ORIGINAL CONTRIBUTION Boehler's angle; fracture, ankle
Boehler's Angle: A Reappraisal Study objectives: To reappraise Boehler's angle and evaluate factors, including centering of the central beam, sex of subjects, and side of the body, that m a y affect angle measurement. Design: Retrospective clinical review, Setting: Emergency department, Level I trauma center. Type of participants: 120 consecutive patients radiographed for ankle injury who had normal bones on the ankle and~or foot radiographs. M e a s u r e m e n t s and m a i n results: The mean and SD of Boehler's angle were 30 ° +_ 6° (range, 14° to 50°). There was no difference in Boehler's angle between male and female subjects (P > .05) or between left and right feet (P > .05). Slight variations in central beam location .for ankle and foot radiographs had no significant effect on Boehler's angle. Conclusion: If 28 ° is taken as the lower limit of normal for Boehler's angle, 37 cases (31%) would be false-positive "'abnormal." The use of 20 ° as the lower limit m a y decrease the number of false-positive to three cases (2.5%); using 18° (mean - 2 SD) reduces the false-positive rate to less than i % (one case). [Chen MYM, Bohrer SP, Kelley TF: Boehler's angle: A reappraisal. Ann Emerg Med February 1991;20:122-124.]
Michael Y M Chert, MD* Stanley P Bohrer, MD* Timothy F Kelley, MDt Winston-Salem, North Carolina From the Departments of Radiology* and Surgery,t Bowman Gray School of Medicine, Wake Forest University, WinstonSalem, North Carolina. Received for publication May 3, 1990. Revision received July 16, 1990. Accepted for publication August 2, 1990. Address for reprints: Michael Y M Chen, MD, Bowman Gray School of Medicine, 300 South Hawthorne Road, WinstonSalem, North Carolina 27103.
INTRODUCTION In 1931 Boehler described the "tuber-joint angle" of the calcaneus as a useful radiographic m e a s u r e m e n t to aid in the diagnosis of c o m p r e s s i o n fractures of the central portion of the bone.t H e cited the n o r m a l angle as 30 ° to 35 °. This range has b e c o m e k n o w n as "Boehler's angle." Boehler's angle has been reported in textbooks as 20 ° to 400, 2-4 28 ° to 400, 5,6 20 ° to 44o, 7 and 25 ° to 450. 8 The variations in these m e a s u r e m e n t s drew our a t t e n t i o n to the need for reappraisal of Boehler's angle w i t h regard to some factors that m a y affect angle m e a s u r e m e n t , including different centering of the central beam, sex of subjects, and different sides.
PATIENTS A N D M E T H O D S One h u n d r e d t w e n t y patients m o r e t h a n 15 years old who had a foot or ankle e x a m i n a t i o n n o t associated w i t h significant b o n y t r a u m a were cons e c u t i v e l y s e l e c t e d for t h i s s t u d y . P a t i e n t s i n c l u d e d 63 m e n a n d 57 women, w i t h an age range of 16 to 81 years (mean, 34 years). Of these 120 patients, 77 had anlde radiographs, 25 had foot radiographs, and 18 had both ankle and foot radiographs. Lateral foot and ankle films were m a d e in the standard m e d i o l a t e r a l projection. 9 T h e lateral side of the ankle was placed against the film, and the central radiograph b e a m was directed to the m e d i a l m a l l e o l u s for ankle e x a m i n a t i o n s and to the navicular bone for lateral foot examinations. W h e n b o t h ankle and foot radiographs were requested, the radiograph b e a m for the lateral projection was usually centered s o m e w h e r e b e t w e e n the m e d i a l m a l l e o l u s and the navicular bone, but some technologists centered this e x a m i n a t i o n as for a lateral foot or a lateral ankle radiograph. The lateral projections of ankle and/or foot were used for m e a s u r e m e n t . Boehler's angle was m e a s u r e d by a line drawn on the superior aspect of the calcaneus from the posterior t u b e r o s i t y to the apex of the posterior facet. A second line was drawn from this p o i n t to the apex of the anterior process (Figure 1).
