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Three-dimensional analysis of acute plastic bowing deformity of ulna in radial head dislocation or radial shaft fracture using a computerized simulation system
J Shoulder Elbow Surg (2012) 21, 1644-1650
www.elsevier.com/locate/ymse
Three-dimensional analysis of acute plastic bowing deformity of ulna in radial head dislocation or radial shaft fracture using a computerized simulation system Eugene Kim, MD, PhDa, Hisao Moritomo, MD, PhDb,*, Tsuyoshi Murase, MD, PhDb, Takashi Masatomi, MD, PhDc, Junichi Miyake, MD, PhDb, Kazuomi Sugamoto, MD, PhDb a
Department of Orthopaedic Surgery, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, South Korea b Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, Osaka, Japan c Department of Orthopaedic Surgery, Yukioka Hospital, Osaka, Japan Background: Little 3-dimensional biomechanical investigation of plastic bowing deformity of the ulna has been reported, and the purpose of this study was to conduct such an investigation to elucidate mechanisms of injury and appropriate treatments. Methods: Ten cases of traumatic plastic deformity of the ulna in pediatric patients, 4 with chronic radial head dislocations (Monteggia equivalent) and 6 with malunited radial shaft fractures, were analyzed for rotational deformities in the axial plane and bending deformities in the sagittal and coronal planes in Euler angle space by use of a 3-dimensional computerized simulation system with a markerless registration technique. Results: Deformed ulnae with radial head dislocations had 18.7 17.4 of external rotation in the axial plane and 10.4 7.0 of extension in the sagittal plane whereas those with malunited radial shaft fractures had 12.5 12.7 of internal rotation and 6.3 5.6 of flexion displacement compared with mirror images of the opposite ulnae. Absolute values of rotational deformities in both groups were larger than those of sagittal and coronal bending deformities. Discussion: Most major traumatic plastic bowing deformities of the ulna involved rotation rather than bending. External rotational stress on the ulna is suspected to cause radial head dislocation, and internal rotational stress results in radial shaft fracture during falls onto outstretched arms. Therefore the correction of rotational deformities of the ulna should be considered in the treatment of chronic radial head dislocations and malunited radial shaft fractures. Level of evidence: Basic Science, Anatomic Study, Imaging. Ó 2012 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Computerized simulation; plastic bowing deformity; radial head dislocation; radial shaft fracture; 3-dimensional; ulna
Ethical board review statement: Each author certifies that the institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles for research, and that informed consent for participation in the study was obtained (institutional review board of Osaka University Graduate School of Medicine No. 08332).
*Reprint requests: Hisao Moritomo, MD, PhD, Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, 2-2, Yamada-oka, Suita, Osaka 565-0871, Japan. E-mail address: [email protected] (H. Moritomo).
1058-2746/$ - see front matter Ó 2012 Journal of Shoulder and Elbow Surgery Board of Trustees. doi:10.1016/j.jse.2011.12.006
Plastic bowing deformity of ulna
1645
Figure 1 Traumatic plastic bowing of ulna in a patient with radial head dislocation (Monteggia-equivalent lesion) (A) and in a patient with radial shaft fracture (B).
