MRI classification of calf injuries - a reliability study and correlation with return to play in professional rugby...

To assess the validity and reliability of the calf injury classification system proposed by the Olympic Park group which focuses on connective tissue structure integrity on MRI.

A retrospective study analysing calf muscle group injuries in an English Premiership professional rugby union club using the MRI classification proposed by the Olympic Park group. Classification on MRI examinations of 28 calf injuries sustained over a 6-year period was performed by three independent musculoskeletal radiologists to determine the inter-observer variability and correlation of the grade of injury with return-to-full-training (RTFT) time.

RTFT time ranged from 5 to 110 days (mean = 40.1, SD = 26.4) following calf muscle injury. The Olympic Park classification injury grade demonstrated moderate to strong correlation with RTFT time (Spearman's rank correlation coefficient, 0.661-0.715, p < 0.01). RTFT time was statistically different between different injury grades (one-way ANOVA, p < 0.01). Inter-observer agreement of the overall grade between radiologist pairs was fair to moderate (weighted kappa 0.406-0.583).

The Olympic Park classification system demonstrates moderate to strong correlation with time to RTFT following calf injury. Inter-observer reliability is fair to moderate.