Early versus delayed lengthening exercises for acute hamstring injury in male athletes: a randomised controlled clinical trial.

BACKGROUND: To evaluate the efficacy of early versus delayed introduction of lengthening (ie, eccentric strengthening) exercises in addition to an established rehabilitation programme on return to sport duration for acute hamstring injuries in a randomised controlled superiority trial. METHODS: 90 male participants (age: 18-36 years, median 26 years) with an MRI-confirmed acute hamstring injury were randomised into an early lengthening (at day 1 of rehabilitation) group or a delayed lengthening (after being able to run at 70% of maximal speed) group. Both groups received an established rehabilitation programme. The primary outcome was time to return to sport (ie, time from injury to full unrestricted training and/or match play). The secondary outcome was reinjury rate within 12 months after return to sport. Other outcomes at return to sport included the Askling H-test, hamstring strength, clinical examination and readiness questions. RESULTS: The return to sport in the early lengthening group was 23 (IQR 16-35) days and 33 (IQR 23-40) days in the delayed lengthening group. For return to sport (in days), the adjusted HR for the early lengthening group compared with the delayed lengthening group was 0.95 (95% CI 0.56 to 1.60, p=0.84). There was no significant difference between groups for reinjury rates within 2 months (OR=0.94, 95% CI 0.18 to 5.0, p=0.94), from 2 to 6 months (OR=2.00, 95% CI 0.17 to 23.3, p=0.58), and 6 to 12 months (OR=0.57, 95% CI 0.05 to 6.6, p=0.66). CONCLUSION: Accelerating the introduction of lengthening exercises in the rehabilitation of hamstring injury in male athletes did not improve the time to return to sport nor the risk of reinjury.

Classifying radiographic changes of the pubic symphysis in male athletes: Development and reproducibility of a new scoring protocol.

PURPOSE: To develop a specified radiographic scoring system for the pubic symphysis and adjacent bones, and to examine the intra- and inter-rater reproducibility of this system. METHOD: Development of the scoring protocol was performed in three stages using AP pelvis radiographs of 102 male adult athletes. The final protocol included 5 overall scoring items, which included further specification of locations: 1) bone lucency (erosion-like configuration and cysts), 2) proliferation, 3) fragmentation, 4) sclerosis, and 5) joint space width. Intra- and inter-rater reproducibility were determined using Cohen's kappa statistic (κ) and intraclass correlation coefficient (ICC). The standard error of measurement (SEM) and minimal detectable difference (MDD) were also determined. RESULTS: We present a radiographic scoring protocol with clear definitions and examples to improve clinical usability. Intra-rater reproducibility was: bone lucency (erosion-like configuration or cysts): κ = 0.67 (95 %CI 0.56-0.78), proliferation: κ = 0.54 (95 %CI 0.38-0.70), fragmentation: κ = 0.80 (95 %CI 0.67-0.93), sclerosis: κ = 0.60 (95 %CI 0.49-0.71), and joint space width: ICC(2.1) 0.85 (95 %CI 0.78-0.89), SEM 0.4 mm, MDD 1.2 mm. Inter-rater reproducibility was: bone lucency: κ = 0.61 (95 %CI 0.50-0.72), proliferation: κ = 0.34 (95 %CI 0.20-0.48), fragmentation: κ = 0.67 (95 %CI 0.50-0.84), sclerosis: κ = 0.30 (95 %CI 0.17-0.43), and joint space width: ICC(2.1) 0.72 (95 %CI 0.59-0.81), SEM 0.5 mm., MDD 1.5 mm. CONCLUSIONS: The Aspetar pubic symphysis radiographic scoring protocol contains five overall scoring items, with additional specifications. These five items showed moderate to almost perfect intra-rater reproducibility, and fair to substantial inter-rater reproducibility. This protocol provides the basis for use in clinical practice, and will allow future investigations of the clinical significance of radiographic changes at the pubic symphysis in athletes.

Complete resolution of a hamstring intramuscular tendon injury on MRI is not necessary for a clinically successful return to play.