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Annals of Emergency Medicine
20:2 February 1991
BOEHLER'S ANGLE Chen, Bohrer & Kelley
FIGURE 1. Measurement of Boehler's angle. A line is drawn from the posterior tuberosity (right mark) to the apex of the posterior facet (middle mark), and a second line is drawn from this point to the apex of the anterior process (left mark). F I G U R E 2. M e a s u r e m e n t s
of Boehler's angle on the specimen with different central beam of radiograph. Black dot represents the center of radiograph beam.
An a r t i c u l a t e d s p e c i m e n of f o o t bones was r a d i o g r a p h e d in a l a t e r a l position w i t h d i f f e r e n t c e n t e r i n g points - just b e l o w the t a l a r d o m e (medial malleolus), 7 c m above the medial malleolus, and at the navicufar bone. RESULTS Boehler's angle m e a s u r e d on t h e lateral a n k l e or foot radiographs of 120 patients was 30 ° --_ 6 ° (range, 14° to 50°). Boehler's angle was 30 ° -+ 6 ° in m e n a n d 29 ° + 6 ° in w o m e n . There w a s no d i f f e r e n c e b e t w e e n right and left feet. The m e a s u r e m e n t s of Boehler's angle with different central ray centering p o s i t i o n s on t h e s p e c i m e n are shown (Figure 2). Boehler's angle was 30° - 6° on lateral ankle radiographs, 29° -+ 6 ° on lateral foot radiographs, and 28 ° _+ 6 ° on both ankle and foot radiographs. DISCUSSION Boehler s t a t e d t h a t a t u b e r - j o i n t angle (later called Boehler's angle) is normally 30 ° to 35 ° and that this angle became smaller, straight, or even reversed w i t h central fractures of the calcaneus. 1 C a l c a n e u s fractures are more c o m m o n than fractures of any other tarsal bone and account for 1% to 2% of all fractures. 3 In falling from a height and landing on the feet, the areas of the body that are m o s t prone 20:2 February 1991
Center at medial malfedus
Center 7 cm above medial malleolus
34 °
35 °
Center at the navicular bone, middle of the foot 34 °
2
to fracture are the calcaneus and the l o w e r s p i n a l v e r t e b r a l bodies. T h e m e c h a n i s m p r o d u c i n g this injury is t h e d o w n w a r d f o r c e of t h e b o d y t r a n s m i t t e d through the talus, w h i c h acts as a wedge, crushing and splitring the m i d p o r t i o n of the calcaneus. The m a j o r i t y of crushing injuries of the c a l c a n e u s depress the p o s t e r i o r facet, reducing Boehler's angle. W h e n t h e c a l c a n e u s is r a d i o graphed, a l a t e r a l f i l m of t h e calcaneus should be t a k e n for measurem e n t of Boehler's angle. Boehler's angle w i l l be d e c r e a s e d in c a l c a n e a l fractures and may even become a negative angle. Reduction or reversal of this angle u s u a l l y i n d i c a t e s t h a t the posterior calcaneal facet has been depressed. A false-positive s m a l l angle m a y occur if the posterior tuberosity and/or the anterior process are u n u s u a l l y high. T h e difference in B o e h l e r ' s angle b e t w e e n left a n d r i g h t feet on t h e s a m e p a t i e n t ranges from 0 ° to less t h a n 3 °, w i t h n o d i f f e r e n c e in t h e m e a n values. 3 Bilateral films m a y be t a k e n for c o m p a r i s o n if Boehler's angle is significantly decreased on one foot. N o r m a l values for Boehler's angle have been v a r i o u s l y r e p o r t e d as bet w e e n 20 ° and 450. 2-8 The upper l i m i t of n o r m a l has no p r a c t i c a l signific a n c e in t h e d i a g n o s i s of f r a c t u r e s a n d n e e d n o t be d i s c u s s e d f u r t h e r . The lower l i m i t is that of i m p o r t a n c e for the diagnosis of the fractures, esp e c i a l l y w h e n the p o s s i b i l i t y exists of fracture of both calcanei, because c o m p a r i s o n to a n o r m a l side is n o t possible. In o u r s t u d y , B o e h l e r ' s a n g l e s ranged from 14° to 50 °. Using a lower l i m i t of 28 °, 37 cases (31%) w o u l d be Annals of Emergency Medicine
