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Correlation between Lower Extremity Biomechanical Parameters and Injuries in Dancers: Longitudinal and Biomechanical Perspectives

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Correlation between Lower Extremity Biomechanical Parameters and Injuries in Dancers: Longitudinal and Biomechanical Perspectives

Cheng-Feng Lin, PhD Grant Number: NSC 96-2314-B-006 -007 - 關鍵字:下肢傷害、芭蕾、平衡 芭蕾是一種容易受傷的專業技術。在所有與芭蕾相關的傷害中,腳踝與足部的傷害 就佔了 35%~55%。舞者或許有良好的單腳站平衡能力,但是在所需的芭蕾舞特殊技巧 平衡上卻沒有令人滿意的表現。因此本篇研究的目的是決定跳躍動作的模式與之前受傷 史的關係。本實驗徵召了22 個芭蕾女大學生,舞者在過去一年內下肢有與執行芭蕾動 作相關所造成的受傷被分到BI組,過去一年內沒受傷者則被分到BU組,各11位。另 徵召了11個年齡相符的正常受試者為控制組(C)。測試內容包括古典芭蕾的基本動作一 位和五位、腳尖點地(Pointé), 分腿跳(Sissonné Ferméé)。實驗器材包括反光球以及力板。 結果顯示相較於BU組和C組而言,BI組的平衡控制能力是比較差的。這些BI組的舞 者都有腳踝扭傷的受傷史,這可能導致他們本體覺的缺損進而造成較差的內外側穩定 度。執行基本動作五位時,我們發現BI組的壓力中心在內外側有不穩定的情形。BI組 在執行腳尖點地時,其壓力中心的位移範圍在任一方向都比BU組來的大。在分腿跳的 執行終期(terminal phase),BI組的舞者有比較小的後足相對於脛骨(hindfoot to tibia)的外 展角度、以及比較小的負荷率(loading rate)。在上升期(rising phase),BI組著重在抬起 前腳且忽略後腳的穩定度,這可能會造成BI 組比BU 組還要不穩定的原因。總結,我 們發現舞者的腳踝受傷史與內外側平衡能力有高度相關,我們建議舞者應該要根據特定 的芭蕾舞動作進行肌肉和平衡控制訓練。未來進一步的研究是要決定訓練計劃如何影響 受傷率。

Introduction

Ankle and foot injuries are common in the ballet dancers. As estimated that

approximately 10% to 30% of all musculoskeletal injuries associated with ballet occurred in the ankle (Conti and Stone 1995). Nicholas (1975) expressed that the total score in

neuromuscular and physical factors, mental and psychometric factors and environmental factors of classical ballet is equivalent to professional football in a comparison of 61 common sports on athletic performance. Ballet dancers always perform with extreme positions and alignment with long duration and somehow with inappropriate trainings and instructions. Those are causations contributing to the injuries. Injuries occurred mostly during the practice, rehearsal or on stage and may result from the poor technique or long duration on the practice. Repetitive movements with excessive but inappropriate range of motion induce the

occurrence of injuries. Anatomical structures, alignment of lower extremity and muscle strength are other considerations. Studies had discussed the possible injury mechanism, but the relative movements between midfoot and hindfoot occurred in the relevé en pointé, Sissonné Ferméé and jump-landing with turnout second position had not been further

investigated. The foot pressure patterns between injured and uninjured groups and the effects of the pressure distribution on the lower extremity injuries are unclear in current literature. The relative movements between midfoot and hindfoot segment are important to assist people to understand the injury mechanism and their influences on other lower extremity especially for the leg and knee joint. Literature also showed the inappropriate foot position, excessive calcaneus eversion, and foot-leg alignment would result in excessive muscle strain on the medial side of the foot and knee joint. How those factors interrelated is not well understood now. This project was to determine the relative movements between the midfoot

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and hindfoot segments and to determine the effects of the relative movements on the injuries and knee joints in ballet dancers. This project also tried to find the differences in the relative movements of foot segments between injured and uninjured groups and link the differences to ankle, foot, and knee injuries. The purposes of this study centered on determining whether the movement pattern of jump landing was related to the previous injuries. The movement pattern was represented by joint angle of lower extremity and landing force.

