESULTS: A total of 19 and 14 athletes were included in the Early RTP (mean RTP = 28.84 ± 8.62 days) and Late RTP groups (mean 51.93 ± 10.54 days), respectively, after having been diagnosed with a first HSI. For the clinical results, height and a greater flexibility asymmetry measure with the AKE or SLR when compared with both ipsilateral preseason and acute contralateral values significantly increases the chance of facing a long delay before returning to play (ie, RTP). For the POCUS-related results, the Peetrons severity score, extent of the longitudinal fibrillary alteration, and novel score lead to similar results. CONCLUSIONS: Early hamstring flexibility asymmetry following acute HSI, particularly the AKE, along with some POCUS-related measures are valuable in prognosticating late RTP following among Canadian university football athletes.

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.

Hamstrings on focus: Are 72 hours sufficient for recovery after a football (soccer) match? A multidisciplinary approach based on hamstring injury risk factors and histology.

This study aimed to assess acute and residual changes in sprint-related hamstring injury (HSI) risk factors after a football (soccer) match, focusing on recovery within the commonly observed 72-h timeframe between elite football matches. We used a multifactorial approach within a football context, incorporating optical and ultrastructural microscopic analysis of BFlh (biceps femoris long head) muscle fibres, along with an examination of BFlh fibre composition. Changes in sprint performance-related factors and HSI modifiable risk factors were examined until 3 days after the match (MD +3) in 20 football players. BFlh biopsy specimens were obtained before and at MD +3 in 10 players. The findings indicated that at MD +3, sprint-related performance and HSI risk factors had not fully recovered, with notable increases in localized BFlh fibre disruptions. Interestingly, match load (both external and internal) did not correlate with changes in sprint performance or HSI risk factors nor with BFlh fibre disruption. Furthermore, our study revealed a balanced distribution of ATPase-based fibre types in BFlh, with type-II fibres associated with sprint performance. Overall, the results suggest that a 72-h recovery period may not be adequate for hamstring muscles in terms of both HSI risk factors and BFlh fibre structure following a football match.

Anterior pelvic tilt increases hamstring strain and is a key factor to target for injury prevention and rehabilitation.

PURPOSE: Hamstring muscle strain injury is very common in sports involving high-speed running. Hamstring muscles originate from the ischial tuberosity and thus pelvic position may influence hamstring strain during different sports movements like sprinting, but this has only been evaluated by indirect methods. This study tested the hypothesis that a change in anterior pelvic tilt causes elongation of the overall hamstring complex and disproportionately elongates proximal relative to distal muscle regions. METHODS: Seven fresh-frozen specimens (full lower limb with pelvis and lumbar spine) were used for this in vitro study. Specimens were dissected to enable visualization of the hamstring muscles and then fixed into a custom-made testing bench that allowed controlled movement of the pelvis over a fixed femur and tibia. Nine markers were inserted into the hamstring muscles to allow intra- and intermuscle difference measurements. Then, six different anterior pelvic angles were used to measure the difference in hamstring muscle lengthening through a three-dimensional reconstruction system based on stereoscopic machine vision technology. RESULTS: An increase in anterior pelvic tilt produced a significant non-uniform increase in tissue elongation in all regions of the three hamstring muscles (semitendinosus, semimembranosus [SMB] and biceps femoris long head), which was greater in the proximal (>1 cm every 5°) compared to the distal region (≈0.4 cm every 5°). At the proximal hamstring region, SMB showed significantly greater length changes compared to conjoint tendons with nonstatistically significant elongation differences between muscles at the distal region. CONCLUSION: Considering the results of the study, the pelvis segment will likely play a fundamental role as a strain regulator of hamstring muscles. These results will have an impact on injury rehabilitation and prevention processes of hamstring injuries, as well as optimize future musculoskeletal models and avoid potential underestimation of the hamstring muscle-tendon complex lengthening during high-speed running. LEVEL OF EVIDENCE: N/A.

Non-surgical management of acute proximal hamstring avulsions can produce clinically acceptable results.

PURPOSE: To evaluate the mid-term clinical outcomes for the non-surgical and surgical management of acute proximal hamstring avulsions. METHODS: Sixty physically active individuals were offered surgical or non-surgical management for their proximal hamstring avulsion injuries. Distal retraction was defined as greater than 2 cm. Primary outcome measures were the Victorian Institute of sport assessment-proximal hamstring tendons (VISA-H) and functional assessment scale for acute hamstring injuries (FASH). Secondary outcome measures included palpable gap (cm), return to sport (RTS) and the ability to perform Nordic hamstring curls. Outcome variables were adjusted in regression models for gender, age, and treatment. RESULTS: Thirty-one patients elected to undertake non-surgical management, and 29 chose surgery with a mean follow-up of 34.8 ± 8.7 and 34.9 ± 7.0 months, respectively. The mean VISA-H for the non-surgical and surgical groups were 87.3 ± 3.4 and 87.9 ± 4.1 (n.s.), respectively. The mean FASH for the non-surgical group was 89.3 ± 2.4 and 88 ± 3.6 for the surgical group (n.s.). This was consistent after adjusting for confounders. The mean gap for the non-surgical group was 4.5 ± 1.09 and 4.9 ± 1.19 cm for the surgical group (n.s.). No significant differences were found in the abilities to perform Nordic hamstring curls (n.s.). Both groups achieved comparable RTS rates (n.s.). On average, the non-surgical group achieved RTS at 5.5 ± 1.2 months post-injury, whereas the surgical group was at 5.7 ± 0.7 months (n.s.). CONCLUSION: Physically active individuals with acute proximal hamstring avulsions and distal retraction of the tendon stump can be managed non-surgically, achieving similar functional levels and RTS compared to patients treated surgically. LEVEL OF EVIDENCE: Level III.

