Dance Medicine in The Netherlands: An update from dance related research in the Medical Centre for Dancers and MusiciansAuteur: Anandi van Loon-Felter
Dit artikel is eerder verschenen in: Koolen, H., J. Naafs, R. Naber, L. Wildschut (eds.) (2015), Danswetenschap in Nederland – Deel 8. Vereniging voor Dansonderzoek, pp.40-50.
Medical Centre for Dancers and Musicians
The Medical Centre for Dancers and Musicians (MCDM) offers specialised medical care for dancers and musicians. The goal is maintaining dancers’ and musicians’ health by the prevention, diagnosis and treatment of injuries and conditions arising from dancing or making music. But the care also extends to other injuries that may hamper performance. The MCDM cares for both professionals and amateurs. The treatment is primarily for injuries of the locomotor apparatus. The doctors currently working in the MCDM are Boni Rietveld, orthopaedic surgeon, and two medical residents, Anandi van Loon-Felter and Fleur Hagemans.
The centre is part of the Medisch Centrum Haaglanden (MCH) in The Hague and its members contribute at national and international levels to the development of specialised medical care for dancers and musicians. This is accomplished by active involvement with the Dutch Performing Arts Medicine Association (NVDMG, www.nvdmg.org), with other national Performing Arts Medicine Associations and with the International Association for Dance Medicine and Science (IADMS).
Dancers and musicians (professionals and amateurs) together constitute approximately 19% of the Dutch population. Because of their high and specific physical demands, dancers are vulnerable for injuries. Long and hard exercise and training are required for artistic top performances under the scrutiny of the audience and the stress of the media. Dance requires maximal propriocepsis and coordination combined with stamina and perseverance.
The goal of this article is to give a brief summary of clinical research concerning the health of dancers that has been executed in the MCDM. First, research is described about health care seeking behaviour and perceptions among dancers in the Netherlands. Secondly a description is given for the need of a dance specific rehabilitation program. After that follows a section, concerning hip problems and common foot and ankle problems in dancers: rolling in of the feet (hyperpronation) and use of inlays, tarsal coalition, accessory navicular, Freiberg disease and dancers heel.
Health care seeking behavior and perceptions of the medical profession among pre- and post-retirement age Dutch dancers
A cross-sectional, descriptive survey and a medical chart review of 154 pre and post-retirement age (> 35 years) injured dancers living in the Netherlands were performed. The purpose was to examine dancers’ health care seeking behavior and perceptions of the medical profession in context of the current health care system in The Netherlands, which includes both universal access and expertise in performing arts medicine. No logistical or perceptual restrictions to health care were reported by the dancers in this study. Only three younger dancers (< 35 years) lacked a primary care physician. No dancer reported monetary or insurance hindrances to acquiring an appointment or fear of going to the doctor. A small percentage of the younger group (18%), but none of the older dancers, reported that they felt the doctor would not understand them. Dancers in both age groups most often sought first treatment from either a physiotherapist (36% to 40%) or a medical doctor (38.8% to 40.8%). When a physician was not consulted first, the primary reason was that dancers had already seen a physiotherapist and thought this treatment was sufficient. Approximately one-third of the dancers expected their medical problem to go away on its own. The majority of dancers were satisfied or very satisfied with their medical treatment prior to presenting to the dance medicine specialist (67% older dancers, 52% younger). Nearly every dancer was satisfied or very satisfied after treatment by the specialist (100% older dancers, 93% younger dancers), and moderately or completely confident of full recovery (80%, each group). Differences in older and younger dancers’ perceptions and behaviors were nevertheless found. Older dancers were significantly more likely to continue to dance when injured than younger dancers (100% versus 82%), although pain and perceived level of artistic hindrance were similar between the groups at first presentation to a dance medicine clinic. Average time to seek treatment from a medical doctor was four times longer among older than younger dancers (8.4 versus 2.1 months, respectively), and older dancers had less confidence in full recovery at first visit (40% versus 61%).
Thus, the medical system of The Netherlands is one that confers improved health care access and perceptions of the medical profession among dancers, yet there remain areas to be addressed in terms of equalization of health care delivery.