‘‘Plastic bowing deformation’’ is defined as a bowing deformity that remains after compressing longitudinal forces are applied to a curved tubular bone in its stress-strain curve.10 Since Borden6 described traumatic bowing of the ulna and radius in children for the first time, several pediatric cases have been reported3,22,24,25,34; in addition, some cases have been reported in adults.1,13,27,28 Some Monteggia fractures in children show no fractures of the ulna but rather show a bend, which is called a Monteggia-equivalent lesion (Fig. 1, A).16 Lincoln and Mubarak17 insisted that no isolated radial head dislocation could be present; rather, they indicated the presence of plastic bowing in the ulna on plain radiography, which they called the ‘ulnar bow sign’. Plastic bowing deformity in the ulna can also be produced in radial shaft fractures in children (Fig. 1, B).5,6 Such lesions are often overlooked, and only the radius is treated because the deformity of the ulna is relatively minor on plain radiography and the deformity often causes limitations of forearm motion.9,34 Deformities of the ulna have been assessed by plain radiography,26 and it has been reported that such deformities should be corrected if the maximum ulnar bow is more than 5 mm.17 However, there have been few reports on the biomechanics of these deformities, and we believe that assessment of ulnar bowing with 2-dimensional plain radiography is insufficient. Alternatively, 3-dimensional assessment of the deformity could be valuable. We hypothesized that the deformation of bowed bones is 3-dimensional, not just 2-dimensional. We also considered malunited radial shaft fractures to represent 3-dimensional deformities of the ulna. We evaluated their rotational, sagittal, and coronal bending deformities in Euler angle space using 3-dimensional computed tomography (CT) and a markerless registration technique.15
This novel method may result in improved treatment and provide a better assessment of mechanisms of injuries of Monteggia-equivalent and radial shaft fractures.
Materials and methods Between 2003 and 2008, 10 children with plastic bowing of the ulna underwent corrective osteotomy to treat functional deficits, including limitation of motion and pain or cosmetic issues. Among them, 4 had traumatic ulnar bowing deformities with chronic radial head dislocation after a Monteggia-equivalent lesion and 6 had ulnar bowing deformities with malunited radial shaft fractures. The mean age at evaluation for reconstruction was 13.3 years (range, 9-19 years). The mean time elapsed from the first trauma to assessment was 14.9 months (range, 1-38 months). One Monteggia-equivalent lesion was initially managed with open reduction of the radial head. Three other cases were managed with closed reduction. Among the 6 cases of malunited radii, 3 were initially treated with casts whereas 3 underwent percutaneous pinning after closed reduction (Table I). All patients had angular deformities of the ulna, radius, or both on plain radiography. CT data obtained from the patients were analyzed for this study.
Analysis of deformity The affected and contralateral radius and ulna of all cases underwent CT scanning (Light Speed Ultra 16; General Electric, Waukesha, WI, USA) with a scan time of 0.5 seconds, scan pitch of 0.562:1, tube current of 30 mA, and tube voltage of 120 kV. For scanning, the patient was positioned prone with the shoulder at full elevation, elbow at full extension, forearm neutral, and both arms overhead. DICOM (Digital Imaging and Communications in Medicine) data were sent to a workstation (Dell Precision Workstation 390; Dell, Round Rock, TX, USA).
1646 Table I
E. Kim et al. Demographic and clinical data of patients with plastic bowing deformity of ulna
Type
Case
Sex
Age (y)
Time from injury to assessment (mo)
Initial treatment
Symptoms
Radial head dislocation
1 2 3 4 5 6 7 8 9 10
Female Female Male Male Male Male Male Male Female Female
9 13 12 7 19 9 16 13 12 15
4 1 3 10 38 8 6 9 24 26
Open reduction Closed reduction Closed reduction Closed reduction Cast Pinning Pinning Cast Pinning Cast
Limitation of motion Limitation of motion Limitation of motion Limitation of motion Limitation of motion Limitation of motion Limitation of motion Limitation of motion Limitation of motion, pain Limitation of motion, cosmetic problem
Malunited radius