BACKGROUND: Clinical decision-making around intramuscular tendon injuries of the hamstrings is a controversial topic in sports medicine. For this injury, MRI at return to play (RTP) might improve RTP decision-making; however, no studies have investigated this. OBJECTIVE: Our objectives were to describe MRI characteristics at RTP, to evaluate healing and to examine the association of MRI characteristics at RTP with reinjury for clinically recovered hamstring intramuscular tendon injuries. METHODS: We included 41 athletes with hamstring intramuscular tendon injuries and an MRI at baseline and RTP. For both MRIs, we used a standardised scoring form that included intramuscular tendon injury characteristics. We recorded reinjuries during 1-year follow-up. RESULTS: At RTP, 56% of the intramuscular tendons showed a partial or complete thickness tendon discontinuity. Regarding healing from injury to RTP, 18 of 34 (44% overall) partial-thickness tendon discontinuities became continuous and 6 out of 7 (15% overall) complete thickness tendon discontinuities became partial-thickness tendon discontinuities. Waviness decreased from 61% to 12%, and 88% of tendons became thickened. We recorded eight (20%) reinjuries within 1 year. Intramuscular tendon characteristics at RTP between participants with or without a reinjury were similar. CONCLUSION: Complete resolution of an intramuscular tendon injury on MRI is not necessary for clinically successful RTP. From injury to RTP, the intramuscular tendon displayed signs of healing. Intramuscular tendon characteristics of those with or without a reinjury were similar.

Intramuscular tendon injury is not associated with an increased hamstring reinjury rate within 12 months after return to play.

BACKGROUND: Acute hamstring injury that includes intramuscular tendon injury has been suggested to be associated with increased reinjury risk. These observations were based on a relatively small number of retrospectively analysed cases. OBJECTIVE: To determine whether intramuscular tendon injury is associated with higher reinjury rates in acute hamstring injury. METHODS: MRIs of 165 athletes with an acute hamstring injury were obtained within 5 days of injury. Treatment consisted of a standardised criteria-based rehabilitation programme. Standardised MRI parameters and intramuscular tendon injury, the latter subdivided into tendon disruption and waviness, were scored. We prospectively recorded reinjuries, defined as acute onset of posterior thigh pain in the same leg within 12 months after return to play. RESULTS: Participants were predominantly football players (72%). Sixty-four of 165 (39%) participants had an index injury with intramuscular hamstring tendon disruption, and waviness was present in 37 (22%). In total, there were 32 (19%) reinjuries. There was no significant difference (HR: 1.05, 95% CI 0.52 to 2.12, P=0.898) in reinjury rate between index injuries with intramuscular tendon disruption (n=13, 20%) and without tendon disruption (n=19, 20%). There was no significant difference in reinjury rate (X²(1)=0.031, P=0.861) between index injuries with presence of waviness (n=7, 19%) and without presence of waviness (n=25, 20%). CONCLUSION: In athletes with an acute hamstring injury, intramuscular tendon injury was not associated with an increased reinjury rate within 12 months after return to play.

Cohen's MRI scoring system has limited value in predicting return to play.

PURPOSE: Numerous authors have hypothesised that MRI scoring systems provide a valid means of predicting return to play duration following an acute hamstring muscle strain. The purpose is to prospectively investigate the predictive value of the MRI scoring system of Cohen for return to sport (RTS), following an acute hamstring injury. METHODS: Male football (soccer) players (n = 139) with acute onset posterior thigh pain underwent standardised clinical and MRI examinations within 5 days after injury. All players underwent a standardised physiotherapy regimen with RTS documented. The MRI scoring was statistically evaluated against RTS. RESULTS: One hundred and ten MRI-positive hamstring injuries were evaluated with RTS duration ranging from 1 to 66 days. Total Cohen's MRI score accounted for approximately 4% of the variance in RTS duration. When comparing those with an MRI score of 10 or more took on average 9.8 days longer to RTS than those with an MRI score less than 10 (effect size: 0.85, p < 0.01). CONCLUSIONS: Utilising the Cohen's MRI scoring system previously described, we were unable to provide a clinically useful prognosis for RTS in male soccer players. This may reflect the broader challenges of attempting to accurately determine RTS duration from imaging performed at a single point in time. LEVEL OF EVIDENCE: Prospective case series, IV.

Intramuscular tendon involvement on MRI has limited value for predicting time to return to play following acute hamstring injury.