Dance-specific, graded rehabilitation: advice, principles, and schedule for the general practitioner
(Air & Rietveld, 2008)
Dancers frequently experience lower-extremity injuries which require dance activity restriction, if not full time off, or surgery. Recovering dancers are frequently over-eager to return to dance, but engaging in too high an activity level too soon can be detrimental. Currently, there are no formal guidelines for general physicians about advising injured or postoperative dancer-patients about when or how to return to dance activity. Socioeconomic hurdles further prohibit many dancers from seeking rehabilitative services from a dance physical therapist. Therefore, there is a need for physician education about general dance-rehabilitation principles, as well as access to a dance-specific structured rehabilitation program. The MCDM developed a rehabilitation advice and program for injured or postoperative dancer-patients with lower-extremity injuries.
Femuro-Acetabular Impingement in Dancers, the correlation between clinical and radiographic findings
(Chow & Rietveld, research in progress)
Femuro-Acetabular Impingement (FAI) is a pathologic hip condition which occurs when there’s an abutment (contact) between the proximal femur (thigh bone) and acetabulum (the cup-shaped socket that receives the head of the thigh bone). There are four different types of FAI: pincer type, CAM type, mixed type (see image 1) and FAI caused by microtraumata in hyper mobile patients.
Image 1: Different types of FAI
Patients with FAI will have an increasingly reduced range of motion and motion dependent, deep central located, anterior hip pain, which is worse in hipflexion. FAI will therefore be very disabling for a (classical) dancer.
Even though a lot is known about the etiology of FAI and how to recognize it on plain x-rays and Magnetic Resonance Imaging (MRI), less is known about the prevalence of FAI in dancers. Besides that, from clinical experience in MCDM it is known that dancers can have the typical symptoms of FAI without having the radiographic features of it, with the expectation that they have FAI caused by microtraumata. Until now, nothing is known about these patients and the best treatment for them.
The aim of this retrospective study is to analyze the prevalence of hip complaints in dancers, to see what the patient characteristics are for having hip complaints, what the symptoms exactly are, the range of motion of the hips at the moment of presentation and correlate them to the plain x-rays, with or without pathologic features, of the dancer. In the end we hope to conclude that there are a lot of dancers who don’t have pathologic findings on plain x-rays, but do have the typical symptoms of FAI, and that they should be treated the same as someone with radiographic features of FAI. This research is currently being executed.
Foot and ankle problems
Most common problems in dancers are in the lower extremity and especially in the foot and ankle. An important group of common dance injuries form the causes of limited and painful ‘relevé’ in dancers, like ‘dancer’s heel’ (posterior ankle impingement syndrome), ‘dancer’s tendinitis’ (tenovaginitis of the m.flexor hallucis longus), hallux rigidus and more rare, Freiberg’s disease. Because foot and ankle problems are so common and can be very restricting for a dancer, special attention is given to this.
Hyperpronation in dancers, incidence and relation to calcaneal angle
(Nowacki, Air & Rietveld, 2012)
Rolling in of the feet, or hyperpronation, is a common finding when examining the dancer-patient and is thought to be implicated in several dance-related injuries. Little is known about the incidence of hyperpronation-related symptoms in dancers. Additionally, there is no current easy method for estimating the degree of hyperpronation. This study was designed to investigate the incidence of symptoms related to foot hyperpronation in dancer-patients and to evaluate the potential correlation between the patient’s calcaneal angle and severity of hyperpronation. The calcaneus is the heel bone and the calcaneal angle is the angle the calcaneus has in relation to the lower leg (see image 2).
Image 2: Measuring the calcaneal angle. The calcaneal angle is the angle the calcaneus (heelbone) has in relation to the lower leg
A retrospective study of 2.427 dancers’ charts over the past 6 years was undertaken to identify dancers who presented with complaints of the musculoskeletal system or problems related to hyperpronation. Physical exam data and diagnoses were collected. Among 24 new dancer-patients presenting
with hyperpronation-related symptoms, the calcaneal angle was measured and correlated with a clinical grading scale. Per chart review, the incidence of symptomatic hyperpronation resulting in prescription for orthotics or inlays was 30% (739 dancers out of 2.427). The most common related diagnosis was patello-femoral (knee) pain (10%). Clinical severity of hyperpronation was linearly related to the calcaneal angle. The calcaneal angles among mild, moderate, and severe hyperpronators differed significantly.