Materials and Methods

Twenty-two college female ballet students were recruited for this study. The ballet subjects were divided into injured in past year (BI) group and un-injured in past year (BU) group. Each of the BI and BU group had eleven subjects. The injury criteria were the dancers suffered from one or more lower extremity injuries related to the ballet in the past year and the injury influenced or interrupted the dance rehearsal for at least twenty-four hours. The injured history of BI group in the past year was listed in the table 1. The ballet subjects all had the experience of ballet dance at least seven years and wearing hard shoes at least two years. The hard shoes were the specific shoes for ballet dance. The forefoot part of the hard shoes was made of a hard material to support the body weight during pointé. And, the rest part was flexible. All the subjects signed a consent form approved by University IRB. They were informed for the balance and movement tests prior to data collection to have better understanding of the data collection procedure. All of the ballet subjects filled out the self-reported questionnaire about the previous injuries history correlated with the ballet and the training history before assigning group and data collection.

Table 1: Injured history of BI group

Subject Number Injury Side Injury Site

Dominant Ankle sprain

6

Non-dominant No

Dominant Ankle sprain

2

Non-dominant Knee soreness or pain

Dominant Ankle sprain

1

Non-dominant Ankle sprain

Dominant Ankle sprain, knee arthritis 1

Non-dominant Ankle sprain

Dominant Ankle sprain, foot injury 1

Non-dominant Ankle sprain, foot injury

After completing the questionnaire, all of the subjects received physical evaluation. The evaluation form of lower extremity was divided into five parts including: anthropometric data, maximal isometric muscle strength, range of motion, and flexibility test (Table 2). The

maximal isometric muscle strength was determined from manual muscle test with

dynamometer. The range of motion was measured from goniometer. The standing turnout angle was determined from the angle between two feet of turnout position. The sit and reach test represented the distance from middle finger to the great toe. The value of the distance was positive when the middle finger is farther than the great toe and vice versa. In the straight leg raising test, subjects were supine on the bed and passive hip flexion with knee extension was done until knee bending or pelvic rotation. Then, we measured the angle between the

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from the ground. Then, we measured the angle between the shank and the longitudinal line. Table 2: Evaluation form of lower extremity

Anthropometric Data Basic measurement

Standing height(cm), Body weight(kg), Dominant leg Lower extremity (standing position)

Barefoot length and width, Height of the foot arch(cm), Length of tibia and femur(cm), Circumference of leg and thigh(cm)

Maximal Isometric Muscle Strength Ankle joint

Plantarflexors, Dorsiflexors, Evertors, Invertors Knee joint

Flexors, Extensors Hip joint

Extensors, Flexors, Internal rotators, External rotators Range of Motion

Medial longitudinal arch angle, Q-angle, Standing turnout angle, Hallux valgus Joint Motion

Ankle plantarflexion, dorsiflexion, inversion, eversion Knee flexion

Hip extension, internal rotation, external rotation, flexion Flexibility Test

Sit-and-reach test

Shortness of two-joint hip flexors Shortness of one-joint hip flexors Straight-leg-raising test

Ankle flexibility

The testing task was called Sissonné Ferméé. Sissonné Ferméé (Figure 1) is a jumping movement that takes off with separated forward leg and finishes with the later foot gliding along the floor into the demi-plié in the Basic Position Five which represented overlapped feet with the front toes touching the rear heel and vice versa. It can be preceded to any direction. In our study, it was executed in a forward direction and needed to perform with the hard shoes.The execution of Sissonné Ferméé was divided into three phases with four specific time points. Those three phases were the rising, flying and terminal phase in

sequence. Four time points were the start, maximal, impact and end time point. The start time point was the moment the front foot started to move. The maximal time point was the

moment the front foot reached the maximal vertical height. The impact time point was the time the front foot impacted the ground. The end time point was the moment the back foot stopped moving. According to the definitions of these four time points, the first phase was called rising phase, the second phase was called flying phase and the third phase was named terminal phase.

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Figure 1: Sissonné Ferméé.

