Stress fractures in ballet dancers* NANCY J. KADEL,†‡ MD, CAROL C. TEITZ,† MD, AND RICHARD A. KRONMAL,§ PhD From the
Departments of †Orthopaedic Surgery and §Biostatistics, University of Washington, Seattle, Washington orrheic runners2,21,22 25 and dancers4° than in their eumenorrheic peers. The combination of nutritional deficiencies, menstrual abnormalities, and strenuous training schedules may leave the ballet dancer at risk for skeletal injury. In this study, we compared dancers with and without stress fractures, considering menstrual status, menstrual history, use of oral contraceptives, calcium intake, and daily hours of training.
ABSTRACT We surveyed 54 female dancers in two professional ballet companies. A total of 27 fractures were reported in 17 dancers. Metatarsal fractures were the most common (63%), followed by fractures of the tibia (22%) and spine (7%). Dancers who danced >5 hours per day were significantly more likely to have a stress fracture than those dancing 38 days, but 5 and duration of amenorrhea >6 months were considered together in a logistic regression analysis, each variable was found to contribute independently to the risk of stress fracture (P 0.015 and P 0.002, respectively). The estimated odds ratio for duration of amenorrhea >6 months was 93 with 95% confidence limits of 5.3 to 1644. In other words, a dancer who has been amenorrheic >6 months has an estimated risk for stress fracture that is 93 times that of a dancer who is not amenorrheic. The estimated odds ratio for hours danced per day >5 was 16 with 95% confidence limits of 1.7 to 150. In fact, there were four dancers with both significant risk factors (i.e., they danced >5 hours per day and were amenorrheic >6 months) and all four sustained stress fractures. Similarly, of the 17 dancers with stress fractures, only 1 had neither risk factor. No significant difference was found between the stress fracture group and the group without fracture for other variables (Table 5). All dancers began training before the onset of menarche. Mean age at menarche for both groups combined was 14.8 ± 1.6 years, which is significantly higher (P < 0.05) than the reported mean age at menarche in the United States of 12.8 ± 1.2 years.42 The overall incidence of delayed menarche was 80%. Sixty-five percent of the dancers with stress fractures reported delayed menarche, while dancers without fractures had an 88% incidence of delayed menarche. The height-to-weight ratio in both groups was identical. The overall frequency of oral contraceptive use was 26%. Of the dancers with stress fractures, 35% had used oral contraceptives at some time since menarche, while 22% of the dancers without stress fractures reported a history of contraceptive use. The difference was not significant. The mean weekly calcium intake was 4788 mg, well below the minimum recommended dietary allowance (RDA) of 8400 mg per week.&dquo; Only 12 dancers met or exceeded the RDA for calcium in their diets; 76% in each group had weekly calcium intakes below the RDA. =
=
DISCUSSION The etiology of stress fractures is complex.1,8,13,21,26,27,29,38,39 Our data suggest that both excessive training and duration of amenorrhea are associated with increased stress fractures and that statistically they contribute independently to the risk of fracture. Hours danced per day was a significant risk factor for hours per day, stress fracture. Of 31 dancers dancing 5 hours per day, 9 (50%) suffered fractures. In studies of female runners, the women who had menstrual abnormalities also ran more miles, had faster running times, and a longer duration of training than their eumenorrheic
counterparts.21,22 Duration of amenorrhea was also found to be significantly our dancers with stress fractures (P < 0.001). All of the dancers who were defined as amenorrheic (no menses for 90 days) in fact had no menses for 6 months or more. Furthermore, the longer the duration of amenorrhea, the more likely a dancer was to suffer a stress fracture. This finding supports the study by Warren et aI.,40 but is somewhat different from the results obtained by Drinkwater et al.1,12 They found that the cumulative length of amenorrheic intervals was not a predictive variable for bone density. However, their phrase &dquo;cumulative length of amenorrheic intervals&dquo; and our &dquo;duration of amenorrhea&dquo; are not the same and have different implications. Subjects in the studies by Drinkwater et al. might have had the same cumulative length of amenorrhea, e.g., 9 months, but very different menstrual histories. One subject might have been amenorrheic for 9 months in a row, whereas the other might have had three separate amenorrheic intervals of 3 months each, possibly years apart. Although their cumulative amenorrheic period was the same, the pattern of bone loss might be very different. A woman with short intervals of amenorrhea might be able to regain any bone lost during that brief interval, whereas a woman with a prolonged interval of amenorrhea might not. In our study, duration of amenorrhea was defined as the longest single period of time without menstruating. With one exception, all dancers who were amenorrheic >6 months sustained stress fractures. Obviously the risk of stress fractures in these dancers is extremely high, approaching 100%. The logistic regression analysis considering both risk factors together showed that amenorrheic dancers, those who danced >5 hours per day and those with both factors, appeared to be at a much higher risk for stress fracture than dancers who danced 5 hours per day.
