Excellent reliability for MRI grading and prognostic parameters in acute hamstring injuries =========================================================================================== * B Hamilton * R Whiteley * E Almusa * B Roger * C Geertsema * Johannes L Tol ## Abstract **Background** Categorical grading and other measurable MRI parameters are frequently utilised for predicting the outcome of hamstring injuries. However, the reliability and smallest detectable difference (SDD) have not been previously evaluated. It therefore remains unclear if the variability in previously reported results reflects reporting variation or actual injury status. **Methods** 25 hamstring injuries were scored by two experienced radiologists using the Peetrons grading and specific prognostic MRI parameters: distance from ischial tuberosity (cm), extent (cranio to caudal, anterior to posterior, medial to lateral; (cm)), maximum cross-sectional area (%), volume (cm3) of the oedema. The interobserver and intraobserver reliability was calculated along with the SDDs for each scale variable. **Results** There were 3 Grade 0 (12%), 11 grade 1 (44%), 9 grade 2 (36%) and 2 grade 3 (8%) injuries. Cronbach's α values for grading were 1.00 (inter) and 0.96 (intra), respectively. The intraclass correlation coefficients for the prognostic MRI parameters were between 0.77 and 1.0. The SDDs varied between each parameter. **Conclusions** Excellent interobserver and intraobserver reliability was found for grading and prognostic MRI parameters in acute hamstring injuries. In daily practice and research, we can be confident that scoring hamstring injuries by experienced radiologists is reproducible. The documented SDDs allow meaningful clinical inferences to be made when assessing observed and reported changes in MRI status. * Hamstring injuries * MRI ## Introduction Muscle injuries account for up to 30% of all sporting injuries, with the hamstring complex being the most frequently injured site.1–4 MRI is considered useful in confirming injury diagnosis, severity and prognosis, with categorical and continuous scoring systems constituting validated indicators of time to return to a sport.5–9 A recent cohort study in European football established the clinical relevance of a widely used categorical grading system.10 ,11 However, hamstring injuries may be considered a heterogeneous group and other researchers have focused on prognostic MRI parameters such as intramuscular location and extent of the injury.7 ,9 For example, the location, in particular the continuous distance to the ischial tuberosity, has a fair5 to good6 correlation with time to return to preinjury function. Similarly, measurements of the extent of the injury in three planes have shown correlation coefficients between 0.39 and 0.74 (table 1).5–8 With increasing MRI availability, understanding of the clinical relevance of each of these variables continues to evolve. View this table: [Table 1](http://bjsm.bmj.com/content/48/18/1385/T1) Table 1 Prognostic MRI parameters Despite the frequent application of these MRI parameters, there are no data published regarding the reliability and smallest detectable differences (SDDs) in the MRI interpretation of hamstring muscle injuries. As a result, it remains unclear if the variability in study findings reflects a variability in the reporting or actual MRI status. The aim of this study was to evaluate the interobserver and intraobserver reliability and document SDDs of MRI grading and other prognostic parameters in acute hamstring injuries. ## Methods The investigation formed part of a randomised controlled trial evaluating acute hamstring injuries (ClinicalTrial.gov number [NCT01812564](http://bjsm.bmj.com/lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT01812564&atom=%2Fbjsports%2F48%2F18%2F1385.atom)). Approval was obtained from the Ethics Committee of Aspetar, Qatar Orthopaedics and Sports Medicine Hospital and informed consent was obtained from all included patients. Patients were recruited between November 2009 and December 2012 at an orthopaedic and sports medicine hospital in Qatar. For this substudy, 25 patients out of the recruited cohort who met distinct inclusion criteria (acute onset of posterior thigh pain, MRI performed within 5 days from injury, age >18 years and male) were randomly selected. One investigator randomly selected 25 patients by circling the unique anonymised patient study number on a list of all patients. ### MRI The players were positioned supine and examined with a 1.5 Tesla Siemens Espree. In addition to a phased array coil, two-body matrix coils were strapped over the thigh and centred over the painful area, identified by the athlete and marked by the physician. Axial and coronal proton density with fat saturation along the longitudinal axis of the thigh (TR/TE 3490/27 and a 512×326 matrix for the coronal images and TR/TE 3000/32 and a 512×333 matrix for the axial images) with one signal average each were obtained. The field of view used on the coronals was 25 cm and 24 cm with the axial images and a 3.5 mm section thickness with no gap. ### MRI assessment Prior to the study, two radiologists were familiarised with the MRI scoring protocol, in a trial involving 10 patients. Each radiologist scored the MRIs in random order between May 2012 and January 2013. Radiologist one (EA), who was also involved in other hamstring diagnostic studies, scored 128 MRIs in this period. During this process, MRIs were randomly allocated each week in sets of 3–5 with at least 2 months between the first and second evaluations of the same MRI. Radiologist two (BR) scored sets of 3–5 MRIs on a weekly basis in the same manner. The radiologists, each with more than 9 years of experience in musculoskeletal radiology and blinded to the clinical status of the injury, independently interpreted the MRIs, scoring them according to a modified Peetrons classification system;10 ,11 grade 0: no abnormalities; grade I: oedema without architectural distortion; grade II: oedema with architectural distortion; and grade III: complete tear. Additional prognostic MRI parameters measured were: craniocaudal, transverse and anteroposterior dimensions (cm) of identified oedema, and distance from the most proximal site of oedema to the ischial tuberosity (cm). We subsequently calculated the volume (cm3) of muscle involved and the maximum involved cross-sectional area as a percentage of the total muscle cross-sectional area in the transversal plane. When more than one muscle was involved, the muscle with the most extensive oedema or tear was scored. ### Data analysis Interobserver and intraobserver reliability was calculated with a one-way random model. For the categorical variable of overall grade, a scoring system (with choices of 0, 1, 2 or 3) per observer per hamstring injury was recorded.10 ,11 The interobserver reliability for these measures was estimated using Cronbach's α. For the parametric values, the intraclass correlation coefficient (ICC(2,1)) was calculated to estimate reliability. The inter-rater reliability is considered excellent if the ICC is >0.75, fair to good if 0.4