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

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1 Correlation between Lower Extremity Biomechanical Parameters and Injuries in Dancers: Longitudinal and Biomechanical Perspectives Cheng-Feng Lin, PhD Grant Number: NSC B 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 1% to 3% 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 1

2 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: history of BI group Subject Number Injury Side Injury Site 6 Dominant Ankle sprain Non-dominant No 2 Dominant Ankle sprain Non-dominant Knee soreness or pain 1 Dominant Ankle sprain Non-dominant Ankle sprain 1 Dominant Ankle sprain, knee arthritis Non-dominant Ankle sprain 1 Dominant Ankle sprain, foot injury 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 thigh and the original horizontal line as a straight leg raising angle. Ankle flexibility was determined from the position of hip extension, knee extension and ankle dorsiflexion with foot flat on the ground. The subjects tried to move the shank forward without leaving the foot 2

3 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. 3

4 Rising Phase Flying Phase Terminal 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 2 nd and 3 rd 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 3 rd 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 3 rd 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. 4

5 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 1 points and divided into three phases as previously described. The joint movement patterns were highly correlated (The Pearson correlation coefficient >.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 9 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:.6±17.1, BU: 1.4±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 5

6 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 (<.1body 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 (22). "Musculoskeletal injuries in the Norwegian National Ballet: a prospective cohort study." Scand J Med Sci Sports 12(6): Coplan, J. A. (22). "Ballet dancer's turnout and its relationship to self-reported injury." J Orthop Sports Phys Ther 32(11): Fetzer, G. B. and R. W. Wright (26). "Metatarsal shaft fractures and fractures of the proximal fifth metatarsal." Clin Sports Med 25(1): 139-5, x. Garrick, J. G. and R. K. Requa (1993). "Ballet injuries. An analysis of epidemiology and financial outcome." Am J Sports Med 21(4): Hardaker, W. T., Jr. (1989). "Foot and ankle injuries in classical ballet dancers." Orthop Clin North Am 2(4): Harrington, T., K. J. Crichton, et al. (1993). "Overuse ballet injury of the base of the second metatarsal. A diagnostic problem." Am J Sports Med 21(4): Hrysomallis, C. (27). "Relationship between balance ability, training and sports injury risk." Sports Med 37(6):

7 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): Macintyre, J. and E. Joy (2). "Foot and ankle injuries in dance." Clin Sports Med 19(2): McGuine, T. A., J. J. Greene, et al. (2). "Balance as a predictor of ankle injuries in high school basketball players." Clin J Sport Med 1(4): Milan, K. R. (1994). "Injury in ballet: a review of relevant topics for the physical therapist." J Orthop Sports Phys Ther 19(2): 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): Negus, V., D. Hopper, et al. (25). "Associations between turnout and lower extremity injuries in classical ballet dancers." J Orthop Sports Phys Ther 35(5): Nilsson, C., J. Leanderson, et al. (21). "The injury panorama in a Swedish professional ballet company." Knee Surg Sports Traumatol Arthrosc 9(4): 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): Wiesler, E. R., D. M. Hunter, et al. (1996). "Ankle flexibility and injury patterns in dancers." Am J Sports Med 24(6): Winter, D. A., F. Prince, et al. (1996). "Unified theory regarding A/P and M/L balance in quiet stance." J Neurophysiol 75(6): 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:

8 (+)Flex. / Ext Rising Phase Flying Phase Terminal Phase (+)Abd. / Add (+)Ext. / Int. Rot

9 (+)Flex. / Ext Rising Phase Flying Phase Terminal Phase (+)Abd. / Add (+)Ext. / Int. Rot 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. 9

10 Table 3: Mean (SD) peak joint angle during Sissonné Ferméé BU BI Significance Ankle Flexion 27.5 (6.5) 27.2 (5.1).827 Ankle Abduction 8.1 (2.9) 11.9 (7.6) p<.5* Ankle External Rotation 14.4 (4.6) 13.8 (1.7).81 Flexion 26.4 (1.6) 32.2 (9.9).55 Abduction 1.4 (13.7).6 (17.1) p<.5* External Rotation 22. (11.2) 2.2 (14.3).63 Flexion 1.8 (11.7) 5.5 (14.).16 Abduction 18.1 (11.1) 25. (13.7).64 External Rotation 9.1 (6.1) 12. (15.6).42 *: significant between BI and BU groups Table 4: Mean (SD) range of motion of joint angle during Sissonné Ferméé BU BI Significance Ankle 67.5 (8.4) 64.4 (1.1) P=.248 Flexion/Extension Ankle 12. (5.4) 15.7 (11.9) P=.175 Abduction/Adduction Ankle 13.7 (3.) 13.9 (2.8) P=.859 External/Internal Rotation 43.9 (13.2) 49.2 (13.5) P=.176 Flexion/Extension 18.9 (1.5) 19.1 (1.7) P=.933 Abduction/Adduction 18.4 (5.) 16.1 (5.) P=.118 External/Internal Rotation 51.5 (15.4) 45.4 (9.8) P=.112 Flexion/Extension 25.2 (17.2) 19.2 (9.8) P=.144 Abduction/Adduction External/Internal Rotation 19.5 (8.6) 16.5 (6.) P=.164 1