TABLE. Correlation of lower limit degrees and outliers Lower Limit (Degrees) 30 28 26 24 22 20 18
No. of Outliers (%) 58 (48) 37 (31) 31 (26) 17 (14) 9 (7.5) 3 (2.5) 1 (0.8)
misdiagnosed as a b n o r m a l (Table). If the lower l i m i t is established using m e a n - 2 SD (18°), o n l y o n e c a s e (0.8%) w o u l d be equal to or less than this v a l u e as a false-positive. T h r e e cases had m e a s u r e m e n t s equal to or less t h a n t h e o f t e n - u s e d 20 ° l o w e r l i m i t of normal. M e a s u r e m e n t is n o t s i g n i f i c a n t l y affected by slightly different central ray centering points. In our study, the difference in Boehler's angle varied only 1° to 2 ° between foot and ankle projections, and this was not statistically significant. There was a 4 ° to 5 ° difference b e t w e e n the s p e c i m e n m e a s u r e m e n t s and the m e a n values for the patients studied (Figure 2). As expected, this was m o s t l i k e l y due to the single s p e c i m e n s t u d i e d h a v i n g an angle a p p r o x i m a t e l y 1 SD above the m e a n of the cases studied. The results of Hauser and Kroeker w e r e i n c o n c l u s i v e in c o r r e l a t i n g a low calcaneal i n c l i n a t i o n angle (pronated foot) w i t h a low Boehler's angle or a high calcaneal i n c l i n a t i o n angle (supinated foot) w i t h a high Boehler's angle. 7 123/29
BOEHLER'S ANGLE Chen, Bohrer & Kelley
CONCLUSION The m e a n Boehler's angle in our study was 30 ° -+ 6 °. Thus, the lower limit of "normal" (mean - 2 SD) was 18 °, considerably lower than the figure given in m o s t textbooks. The angle was unchanged w i t h small differences in tube centering (for foot and ankle examinations). It was the same in m e n and w o m e n and for right and left feet.
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REFERENCES l. Boehler L: Diagnosis, pathology and treatment of fractures of the os calcis. J Bone Joint Surg 1931;13: 75-89. 2. Roger LF: Radiology of Skeletal Trauma. New York, Churchill Livingstone, vol 2, 1982, p 864-878. 3. Harris JH Jr, Harris WH: The Radiology of Emergency Medicine, ed 2. Baltimore, Williams & Wilkins, I981, p 640-660. 4. Kleiger B: The mechanism and the roentgenographic evaluation of fracture of the tarsal bones, in DePalma AF (edl: Clinical Orthopaedics and Related Research. Philadelphia, JB Lippincott Co, 1963, p 18.
Annals of Emergency Medicine
5. Keats TE, Lusted LB: Atlas of Roentgenographic Measurement. ed 5. Chicago, Year Book Medical Publishing Inc, 1985, p 225. 6. Montagne J, Chevrot A, Galmiche JM: Atlas of Foot Radiolog~ N e w York, Massion Publishing USA, In¢, 1981, p 51. 7. Hauser ML, Kroeker RO: Boehler's angle: A review and study. J Am Podiatr Assoc 1975;65:517-521. 8. Weissman SD: Radiology of the Foot. Baltimore, Williams & Wilkins, 1983, p 276-277. 9. Ballinger PW: Merrilt's Atlas of Radiographic Positions and Radiologic Procedures, ed 6. St Louis, CV Mosby Co, vol 1, I986, p 174.