CONCLUSIONS
normalities, and eating disorders may be confounding variables. Nevertheless, we found that the risk of stress fractures in professional ballet dancers was increased in dancers who danced >5 hours per day and in those with amenorrheic intervals exceeding 6 months. Although excessive training is a commonly accepted cause of stress fractures in athletes, duration of the amenorrheic interval as a risk factor has not been examined. This variable deserves further study in a broader group of amenorrheic athletes.
ACKNOWLEDGMENTS We thank the dancers and administrators of both companies who made this study possible and James G. Garrick, MD, and Ralph K. Requa, MSPH, for their editorial assistance. REFERENCES 1. Abraham SF, Beaumont PJV, Fraser IS, et al: Body weight, exercise and menstrual status among ballet dancers in training. Br J Obstet Gynaecol
89: 507-510, 1982 2. Barrow GW, Saha S. Menstrual irregulanty and stress fractures in collegiate female distance runners. Am J Sports Med 16: 209-216, 1988 3. Breslow NE, Day NE: Statistical Methods m Cancer Research Volume I. Lyon, International Agency Research Center, 1980 4. Calabrese LH, Kirkendall DT: Nutritional and medical considerations in dancers. Clin Sports Med 2: 539-554, 1983 5. Calabrese LH, Kirkendall DT, Floyd M, et al: Menstrual abnormalities, nutritional patterns, and body composition in female classical ballet dancers.
Physician Sportsmed 11 (2): 86-98, 1983
6. Cann CE, Cavanaugh DJ, Schnurpfiel K, et al: Menstrual history is the primary determinant of trabecular bone density in women runners. Med Sci Sports Exerc 20: 559, 1988 7. Cann CE, Martin MC, Genant HK, et al: Decreased spinal mineral content in amenorrheic women. JAMA 251: 626-629, 1984 8. Clark N, Nelson M, Evans W: Nutrition education for elite female runners. Physician Sportsmed 16(2): 124-136, 1988 9. Cohen JL, Kim CS, May PB, et al: Exercise, body weight, and amenorrhea in professional ballet dancers. Physician Sportsmed 10(4): 92-101, 1982 10. Cook SD, Harding AF, Thomas KA, et al: Trabecular bone density and menstrual function in women runners. Am J Sports Med 15: 503-507, 1987 11. Drinkwater BL, Bruemner B, Chesnut CH III: Menstrual history as a determinant of current bone density in young athletes. JAMA 263: 545-
548, 1990 12. Drinkwater BL, Bruemner B, Chesnut CH III: Menstrual history and bone mineral density in female athletes. Med Sci Sports Exerc 19: S12, 1987 13. Drinkwater BL, Nilson K, Chesnut CH III, et al: Bone mineral content of amenorrheic and eumenorrheic athletes. N Engl J Med 311: 277-281,
1984 14. Giladi M, Ziv Y, Nili E, et al: Comparison between radiography, bone scan, and ultrasound in the diagnosis of stress fractures. Milit Med 149: 459-
461, 1984 15. Hammond CB, Maxson WS: Current status of estrogen therapy for the menopause. Fertil Steril 37. 5-25, 1982 16. Heaney RP Nutritional factors and estrogen in age-related bone loss. Clin Invest Med 5(2,3): 147-155, 1982 17. Heath H: Athletic women, amenorrhea, and skeletal integrity. Ann Intern Med 102: 258-260, 1985 18. Horsman A, Jones M, Francis R, et al: The effect of estrogen dose on postmenopausal bone loss. N Engl J Med 309: 1405-1407, 1983 19. Hutchinson TA, Polansky SM, Feinstein AR: Post-menopausal estrogens protect against fractures of hip and distal radius. Lancet 2: 705-709, 1979 20 Jensen GF, Christiansen C, Tranbøl I: Fracture frequency and bone preservation in postmenopausal women treated with estrogen Obstet Gynecol
21.