It was concluded that measuring the calcaneal angle may be a useful adjunct to the other clinical grading scale for grading the clinical severity of a dancer’s hyperpronation. Healthcare providers working with dancers should be aware of the presence of hyperpronation, its relation to compensatory turnout techniques, and association with injuries in the foot, ankle, knee, hip, and low back. A standard, time-efficient method of measuring and grading hyperpronation is still needed.
Use and effectiveness of orthotics in hyperpronated dancers
(Nowacki, Air & Rietveld, 2013)
Hyperpronation or rolling in is a common foot problem in dancers as described in our previous article. The aim of this study was to investigate the usage and effectiveness of orthotics or inlays (see image 3) in the management of symptomatic hyperpronation among dancers.
Image 3: The use of orthotics or inlays in the management of symptomatic hyperpronation among dancers
A prospective cohort study of all dancer-patients in the Medical Centre for Dancers and Musicians who were prescribed orthotics for new symptoms related to hyperpronation between July 2008 and January 2009 was conducted.
In this group, the longitudinal medial arch angle of the foot was measured by the foot build registration system (FBRS), both barefoot and while wearing the orthotics. In addition, patients filled out questionnaires addressing perceived effectiveness of the orthotics for pain reduction and dance ability, among other items. A second retrospective study was conducted in order to obtain longitudinal data regarding dancers’ compliance with, and subjective evaluation of, wearing orthotics over the preceding 6 years. Among participating dancers who met criteria for the prospective (N = 24) or retrospective (N = 81) aspects of the study (total N = 105), 67% wore orthotics at the time of follow-up. The average compliance in usage was 6 days per week and 7.5 hours per day. The average rate of satisfaction was 67.9 on the 100 mm Visual Analogue Scale (VAS) (± 26.5), average degree of relief in symptoms was 58.3 (± 28.3), and self-reported degree of improvement in dance ability was 45.7 (± 27.9). There was a significant decrease in pain from the day of orthotics prescription to follow-up (25.9%, or 18.9 mm decrease on the VAS) in the prospective group (N = 24). Orthotics were found to decrease the medial longitudinal arch angle significantly during static stance with the orthotic in place.
It is concluded that the dancers in this study demonstrated a high rate of compliance in obtaining and wearing their orthotics and experienced a significant decrease in pain.
Tarsal coalitions in dancers: presentation, treatment and outcome. A retrospective case series
(Rietveld & Van Loon-Felter, submitted for publication)
A coalition, or bar, is a bony, cartilaginous or fibrous connection between two or more bones. A tarsal coalition can occur between any of the seven tarsal bones (foot). Most common are the connection between the heelbone (calcaneus) and navicular bone (calcaneo-navicular coalition) and the connection between the calcaneus and talus (talo-calcaneal (subtalar) coalition) (see image 4).
Image 4: A CT-scan of two feet, one with a connection between the calcaneus and the talus (talo-calcaneal coalition)
Tarsal coalitions are a rare entity in dancers and may easily be missed, unless specifically looked for. We describe the presentation, types, and treatment of tarsal coalitions, in six female dancers and one male dancer (age 10 to 26 years) diagnosed between 2008 and 2011. The presenting complaints were ankle pain, a sense of instability, a painfree foot deformity, problems with toe stand (relevé or demi-pointe), and pointing the feet both with and without point shoes. Physical examination revealed a stiff subtalar joint. Three patients with a coalition between calcaneus and os naviculare were treated successfully by resection of the coalition. Four patients with a coalition between calcaneus and talus were conservatively treated with a custom made insole for activities in daily life, in combination with strengthening exercises of the ankle muscles. Three of these four dancers were able to continue their dancing career with only minor limitations.
In conclusion, six out of seven dancers with a tarsal coalition were able to continue their dancing career. Treatment in dancers depends on the type and extent of the coalition: in calcaneo-navicular coalition early resection of the “bar” is the treatment of choice. In our opinion the only option for talo-calcaneal coalition in dancers is conservative treatment.
Surgical treatment of the accessory navicular (os tibiale externum) in dancers. A retrospective case series.
(Diemer & Rietveld, submitted for publication)
The accessory navicular, or os tibiale externum, is an accessory bone on the medial side of the foot. It can cause foot pain and a limited and painful relevé in dancers. There are different surgical procedures. Due to fast rehabilitation possibilities, the MCDM has chosen the excision of the bone without tendon transplantation. The results of this procedure in a case series are described. This is the first report on operative treatment of an accessory navicular in dancers.