20:2 February 1991
Boehler's Angle: A Reappraisal Study objectives: To reappraise Boehler's angle and evaluate factors, including centering of the central beam, sex of subjects, and side of the body, that m a y affect angle measurement. Design: Retrospective clinical review, Setting: Emergency department, Level I trauma center. Type of participants: 120 consecutive patients radiographed for ankle injury who had normal bones on the ankle and~or foot radiographs. M e a s u r e m e n t s and m a i n results: The mean and SD of Boehler's angle were 30 ° +_ 6° (range, 14° to 50°). There was no difference in Boehler's angle between male and female subjects (P > .05) or between left and right feet (P > .05). Slight variations in central beam location .for ankle and foot radiographs had no significant effect on Boehler's angle. Conclusion: If 28 ° is taken as the lower limit of normal for Boehler's angle, 37 cases (31%) would be false-positive "'abnormal." The use of 20 ° as the lower limit m a y decrease the number of false-positive to three cases (2.5%); using 18° (mean - 2 SD) reduces the false-positive rate to less than i % (one case). [Chen MYM, Bohrer SP, Kelley TF: Boehler's angle: A reappraisal. Ann Emerg Med February 1991;20:122-124.]
Michael Y M Chert, MD* Stanley P Bohrer, MD* Timothy F Kelley, MDt Winston-Salem, North Carolina From the Departments of Radiology* and Surgery,t Bowman Gray School of Medicine, Wake Forest University, WinstonSalem, North Carolina. Received for publication May 3, 1990. Revision received July 16, 1990. Accepted for publication August 2, 1990. Address for reprints: Michael Y M Chen, MD, Bowman Gray School of Medicine, 300 South Hawthorne Road, WinstonSalem, North Carolina 27103.
INTRODUCTION In 1931 Boehler described the "tuber-joint angle" of the calcaneus as a useful radiographic m e a s u r e m e n t to aid in the diagnosis of c o m p r e s s i o n fractures of the central portion of the bone.t H e cited the n o r m a l angle as 30 ° to 35 °. This range has b e c o m e k n o w n as "Boehler's angle." Boehler's angle has been reported in textbooks as 20 ° to 400, 2-4 28 ° to 400, 5,6 20 ° to 44o, 7 and 25 ° to 450. 8 The variations in these m e a s u r e m e n t s drew our a t t e n t i o n to the need for reappraisal of Boehler's angle w i t h regard to some factors that m a y affect angle m e a s u r e m e n t , including different centering of the central beam, sex of subjects, and different sides.
PATIENTS A N D M E T H O D S One h u n d r e d t w e n t y patients m o r e t h a n 15 years old who had a foot or ankle e x a m i n a t i o n n o t associated w i t h significant b o n y t r a u m a were cons e c u t i v e l y s e l e c t e d for t h i s s t u d y . P a t i e n t s i n c l u d e d 63 m e n a n d 57 women, w i t h an age range of 16 to 81 years (mean, 34 years). Of these 120 patients, 77 had anlde radiographs, 25 had foot radiographs, and 18 had both ankle and foot radiographs. Lateral foot and ankle films were m a d e in the standard m e d i o l a t e r a l projection. 9 T h e lateral side of the ankle was placed against the film, and the central radiograph b e a m was directed to the m e d i a l m a l l e o l u s for ankle e x a m i n a t i o n s and to the navicular bone for lateral foot examinations. W h e n b o t h ankle and foot radiographs were requested, the radiograph b e a m for the lateral projection was usually centered s o m e w h e r e b e t w e e n the m e d i a l m a l l e o l u s and the navicular bone, but some technologists centered this e x a m i n a t i o n as for a lateral foot or a lateral ankle radiograph. The lateral projections of ankle and/or foot were used for m e a s u r e m e n t . Boehler's angle was m e a s u r e d by a line drawn on the superior aspect of the calcaneus from the posterior t u b e r o s i t y to the apex of the posterior facet. A second line was drawn from this p o i n t to the apex of the anterior process (Figure 1).