60: 493-496, 1982 Lindberg JS, Fears WB, Hunt MM, and bone
Because stress fractures are multifactorial, they are difficult to study in ballet dancers, whose schedules, menstrual ab-
22.
et al Exercise-induced amenorrhea
density. Ann Intern Med 101: 647-648, 1984 Lloyd T, Triantafyllou SJ, Baker ER, et al: Women athletes with menstrual irregularities have increased musculoskeletal injuries. Med Sci Sports Exerc 18: 374-379, 1986
449 23 Loucks AB, Horvath SM Athletic amenorrhea A review Med Sci Sports Exerc 17 56-72, 1985 24. Mansfield MJ, Emans SJ Anorexia nervosa, athletics, and amenorrhea Pediatr Clin North Am 36 : 533-549, 1989 25. Marcus R, Cann C, Madvig P, et al Menstrual function and bone mass in elite women distance runners Endocrine and metabolic features Ann Intern Med 102: 158-163, 1985 26 Matheson GO, Clement DB, McKenzie DC, et al Stress fractures in athletes A study of 320 cases Am J Sports Med 15. 46-58, 1987 27 McBryde AM Stress fractures in runners Clin Sports Med 4 737-752, 1985 28. Monsen ER The 10th edition of the Recommended Dietary Allowances What’s new in the 1989 RDAs? J Am Diet Assoc 89(12). 1748-1752, 1989 29 Nordin M, Frankel VH: Biomechanics of whole bones and bone tissue, in Frankel VH, Nordin M (eds) Biomechanics of the Skeletal System. Philadelphia, Lea & Febiger, 1980, pp 15-60 30 Nordin BEC, Speed R, Aaron J, et al. Bone formation and resorption as the determinants of trabecular bone volume in post-menopausal osteoporosis. Lancet : 277-279, 1981 31 Peterson MS Nutritional concerns for the dancer Physician Sportsmed 32
10(3) : 137-143, 1982 Rigotti NA, Nussbaum SR, Herzog DB, et al Osteoporosis in women with anorexia nervosa N Engl J Med 311 . 1601-1606, 1984
33 Riis B, Thomsen K, Christiansen C Does calcium supplementation prevent postmenopausal bone loss? N Engl J Med 316 173-177, 1987 34. Rosner BA Fundamentals of Biostatistics Boston, Duxbury Press, 1982 35 Sanborn CF: Menstrual dysfunction in the female athlete, in Teitz CC (ed): Scientific Foundations of Sports Medicine Toronto, BC Decker, 1989, pp 117-134 36 Sanborn CF, Martin BJ, Wagner WW: Is athletic amennorrhea specific to runners? Am J Obstet : Gynecol 143 859-861, 1982 37 Shade AR Gynecological and obstetric problems of the female dancer. Clin Sports Med 2 515-523, 1983 38 Stanitski CL, McMaster JH, Scranton PE On the nature of stress fractures. Am J Sports Med 6 : 391-396, 1978 39. Tauton JE, Clement DB, Webber D Lower extremity stress fractures in athletes Physician Sportsmed 9(1) 77-86, 1981 40 Warren MP, Brooks-Gunn J, Hamilton LH, et al. Scoliosis and fractures in young ballet dancers Relation to delayed menarche and secondary amenorrhea . N Engl J Med 314 1348-1353, 1986 41. Weiss NS, Ure CL, Ballard JH, et al: Decreased risk of fractures of the hip and lower forearm with postmenopausal use of estrogen. N Engl J Med
. 1195-1198, 1980 303 42 Zacharias L, Rand WM, Wurtman RJ A prospective study of sexual development and growth in American girls The statistics of menarche Obstet Gynecol Surv 31 : 325-337, 1976
Departments of †Orthopaedic Surgery and §Biostatistics, University of Washington, Seattle, Washington orrheic runners2,21,22 25 and dancers4° than in their eumenorrheic peers. The combination of nutritional deficiencies, menstrual abnormalities, and strenuous training schedules may leave the ballet dancer at risk for skeletal injury. In this study, we compared dancers with and without stress fractures, considering menstrual status, menstrual history, use of oral contraceptives, calcium intake, and daily hours of training.