Magnetic resonance imaging should be the first-line imaging modality for investigating suspected proximal hamstring avulsion injuries.

PURPOSE: The purpose of the study was to evaluate how the initial diagnostic tool used-specifically ultrasound (US) or magnetic resonance imaging (MRI)-for diagnosing proximal hamstring avulsion injury affects the delay before surgery and, secondarily, the outcomes of these injuries. METHODS: This was a retrospective analysis of prospectively collected data (2012-2020). It targeted patients primarily treated for proximal hamstring avulsion injury. It included all patients with a preoperative US and/or MRI. Patients were divided into two groups based on the initial diagnostic tool used (US-first vs. MRI-first groups). The primary outcomes measure was the time from initial injury to surgical intervention (surgical delay). The secondary outcomes were the Parisien Hamstring Avulsion Score, as well as the activity level as measured by the University of California, Los Angeles (UCLA) Activity Scale and Tegner Activity Scale. RESULTS: The analysis included 392 patients with a mean age of 43.8 ± 13.6 years for the MRI-first group and 47.6 ± 12.0 years for US-first group. Patients in the MRI-first group had a significantly shorter median time from injury to surgery of 20.0 days (interquartile range [IQR]: 11.0-61.0) compared to 30 days (IQR: 18-74) in the US-first group. At the final follow-up (4.2 ± 2.2 years for the MRI-first group and 5.1 ± 1.9 years for the US-first group), the MRI-first group had significantly higher mean Tegner Activity Scale and UCLA scores than the US-first group: The Tegner Activity Scale was median 5 (IQR: 3-7) for the MRI-first group versus median 4 (IQR: 2-6) for the US-first group (p < 0.05). The UCLA scores were 7.9 ± 2.4 for the MRI-first group compared to 7.3 ± 2.4 for the US-first group (p < 0.05). This difference was more pronounced when comparing the MRI-first group with the patient-false negative initial ultrasound. No difference was found regarding the Parisien Hamstring Avulsion Score. CONCLUSION: MRI as the initial diagnostic tool for proximal hamstring avulsion injury is associated with a shorter time to surgery and better postoperative outcomes in Tegner Activity Scale and UCLA scores, compared to US. LEVEL OF EVIDENCE: Level III.

Assessment of fatty infiltration of the hamstring muscles in chronic proximal hamstring ruptures and effect on clinical outcomes after surgical repair: a novel application of the Goutallier classification.

INTRODUCTION: Increased time to surgery has been previously associated with poorer clinical outcomes after surgical treatment of proximal hamstring ruptures, though the etiology remains unclear. The purpose of this study was to evaluate whether degree of muscle atrophy, as assessed using the Goutallier classification system, is associated with worse outcomes following surgical treatment of chronic proximal hamstring ruptures. MATERIALS AND METHODS: This was a retrospective case series of patients who underwent repair of proximal hamstring ruptures from 2012 to 2020 with minimum 2-year follow-up. Patients were included if they underwent primary repair of a proximal hamstring rupture ≥ 6 weeks after the date of injury and had accessible preoperative magnetic resonance imaging (MRI). Exclusion criteria were allograft reconstruction, endoscopic repair, or prior ipsilateral hip surgery. Patients were administered validated surveys: the modified Harris Hip Score (mHHS) and Perth Hamstring Assessment Tool (PHAT). Fatty atrophy on preoperative MRI was independently graded by two musculoskeletal radiologists using the Goutallier classification. Multivariate regression analysis was performed to evaluate associations of preoperative characteristics with muscle atrophy, as well as mHHS and PHAT scores. RESULTS: Complete data sets were obtained for 27 patients. A majority of this cohort was male (63.0%), with a mean age of 51.5 ± 11.8 years and BMI of 26.3 ± 3.8. The mean follow-up time was 62.6 ± 23.1 months, and the mean time from injury-to-surgery was 20.4 ± 15.3 weeks. The Goutallier grading inter-reader weighted kappa coefficient was 0.655. Regression analysis demonstrated that atrophy was not significantly associated with PHAT (p = 0.542) or mHHS (p = 0.574) at latest follow-up. Increased age was significantly predictive of muscle atrophy (ß = 0.62, p = 0.005) and was also found to be a significant predictor of poorer mHHS (ß = - 0.75; p = 0.037). CONCLUSIONS: The degree of atrophy was not found to be an independent predictor of clinical outcomes following repair of chronic proximal hamstring ruptures. Increasing age was significantly predictive of increased atrophy and poorer patient-reported outcomes.