Starting, maximal, impact and end time points were shown from the left to the right. Three phases were also presented.

A number of 22 reflective makers were attached to subject’s bony landmark of interest. The reflective markers including sacrum, anterior superior iliac spines, thigh, medial and lateral femoral condyles at knee joint line, shank, medial and lateral malleolus, heel, toe between the 2nd and 3rd metatarsals were placed on the bilateral lower extremities to establish the pelvic, thigh, shank, foot coordinate system. However, the relative movement between forefoot and rear foot may be specific and crucial in ballet jump landing. The relative

movement between heel and shank may also explain the precise alignment between foot and shank. The forefoot coordinate system was established by three markers in an equal distance of triangle shape (triad marker). The triad marker was placed on the middle of metatarsal bones and two of them were aligned along the 3rd metatarsal bone. Therefore, we could acquire the plane consisted of the triad marker and paralleled to the metatarsal bones. The Z axis perpendicular to this plane represented the upward direction axis and in consistent with the axis of external and internal rotation. We also had two markers aligned along the 3rd metatarsal bone to create a temporary axis. The cross product of Z axis and temporary axis was the X axis representing the axis of flexion and extension. The cross product of X and Z axis was the axis of abduction and adduction called Y axis. The rear foot coordinate system was established by two markers attached on a rigid straight plate and ankle joint center

(Figure 2). The rigid plate had a rigid hook to the calcaneus. Therefore, these two markers on the rigid plate stood for the movement of the heel and created the Z axis. The line connected the upper marker on the plate and the ankle joint center becoming a temporary axis toward the toe. The cross product of Z axis and temporary axis was the X axis. The cross product of X and Z axis was Y axis. The forefoot and rear foot marker sets were only used on the dominant side. The non-dominant side only established the general foot coordinate system mentioned above. Those kinematic data were collected by Motion Analysis software.

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Figure 2: Forefoot and rear foot marker sets. Results

The courses of joint angles in Sissonné Ferméé were presented in the average of three trials with each subject in BI and BU groups. The time series was normalized to 100 points and divided into three phases as previously described. The joint movement patterns were highly correlated (The Pearson correlation coefficient > 0.7) between BI and BU groups except for the hindfoot to tibia abduction, forefoot to hindfoot abduction and rotation (Figure 3). However, the significant differences in peak angle were found in the ankle and hindfoot to tibia abduction between BI and BU subjects (Table 3). Peak angle of the ankle abduction was significantly higher in the BI group than that in the BU group and the hindfoot to tibia

abduction was on the contrary. No significant difference was found in the range of motion during Sissonné Ferméé (Table 4).

Discussion

The ballet dancers had significantly greater foot width than that of the normal subjects which indicated greater base of support to assist the maintenance of balance. However, the BI dancers still showed the poor balance ability than that of the normal healthy subjects. We may presume the BI dancers had impaired somatosensory due to the injured ankle joint and result in poor balance ability again. The maximal isometric muscle strength of hip and knee flexors showed significantly higher value on dominant side in the BI group than that in the BU group. However, the hip flexors (vastus medialis, vastus lateralis) and knee flexors/hip extensors (hamstring) showed significantly lower muscle effort during the challenging balance movement in the BI dancers which also present poor balance control than that in the BU subjects. This may suggest the BI subjects adopted less efficient strategy to encounter the balance challenges. The ankle dorsiflexion angle of non-dominant side was significantly greater in the BI dancers than that in the normal subjects which may result from the ballet movement of pliés. The plies were performed with bilateral hip external rotation 90 degree and semi-squat or full-squat. It can increase the range of motion in ankle dorsiflexion. However, only the non-dominant side ankle dorsiflexion had significant difference which suggested the originally greater range of motion in the BI dancers than that in the normal subjects. The BI dancers can’t do the same range of motion at the injured side as the

non-dominant side did due to the previous ankle injury and result in no significant difference between BI and normal subjects. Also, the ballet dancers had significantly higher flexibility compared with the normal subjects as expectation. The ballet dancers often complained pain caused from the over normal range motion, such as turn out position and Pointé. However, in this study we didn’t collect enough information to explain the relationship between the over normal range motion and injury history.