BACKGROUND: Hamstring injury with intramuscular tendon involvement is regarded as a serious injury with a delay in return to play (RTP) of more than 50 days and reinjury rates up to 63%. However, this reputation is based on retrospective case series with high risk of bias. OBJECTIVE: Determine whether intramuscular tendon involvement is associated with delayed RTP and elevated rates of reinjury. METHODS: MRI of male athletes with an acute hamstring injury was obtained within 5 days of injury. Evaluation included standardised MRI scoring and scoring of intramuscular tendon involvement. Time to RTP and reinjury rate were prospectively recorded. RESULTS: Out of 70 included participants, intramuscular tendon disruption was present in 29 (41.4%) injuries. Injuries without intramuscular tendon disruption had a mean time to RTP of 22.2±7.4 days. Injuries with <50%, 50%-99% and 100% disruption of tendon cross-sectional area had a mean time to RTP of 24.0±9.7, 25.3±8.6 and 31.6±10.9 days, respectively. Injuries with full-thickness disruption took longer to RTP compared with injuries without disruption (p=0.025). Longitudinal intramuscular tendon disruption was not significantly associated with time to RTP. Waviness was present in 17 (24.3%) injuries. Mean time to RTP for injuries without and with waviness was 22.6±7.5 and 30.2±10.8 days (p=0.014). There were 11 (15.7%) reinjuries within 12 months, five (17.2%) in the group with intramuscular tendon disruption and six (14.6%) in the group without intramuscular tendon disruption. CONCLUSION: Time to RTP for injuries with full-thickness disruption of the intramuscular tendon and waviness is significantly longer (by slightly more than 1 week) compared with injuries without intramuscular tendon involvement. However, due to the considerable overlap in time to RTP between groups with and without intramuscular tendon involvement, its clinical significance for the individual athlete is limited.

MRI appearance does not change in the first 7 days after acute hamstring injury-a prospective study.

BACKGROUND: The optimal timing of MRI following acute hamstring injury is not known and is mainly based on expert opinions. AIMS: To describe the day-to-day changes in the extent of oedema and investigate the optimal timing for detection of fibre disruption on MRI following acute hamstring injuries. STUDY DESIGN: Prospective, descriptive study. METHODS: We performed standardised MRI (1.5T) ≤1 day after injury in male athletes with acute hamstring injury. If initial MRI revealed positive signs of injury (increased signal intensity on fluid sensitive sequences), consecutive MRIs were obtained daily throughout the subsequent week (ie, 7 times). The MRI parameters (day 1-7) were scored by a single radiologist using a standardised scoring form. The day-to-day changes in the extent of oedema (distance from tuber, craniocaudal length, mediolateral width and anteroposterior depth) and the presence and extent of fibre disruption (tear) were assessed with descriptive statistics and repeated measures using analysis of variance of log-transformed data. The overall main effect for time was reported with a significance level set at p<0.05. RESULTS: 13 out of 132 male athletes assessed for eligibility between January 2014 and December 2015 were included. 1 dropped out, while 12 (31 years, range 20-49) completed the study; 11 had 7 MRI scans each and one had 5 MRI scans performed. There were no significant day-to-day changes for any of the extent of oedema measures (p values ranging from 0.12 to 0.81). Fibre disruption (tear), present in 5 of the athletes, was detectable from day 1, with small and insignificant day-to-day changes (p values ranging from 0.45 to 0.95). CONCLUSIONS: We observed insignificant day-to-day changes in the extent of oedema throughout the first week following acute hamstring injury. Fibre disruption (tear) was detectable from the first day after injury. These findings indicate that MRI can be performed on any day during the first week following an acute (hamstring) muscle injury.

Hamstring Reinjuries Occur at the Same Location and Early After Return to Sport: A Descriptive Study of MRI-Confirmed Reinjuries.

BACKGROUND: Despite relatively high reinjury rates after acute hamstring injuries, there is a lack of detailed knowledge about where and when hamstring reinjuries occur, and studies including imaging-confirmed reinjuries are scarce. PURPOSE: To investigate the location, radiological severity, and timing of reinjuries on magnetic resonance imaging (MRI) compared with the index injury. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: A MRI scan was obtained ≤5 days after an acute hamstring index injury in 180 athletes, and time to return to sport (RTS) was registered. Athletes with an MRI-confirmed reinjury in the same leg ≤365 days after RTS were included. Categorical grading and standardized MRI parameters of the index injury and reinjury were scored by a single radiologist (with excellent intraobserver reliability). To determine the location of the reinjury, axial and coronal views of the index injury and reinjury were directly compared on proton density-weighted fat-suppressed images. RESULTS: In the 19 athletes included with reinjury, 79% of these reinjuries occurred in the same location within the muscle as the index injury. The median time to RTS after the index injury was 19 days (range, 5-37 days; interquartile range [IQR], 15 days). The median time between the index injury and reinjury was 60 days (range, 20-316 days; IQR, 131 days) and the median time between RTS after the index injury and the reinjury was 24 days (range, 4-311 days; IQR, 140 days). More than 50% of reinjuries occurred within 25 days (4 weeks) after RTS from the index injury and 50% occurred within 50 days after the index injury. All reinjuries with more severe radiological grading occurred in the same location as the index injury. CONCLUSION: The majority of the hamstring reinjuries occurred in the same location as the index injury, early after RTS and with a radiologically greater extent, suggesting incomplete biological and/or functional healing of the index injury. Specific exercise programs focusing on reinjury prevention initiated after RTS from the index injury are highly recommended.