Characterizing Muscle Activity in Soccer Players with a History of Hamstring Strain Injuries during Accelerated Sprinting.

This study aimed to characterize muscle activity in male soccer players with a history of hamstring strain injuries (HSI) during accelerated sprinting. Thirteen patients each in the HSI group (history of HSI) and in the healthy group (with no history of HSI) were included. 26 male soccer players of which 13 with and 13 without HSI history were included in this study. Ten muscles were evaluated on electromyography activity during overground sprinting. The testing protocol consisted of a maximal sprint over a distance of 30 meters. One running stride was divided into the early stance phase, late stance phase, early swing phase, mid-swing phase, and late swing phase, and the average muscle activity per phase and the timing of the peak root-mean-square value appearance during each stride were calculated. Statistical analysis was performed using repeated-measures two-way ANOVA (group × phase), and multiple comparison tests were performed using the Bonferroni method when the interaction or main effect was significant. The statistical significance level was set at p < 0.05. Gluteus maximus (Gmax), gluteus medius (Gmed), and external oblique (EO) showed activity differences based on HSI history. Gmax was 30% lower, EO was 20% lower, and Gmed was 40% higher in HSI group. This study suggests that, despite previous findings that HSI is most likely during the late swing phase, the HSI group shows a higher injury risk in the early stance phase. This is due to differences in trunk and gluteal muscle activity between the late swing and early stance phases compared to the healthy group. In summary, HSI group had lower activity in the muscles contributing to trunk instability, especially EO and Gmax, before and after ground impact during accelerated sprinting, compared to Healthy.

Thoracolumbar Fascia and Lumbar Muscle Stiffness in Athletes with A History of Hamstring Injury.

The purpose of this study was to examine the differences in thoracolumbar fascia (TLF) and lumbar muscle modulus in individuals with and without hamstring injury using shear wave elastography (SWE). Thirteen male soccer players without a previous hamstring injury and eleven players with a history of hamstring injury performed passive and active (submaximal) knee flexion efforts from 0°, 45° and 90° angle of knee flexion as well as an active prone trunk extension test. The elastic modulus of the TLF, the erector spinae (ES) and the multifidus (MF) was measured using ultrasound SWE simultaneously with the surface electromyography (EMG) signal of the ES and MF. The TLF SWE modulus was significantly (p < 0.05) higher in the injured group (range: 29.86 ± 8.58 to 66.57 ± 11.71 kPa) than in the uninjured group (range: 17.47 ± 9.37 to 47.03 ± 16.04 kPa). The ES and MF modulus ranged from 14.97 ± 4.10 to 66.57 ± 11.71 kPa in the injured group and it was significantly (p < .05) greater compared to the uninjured group (range: 11.65 ± 5.99 to 40.49 ± 12.35 kPa). TLF modulus was greater than ES and MF modulus (p < 0.05). Active modulus was greater during the prone trunk extension test compared to the knee flexion tests and it was greater in the knee flexion test at 0° than at 90° (p < 0.05). The muscle EMG was greater in the injured compared to the uninjured group in the passive tests only (p < 0.05). SWE modulus of the TLF and ES and MF was greater in soccer players with previous hamstring injury than uninjured players. Further research could establish whether exercises that target the paraspinal muscles and the lumbar fascia can assist in preventing individuals with a history of hamstring injury from sustaining a new injury.

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.

Injury mechanisms and situational patterns of severe lower limb muscle injuries in male professional football (soccer) players: a systematic video analysis study on 103 cases.

OBJECTIVE: The objective of this study is to describe the mechanism of injury and situational patterns (based on ball possession and playing action leading to injury) of severe (lay-off time >28 days) lower limb muscle injuries in professional male football (soccer) players during match play. METHODS: Players experiencing a severe muscle injury of the lower limb during Italian first (Serie A) division male football matches over three consecutive seasons (2018-2021) were identified. Video footage was obtained and three raters independently categorised injury mechanism and situational patterns using a standardised checklist. Injury epidemiology (month), timing of injuries within the match and location of injuries on the pitch were also examined. RESULTS: We identified 121 lower limb severe muscle injuries. Videos of sufficient quality were available for 103 (85%) cases, including 61 (60%) hamstring, 17 (16%) calf, 16 (15%) adductor and 9 (9%) quadricep muscle injuries. Nearly two-thirds of injuries involved the dominant/kicking leg (n=65, 63%). Eighty-five (83%) injuries were non-contact and 18 (17%) indirect contact. Four main situational patterns were identified and accounted for 88% of injuries: (1) running/acceleration (n=35, 34%); (2) closed kinetic chain stretching (n=21, 20%); (3) open kinetic chain stretching (n=19, 18%) and (4) kicking (n=16, 16%), with differences between muscle groups. 71% of injuries occurred in the first half of the match (p<0.01), with a gradual increase through the first half. CONCLUSION: Most severe muscle injuries during football matches were non-contact and occurred in the first half during running/acceleration, open and closed kinetic chain stretching, or kicking.

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.

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.