First, we used commercially available software (Bone Viewer; Orthree, Osaka, Japan) to construct 3-dimensional surface models of the entire bilateral radii and ulnae by applying 3-dimensional generation of the surface of the cortex without a marker19,21 using 1.25-mm slice digital data. The proximal part of the affected bone was superimposed onto its mirror image of the contralateral normal bone. The same procedure was applied to the distal part followed by semiautomatic adjustment with use of independent implementation of an interactive closest-point algorithm for surface-based registration,4 which was performed with software (Bone Simulator; Orthree). The accuracy of this surface-based registration technique is 1.7 in rotation and 0.2 mm in translation.14 The technique’s interobserver reliability is over 0.9.29 Second, the amount of 3-dimensional displacement of the distal part of the affected side relative to the mirror image of the normal side was quantified with 6 df in Euler angles as proposed by the International Society of Biomechanics.35 In the ulna, the origin of the axis, Yu, intersects the approximate center of the tubular bone along the principal axis of inertia, which in the distal ulna is at the level of the dome of the ulnar head and in the proximal ulna is at the level of the coronoid process. Xu is the line perpendicular to the Yu axis and along a vector passing through the tip of the coronoid process. Zu is the common line perpendicular to the Xu and Yu axes (Fig. 2). In the radius, the origin of the axis, Yr, crosses at the ridge between the radioscaphoid fossa and radiolunate fossa to the depression of the radial head. Zr is the line perpendicular to Yr and parallel to the plane between the radial styloid process and the base of concavity of the sigmoid notch. Xr is the line perpendicular to Yr and Zr.35 When the rotational angles of the distal parts of the ulna and radius matched their mirror images, this was considered to indicate the deformity angle in 3 directions. We quantified bending deformity of extension (þ) or flexion (–) in the sagittal plane (XY), bending deformity of valgus (þ) or varus (–) in the coronal plane (YZ), and internal (þ, clockwise) or external (–, counterclockwise) rotational deformity in the axial plane (XZ) in Euler angle space (Fig. 3). We compared the differences in these 3 kinds of deformity between the group of patients with radial head dislocation and the group with malunited radial shaft, and differences among the 3 kinds of deformity angles in each group were also compared. Absolute values of deformity angles of the 2 groups were compared. Furthermore, we conducted analyses to detect correlations between the deformity angles of the ulna and radius in the malunited radial shaft group.
Figure 2 Anatomic coordinate system of 3-dimensional deformity in Euler angle space proposed by International Society of Biomechanics. The deformed ulna is superimposed onto the mirror image of the normal side (semi-lucent ulna).
Statistical analysis Statistical software (SPSS 19.0; IBM, Armonk, NY, USA) was used for all analyses. Results are expressed as the median (interquartile range). Differences between the 2 groups were analyzed by Mann-Whitney U tests, and linear correlations were assessed by the Spearman r coefficient. The results were considered significant if P < .05.
Results Table II shows the 3 deformity angles of the distal part relative to the proximal part for each patient in Euler angle space. The radial head dislocation group had extended sagittal angulation (10.4 7.0 ), whereas the radial shaft malunion group had flexed sagittal angulation (–6.3 5.6 ) (P < .05). No difference was found in coronal angulation between the 2 groups (P ¼ .7). All 4 cases with anterior dislocations of the radial head had a mean of 18.7 17.4 of external rotation (–) without internal
Plastic bowing deformity of ulna
1647
Figure 3 Three kinds of deformed angles in Euler angle space. The deformed ulna is superimposed onto the mirror image of the normal side (semi-lucent ulna) in the sagittal plane for extended or flexed angulation (YX) (A) in the coronal plane for valgus or varus angulation (YZ) (B) and in the axial plane for rotational angulation (XZ) (C).
rotation. In the 6 cases of ulnar bowing deformity with malunited radial shaft fracture, there was a mean of 12.5 12.7 of internal rotation (þ) of the ulna (P < .05), with 1 case showing almost no rotational deformity (case 7) (Table II). Rotational deformities of each group were statistically larger than their sagittal or coronal deformities (P < .05). Furthermore, the mean absolute value of rotational deformity in the axial plane of all 10 cases was 15.1 13.9 , which was significantly greater than the mean values of coronal deformity (8.7 5.2 ) and sagittal deformity (4.0 4.4 ) (P < .05). There was no linear correlation among sagittal, coronal, and axial deformity of the ulna in Monteggia-equivalent cases. In addition, no linear correlation was found between deformities of the ulna and radial deformities in patients with malunion of the radius (r < 0.7). In terms of the radial deformities in the malunited radial shaft fractures, most of the patients had internal rotational deformities, which were significantly greater than the bending deformities (P < .05).