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Annals of Emergency Medicine
20:2 February 1991
BOEHLER'S ANGLE Chen, Bohrer & Kelley
FIGURE 1. Measurement of Boehler's angle. A line is drawn from the posterior tuberosity (right mark) to the apex of the posterior facet (middle mark), and a second line is drawn from this point to the apex of the anterior process (left mark). F I G U R E 2. M e a s u r e m e n t s
of Boehler's angle on the specimen with different central beam of radiograph. Black dot represents the center of radiograph beam.
An a r t i c u l a t e d s p e c i m e n of f o o t bones was r a d i o g r a p h e d in a l a t e r a l position w i t h d i f f e r e n t c e n t e r i n g points - just b e l o w the t a l a r d o m e (medial malleolus), 7 c m above the medial malleolus, and at the navicufar bone. RESULTS Boehler's angle m e a s u r e d on t h e lateral a n k l e or foot radiographs of 120 patients was 30 ° --_ 6 ° (range, 14° to 50°). Boehler's angle was 30 ° -+ 6 ° in m e n a n d 29 ° + 6 ° in w o m e n . There w a s no d i f f e r e n c e b e t w e e n right and left feet. The m e a s u r e m e n t s of Boehler's angle with different central ray centering p o s i t i o n s on t h e s p e c i m e n are shown (Figure 2). Boehler's angle was 30° - 6° on lateral ankle radiographs, 29° -+ 6 ° on lateral foot radiographs, and 28 ° _+ 6 ° on both ankle and foot radiographs. DISCUSSION Boehler s t a t e d t h a t a t u b e r - j o i n t angle (later called Boehler's angle) is normally 30 ° to 35 ° and that this angle became smaller, straight, or even reversed w i t h central fractures of the calcaneus. 1 C a l c a n e u s fractures are more c o m m o n than fractures of any other tarsal bone and account for 1% to 2% of all fractures. 3 In falling from a height and landing on the feet, the areas of the body that are m o s t prone 20:2 February 1991
Center at medial malfedus
Center 7 cm above medial malleolus
34 °
35 °
Center at the navicular bone, middle of the foot 34 °
2
to fracture are the calcaneus and the l o w e r s p i n a l v e r t e b r a l bodies. T h e m e c h a n i s m p r o d u c i n g this injury is t h e d o w n w a r d f o r c e of t h e b o d y t r a n s m i t t e d through the talus, w h i c h acts as a wedge, crushing and splitring the m i d p o r t i o n of the calcaneus. The m a j o r i t y of crushing injuries of the c a l c a n e u s depress the p o s t e r i o r facet, reducing Boehler's angle. W h e n t h e c a l c a n e u s is r a d i o graphed, a l a t e r a l f i l m of t h e calcaneus should be t a k e n for measurem e n t of Boehler's angle. Boehler's angle w i l l be d e c r e a s e d in c a l c a n e a l fractures and may even become a negative angle. Reduction or reversal of this angle u s u a l l y i n d i c a t e s t h a t the posterior calcaneal facet has been depressed. A false-positive s m a l l angle m a y occur if the posterior tuberosity and/or the anterior process are u n u s u a l l y high. T h e difference in B o e h l e r ' s angle b e t w e e n left a n d r i g h t feet on t h e s a m e p a t i e n t ranges from 0 ° to less t h a n 3 °, w i t h n o d i f f e r e n c e in t h e m e a n values. 3 Bilateral films m a y be t a k e n for c o m p a r i s o n if Boehler's angle is significantly decreased on one foot. N o r m a l values for Boehler's angle have been v a r i o u s l y r e p o r t e d as bet w e e n 20 ° and 450. 