MRI does not add value over and above patient history and clinical examination in predicting time to return to sport after acute hamstring injuries: a prospective cohort of 180 male athletes.

BACKGROUND: MRI is frequently used in addition to clinical evaluation for predicting time to return to sport (RTS) after acute hamstring injury. However, the additional value of MRI to patient history taking and clinical examination remains unknown and is debated. AIM: To prospectively investigate the predictive value of patient history and clinical examination at baseline alone and the additional predictive value of MRI findings for time to RTS using multivariate analysis while controlling for treatment confounders. METHODS: Male athletes (N=180) with acute onset posterior thigh pain underwent standardised patient history, clinical and MRI examinations within 5 days, and time to RTS was registered. A general linear model was constructed to assess the associations between RTS and the potential baseline predictors. A manual backward stepwise technique was used to keep treatment variables fixed. RESULTS: In the first multiple regression model including only patient history and clinical examination, maximum pain score (visual analogue scale, VAS), forced to stop within 5 min, length of hamstring tenderness and painful resisted knee flexion (90°), showed independent associations with RTS and the final model explained 29% of the total variance in time to RTS. By adding MRI variables in the second multiple regression model, maximum pain score (VAS), forced to stop within 5 min, length of hamstring tenderness and overall radiological grading, showed independent associations and the adjusted R(2) increased from 0.290 to 0.318. Thus, additional MRI explained 2.8% of the variance in RTS. SUMMARY: There was a wide variation in time to RTS and the additional predictive value of MRI was negligible compared with baseline patient history taking and clinical examinations alone. Thus, clinicians cannot provide an accurate time to RTS just after an acute hamstring injury. This study provides no rationale for routine MRI after acute hamstring injury. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov Identifier: NCT01812564.

Platelet-rich plasma does not enhance return to play in hamstring injuries: a randomised controlled trial.

BACKGROUND: To evaluate the efficacy of a single platelet-rich plasma (PRP) injection in reducing the return to sport duration in male athletes, following an acute hamstring injury. METHODS: A randomised, three-arm (double-blind for the injection arms), parallel-group trial, in which 90 professional athletes with MRI positive hamstring injuries were randomised to injection with PRP-intervention, platelet-poor plasma (PPP-control) or no injection. All received an intensive standardised rehabilitation programme. The primary outcome measure was time to return to play, with secondary measures including reinjury rate after 2 and 6 months. RESULTS: The adjusted HR for the PRP group compared with the PPP group was 2.29 (95% CI 1.30 to 4.04) p=0.004; for the PRP group compared with the no injection group 1.48 (95% CI 0.869 to 2.520) p=0.15, and for the PPP group compared with the no injection group 1.57 (95% CI 0.88 to -2.80) p=0.13. The adjusted difference for time to return to sports between the PRP and PPP groups was -5.7 days (95% CI -10.1 to -1.4) p=0.01; between the PRP and no injection groups -2.9 days (95% CI -7.2 to 1.4) p=0.189 and between the PPP and no injection groups 2.8 days (95% CI -1.6 to 7.2) p=0.210. There was no significant difference for the secondary outcome measures. No adverse effects were reported. CONCLUSIONS: Our findings indicate that there is no benefit of a single PRP injection over intensive rehabilitation in athletes who have sustained acute, MRI positive hamstring injuries. Intensive physiotherapy led rehabilitation remains the primary means of ensuring an optimal return to sport following muscle injury. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov Identifier: NCT01812564.

No association between fibrosis on magnetic resonance imaging at return to play and hamstring reinjury risk.