Discussion Fractures or dislocations of the radius in children often occur because of falls from heights onto outstretched hands. Among these very common injuries of the forearm, plastic bowing deformities are considered to be relatively rare. A biomechanical study of plastic deformation proposed that compressive, longitudinal force exceeding the zone of elastic deformation but not the point of fracture during the plastic phase allows bowing.8 The forearm is vulnerable to plastic deformity because of its 2 naturally curved bones, but plastic deformity commonly takes place in a single bone rather than in both the radius and the ulna.2,6
Moreover, plastic deformity of the ulna is more prevalent2,3,5 than that of the radius.34 The flexibility of the ulna in children allows for bowing without fracture and dislocation of the radial head.5,12 Evans12 suggested that rotational force at the wrist causes rupture of the annular ligament and then dislocates the radial head. Tompkins32 mentioned hyperextension of the elbow as being responsible for bowing and dislocation, but rotational force in addition to axial force seems to be more related to plastic bowing and dislocation. Therefore it is reasonable to hypothesize that considerable rotational stress around the forearm axis would be produced. However, the factor that determines whether external or internal rotation occurs was uncertain. Several biomechanical studies about rotational deformity of the forearm showed a change in the range of motion. In vitro studies that produced artificial malunions of the ulna caused decreased range of rotational movement of the forearm.11,30,33,36 Recently, in vivo kinematic studies have also been reported.20,31 A few 3-dimensional analyses of malunion21 and the importance of rotational deformity in corrective osteotomy9 have been reported, but to our knowledge, there are no studies concerning 3-dimensional analysis of plastic bowing of the forearm in children. We believe that 3-dimensional assessment of plastic bowing deformity gave important information about torque and the direction of force of the initial injuries, which could yield presumptions regarding the mechanism of the injury. On the basis of the results of our study, anterior radial head dislocation appeared to be caused by external rotational deformities of the ulna as well as sagittal extension deformity. Almost all radial shaft fractures had internal rotational deformities with sagittal flexion deformity, except for 1 case with almost no rotational deformity (case 7) (Table II). Therefore we suggest the following mechanism of injury in forearm bones: During falling injuries, the
1648 Table II Type
E. Kim et al. Data of 3-dimensional angular deformity of radius and ulna Case Deformity of ulna ( ))
Radial head dislocation
Radial shaft malunion
)
1 2 3 4 Mean SD 5 6 7 8 9 10 Mean SD
Sagittal extension
Coronal valgus angulation
4.51 4.24 17.72 15.00 10.37 7.01 4.93 4.83 13.35 3.10 7.94 10.06 6.33 5.64
4.91 1.75 3.21 0.34 1.68 2.96 0.03 0.55 3.14 14.42 4.60 7.83 5.09 5.38
Axial internal rotation 8.32) 8.27 44.44 13.81 18.71 17.35 34.61 17.17 0.91 4.73 13.87 5.28 12.46 12.69
Deformity of radius ( )) Sagittal extension
Coronal valgus angulation
Axial internal rotation
18.93 29.06 8.18 19.83 22.51 30.37 8.08 21.25
5.75 5.81 1.19 4.80 0.06 1.64 1.58 4.18
2.72 37.18 15.07 45.20 8.66 20.28 15.74 22.42
A minus signs means opposite direction of data in same column.
elbow is extended with the wrist pronated and extended. While the body shifts laterally around the forearm after contacting the ground, both axial and external rotational stresses are produced on the forearm. This force produces external rotation and posterior bowing of the ulna. At the same time, the radius is pushed by the ulna, and the radial head is compressed forward, causing an anterior dislocation of the radial head. In other cases, when the body shifts medially around the forearm, axial and internal rotational stress is produced on the forearm, which produces internal rotational bowing of the ulna. The pronated distal radius bends dorsally, and the radial head is compressed posteriorly. This force breaks the radial shaft and produces a dorsally angulated fracture of the radial shaft rather than dislocation (Fig. 4). Although some reports have shown good results of ulnar corrective osteotomy in chronic Monteggia-equivalent lesions,15 many complications have been reported, such as redislocation of the radial head and limited motion of the elbow and forearm.7,16,18,23,25 The causes were not clearly explained. Our hypothesis may explain the poor results of treatment of chronic radial head dislocations. In addition, our results indicate the importance of rotational correction because rotational deformities were larger than bowing deformities in our patients. To apply the 3-dimensional corrective osteotomy in the surgical field, a set of marker pins were inserted on the distal and proximal ulnae, and the 2 sets of pins were twisted at deformed rotational degrees to each other. Correction was considered complete when the surgeon rotated the distal fragment until these 2 sets of pins became parallel after osteotomy. Furthermore, the surgeon can predict the rotational deformity by comparing the distal and proximal slices of the CT scans of both arms without using a special computer program such as the program that we used for precise analysis of 3-dimensional deformities.