The joint movement patterns were highly correlated between BI and BU groups except for the hindfoot to tibia abduction, forefoot to hindfoot abduction and rotation. However, the significant differences of peak angle were found in the ankle and hindfoot to tibia abduction between BI and BU dancers. The difference in ankle abduction was small (BI: 11.9±7.6, BU: 8.1±2.9) which might have no clinical difference. The peak angle of hindfoot to tibia

abduction was significantly greater in the BU group than that in the BI group (BI: 0.6±17.1, BU: 10.4±13.7). Generally, the BU subjects had greater angle of hindfoot to tibia abduction than that of the BI subjects in the course of Sissonné Ferméé.

In view of the movement pattern of jump landing, BI dancers exhibited smaller angle of hindfoot to tibia abduction, and smaller loading rate in the terminal phase during Sissonné Ferméé. During rising phase, BI subjects focused on the raising of the front leg and ignored the stabilization of the rear leg which may cause instability more easily compared with the

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BU subjects

The ground reaction force patterns were highly correlated between BI and BU groups, except for the medial-lateral direction which indicated the different control in medial-lateral direction between BI and BU subjects. However, the medial-lateral difference was small (<0.01body weight) which suggested the little clinical significance. The loading rate of Sissonné Ferméé in the BU group was significantly higher than that in the BI group. The reason might be the BI subjects were afraid to impact the ground with the injured leg after the injury occurred in past one year. This result may explain the change of hindfoot to tibia abduction angle between BI and BU group. Due to the fear, the BI subjects adopt the strategy with less loading which result in less joint angle of hindfoot to tibia abduction.

Limitation

This study was a cross sectional study which could not observe changes occurred before or after the injury took place in past one year in terms of the kinetic or kinematic changes between groups. Long-term follow up may be required to identify the risk factors for the ballet dancers. Generally, large standard deviation of COP results was observed in the BI group. This might be due to the onset time of ankle injury varied during the past year and ballet dancers could not identify the date of injury event specifically.

The role of hip joint in the balance maintaining task should be taken into consideration to get full understanding of balance control in ballet dancing.

Self-evaluation of Project

The project has been completed and now we are working on manuscript writing. Some dancing movements were collected but no significant differences were found in motion patterns among groups. More dancers are needed to find any significance. However, our current findings will still enhance our understanding in motion patterns of ballet dancing and shed lights on injury prevention for ballet dancers. Some difficulties we encountered were (1) difficulty in finding qualified ballet dancers; (2) some markers were blocked during

movements and thus took more time to complete data collection; (3) the budget for

equipment came from two sources at different time: one from NSC (once the grant approval result was known) while the other came from NCKU (need to wait for about 6 months to get the budget) and this made us to get equipment at very late stage.

References

Byhring, S. and K. Bo (2002). "Musculoskeletal injuries in the Norwegian National Ballet: a prospective cohort study." Scand J Med Sci Sports 12(6): 365-70.

Coplan, J. A. (2002). "Ballet dancer's turnout and its relationship to self-reported injury." J Orthop Sports Phys Ther 32(11): 579-84.

Fetzer, G. B. and R. W. Wright (2006). "Metatarsal shaft fractures and fractures of the proximal fifth metatarsal." Clin Sports Med 25(1): 139-50, x.

Garrick, J. G. and R. K. Requa (1993). "Ballet injuries. An analysis of epidemiology and financial outcome." Am J Sports Med 21(4): 586-90.

Hardaker, W. T., Jr. (1989). "Foot and ankle injuries in classical ballet dancers." Orthop Clin North Am 20(4): 621-7.

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Leanderson, J., E. Eriksson, et al. (1996). "Proprioception in classical ballet dancers. A prospective study of the influence of an ankle sprain on proprioception in the ankle joint." Am J Sports Med 24(3): 370-4.

Macintyre, J. and E. Joy (2000). "Foot and ankle injuries in dance." Clin Sports Med 19(2): 351-68.

McGuine, T. A., J. J. Greene, et al. (2000). "Balance as a predictor of ankle injuries in high school basketball players." Clin J Sport Med 10(4): 239-44.