Six dancers (ten feet) were treated in the MCDM for a symptomatic accessory navicular. Five of them (eight feet) underwent surgery. Two patients had an unilateral symptomatic accessory navicular, three were operated bilaterally (at the same time). See image 5 for the pre- and postoperative radiographs.
Image 5: On the left two feet with bilaterally an os tibiale externum. On the right the radiographs of these two feet postoperative (exicion of the bones)
All five operated dancers (eight feet, mean follow up 4.7 years) had an excellent result, given the fact that they fully resumed their professional dance activities. One patient stopped dancing for other reasons and became symptom free without further (surgical) treatment.
Although no firm conclusions can be drawn from a retrospective case series and other treatment modalities were not considered, simple excision of a symptomatic accessory navicular seems to be a good choice in dancers.
Freiberg’s disease as a rare cause of limited and painful relevé in dancers
(Air & Rietveld, 2010)
Freiberg’s disease, named after Alfred H. Freiberg who first described it, or osteonecrosis of one of the bones in the foot (the second metatarsal head), is an uncommon cause of forefoot pain that can severely limit a dancer’s relevé. Dancers may be predisposed to the condition due to repetitive microtrauma to the ball of the foot during routine dance movements. Freiberg’s disease is diagnosed by history, physical examination, and plain film radiographs. Conservative treatment in dancers is disappointing, and surgical options fail to produce uniformly good results. Previously published reports of successful surgical outcomes would, for a dancer, result in an unacceptable loss of dorsiflexion of the big toe (MTP joint).
This first case report of Freiberg’s disease in a dancer serves to discuss the orthopaedic and artistic implications of managing the disease in a young, active, adolescent dancer. A new surgical treatment involving modification of Mann’s cheilectomy, normally used for a stiff big toe (hallux rigidus), is presented. The operation corrected the patient’s pain, completely normalized the aberrant relevé, allowed her to resume dance training within three weeks, and return to full dance activity within three months.
Dancers’ heel and dancers’ tendonitis: open versus endoscopic approach.
A retrospective cohort study and review of the literature
(Rietveld & Hagemans, submitted for publication)
‘Dancers’ Heel’, also known as ‘Posterior Ankle Impingement Syndrome’ (PAIS) is a painful, limited plantar flexion of the ankle joint (pointe) due to soft tissue impingement or a bony impediment, often coinciding with ‘Dancers’ Tendonitis’ of the m. flexor hallucis longus (bender of the big toe). The bony impediment is often an os trigonum (see image 6).
Image 6: Os trigonum, causing a Dancers’ Heel or Posterior Ankle Impingement Syndrome
In dancers the presenting complaint is usually a limited and painful relevé. In persistent complaints the bony impediment is removed and/or the tunnel of the m. flexor hallucis longus tendon released. In 2000 an endoscopic approach for this condition was introduced. Reviewing the literature we found ample information on Posterior Ankle Impingement Syndrome, regarding its characteristics, diagnosis and (operative) treatment. We are not aware of any study comparing the results of the open and the posterior endoscopic approach, neither in dancers, nor in non-dancers.
Hypothesis: this novel endoscopic approach was adopted by the first author in 2002, hypothesising that the endoscopic approach in dancers would be superior to the open technique. To test this hypothesis we performed a retrospective cohort study. We compared 20 open procedures with 19 endoscopic procedures in dancers only. The average follow-up was 10.2 years for the open and 1.9 years for the endoscopic group. The outcomes were reviewed by physical examination, reviewing radiographs, clinical evaluation and a questionnaire.
The clinical results in the open group were: 18 excellent (90%), 1 good, 1 poor. In the endoscopic group: 13 excellent (68%), 3 good, 2 moderate, 1 poor. The open group returned to dance earlier. The direct postoperative morbidity in the endoscopic group was less favourable.
What this study adds to existing knowledge: Although the small group of patients and the retrospective character of our study do not allow firm conclusions, the results of endoscopic operations are not always superior to open procedures. The open approach is slightly better than the endoscopic approach in the surgical treatment of ‘dancers’ heel’ and ‘dancers’ tendonitis. As a result of this study in the MCDM, we abandoned the endoscopic approach and returned to the traditional open procedure.
