Pointe Shoes Complicate Biomechanics of Ballet

Pointe shoes complicate biomechanics of ballet

LERMagazine April 2010

7

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Pointe shoes, which elongate a dancer’s legs and accentuate the beauty of classical ballet technique, come with their own set of biomechanical principles—and their own set of risk factors for lower extremity injury.

bySelina Shah, MD

Ballet has intrigued audiences around the world for centuries with its combination of athleticism and elegance. This Western classical dance form originated in aristocratic Italy in the fifteenth century.1 Ballet was later introduced in France, where it gained popularity under the rule of Louis XIV after he established the first school of dance, L’Academie Royal de la Danse, in 1661.1,2 Pierre Buchamps, the king’s choreographer, refined the five basic positions of dance and the concept of turnout (external rotation of the feet to an ideal 180o), which form the basis of dance today (Figure 1).3 George Balanchine is credited with bringing ballet to America centuries later when he opened The School of American Ballet in New York City in 1934.1

Of all of the dance forms, ballet is perhaps the most mystifying because the professional ballerinas perform en pointe, French for “on pointe” (Figure 2), or on the tips of the toes. Generally, men do not perform on pointe. However, at least two companies of all male ballet dancers have performed traditionally female roles wearing tutus and pointe shoes, the St. Petersburg National Male Ballet and Les Ballet Trockadero de Monte Carlo.

The idea of dancing on the toe tips may date back to 1799 when Charles Didelot invented a flying machine that allowed actors and dancers to take off and land from the tips of their toes. Sparse records indicate that dancing on pointe originates from either England or France between 1815 and 1835.2,4 The first definitive records are from 1832 when ballerina Marie Taglioni danced on pointe during the first performance of La Sylphide in Paris and AmaliaBrugnoli danced on pointe in London.2,4 The first known turn performed in pointe shoes was in 1833 by Pauline Montessu in Paris.4

Pointe Shoes

Figure 1: The five basic positions of dance. A. First position B. Second position C. Third position D. Fourth position E. Fifth position. (Reprinted with permission from Shah S. Determining a young dancer’s readiness for dancing on pointe. Curr Sports Med Rep 2009;8(6):295-299.2)

Pointe shoe design remains a highly skilled art and has not changed much since its inception. The first pointe shoe worn by Marie Taglioni was designed by a cobbler in Paris and consisted of soft satin slippers with flexible leather soles that were heavily darned at the tip.4 Today’s pointe shoes consist of an outer material (usually satin fabric), a toe box, a shank, and a flexible rubber or suede sole that is held onto the foot and ankle with elastic and ribbons (Figure 2). The toe box is constructed from layers of paper, glue, and fabric (usually burlap).2 The shoes must be strong enough to support the dancers on pointe, but also malleable enough to allow the dancers to execute movements articulating through the intrinsic muscles and joints of the foot and ankle. When first worn, pointe shoes are stiff, and dancers use a variety of methods to “break them in,” or soften the shoes to make them better suited for dancing. Eventually, the glue bonds break, resulting in a shank and toe box that are too soft to dance in. Some dancers may try to reinforce the shoes with jet glue to make them last longer. Some brands have used plastic to increase the longevity of the pointe shoes. However, these shoes tend to be stiffer and thus less appealing for many dancers. Often, principal dancers will go through several pairs of shoes in one performance alone, which becomes quite costly given the price of pointe shoes, which at the elite level start at approximately $60 per pair.

Fitting a pointe shoe requires an expert, especially for the novice pointe dancer. Often, dance stores that sell pointe shoes will have a member on staff specialized in fitting pointe shoes. Shoes vary in strength and stiffness, but dancers do not necessarily choose shoes based on these characteristics. Rather, they choose them based on comfort.5 Pointe shoes should be snug but not too tight, which can lead to blister and callus formation.

When choosing a pointe shoe, it is important to understand the basic construction and structure to assure the best fit possible (Figure 2). The top of the toe box, called the vamp, varies in length and width depending on the dancer’s forefoot length and width. The vamp should cover the entire length of the third phalanx and slightly beyond.4The platform is the exterior, flat-end of the toe box which allows the dancer to stand on pointe. When fitting a pointe shoe, a dancer should perform a demi-plié in parallel position because this is the longest the feet will be in the shoes. The dancer’s toes should just be touching the end of the platform without bending. The shank is usually made of shoulder leather and is a narrow supporting spine that is glued to the back of the insole.2,4 The shank helps support the arch of the foot when dancing on pointe and can be reinforced by adding an additional layer for a dancer with a more flexible foot to slow the break down of the shoe. Dancers must sew their own elastic and ribbons. The elastic should wrap snugly over the ankle joint. When standing on pointe after the ribbons are sewn on, the toes should be perpendicular to the floor and should not curl.

Figure 2: Relevé on pointe in fifth position and pointe shoe anatomy

There are more than 20 different manufacturers of pointe shoes, each with varying styles to accommodate different foot types. A good pointe shoe fitter will know the characteristics of the different shoes and be able to recommend shoes based on the dancer’s foot type. The peasant foot (toes are of even length) is the “ideal foot type” for weight distribution while on pointe. Dancers with a peasant foot will require a wider toe box. Dancers with a Grecian foot (second toe is longest) must find the width of toe box that feels most comfortable. Dancers with an Egyptian foot (tapering toe length) will usually purchase shoes with a narrower toe box. To this day, the majority of pointe shoes are handmade, so there is variability even within one specific brand and style. Thus, some dancers prefer to have their shoes made by a specific cobbler whose construction they are accustomed to.

