Background The cartilage of the epiphyseal plate might be 2–5 times weaker than surrounding fibrous tissue; therefore epiphyseal (growth) plates are very sensitive to their surrounding mechanical environment.

Objective The specific aim of the study was to investigate and compare epiphyseal length and extension in the proximal humerus, closure in the growth plate and bone marrow signal intensity related to the proximal humeral physis in the dominant arm and the non-dominant arm of the asymptomatic adolescent elite tennis player.

Design Cross-sectional study. According to a pre-defined protocol including measurements of epiphyseal extension, epiphyseal length, closure of the growth plate and bone marrow signal intensity related to the proximal humeral physis the MRI scans were evaluated.

Setting The study was an independent complement to the national high-performance program conducted by the Swedish Tennis Association.

Patients (or Participants) Our study sample included 35 asymptomatic elite young tennis players (15 male, 20 female, mean age 17.4 years ±2.7).

Interventions (or Assessment of Risk Factors) Each player contributed with two shoulders to the MRI evaluation. The non-dominant arm was used as a control. Two fellowship-trained musculoskeletal radiologists independently from each other reviewed magnetic resonance images.

Main Outcome Measurements Epiphyseal extension and length, closure in the growth plate and bone marrow signal intensity related to the proximal humeral physis in the dominant arm (DA) and the non-dominant arm (NDA).

Results Statistically significant differences between dominant arm and non-dominant arm in epiphyseal length (mm) laterally (DA 27.33 vs NDA 26.70) were shown. Statistically significant differences were also found in epiphyseal extension (mm) laterally (DA 36.10 vs NDA 35.10) and ventrally (DA 36.23 vs NDA 34.76).

Conclusions Significant findings assessing MRI measurements of the epiphyseal plate in the asymptomatic adolescent elite tennis player might reflect a development of consecutive alterations in the epiphyseal plate in the dominant arm.