ABSTRACT We surveyed 54 female dancers in two professional ballet companies. A total of 27 fractures were reported in 17 dancers. Metatarsal fractures were the most common (63%), followed by fractures of the tibia (22%) and spine (7%). Dancers who danced >5 hours per day were significantly more likely to have a stress fracture than those dancing 38 days, but 5 and duration of amenorrhea >6 months were considered together in a logistic regression analysis, each variable was found to contribute independently to the risk of stress fracture (P 0.015 and P 0.002, respectively). The estimated odds ratio for duration of amenorrhea >6 months was 93 with 95% confidence limits of 5.3 to 1644. In other words, a dancer who has been amenorrheic >6 months has an estimated risk for stress fracture that is 93 times that of a dancer who is not amenorrheic. The estimated odds ratio for hours danced per day >5 was 16 with 95% confidence limits of 1.7 to 150. In fact, there were four dancers with both significant risk factors (i.e., they danced >5 hours per day and were amenorrheic >6 months) and all four sustained stress fractures. Similarly, of the 17 dancers with stress fractures, only 1 had neither risk factor. No significant difference was found between the stress fracture group and the group without fracture for other variables (Table 5). All dancers began training before the onset of menarche. Mean age at menarche for both groups combined was 14.8 ± 1.6 years, which is significantly higher (P < 0.05) than the reported mean age at menarche in the United States of 12.8 ± 1.2 years.42 The overall incidence of delayed menarche was 80%. Sixty-five percent of the dancers with stress fractures reported delayed menarche, while dancers without fractures had an 88% incidence of delayed menarche. The height-to-weight ratio in both groups was identical. The overall frequency of oral contraceptive use was 26%. Of the dancers with stress fractures, 35% had used oral contraceptives at some time since menarche, while 22% of the dancers without stress fractures reported a history of contraceptive use. The difference was not significant. The mean weekly calcium intake was 4788 mg, well below the minimum recommended dietary allowance (RDA) of 8400 mg per week.&dquo; Only 12 dancers met or exceeded the RDA for calcium in their diets; 76% in each group had weekly calcium intakes below the RDA. =
=
DISCUSSION The etiology of stress fractures is complex.1,8,13,21,26,27,29,38,39 Our data suggest that both excessive training and duration of amenorrhea are associated with increased stress fractures and that statistically they contribute independently to the risk of fracture. Hours danced per day was a significant risk factor for hours per day, stress fracture. Of 31 dancers dancing 5 hours per day, 9 (50%) suffered fractures. In studies of female runners, the women who had menstrual abnormalities also ran more miles, had faster running times, and a longer duration of training than their eumenorrheic
counterparts.21,22 Duration of amenorrhea was also found to be significantly our dancers with stress fractures (P < 0.001). All of the dancers who were defined as amenorrheic (no menses for 90 days) in fact had no menses for 6 months or more. Furthermore, the longer the duration of amenorrhea, the more likely a dancer was to suffer a stress fracture. This finding supports the study by Warren et aI.,40 but is somewhat different from the results obtained by Drinkwater et al.1,12 They found that the cumulative length of amenorrheic intervals was not a predictive variable for bone density. However, their phrase &dquo;cumulative length of amenorrheic intervals&dquo; and our &dquo;duration of amenorrhea&dquo; are not the same and have different implications. Subjects in the studies by Drinkwater et al. might have had the same cumulative length of amenorrhea, e.g., 9 months, but very different menstrual histories. One subject might have been amenorrheic for 9 months in a row, whereas the other might have had three separate amenorrheic intervals of 3 months each, possibly years apart. Although their cumulative amenorrheic period was the same, the pattern of bone loss might be very different. A woman with short intervals of amenorrhea might be able to regain any bone lost during that brief interval, whereas a woman with a prolonged interval of amenorrhea might not. In our study, duration of amenorrhea was defined as the longest single period of time without menstruating. With one exception, all dancers who were amenorrheic >6 months sustained stress fractures. Obviously the risk of stress fractures in these dancers is extremely high, approaching 100%. The logistic regression analysis considering both risk factors together showed that amenorrheic dancers, those who danced >5 hours per day and those with both factors, appeared to be at a much higher risk for stress fracture than dancers who danced 5 hours per day.