Biomechanics

Dancing on pointe requires complete plantar flexion of the foot and ankle to a combined minimum of 90o.2 Dancers will achieve full relevé (dancing on the tips of the toes in pointe shoes, or on the metatarsal heads in ballet slippers) by either stepping directly into relevé or by rolling through the feet and rising to relevé with or without a demi-plié (feet are turned out, knees maximally flexed without raising the heels) (Figure 3). The ankle is stable in the full pointe position because the posterior lip of the tibia locks onto the calcaneus and the subtalar joint is locked with the heel and forefoot in varus.6 The vamp, sole and closed pack position of the foot in the pointe shoe play a major role in stabilizing the midfoot while on pointe.7

Simply walking in pointe shoes doubles the peak pressures acting on the foot compared to barefoot (41 N/cm2 vs 86 N/cm2).8 Rising into the relevé position from a flat footed position increases the peak pressure to 115 N/cm2.8 The dancer’s body weight is supported on the tips of the toes, which are in a relatively neutral position relative to the longitudinal axis of the foot.7 The average pressure on the toe box while on pointe is 220 psi or 1.5 MPa.9 The majority of the weight is borne by the first toe (0.14 – 0.58 MPa) regardless of the length of the second toe.8 In dancers with tapering toes, capping the second toe increases the pressure absorbed by the second toe but does not significantly change the pressure on the first toe.9

Pointe shoes absorb some of the impact from jump landings, but the load is also distributed through the foot and ankle complex. One study compared five popular pointe shoe styles and found that the compressive strengths of the shoes were 4300 N or less.5 A 60-kg ballerina landing on pointe from a height of one meter generates an impact force of approximately 4950 N or 700 psi.5 This increased force could be a risk factor for the development of injuries, but has not been studied.

Age

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There is no specific age at which a dancer automatically becomes ready to dance on pointe.2 Often the age of 12 is chosen because a dancer usually does not develop the skill necessary for pointe work until then.2 However, determining when a dancer may go on pointe is multifactorial and requires at least the following: adequate strength, flexibility, postural control, proper placement, physical and mental maturity, balance, technique, alignment, and the ability to listen, learn choreography, and apply corrections.2 Prematurely allowing a dancer to transition to pointe may lead to injuries due to falls, missteps, and ankle inversions or eversions, to name a few mechanisms.

Injuries

Research on the implications of dancing on pointe is sparse. The annual incidence of injuries in ballet ranges from 75% to 85%, based primarily on retrospective studies, with a few prospective studies.10-14 The primary location of injuries involves the foot and ankle, with ankle sprains being the most common.10-14 However, no distinction is made between dancing on pointe versus dancing in ballet slippers.

Observational studies and case reports have described certain injuries that are common in ballet. However, none show a direct correlation with dancing on pointe. In fact, one small study conducted on recreational dancers before and after dancing on pointe showed no statistically significant difference with regard to prevalence of instability or number of painful sites.15

Figure 3: Demi-plié in first position in turn-out

Bunions are common in ballerinas, but not all professional ballerinas retire with them. One study found that standing on pointe increased the pressure on the first toe, forcing it into valgus, which may contribute to halluxvalgus deformity.16 However, it is unclear if dancing on pointe can cause halluxvalgus deformity or if it merely accentuates halluxvalgus formation in a person who would have been prone to it regardless.

Traumatized toenails are common in ballerinas. Toenails cut too short, especially on the medial edge, may lead to ingrown toe nails and increase the risk of infection. The great toenail is most often traumatized and has been shown to bend while on pointe. 16Subungual hematomas and onycholysis of the great toenail are common.16

Corns and calluses also commonly occur in ballerinas because of tight fitting pointe shoes. Corns occur over the proximal interphalangeal joints, between the toes, and at the fifth metatarsal head. 17

Cortical hypertrophy is observed in the first, second and third metatarsals in ballerinas.17,18 The second metatarsal is affected with a circumferential thickening, while the first metatarsal is least involved and shows an asymmetrical thickening of the lateral cortex of the shaft.18 Stress fractures also occur in the foot and ankle and occur more commonly in female dancers than in their male counterparts.17 In the foot, stress fractures usually occur in the proximal shaft or metaphysis of the second or third metatarsals, which are the bones with the least mobility.17,19 Stress injuries have also been observed in the talus, presumably due to the force transmitted through the talus while dancing on pointe.20

Posterior impingement syndrome describes a syndrome of pain and impingement in the posterior ankle.21It can occur secondary to either an ostrigonum, prominent posterior process of the talus, or prominence of the dorsum of the calcaneus. In ballerinas, this syndrome occurs from the repetitive plantar flexion required in ballet, including dancing on pointe.

Injuries of the flexor hallucislongus (FHL) and peroneal tendons also occur in ballet dancers. The FHL tendon actively plantar flexes the great toe at the interphalangeal joint, while the peroneuslongus plantar flexes the first metatarsal. Both also function as dynamic stabilizers of the longitudinal arch of the foot.22Repetetive plantar flexion and dorsiflexion of the foot and ankle, including repetitive rising to and from pointe, can lead to injuries of the FHL and peroneuslongus in ballerinas.

Conclusion

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Ballerinas have been dancing on pointe for centuries. The great toe bears most of the weight regardless of the length of the other toes. Despite this unnatural loadbearing, no studies have been done to show that dancing on pointe increases the risk for injury. Ballet dancers do suffer from injuries, most commonly involving the foot and ankle. Problems that have been attributed to dancing on pointe include halluxvalgus deformities, toe nail injuries, corns, and callouses. Injuries common to ballet include ankle sprains, stress fractures, impingement syndromes, and tendon problems.

Selina Shah, MD, FACP, is dance company physician for Company C, Diablo Ballet, andLiss Fain Dance Company, all in the San Francisco Bay Area. She is also medical director of dance medicine for the Center for Sports Medicine at St. Francis Memorial Hospital in San Francisco.