Figure 4 Suggested mechanism of Monteggia-equivalent lesion and radial shaft fracture. (A) Bowed ulna with radial head dislocation. (B) Bowed ulna with radial shaft fracture. The large arrows indicate the direction of the loading force of the injuries, the small arrows indicate the direction of force to the radial head, and the curved arrows indicate the rotational direction of the forearms. The curved lines and lightning bolt show the direction of the curvature caused by the plastic deformity and the breaking force. The outside force to the body causes external rotation of the forearm, and the inside force results in internal rotation.
One of the limitations of this study was the small number of subjects. Although cases of traumatic bowed bones rarely present clinically, the inclusion of more cases would yield greater confidence in our conclusions. The other limitation was that this study still could not give us the exact correlation between rotational deformity and limitation of motion of the elbow or forearm. The data we report were calculated in the hypothetical coordinate system, so they could not quantify what deformity would have been present in the real surgical field.
Plastic bowing deformity of ulna In future studies, it will be necessary to report surgical outcomes after long-term follow-up and also to evaluate larger numbers of cases. More accurate surgical application of analyzed data, such as the use of a surgical navigation system, should be developed. In addition, biomechanical studies performed to seek the correlation between rotational deformity and limited motion of the elbow and forearm are needed to overcome the limitations of our study and validate our hypothesis.
Conclusion Traumatic plastic bowing deformity of the ulna included external rotational deformity in patients with radial head dislocation of Monteggia-equivalent lesions and internal rotational deformity in patients with radial shaft fractures rather than bending deformities. External rotational and axial stress on the ulna was suspected to result in radial head dislocation and internal rotational and axial stress was suspected to result in radial shaft fracture during injury involving falling onto an outstretched arm. Therefore rotational deformity should be considered in treatment strategies.
Acknowledgments We thank Ryoji Nakao and Sumika Ikemoto, Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, for development of software and assistance in simulation work.
Disclaimer Tsuyoshi Murase, MD, PhD, and Eugene Kim, MD, PhD, received a grant from the Japan Science and Technology Agency (No. 1810), and Eugene Kim, MD, PhD, was partially supported by the National Research Foundation grant funded by the Korean government (MEST) (No. 2010-0027294).
References 1. Anderson IF, Hume KF, Chong AL. Plastic bowing of the forearm in the more mature skeleton. Aust N Z J Surg 1994;64:132-4. 2. Aponte JE Jr, Chiatas A. Acute plastic bowing deformity. A review of the literature. J Emerg Med 1989;7:181-4. 3. Attia MW, Glasstetter DS. Plastic bowing type fracture of the forearm in two children. Pediatr Emerg Care 1997;13:392-3. 4. Besl PJ. A method for registration of 3-D shapes. IEEE Trans Pattern Anal Mach Intell 1992;14:239-56.
