Musculoskeletal injuries are considered to be very common among dancers. Incidence of injury varies from 17% to 95% (Bronner et al., 2003). It has also been stated that injury incidence is 4.4 per 1000 hours, and 6.8 injuries per dancer within a year (Allen et al., 2012). Overuse injuries are predominant, such as tendinosis, stress fractures and apophyseal injuries that manifest at the lower limb, hip and spine (Allen et al., 2012; Hincapie et al., 2008; Jacobs et al., 2012; Motta-Valencia, 2006; Steinberg et al., 2013). Thus, mastering dance technique requires repetitive physical loading that may exceed the limits of anatomical and physiological capabilities, and lead to injuries. Further understanding of the biomechanics of dance is essential to identify the specific musculoskeletal demands placed on the body and to uncover pathomechanics that may lead to injury (Motta-Valencia, 2006). To reduce both the injury incidence and prevalence it is crucial to enhance effective injury prevention strategies, rehabilitation, and biomechanically safe and efficient technique training practices as well dance pedagogy.
Research to date in dance biomechanics has focused on impact (such as jumps) and high pressure (e.g. pirouettes) movements as well as describing typical ballet movements. Other areas of interest include point shoes, motor control, dancing regimens, dance floor, motor skills of novice and professional dancers, and differences between barre work and center floor (Kadel and Couillandre, 2007; Koutedakis et al., 2008; Krasnow et al. 2011; Krasnow, 2012; Laws, 1985; Ward 2012). To our knowledge, there is little research on the effect of the commonly found apophyseal injury on dancer's movement patterns and the challenges these injuries may pose to technical demands of dance and dance pedagogy. In the present case report, the aim is to compare the kinematics of the symptomatic (i.e. ischial apophyseal symptoms) and contralateral lower limbs, as well as associated reported pain of a ballet dancer with a left ischial apophysitis during ballet exercises. The purpose of this study is to inform dancers, their teachers and health professionals about movement changes that may present with this common but complex and underreported injury in a dance context.
A 27-year-old professional male classical dancer with left ischial apophysitis volunteered to participate in the study. The diagnosis was made by a specialist physiotherapist with relevant PhD, supported by clinical history, physical assessment, MRI findings and medical specialist's (sports physician) opinion. The participant also presented with concomitant, but less symptomatic, left heel and achilles pain, and longstanding right groin pain primarily at the origin of adductor muscles (i.e. right pubis and the symphysis pubis).
The pain in the ischial tuberosity had been ongoing for about 6-8 months, and was described as vague. Self-reported pain via numeric rating scale (NRS; self-reported pain score in integers: 0-10) (Ferreira-Valente et al., 2011; Jensen et al., 1986) was usually 3, and 6 on its highest. The pain was aggravated mainly by stretching and during rapid movements. The participant reported that both the injuries at the pelvis had been treated with relative rest to relieve the pain (e.g. modification in training load and limitation of pain aggravating activities), therapeutic exercises, ice and ultrasound. The dancer stated that the injuries restricted range of motion (ROM) in general.
Data collection took place on an indoor synthetic track surface in the Motion Laboratory at the University of the Sunshine Coast (Australia). Prior to the testing, the participant was provided with a Research Project Information Sheet and given the opportunity to ask questions about the test protocols before signing a consent form. The participant also completed a medical screening questionnaire prior to the test. The study was approved by the institutional Human Research Ethics Committee.
Three-dimensional (3-D) kinematic data were collected at a sampling rate of 500 Hz, with a nine-camera motion analysis system (Qualysis Motion Capture System; Qualysis AB, Gothenburg, Sweden). Kinetic data (ground reaction force, GRF, x, y, z) were recorded via two force plates (Bertec; Bertec Corporation, Ohio, USA), sampling at 2000 Hz. Anthropometric parameters (including height and weight) were also measured.
A total of 40 individual retro-reflective markers (16 mm) and four clusters (4 markers each) were attached at specific anatomical locations on the head, upper and lower limbs, and trunk according to the protocol of the University of the Sunshine Coast. Specific marker sites were right and left temples, right and left zygomatic bones, right and left lateral sides of acromions, manubrium of sternum and inferior part of sternum (sternal body), 7th cervical spinous process (C7), 6th and 12th thoracic spinous process (T6, T12), 2nd and 4th lumbar spinous process (L2, L4), sacrum (S2), right and left posterior and anterior superior iliac spines, both the greater trochanters, clusters of markers for right and left thigh segments, both the lateral and medial femoral epicondyles in the right and left, right and left lateral and medial sides of tibial condyles, right and left tibial tuberosities, cluster of markers for shanks, right and left malleoli, both the heels (LHEEL, RHEEL) and 1st and 5th metatarsal bones in the right and left. (Bishop and Kerr, 2010) The acromion landmark was modified from...