Kinematic Analysis of the Gait in Professional Ballet Dancers The Effect of Rehabilitation Intervention on Movement of Lower Limbs and Pelvis during the Gait in Professional Ballet Dancers

Background: A ballet dance routine places extreme functional demands on the musculoskeletal system and affects the motor behaviour of the dancers. An extreme ballet position places high stress on many segments of the dancer’s body and can significantly influence the mobility of the lower limb joints. Objective: The aim of this study was to observe the differences in the gait pattern between ballet dancers and non-dancers. Methods: Thirteen professional ballet dancers (5 males, 8 females; age 24.1 ± 3.8 years; height 170.2 ± 8.5 cm; weight 58.3 ± 11.2 kg) participated in this research. We compared these subjects with twelve controls (3 males, 9 females; mean age 24.3 ± 2.75 years; height 173.3 ± 6.01 cm; weight 72.2 ± 12.73 kg). None of the participants had any history of serious musculoskeletal pathology or injury or surgery in the lower limbs. Control group had no ballet experience. Each participant performed five trials of the gait at self-selected walking speed. Kinematic data was obtained using the Vicon MX optoelectronic system. The observed data was processed in the Vicon Nexus and Vicon Polygon programmes and statistically evaluated in Statistica. Non-parametric test (Mann-Whitney U test, p < .05) was applied for comparing the dancers and the controls. Results: Significant differences (p < .05) were found in all lower limb joints. In the dancers, greater hip extension (–15.30 ± 3.31° vs. –12.95 ± 6.04°; p = .008) and hip abduction (–9.18 ± 5.89° vs. –6.08 ± 2.52°; p < .001) peaks together with increased pelvic tilt (3.33 ± 1.26° vs. 3.01 ± 1.46°; p = .020), pelvic obliquity (12.46 ± 3.05° vs. 10.34 ± 3.49°; p < .001) and pelvic rotation (14.29 ± 3.77° vs. 13.26 ± 4.91°; p = .029) were observed. Additionally, the dancers demonstrated greater knee flexion (65.67 ± 4.65° vs. 62.45 ± 5.24°; p = .002) and knee extension (3.80 ± 4.02° vs. –1.54 ± 5.65°; p < .001) peaks during the swing phase when compared to the controls. Decreased maximal ankle plantar flexion was observed during the loading response (–8.84 ± 3.74° vs. –10.50 ± 3.99°) and increased maximal ankle plantar flexion in terminal stance (–20.30 ± 4.93° vs. –17.00 ± 3.99°; p = .025) was observed for the dancers. Conclusion: The results confirm that long-term intensive ballet training affects the kinematic pattern of particular joints during gait performance. The findings suggest overloading in the lumbosacral region and dysfunction or weakness of several muscles in ballet dancers.


METHODS
Thirteen professional ballet dancers (5 males, 8 females; mean age 25.8±5.6 years; height 172.8±8.1 cm; weight 59.8±12.2 kg) participated in this study. This experimental group participated in rehabilitation intervention for six week. Rehabilitation program consisted of neuromuscular exercise techniques and manual therapy. We evaluated performance of the gait in dancers before and after this rehabilitation.
The experimental group was compared with the group of twelve controls (3 males, 9 females; mean age 24.3±2.75 years; height 173.3±6.01cm; weight 72.2±12.73 kg). The exclusion criteria for all subjects were any serious musculoskeletal injuries or surgery of the lower limbs. Additionally, control group had no ballet experience. Kinematic data were obtained using the optoelectronic system Vicon MX (Vicon Motion Systems, Oxford, London). Reflective markers of kinematic model PlugInGait were placed at the pelvis and the lower limbs. Each participant performed five successful trials of gait at self-selected walking speed.
Angle variables of lower limbs and pelvis were evaluated in all three planes. The data was evaluated in Statistica (Version 9.0, Stat-Soft, Inc., Tulsa, OK, USA) using Wilcoxon test (p<0.05) for comparison of differences between dancers before and after rehabilitation and Mann-Whitney test (p<0.05) for comparison of dancers and control group. Table 1. To compare the experimental group before and after rehabilitation, dancers demonstrated decreased hip adduction (p < 0.05) after intervention. Dancers also demonstrated significantly greater maximal ankle dorsal flexion during the stance phase (p < 0.05) as well as greater maximal hip abduction (p < 0.01) before and after rehabilitation compared to the control group. Dancers reached significant greater internal knee rotation (p < 0.05) and smaller external rotation (p < 0.05) after rehabilitation in comparison with the control group. The other kinematic variables were not statistically significant.  Legend: C -controls; D1 -dancers before rehabilitation; D2 -dancers after rehabilitation; Statistically significant differences (p < 0.05): * between controls and dancers before rehabilitation; & between controls and dancers after rehabilitation; # between dancers before and after rehabilitation.

DISCUSSION
The observed increased dorsal ankle flexion in dancers can be explained by special ballet position (e.g. grand plié, demi-plié), which require excessive range of dorsal ankle flexion. If the foot is frequently forced into extreme range of movements, it loses ability to support the medial arch and act as a shock absorption. Dancers subsequently overload the medial part of the foot. This causes increased pronation (Rusell, 2010). Insufficient range of movement in hips together with hyperpronation is compensated by increased external tibia rotation, which was demostrated in dancers before rehabilitation. This causes greater medial load of the knee, which can predispose to injury (Cimelli and Curran, 2012;Clippinger, 2007). In addition, chronic ankle instability is often associated with hip abductor weakness (Rusell, 2010). The increased range of hip can be caused by inadequate coordination between adductors and abductors.
The results show that six-week long rehabilitation did not affect performance of walking in professional dancers. However, the observed parameters in dancers after rehabilitation can predict improved alignment of these joints during gait, which may reduce stress load being applied on the lower limb´s structures. The results confirm that the long-term rehabilitation should be a necessary part of comprehensive care about dancers to improve their ballet techniques and prevent injuries.