1649 5. Borden SIV. Roentgen recognition of acute plastic bowing of the forearm in children. Am J Roentgenol Radium Ther Nucl Med 1975;125:524-30. 6. Borden S. Traumatic bowing of the forearm in children. J Bone Joint Surg Am 1974;56:611-6. 7. Bruce HE, Harvey JP Jr, Wilson JC Jr. Monteggia fractures. J Bone Joint Surg Am 1974;56:1563-76. 8. Chamay A. Mechanical and morphological aspects of experimental overload and fatigue in bone. J Biomech 1970;3:2630-3. 9. Chia DS, Lim YJ, Chew WY. Corrective osteotomy in forearm fracture malunion improves functional outcome in adults. J Hand Surg Eur 2011;36:102-6. doi:10.1177/1753193410380585 10. Demster W, Liddicoat RT. Compact bone as a nonisotropic material. Am J Anat 1952;91:331-62. 11. Dumont CE, Thalmann R, Macy JC. The effect of rotational malunion of the radius and the ulna on supination and pronation. J Bone Joint Surg Br 2002;84:1070-4. doi:10.1302/0301-620X.84B7.12593 12. Evans EM. Pronation injuries of the forearm, with special reference to the anterior Monteggia fracture. J Bone Joint Surg Br 1949;31:578-88. 13. Gordon L, Beaton W, Thomas T, Mulbry LW. Acute plastic deformation of the ulna in a skeletally mature individual. J Hand Surg Am 1991;16:451-3. 14. Goto A, Moritomo H, Murase T, Oka K, Sugamoto K, Arimura T, et al. In vivo three-dimensional wrist motion analysis using magnetic resonance imaging and volume-based registration. J Orthop Res 2005; 23:750-6. doi:10.1016/j.jse.2010.11.020 15. Hirayama T, Takemitsu Y, Yagihara K, Mikita A. Operation for chronic dislocation of the radial head in children. J Bone Joint Surg Br 1987;69:639-42. 16. Letts M, Locht R, Wiens J. Monteggia fracture-dislocations in children. J Bone Joint Surg Br 1985;67:724-7. 17. Lincoln TL, Mubarak SJ. Isolated traumatic radial-head dislocation. J Pediatr Orthop 1994;14:454-7. 18. Lloyd-Roberts GC, Bucknill TM. Anterior dislocation of the radial head in children. Aetiology, natural history and management. J Bone Joint Surg Br 1977;59:402-7. 19. Lorensen WE, Cline HE. Marching cubes. A high resolution 3D surface construction algorithm. Comput Graph 1987;21:163-9. 20. Matsuki KO, Matsuki K, Mu S, Sasho T, Nakagawa K, Ochiai N, et al. In vivo 3D kinematics of normal forearms. Analysis of dynamic forearm rotation. Clin Biomech (Bristol, Avon) 2010;25:979-83. doi: 10.1016/j.clinbiomech.2010.07.006 21. Murase T, Oka K, Moritomo H, Goto A, Yoshikawa H, Sugamoto K. Three-dimensional corrective osteotomy of malunited fractures of the upper extremity with use of a computer simulation system. J Bone Joint Surg Am 2008;90:2375-89. doi:10.1016/j.jhsa.2008.02.008 22. Neviaser RJ, Lefevre GW. Irreducible isolated dislocation of the radial head. A case report. Clin Orthop Relat Res 1971;80:72-80. 23. Rodgers WB, Waters PM, Hall JE. Chronic Monteggia lesions in children. Complications and results of reconstruction. J Bone Joint Surg Am 1996;78:1322-9. 24. Rydholm U, Nilsson JE. Traumatic bowing of the forearm. A case report. Clin Orthop Relat Res 1979:121-4. 25. Sai S, Fujii K, Chino H, Inoue J. Radial head dislocation with acute plastic bowing of the ulna. 5 case J Orthop Sci 2005;10:103-7. doi:10. 1007/s00776-004-0860-x 26. Schemitsch EH, Richards RR. The effect of malunion on functional outcome after plate fixation of fractures of both bones of the forearm in adults. J Bone Joint Surg Am 1992;74:1068-78. 27. Sclamberg J, Sonin AH, Sclamberg E, D’Sonza N. Acute plastic bowing deformation of the forearm in an adult. AJR Am J Roentgenol 1998;170:1259-60. 28. Tada K, Ikeda K, Tsubouchi H, Tomita K. Acute plastic bowing of the forearm in adults. A report of two cases. J Orthop Surg 2008;16:241-2. 29. Takeyasu Y, Murase T, Miyake J, Oka K, Arimitsu S, Moritomo H, et al. Three-dimensional analysis of cubitus varus deformity after supracondylar fractures of the humerus. J Shoulder Elbow Surg 2011; 20:440-8. doi:10.1016/j.jse.2010.11.020
1650 30. Tarr RR, Garfinkel AI, Sarmiento A. The effects of angular and rotational deformities of both bones of the forearm. An in vitro study. J Bone Joint Surg Am 1984;66:65-70. 31. Tay SC, van Reit R, Kazunari T, Amrami KK, An KA, Berger RA. In-vivo kinematic analysis of forearm rotation using helical axis analysis. Clin Biomech (Bristol, Avon) 2010;25:655-9. doi:10.1016/ j.clinbiomech.2010.03.010 32. Tompkins DG. The anterior Monteggia fracture. Observations on etiology and treatment. J Bone Joint Surg Am 1971;53:1109-14. 33. Tynan MC, Fornalski S, McMahon PJ, Utkan A, Green SA, Lee TQ. The effects of ulnar axial malalignment on supination and pronation. J Bone Joint Surg Am 2000;82:1726-31.