Milan, K. R. (1994). "Injury in ballet: a review of relevant topics for the physical therapist." J Orthop Sports Phys Ther 19(2): 121-9.

Nashner, L. M. and G. McCollum (1985). "The organization of human postural movements: a formal basis and experimental synthesis." Behavioral and brain sciences(Print) 8(1): 135-172.

Negus, V., D. Hopper, et al. (2005). "Associations between turnout and lower extremity injuries in classical ballet dancers." J Orthop Sports Phys Ther 35(5): 307-18. Nilsson, C., J. Leanderson, et al. (2001). "The injury panorama in a Swedish professional

ballet company." Knee Surg Sports Traumatol Arthrosc 9(4): 242-6.

Pecina, M. M. and I. Bojanic (1993). Overuse injuries of the musculoskeletal system. Boca Raton, FL, CRC Press.

Ramel, E. and U. Moritz (1994). "Self-reported musculoskeletal pain and discomfort in professional ballet dancers in Sweden." Scand J Rehabil Med 26(1): 11-6.

Wiesler, E. R., D. M. Hunter, et al. (1996). "Ankle flexibility and injury patterns in dancers." Am J Sports Med 24(6): 754-7.

Winter, D. A., F. Prince, et al. (1996). "Unified theory regarding A/P and M/L balance in quiet stance." J Neurophysiol 75(6): 2334-43.

Winter, D. A., F. Prince, et al. (1993). "Medial-lateral and anterior-posterior motor responses associated with centre of pressure changes in quiet standing." Neurosci Res Commun 12: 141-148.

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Hindfoot to Tibia

-40 -20 0 20 40 0 45 90 Time Cycle (%) (+)A b d . / A d d Uninjured Injured

Hindfoot to Tibia

-40

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Figure 3: The hindfoot to tibia, and forefoot to hindfoot angles during Sissonné Ferméé in the BU group and BI group. Sissonné Ferméé was divided into three phase: rising, flying, and terminal phase.

Forefoot to Hindfoot

-100

-50

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Table 3: Mean (SD) peak joint angle during Sissonné Ferméé (degree)

BU BI Significance

Ankle Flexion 27.5 (6.5) 27.2 (5.1) 0.827 Ankle Abduction 8.1 (2.9) 11.9 (7.6) p<0.05* Ankle External Rotation 14.4 (4.6) 13.8 (10.7) 0.810 Hindfoot to Tibia Flexion 26.4 (10.6) 32.2 (9.9) 0.055 Hindfoot to Tibia Abduction 10.4 (13.7) 0.6 (17.1) p<0.05* Hindfoot to Tibia External Rotation 22.0 (11.2) 20.2 (14.3) 0.630 Forefoot to Hindfoot Flexion 10.8 (11.7) 5.5 (14.0) 0.160 Forefoot to Hindfoot Abduction 18.1 (11.1) 25.0 (13.7) 0.064 Forefoot to Hindfoot External Rotation 9.1 (6.1) 12.0 (15.6) 0.402 *: significant between BI and BU groups

Table 4: Mean (SD) range of motion of joint angle during Sissonné Ferméé (degree)

BU BI Significance Ankle Flexion/Extension 67.5 (8.4) 64.4 (10.1) P=0.248 Ankle Abduction/Adduction 12.0 (5.4) 15.7 (11.9) P=0.175 Ankle External/Internal Rotation 13.7 (3.0) 13.9 (2.8) P=0.859 Hindfoot to Tibia Flexion/Extension 43.9 (13.2) 49.2 (13.5) P=0.176 Hindfoot to Tibia Abduction/Adduction 18.9 (10.5) 19.1 (10.7) P=0.933 Hindfoot to Tibia External/Internal Rotation 18.4 (5.0) 16.1 (5.0) P=0.118 Forefoot to Hindfoot Flexion/Extension 51.5 (15.4) 45.4 (9.8) P=0.112 Forefoot to Hindfoot Abduction/Adduction 25.2 (17.2) 19.2 (9.8) P=0.144 Forefoot to Hindfoot External/Internal Rotation 19.5 (8.6) 16.5 (6.0) P=0.164

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