BACKGROUND: Connective tissue scar (fibrosis) is a common finding on magnetic resonance imaging (MRI) after recovery from acute hamstring injuries. Fibrosis has been suggested as a predisposing factor for reinjury, but evidence from clinical studies is lacking. PURPOSE/HYPOTHESIS: The aim of this study was to examine the association between the presence of fibrosis on MRI at return to play after an acute hamstring injury and the risk of reinjury. The hypothesis was that fibrous tissue on MRI was associated with an increased reinjury risk. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: Magnetic resonance images were obtained from 108 consecutive athletes with modified Peetrons classification grade 1 or 2 hamstring injuries within 5 days of injury and within 7 days of return to play. The presence and extent of abnormally low signal intensity in the intramuscular tissue on MRI, suggestive of fibrosis, were assessed on both T1- and T2-weighted images. Reinjuries were recorded over a 1-year follow-up period. The association between fibrosis and reinjury risk was analyzed with a Cox proportional hazards model. RESULTS: The MRIs of the initial injury showed 45 (43%) grade 1 and 63 (57%) grade 2 injuries. Median time of return to play was 30 days (interquartile range [IQR], 22-42 days). At return to play, 41 athletes (38%) had fibrosis on MRI with a median longitudinal length of 5.8 cm (IQR, 3.3-12.5 cm) and a median volume of 1.5 cm3 (IQR, 1.5-3.9 cm3). In athletes with fibrosis, 24% (10/41) sustained a reinjury, and in the subjects without fibrosis, 24% (16/67) had a reinjury, resulting in a hazard ratio of 0.95 (95% CI, 0.43-2.1; P=.898). CONCLUSION: Fibrosis is commonly seen on MRI at return to play after grade 1 or 2 hamstring injuries but is not associated with reinjury risk.

MR arthrography of the shoulder: optimizing pulse sequence protocols for the evaluation of cartilage and labrum.

OBJECTIVES: To compare axial T1weighted fat-saturated (T1w fs) and T1w non-fs sequences, and coronal T1w-fs and T2w-fs sequences, for evaluation of cartilage and labrum using CT arthrography (CTA) as the reference. METHODS: Patients had MR arthrography (MRA) and CTA of the shoulder on the same day. Cartilage was assessed for superficial and full thickness focal and diffuse damage. Labral lesions were graded for Bankart variants and SLAP lesions. CTA images were read for the same features. The diagnostic performance of MRA including area under the curve (AUC) was evaluated against CTA. RESULTS: When comparing axial sequences, the diagnostic performance for cartilage lesion detection on T1w non-fs was 61.9% (sensitivity) 93.6% (specificity) and 89.5% (accuracy) with AUC 0.782, while that for T1w fs was 61.9%, 94.0%, 89.8% and 0.783. For labral assessment, it was 89.1%, 93.0%, 91.4% and 0.919 for T1w non-fs, and 89.9%, 94.0%, 92.6% and 0.922 for T1w fs. Comparing coronal sequences, diagnostic performance for cartilage was 42.5%, 97.5%, 89.8% and 0.702 for T1w fs, and 38.4%, 98.7%, 90.2%, and 0.686 for T2w fs. For the labrum it was 85.1%, 87.5%, 86.2%, and 0.868 for T1w fs, and 75.7%, 97.5%, 80.8% and 0.816 for T2w fs. CONCLUSIONS: Axial T1w fs and T1w non-fs sequences are comparable in their ability to diagnose cartilage and labral lesions. Coronal T1w fs sequence offers slightly higher sensitivity but slightly lower specificity than T2w fs sequence for diagnosis of cartilage and labral lesions.

Ligamentous Injuries and the Risk of Associated Tissue Damage in Acute Ankle Sprains in Athletes: A Cross-sectional MRI Study.