E. Kim et al. 34. Uehara M, Yamazaki H, Kato H. Acute plastic bowing of the radius with a distal radioulnar joint injury. A case report. Hand Surg 2010;15: 217-20. doi:10.1142/S0218810410004916 35. Wu G, Van der Helm FC, Veeger HE, Makhsous M, Van Roy P, Anglin C, et al. ISB recommendation on definitions of joint coordinate systems of various joints for the reporting of human joint motion. Part II: shoulder, elbow, wrist and hand. J Biomech 2005;38:981-92. doi: 10.1016/j.jbiomech.2004.05.042 36. Yasutomi T, Nakatsuchi Y, Koike H, Uchiyama S. Mechanism of limitation of pronation/supination of the forearm in geometric models of deformities of the forearm bones. Clin Biomech (Bristol, Avon) 2002;17:456-63. doi:10.1016/S0268-0033(02)00034-7
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Three-dimensional analysis of acute plastic bowing deformity of ulna in radial head dislocation or radial shaft fracture using a computerized simulation system Eugene Kim, MD, PhDa, Hisao Moritomo, MD, PhDb,*, Tsuyoshi Murase, MD, PhDb, Takashi Masatomi, MD, PhDc, Junichi Miyake, MD, PhDb, Kazuomi Sugamoto, MD, PhDb a
Department of Orthopaedic Surgery, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, South Korea b Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, Osaka, Japan c Department of Orthopaedic Surgery, Yukioka Hospital, Osaka, Japan Background: Little 3-dimensional biomechanical investigation of plastic bowing deformity of the ulna has been reported, and the purpose of this study was to conduct such an investigation to elucidate mechanisms of injury and appropriate treatments. Methods: Ten cases of traumatic plastic deformity of the ulna in pediatric patients, 4 with chronic radial head dislocations (Monteggia equivalent) and 6 with malunited radial shaft fractures, were analyzed for rotational deformities in the axial plane and bending deformities in the sagittal and coronal planes in Euler angle space by use of a 3-dimensional computerized simulation system with a markerless registration technique. Results: Deformed ulnae with radial head dislocations had 18.7 17.4 of external rotation in the axial plane and 10.4 7.0 of extension in the sagittal plane whereas those with malunited radial shaft fractures had 12.5 12.7 of internal rotation and 6.3 5.6 of flexion displacement compared with mirror images of the opposite ulnae. Absolute values of rotational deformities in both groups were larger than those of sagittal and coronal bending deformities. Discussion: Most major traumatic plastic bowing deformities of the ulna involved rotation rather than bending. External rotational stress on the ulna is suspected to cause radial head dislocation, and internal rotational stress results in radial shaft fracture during falls onto outstretched arms. Therefore the correction of rotational deformities of the ulna should be considered in the treatment of chronic radial head dislocations and malunited radial shaft fractures. Level of evidence: Basic Science, Anatomic Study, Imaging. Ó 2012 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Computerized simulation; plastic bowing deformity; radial head dislocation; radial shaft fracture; 3-dimensional; ulna
Ethical board review statement: Each author certifies that the institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles for research, and that informed consent for participation in the study was obtained (institutional review board of Osaka University Graduate School of Medicine No. 08332).
