MRI-Based Grading Systems for muscle injuries

MRI-Based Grading Systems for muscle injuries

There are multiple grading systems used for classifying muscle injury on MRI (see table 1).  They aim to classify injury based on a number of different factors depending on system which include:

Direct v. indirect injuries, tears(partial v. incomplete), anatomical factors including, location of injury, muscle involved, tissue involved (muscle, tendon, fascia) and  the amount of edema present.

This article reviews the 4 most common grading systems (Table 1): the British Athletics Muscle Injury Classification system (BAMIC) the Munich Consensus statement on muscle injury (MLG-R), the Chan et al. system, and Peetrons classification system.

Table 1 – Comparison of MRI-based Grading Systems

British Athletics Muscle Injury Classification (BAMIC)
(See https://sportmedschool.com/british-athletics-muscle-injury-classification-bamic/)

The British Athletics Muscle Injury Classification (BAMIC) system is a comprehensive MRI-based grading scheme developed specifically for hamstring injuries in athletes [1,2,4]. This classification system categorizes injuries into four grades (0-3) based on MRI findings and anatomical location of injury [1,2].  Grade 0 represents negative MRI findings despite clinical symptoms, Grade 1 involves focal high signal intensity on fluid-sensitive sequences with less than 10% cross-sectional area involvement, Grade 2 shows disruption of muscle fibers involving 10-50% of cross-sectional area, and Grade 3 represents extensive muscle disruption exceeding 50% of cross-sectional area or complete tendon avulsion [1,2].

The BAMIC system further subdivides injuries based on anatomical location: (a) myofascial injuries involving the intramuscular tendon or aponeurosis, (b) muscle-tendon junction injuries, and (c) proximal free tendon injuries [1,2].  This anatomical subclassification has important prognostic value, with myofascial and proximal free tendon injuries associated with significantly longer recovery times compared to peripheral muscle injuries [1,2].  The BAMIC system has demonstrated good inter-rater reliability and strong correlation with return-to-play times, making it a valuable tool for clinical decision-making and prognostication [1,2].

MLG-R System

The Munich Consensus Statement on muscle injury classification, commonly referred to as the MLG-R system (Munich-London-Glasgow-Regensburg), represents a more recent and comprehensive approach to classifying muscle injuries [4, 5]. This system categorizes injuries into four main types: Type 1 (functional muscle disorders without macroscopic evidence of fiber tear), Type 2 (neuromuscular muscle disorders), Type 3 (structural muscle injuries with fiber disruption), and Type 4 (complete muscle tears or tendon avulsions) [4,5]. Type 3 injuries are further subdivided into 3a (minor partial tear affecting <5% of muscle cross-section), 3b (moderate partial tear affecting >5% of cross-section), and 4 (complete tear or tendon avulsion) [4,5].

The MLG-R system has been specifically validated for predicting return-to-play times in football (soccer) players with hamstring injuries [4]. A machine learning analysis of the MLG-R classification demonstrated that it could accurately predict return-to-play duration, with Type 3b and Type 4 injuries associated with significantly longer recovery times compared to Type 3a injuries [4]. The system’s strength lies in its comprehensive approach, incorporating both structural and functional aspects of muscle injury, as well as its validation in elite athletic populations [4,5]. However, the complexity of the classification may limit its widespread adoption compared to simpler grading systems [5].

Peetrons Classification

The Peetrons classification system is one of the earlier ultrasound and MRI-based grading schemes for muscle injuries, including hamstring strains [1,2]. This system classifies injuries into three grades based on the extent of muscle fiber disruption and associated imaging findings [1]. Grade I injuries show focal areas of increased signal intensity on MRI without architectural disruption. This represents mild muscle fiber damage or edema [1,2].Grade II injuries demonstrate partial muscle fiber disruption with visible gaps in the muscle architecture and associated hematoma formation [1,2].  Grade III injuries involve complete muscle or tendon rupture with retraction of the torn ends and large hematoma [1,2].

While the Peetrons classification provides a straightforward grading system, it has limitations in capturing the anatomical complexity and prognostic nuances of hamstring injuries [1,2].  The system does not specifically account for the location of injury (proximal vs. distal, myofascial vs. peripheral) or the involvement of the intramuscular tendon, factors that have been shown to significantly influence recovery time [1,2]. Nevertheless, the Peetrons classification remains widely used in clinical practice and research due to its simplicity and applicability across different muscle groups [1,2].

Chan et al.

The Chan classification system focuses specifically on the extent of tendon involvement and cross-sectional area of injury, providing detailed anatomical information that correlates with recovery time [1,2]. Some classification systems incorporate both MRI findings and clinical parameters, such as the presence of a palpable defect, loss of strength, and functional limitations [1].