CONCLUSIONS
normalities, and eating disorders may be confounding variables. Nevertheless, we found that the risk of stress fractures in professional ballet dancers was increased in dancers who danced >5 hours per day and in those with amenorrheic intervals exceeding 6 months. Although excessive training is a commonly accepted cause of stress fractures in athletes, duration of the amenorrheic interval as a risk factor has not been examined. This variable deserves further study in a broader group of amenorrheic athletes.
ACKNOWLEDGMENTS We thank the dancers and administrators of both companies who made this study possible and James G. Garrick, MD, and Ralph K. Requa, MSPH, for their editorial assistance. REFERENCES 1. Abraham SF, Beaumont PJV, Fraser IS, et al: Body weight, exercise and menstrual status among ballet dancers in training. Br J Obstet Gynaecol
89: 507-510, 1982 2. Barrow GW, Saha S. Menstrual irregulanty and stress fractures in collegiate female distance runners. Am J Sports Med 16: 209-216, 1988 3. Breslow NE, Day NE: Statistical Methods m Cancer Research Volume I. Lyon, International Agency Research Center, 1980 4. Calabrese LH, Kirkendall DT: Nutritional and medical considerations in dancers. Clin Sports Med 2: 539-554, 1983 5. Calabrese LH, Kirkendall DT, Floyd M, et al: Menstrual abnormalities, nutritional patterns, and body composition in female classical ballet dancers.
Physician Sportsmed 11 (2): 86-98, 1983
6. Cann CE, Cavanaugh DJ, Schnurpfiel K, et al: Menstrual history is the primary determinant of trabecular bone density in women runners. Med Sci Sports Exerc 20: 559, 1988 7. Cann CE, Martin MC, Genant HK, et al: Decreased spinal mineral content in amenorrheic women. JAMA 251: 626-629, 1984 8. Clark N, Nelson M, Evans W: Nutrition education for elite female runners. Physician Sportsmed 16(2): 124-136, 1988 9. Cohen JL, Kim CS, May PB, et al: Exercise, body weight, and amenorrhea in professional ballet dancers. Physician Sportsmed 10(4): 92-101, 1982 10. Cook SD, Harding AF, Thomas KA, et al: Trabecular bone density and menstrual function in women runners. Am J Sports Med 15: 503-507, 1987 11. Drinkwater BL, Bruemner B, Chesnut CH III: Menstrual history as a determinant of current bone density in young athletes. JAMA 263: 545-
548, 1990 12. Drinkwater BL, Bruemner B, Chesnut CH III: Menstrual history and bone mineral density in female athletes. Med Sci Sports Exerc 19: S12, 1987 13. Drinkwater BL, Nilson K, Chesnut CH III, et al: Bone mineral content of amenorrheic and eumenorrheic athletes. N Engl J Med 311: 277-281,
1984 14. Giladi M, Ziv Y, Nili E, et al: Comparison between radiography, bone scan, and ultrasound in the diagnosis of stress fractures. Milit Med 149: 459-
461, 1984 15. Hammond CB, Maxson WS: Current status of estrogen therapy for the menopause. Fertil Steril 37. 5-25, 1982 16. Heaney RP Nutritional factors and estrogen in age-related bone loss. Clin Invest Med 5(2,3): 147-155, 1982 17. Heath H: Athletic women, amenorrhea, and skeletal integrity. Ann Intern Med 102: 258-260, 1985 18. Horsman A, Jones M, Francis R, et al: The effect of estrogen dose on postmenopausal bone loss. N Engl J Med 309: 1405-1407, 1983 19. Hutchinson TA, Polansky SM, Feinstein AR: Post-menopausal estrogens protect against fractures of hip and distal radius. Lancet 2: 705-709, 1979 20 Jensen GF, Christiansen C, Tranbøl I: Fracture frequency and bone preservation in postmenopausal women treated with estrogen Obstet Gynecol
21.
