Nonlinear Interactions of Lower Limb Clinical Measures Associated With Asymptomatic Achilles Tendon Abnormality in Ballet Dancers.

Context: Tendon abnormalities on imaging are commonly observed in individuals with Achilles tendinopathy. Those abnormalities can also be present in asymptomatic individuals, which is an important risk factor for developing tendon symptoms. Ballet dancers are particularly vulnerable due to the high loads placed on their Achilles tendons. Understanding the relationship between clinical measures and tendon abnormality is essential for this population.

Objective: To investigate the predictive value of clinical measures for identifying Achilles tendon abnormality in asymptomatic ballet dancers using a nonlinear statistical analysis.

Design: Cross-sectional study.

Setting: Dance company facility and research laboratory.

Patients or other participants: Thirty-five asymptomatic professional and amateur ballet dancers enrolled (23 female/12 male).

Main outcome measure(s): The presence of Achilles tendon abnormality was investigated using gray-scale ultrasound. Tendons were classified as having an abnormality if presenting with fusiform shape and/or hypoechoic areas. Clinical measures assessed were foot pronation; ankle dorsiflexion angle; hip, knee, and ankle isometric torque; and standing calf endurance. Classification and regression tree analysis was used to explore nonlinear interactions among clinical measures and their role in identifying tendon abnormality.

Results: Sixty-eight tendons were included in the analysis. Structural change was common in asymptomatic dancers, with 80% presenting with tendon abnormality. Hip isometric torque, ankle dorsiflexion range of motion, and calf endurance were measures related to tendon abnormality. Interactions between hip torque and ankle dorsiflexion range of motion were statistically associated with the presence of tendon abnormality. Increased hip abductor torque was linked to a 59% reduction in the probability of tendon abnormality. The classification and regression tree model reached proper accuracy (total classification percentage of 83.8%).

Conclusions: Hip torque was an important clinical measure related to tendon structure. Assessment of dancers should include the whole lower limb as the combination of hip torque and ankle dorsiflexion range of motion accurately identified the presence of tendon abnormality.