Other Classification Systems

Several other classification systems have been proposed for hamstring injuries, each with specific strengths and limitations [1,2]. The Askling classification distinguishes between sprinting-type and stretching-type hamstring injuries based on mechanism and clinical presentation, with stretching-type injuries generally requiring longer recovery periods [1,3]. This functional classification complements anatomical grading systems by incorporating the mechanism of injury, which has independent prognostic value [1,3].

The proliferation of classification systems reflects the complexity of hamstring injuries and the ongoing effort to develop prognostic tools that accurately predict recovery and guide treatment decisions [1,2,4].

Prognostic Value of MRI Grading

MRI-based grading systems have demonstrated significant prognostic value for predicting recovery time and return-to-play in athletes with hamstring injuries [1,2,4,5]. Multiple studies have shown strong correlations between injury grade, anatomical location, and time to return to sport [1,2,4]. Higher-grade injuries (Grade 2-3 in most systems) are consistently associated with longer recovery times, often exceeding 4-6 weeks, compared to Grade 1 injuries which typically resolve within 2-3 weeks [1,2].

Specific MRI features that predict prolonged recovery include:

• involvement of the proximal free tendon
• myofascial injuries affecting the intramuscular tendon or aponeurosis,
• greater longitudinal extent of injury (>10 cm)
• larger cross-sectional area involvement (>50%), and
• complete tendon avulsions [1,2,4].

Conversely, peripheral muscle injuries without tendon involvement and injuries with smaller cross-sectional area (<10%) are associated with faster recovery [1,2]. The prognostic value of MRI grading has important clinical implications, allowing clinicians to provide athletes with realistic recovery timelines, plan rehabilitation protocols, and make informed decisions about the need for surgical intervention [1,2,4,5].  There is an important caveat however, that is that MRI-negative injuries, clinically diagnosed hamstring injuries without MRI findings caused the ajority of absence days in a 2012 study.  Therefroe MRI alone is insufficient for prognostication of return to play. [6]

Conclusion

Modern MRI-based grading systems, including the British Athletics Muscle Injury Classification, Peetrons classification, and MLG-R system, provide valuable prognostic information that guides treatment planning and return-to-play decisions [1,2,4,5]. These classification systems have demonstrated that injury location, particularly involvement of the proximal free tendon or intramuscular tendon, is a critical determinant of recovery time [1,2]. However, the proliferation of different classification systems highlights the need for standardization and further validation research [1,2,4].

Dr. Neil Dilworth (April 7, 2026  – PR AF)

References:

[1] Kerkhoffs, G. M., van Es, N., Wieldraaijer, T., Sierevelt, I. N., Ekstrand, J., & van Dijk, C. N. (2013). Diagnosis and prognosis of acute hamstring injuries in athletes. Knee Surgery, Sports Traumatology, Arthroscopy, 21(2). https://doi.org/10.1007/S00167-012-2055-X

[2] Marrero, L., Patel, D. B., Lesniak, B., & White, E. A. (2025). MRI and US in hamstring sports injury assessment: Anatomy, imaging findings, and mechanisms of injury. Radiographics, 45(1). https://doi.org/10.1148/rg.240061

[3] Hickey, J. T., Timmins, R. G., Maniar, N., Williams, M. D., & Opar, D. A. (2021). Current clinical concepts: hamstring strain injury rehabilitation. Journal of Athletic Training. https://doi.org/10.4085/1062-6050-0707.20

[4] Valle, X., Alentorn-Geli, E., Tol, J. L., Hamilton, B., Garrett, W. E., Pruna, R., Til, L., Gutierrez, J. A., Alomar, X., Balius, R., Malliaropoulos, N. G., Monllau, J. C., Whiteley, R., Witvrouw, E., Samuelsson, K., & Rodas, G. (2022). Return to Play Prediction Accuracy of the MLG-R Classification System for Hamstring Injuries in Football Players: A Machine Learning Approach. Sports Medicine, 52(8). https://doi.org/10.1007/s40279-022-01672-5

[5] Hallén, A., & Ekstrand, J. (2014). Return to play following muscle injuries in professional footballers. Journal of Sports Sciences, 32(13). https://doi.org/10.1080/02640414.2014.905695

[6] Ekstrand, J., Healy, J. C., Waldén, M., Lee, J. C., English, B., & Hägglund, M. (2012). Hamstring muscle injuries in professional football: the correlation of MRI findings with return to play. British Journal of Sports Medicine, 46(2), 112-117. https://doi.org/10.1136/BJSPORTS-2011-090155