60: 493-496, 1982 Lindberg JS, Fears WB, Hunt MM, and bone
Because stress fractures are multifactorial, they are difficult to study in ballet dancers, whose schedules, menstrual ab-
22.
et al Exercise-induced amenorrhea
density. Ann Intern Med 101: 647-648, 1984 Lloyd T, Triantafyllou SJ, Baker ER, et al: Women athletes with menstrual irregularities have increased musculoskeletal injuries. Med Sci Sports Exerc 18: 374-379, 1986
449 23 Loucks AB, Horvath SM Athletic amenorrhea A review Med Sci Sports Exerc 17 56-72, 1985 24. Mansfield MJ, Emans SJ Anorexia nervosa, athletics, and amenorrhea Pediatr Clin North Am 36 : 533-549, 1989 25. Marcus R, Cann C, Madvig P, et al Menstrual function and bone mass in elite women distance runners Endocrine and metabolic features Ann Intern Med 102: 158-163, 1985 26 Matheson GO, Clement DB, McKenzie DC, et al Stress fractures in athletes A study of 320 cases Am J Sports Med 15. 46-58, 1987 27 McBryde AM Stress fractures in runners Clin Sports Med 4 737-752, 1985 28. Monsen ER The 10th edition of the Recommended Dietary Allowances What’s new in the 1989 RDAs? J Am Diet Assoc 89(12). 1748-1752, 1989 29 Nordin M, Frankel VH: Biomechanics of whole bones and bone tissue, in Frankel VH, Nordin M (eds) Biomechanics of the Skeletal System. Philadelphia, Lea & Febiger, 1980, pp 15-60 30 Nordin BEC, Speed R, Aaron J, et al. Bone formation and resorption as the determinants of trabecular bone volume in post-menopausal osteoporosis. Lancet : 277-279, 1981 31 Peterson MS Nutritional concerns for the dancer Physician Sportsmed 32
10(3) : 137-143, 1982 Rigotti NA, Nussbaum SR, Herzog DB, et al Osteoporosis in women with anorexia nervosa N Engl J Med 311 . 1601-1606, 1984
33 Riis B, Thomsen K, Christiansen C Does calcium supplementation prevent postmenopausal bone loss? N Engl J Med 316 173-177, 1987 34. Rosner BA Fundamentals of Biostatistics Boston, Duxbury Press, 1982 35 Sanborn CF: Menstrual dysfunction in the female athlete, in Teitz CC (ed): Scientific Foundations of Sports Medicine Toronto, BC Decker, 1989, pp 117-134 36 Sanborn CF, Martin BJ, Wagner WW: Is athletic amennorrhea specific to runners? Am J Obstet : Gynecol 143 859-861, 1982 37 Shade AR Gynecological and obstetric problems of the female dancer. Clin Sports Med 2 515-523, 1983 38 Stanitski CL, McMaster JH, Scranton PE On the nature of stress fractures. Am J Sports Med 6 : 391-396, 1978 39. Tauton JE, Clement DB, Webber D Lower extremity stress fractures in athletes Physician Sportsmed 9(1) 77-86, 1981 40 Warren MP, Brooks-Gunn J, Hamilton LH, et al. Scoliosis and fractures in young ballet dancers Relation to delayed menarche and secondary amenorrhea . N Engl J Med 314 1348-1353, 1986 41. Weiss NS, Ure CL, Ballard JH, et al: Decreased risk of fractures of the hip and lower forearm with postmenopausal use of estrogen. N Engl J Med
. 1195-1198, 1980 303 42 Zacharias L, Rand WM, Wurtman RJ A prospective study of sexual development and growth in American girls The statistics of menarche Obstet Gynecol Surv 31 : 325-337, 1976