Dancer’s heel and dancer’s tendonitis: results of open surgery
(Haitjema & Rietveld, submitted for publication)
27% of injuries in dancers of all ages are ankle injuries. Posterior impingement of the ankle and tendonitis of the flexor hallucis longus tendon in the ankle account for most of them. In older dancers the percentage of ankle injuries is only 3%. This may be due to the fact that ‘dancer’s heel’ and ‘dancer’s tendonitis’ are younger dancers’ injuries and their operative treatment is highly successful. The body is the dancer’s instrument and for professional dancers their source of income. Therefore it is not only important to treat the injury properly, but also to limit rehabilitation time. As described above, endoscopic technique for dancer’s heel and dancer’s tendonitis has been popularized but it is unclear which approach is more favourable. Hence it is important to describe the results of the ‘traditional’ open approach, to set the goals for orthopaedic surgeons that are operating endoscopically.
The objective is to describe the characteristics and surgical outcome of a dance population treated by open surgery for dancer’s heel and/or dancer’s tendonitis by one orthopaedic surgeon in the MCDM between 1989 and 2010. Clinical data were extracted from clinical files and operative reports. Success rate was defined as a patient satisfaction score ranging from 1-5 (1: terrible – 5: excellent) extracted from the clinical files at the date of discharge.
Results: Included were 127 ankles (80% female), of which 43 (34%) were for posterior impingement of the ankle (all with a bony impediment), 42 (33%) for tendonitis of the flexor hallucis longus tendon and 42 (33%) for both, all treated by open surgery. Median age at presentation was 20 year, 80% was a professional dance student or had finished a professional dance education. In 66% surgery via a medial approach was used, only in isolated cases of posterior impingement a lateral approach was used. Median rehabilitation time was 6 months. Dancers operated on by a lateral approach had a significantly shorter rehabilitation time. There were no major complications: one case of transient CRPS (formaly known as dystrophia), six cases (all medial approaches) of transient nerve damage (neurapraxia) and two superficial infections. 91.8% of the outcomes was rated as ‘good’ (4) or ‘excellent’ (5). There was no difference in long-term outcome between the lateral and medial approach. Outcomes of treatment by open surgery for these diagnoses have not been described before in such a large consecutive number of dancers.
In conclusion, open surgery for dancer’s heel and dancer’s tendonitis has a very high success rate (91.8%) with a short rehabilitation time (6 months) and therefore can be considered the ‘gold standard’ approach.
To conclude, lower extremity, especially hip-, foot- and ankle problems in dancers are very common and thorough analysing and knowledge of these problems are mandatory for a doctor treating dancers with problems of the locomotor apparatus. The field of dance medicine and science is still a relatively young one compared to other fields of research such as orthopaedics or sports medicine. Nonetheless, it is important to practice evidence based medicine and in order to do so, research is mandatory. Not only in more common problems, but also in the more rare causes. For these rare causes case reports or case series are often used. Case reports are sometimes placed on the foot of the hierarchy of clinical evidence given their intrinsic methodological limitations, however these case reports are the start of more research. In other, more common problems, randomised controlled trials are considered to be the top of the hierarchy of clinical evidence. However, large trials are difficult to execute since there usually are not enough dancers with the same problem to combine in a clinical trial during a set period. Because of this reason most research performed in the MCDM is retrospective. In view of this, to perform prospective studies and have enough participants to gain more statistical power, international collaboration might be required.
An example of how evidence based practice is used in our clinic, is the traditional surgical treatment in dancers with dancer’s heel and dancer’s tendinitis. This operation corrected the patient’s pain, completely normalized the aberrant relevé, allowed resume to dance training within three weeks, and return to full dance activity within three months. As a result of these studies in the MCDM, we abandoned the endoscopic approach and returned to the traditional open procedure.
Air, M.E. and A.B.M. Rietveld. (2008). Dance-specific, Graded Rehabilitation: Advice, Principles, and Schedule for the General Practitioner.
Medical Problems of Performing Artists, Volume 23 (3), pp. 114-119
Air, M. E. (2009). Health care seeking behavior and perceptions of the medical profession among pre- and post-retirement age Dutch dancers.
Journal of Dance Medicine & Science, Volume 13 (2), pp. 42-50
Air, M.E. and A.B.M. Rietveld.(2010). Freiberg’s disease as a rare cause of limited and painful relevé in dancers. Journal of Dance Medicine & Science, Volume 14 (1), pp. 32-6
Diemer W. and A.B.M. Rietveld. (2014). Surgical treatment of the accessory navicular (os tibiale externum) in dancers. A retrospective case series.