BACKGROUND: Ankle joint injuries are extremely common sports injuries, with the anterior talofibular ligament involved in the majority of ankle sprains. There have been only a few large magnetic resonance imaging (MRI) studies on associated structural injuries after ankle sprains. PURPOSE: To describe the injury pattern in athletes who were referred to MRI for the assessment of an acute ankle sprain and to assess the risk of associated traumatic tissue damage including lateral and syndesmotic ligament involvement. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: A total of 261 ankle MRI scans of athletes with acute ankle sprains were evaluated for: lateral and syndesmotic ligament injury; concomitant injuries to the deltoid and spring ligaments and sinus tarsi; peroneal, flexor, and extensor retinacula and tendons; traumatic and nontraumatic osteochondral and osseous changes; and joint effusion. Patients were on average 22.5 years old, and the average time from injury to MRI was 5.7 days. Six exclusive injury patterns were defined based on lateral and syndesmotic ligament involvement. The risk for associated injuries was assessed by logistic regression using ankles with no or only low-grade lateral ligament injuries and no syndesmotic ligament damage as the reference. RESULTS: With regard to the injury pattern, there were 103 ankles (39.5%) with complete anterior talofibular ligament disruption and no syndesmotic injury, and 53 ankles (20.3%) had a syndesmotic injury with or without lateral ligament damage. Acute osteochondral lesions of the lateral talar dome were seen in 20 ankles (7.7%). The percentage of chronic lateral osteochondral lesions was 1.1%. The risk for talar bone contusions increased more than 3-fold for ankles with complete lateral ligament ruptures (adjusted odds ratio [aOR], 3.43; 95% CI, 1.72-6.85) but not for ankles with syndesmotic involvement. The risk for associated deltoid ligament injuries increased for ankles with complete lateral ligament injuries (aOR, 4.04; 95% CI, 1.99-8.22) compared with patients with no or only low-grade lateral ligament injuries. CONCLUSION: About 20% of athletes referred for MRI after suffering an acute ankle sprain had evidence of a syndesmotic injury regardless of lateral ligament involvement, while more than half had evidence of any lateral ligament injury without syndesmotic involvement. Concomitant talar osseous and deltoid ligament injuries are common.

Evaluation of the tarsometatarsal joint using conventional radiography, CT, and MR imaging.

The tarsometatarsal, or Lisfranc, joint complex provides stability to the midfoot and forefoot through intricate osseous relationships between the distal tarsal bones and metatarsal bases and their connections with stabilizing ligamentous support structures. Lisfranc joint injuries are relatively uncommon, and their imaging findings can be subtle. These injuries have typically been divided into high-impact fracture-displacements, which are often seen after motor vehicle collisions, and low-impact midfoot sprains, which are more commonly seen in athletes. The injury mechanism often influences the imaging findings, and classification systems based primarily on imaging features have been developed to help diagnose and treat these injuries. Patients may have significant regional swelling and pain that prevent thorough physical examination or may have other more critical injuries at initial posttrauma evaluation. These factors may cause diagnostic delays and lead to subsequent morbidities, such as midfoot instability, deformity, and debilitating osteoarthritis. Missed Lisfranc ligament injuries are among the most common causes of litigation against radiologists and emergency department physicians. Radiologists must understand the pathophysiology of these injuries and the patterns of imaging findings seen at conventional radiography, computed tomography, and magnetic resonance imaging to improve injury detection and obtain additional information for referring physicians that may affect the selection of the injury classification system, treatment, and prognosis.

MRI observations at return to play of clinically recovered hamstring injuries.

BACKGROUND: Previous studies have shown that MRI of fresh hamstring injuries have diagnostic and prognostic value. The clinical relevance of MRI at return to play (RTP) has not been clarified yet. The aim of this study is to describe MRI findings of clinically recovered hamstring injuries in amateur, elite and professional athletes that were cleared for RTP. METHODS: We obtained MRI of 53 consecutive athletes with hamstring injuries within 5 days of injury and within 3 days of RTP. We assessed the following parameters: injured muscle, grading of injury, presence and extent of intramuscular signal abnormality. We recorded reinjuries within 2 months of RTP. RESULTS: MRIs of the initial injury showed 27 (51%) grade 1 and 26 (49%) grade 2 injuries. Median time to RTP was 28 days (range 12-76). On MRI at RTP 47 athletes (89%) had intramuscular increased signal intensity on fluid-sensitive sequences with a mean longitudinal length of 77 mm (±53) and a median cross-sectional area of 8% (range 0-90%) of the total muscle area. In 22 athletes (42%) there was abnormal intramuscular low-signal intensity. We recorded five reinjuries. CONCLUSIONS: 89% of the clinically recovered hamstring injuries showed intramuscular increased signal intensity on fluid-sensitive sequences on MRI. Normalisation of this increased signal intensity seems not required for a successful RTP. Low-signal intensity suggestive of newly developed fibrous tissues is observed in one-third of the clinically recovered hamstring injuries on MRI at RTP, but its clinical relevance and possible association with increased reinjury risk has to be determined.

Knee joint biomechanics: relevance to imaging.

Over the past 2 decades our understanding of the anatomy and biomechanics of the knee joint has dramatically increased. The translation of this knowledge into clinical practice has greatly improved athletic training and medical treatment when injury occurs. Advances in imaging techniques have played a role in this improvement. The next step for imaging is to move beyond merely providing morphology and to assess the functional mechanics of the knee. This article focuses on the biomechanics of the femorotibial joint and its relevance to imaging.