Risk factors for overuse injury in elite adolescent ballet dancers
Injuries are common among young elite ballet dancers, often leading to disruptions in training and in turn the development of talent. Anecdotally, the adolescent period of growth and maturation, and poor lower extremity alignment are thought to increase the risk of injury. Substantial evidence indicates that overuse lower extremity injuries are most common (lumbar spine, pelvis, legs and feet). Little research has been conducted into potential risk factors, and no studies have investigated the use of two-dimensional (2D) video to measure lower extremity alignment in young ballet dancers. The aims of this thesis were to investigate in young elite ballet dancers: 1) the reliability of 2D video assessment of dynamic lower extremity alignment during functional dance movement and 2) the associations between growth, maturation and alignment and lower extremity overuse injury.
A modified knee valgus angle and lateral pelvic tilt were measured during two dance movements (fondu and temps levé), using 2D video analysis. Reliability of the modified knee valgus angle in both the fondu (ICC = 0.88 to 0.89; TE = 3º) and temps levé (ICC = 0.80 to 0.87; TE = 6 to 8º) was high. Reliability of the pelvic angle in the fondu (ICC = 0.67 to 0.79; TE = 1º) was moderate to high, and moderate in the temps levé (ICC = 0.68 to 0.71; TE = 1º). Additionally, there was a significant difference in knee angle between the left and right legs during both the fondu (p = 0.001) and temps levé (p = 0.001). Finally, a strong correlation for the knee angle between the two movements on both the left (r = 0.93) and right (r = 0.94) legs was noted.
As well as knee and pelvic alignment, baseline maturation stage using the Tanner scale, and growth (based on change in foot length) were also recorded in all dancers. Overuse lower extremity dance injuries were diagnosed and recorded by a physiotherapist over a six month period. The injury rate ratio (RR) associated with each baseline variable was estimated using over-dispersed Poisson regression modelling. Changes in right foot length (RR = 1.41, CI = 0.93-2.13), right knee angles during the fondu (RR = 0.68, CI = 0.45-1.03) and temps levé (RR = 0.72, CI = 0.53-0.98), and pelvic angles during the temps levé on the left (RR = 0.52, CI = 0.30-0.90) and fondu on the right (R = 1.28, CI = 0.91-1.80) were associated with clear changes in injury risk.
Simple 2D measures of knee and pelvic alignment during the fondu and temps levé movements in elite adolescent ballet dancers demonstrate moderate to high reliability. Improved right knee alignment is likely associated with a reduction in risk of right lower extremity overuse injury. Rate of growth is likely associated with an increase in risk of lower extremity overuse injury. Therefore, monitoring of growth and screening lower extremity alignment in elite adolescent dancers may assist with injury prevention.