2-8 The upper l i m i t of n o r m a l has no p r a c t i c a l signific a n c e in t h e d i a g n o s i s of f r a c t u r e s a n d n e e d n o t be d i s c u s s e d f u r t h e r . The lower l i m i t is that of i m p o r t a n c e for the diagnosis of the fractures, esp e c i a l l y w h e n the p o s s i b i l i t y exists of fracture of both calcanei, because c o m p a r i s o n to a n o r m a l side is n o t possible. In o u r s t u d y , B o e h l e r ' s a n g l e s ranged from 14° to 50 °. Using a lower l i m i t of 28 °, 37 cases (31%) w o u l d be Annals of Emergency Medicine
TABLE. Correlation of lower limit degrees and outliers Lower Limit (Degrees) 30 28 26 24 22 20 18
No. of Outliers (%) 58 (48) 37 (31) 31 (26) 17 (14) 9 (7.5) 3 (2.5) 1 (0.8)
misdiagnosed as a b n o r m a l (Table). If the lower l i m i t is established using m e a n - 2 SD (18°), o n l y o n e c a s e (0.8%) w o u l d be equal to or less than this v a l u e as a false-positive. T h r e e cases had m e a s u r e m e n t s equal to or less t h a n t h e o f t e n - u s e d 20 ° l o w e r l i m i t of normal. M e a s u r e m e n t is n o t s i g n i f i c a n t l y affected by slightly different central ray centering points. In our study, the difference in Boehler's angle varied only 1° to 2 ° between foot and ankle projections, and this was not statistically significant. There was a 4 ° to 5 ° difference b e t w e e n the s p e c i m e n m e a s u r e m e n t s and the m e a n values for the patients studied (Figure 2). As expected, this was m o s t l i k e l y due to the single s p e c i m e n s t u d i e d h a v i n g an angle a p p r o x i m a t e l y 1 SD above the m e a n of the cases studied. The results of Hauser and Kroeker w e r e i n c o n c l u s i v e in c o r r e l a t i n g a low calcaneal i n c l i n a t i o n angle (pronated foot) w i t h a low Boehler's angle or a high calcaneal i n c l i n a t i o n angle (supinated foot) w i t h a high Boehler's angle. 7 123/29
BOEHLER'S ANGLE Chen, Bohrer & Kelley
CONCLUSION The m e a n Boehler's angle in our study was 30 ° -+ 6 °. Thus, the lower limit of "normal" (mean - 2 SD) was 18 °, considerably lower than the figure given in m o s t textbooks. The angle was unchanged w i t h small differences in tube centering (for foot and ankle examinations). It was the same in m e n and w o m e n and for right and left feet.
30/124
REFERENCES l. Boehler L: Diagnosis, pathology and treatment of fractures of the os calcis. J Bone Joint Surg 1931;13: 75-89. 2. Roger LF: Radiology of Skeletal Trauma. New York, Churchill Livingstone, vol 2, 1982, p 864-878. 3. Harris JH Jr, Harris WH: The Radiology of Emergency Medicine, ed 2. Baltimore, Williams & Wilkins, I981, p 640-660. 4. Kleiger B: The mechanism and the roentgenographic evaluation of fracture of the tarsal bones, in DePalma AF (edl: Clinical Orthopaedics and Related Research. Philadelphia, JB Lippincott Co, 1963, p 18.
Annals of Emergency Medicine
5. Keats TE, Lusted LB: Atlas of Roentgenographic Measurement. ed 5. Chicago, Year Book Medical Publishing Inc, 1985, p 225. 6. Montagne J, Chevrot A, Galmiche JM: Atlas of Foot Radiolog~ N e w York, Massion Publishing USA, In¢, 1981, p 51. 7. Hauser ML, Kroeker RO: Boehler's angle: A review and study. J Am Podiatr Assoc 1975;65:517-521. 8. Weissman SD: Radiology of the Foot. Baltimore, Williams & Wilkins, 1983, p 276-277. 9. Ballinger PW: Merrilt's Atlas of Radiographic Positions and Radiologic Procedures, ed 6. St Louis, CV Mosby Co, vol 1, I986, p 174.
20:2 February 1991