Submitted for publication
Haitjema S. and A.B.M. Rietveld. (2014). Dancer’s heel and Dancer’s tendonitis: Results of open surgery.
Submitted for publication
Nowacki R.M., M.E. Air and A.B.M. Rietveld. (2012). Hyperpronation in dancers, incidence and relation to calcaneal angle.
Journal of Dance Medicine & Science, Volume 16 (3), pp. 126-132
Nowacki R.M., M.E. Air and A.B.M. Rietveld. (2013). Use and effectiveness of orthotics in hyperpronated dancers. Journal of Dance Medicine & Science, Volume 17 (1), pp. 3-10
Rietveld A.B.M. and F.M.T. Hagemans. (2014). Dancers’ Heel & Dancers’ Tendonitis: Open versus endoscopic approach.A retrospective cohort study and review of the literature.
Submitted for publication in Journal of Dance Medicine and Science
Rietveld, A.B.M and A.E. van Loon-Felter. (2014). Tarsal coalitions in dancers: presentation, treatment and outcome. A retrospective case series.
Submitted for publication in Journal of Dance Medicine and Science
Postscript by Anandi van Loon-Felter (May 2019)
Dance Medicine in The Netherlands: An update from dance related research in the Medical Centre for Dancers and Musicians
Medical Centre for Dancers and Musicians: since october 2018 the Medical Centre for Dancers and Musicians (MCDM) is led by a new team of medical specialists: Liesbeth Lim, sports physician, Riekje Kattenbusch and Anandi van Loon-Felter both physiatrist. Dr. Boni Rietveld has retired after he had founded the MCDM in 1993. He has worked here for 25 years.
The research that has been described in the article in Danswetenschap in Nederland in 2015 is still valid. Some of the articles were submitted for publication at the time. All of these articles have now been published in scientific research. Dr. Rietveld has finished his Phd on a painfull and limited relevé in 2017.
- Air, M. E. (2009). Health care seeking behavior and perceptions of the medical profession among pre- and post-retirement age Dutch dancers.
- Journal of Dance Medicine & Science, Volume 13, Number 2, pp. 42-50
- Air, M.E., Rietveld, A.B.M. (2008). Dance-specific, Graded Rehabilitation: Advice, Principles, and Schedule for the General Practitioner. Medical Problems of Performing Artists, Volume 23, Number 3, pp. 114-119
- Air, M.E., Rietveld, A.B.M. (2010). Freiberg's disease as a rare cause of limited and painful relevé in dancers. Journal of Dance Medicine & Science, Volume 14, Number 1, pp 32-6
- Diemer W., Rietveld A.B.M. (2014). Surgical treatment of the accessory navicular (os tibiale externum) in dancers. A retrospective case series.
- Journal of Dance Medicine & Science, Volume 20, Number 3, pp 103-8
- Haitjema S., Rietveld A.B.M. (2014). Posterior Ankle Impingement Syndrome and M. Flexor Hallucis Longus Tendinopathy in Dancers Results of Open Surgery. Journal of Dance Medicine & Science, Volume 22, Number 1, pp 3-10
- Nowacki R.M., Air, M.E., Rietveld A.B.M. (2012). Hyperpronation in dancers, incidence and relation to calcaneal angle. Journal of Dance Medicine & Science, Volume 16, Number 3, pp. 126-132
- Nowacki R.M., Air, M.E., Rietveld A.B.M. (2013). Use and effectiveness of orthotics in hyperpronated dancers. Journal of Dance Medicine & Science, Volume 17, Number 1, pp. 3-10
- Rietveld A.B.M., Hagemans F.M.T. (2014). Operative Treatment of Posterior Ankle Impingement Syndrome and Flexor Hallucis Longus Tendinopathy in Dancers Open Versus Endoscopic Approach. Journal of Dance Medicine & Science, Volume 22, Number 1, pp. 11-18
- Rietveld, A.B.M, Loon-Felter A.E. van (2014). Tarsal coalitions in dancers: presentation, treatment and outcome. A retrospective case series.
- Journal of Dance Medicine & Science, Volume 20, Number 4, pp. 143-150