*Reprint requests: Hisao Moritomo, MD, PhD, Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, 2-2, Yamada-oka, Suita, Osaka 565-0871, Japan. E-mail address: [email protected] (H. Moritomo).
1058-2746/$ - see front matter Ó 2012 Journal of Shoulder and Elbow Surgery Board of Trustees. doi:10.1016/j.jse.2011.12.006
Plastic bowing deformity of ulna
1645
Figure 1 Traumatic plastic bowing of ulna in a patient with radial head dislocation (Monteggia-equivalent lesion) (A) and in a patient with radial shaft fracture (B).
‘‘Plastic bowing deformation’’ is defined as a bowing deformity that remains after compressing longitudinal forces are applied to a curved tubular bone in its stress-strain curve.10 Since Borden6 described traumatic bowing of the ulna and radius in children for the first time, several pediatric cases have been reported3,22,24,25,34; in addition, some cases have been reported in adults.1,13,27,28 Some Monteggia fractures in children show no fractures of the ulna but rather show a bend, which is called a Monteggia-equivalent lesion (Fig. 1, A).16 Lincoln and Mubarak17 insisted that no isolated radial head dislocation could be present; rather, they indicated the presence of plastic bowing in the ulna on plain radiography, which they called the ‘ulnar bow sign’. Plastic bowing deformity in the ulna can also be produced in radial shaft fractures in children (Fig. 1, B).5,6 Such lesions are often overlooked, and only the radius is treated because the deformity of the ulna is relatively minor on plain radiography and the deformity often causes limitations of forearm motion.9,34 Deformities of the ulna have been assessed by plain radiography,26 and it has been reported that such deformities should be corrected if the maximum ulnar bow is more than 5 mm.17 However, there have been few reports on the biomechanics of these deformities, and we believe that assessment of ulnar bowing with 2-dimensional plain radiography is insufficient. Alternatively, 3-dimensional assessment of the deformity could be valuable. We hypothesized that the deformation of bowed bones is 3-dimensional, not just 2-dimensional. We also considered malunited radial shaft fractures to represent 3-dimensional deformities of the ulna. We evaluated their rotational, sagittal, and coronal bending deformities in Euler angle space using 3-dimensional computed tomography (CT) and a markerless registration technique.15
This novel method may result in improved treatment and provide a better assessment of mechanisms of injuries of Monteggia-equivalent and radial shaft fractures.
Materials and methods Between 2003 and 2008, 10 children with plastic bowing of the ulna underwent corrective osteotomy to treat functional deficits, including limitation of motion and pain or cosmetic issues. Among them, 4 had traumatic ulnar bowing deformities with chronic radial head dislocation after a Monteggia-equivalent lesion and 6 had ulnar bowing deformities with malunited radial shaft fractures. The mean age at evaluation for reconstruction was 13.3 years (range, 9-19 years). The mean time elapsed from the first trauma to assessment was 14.9 months (range, 1-38 months). One Monteggia-equivalent lesion was initially managed with open reduction of the radial head. Three other cases were managed with closed reduction. Among the 6 cases of malunited radii, 3 were initially treated with casts whereas 3 underwent percutaneous pinning after closed reduction (Table I). All patients had angular deformities of the ulna, radius, or both on plain radiography. CT data obtained from the patients were analyzed for this study.
Analysis of deformity The affected and contralateral radius and ulna of all cases underwent CT scanning (Light Speed Ultra 16; General Electric, Waukesha, WI, USA) with a scan time of 0.5 seconds, scan pitch of 0.562:1, tube current of 30 mA, and tube voltage of 120 kV. For scanning, the patient was positioned prone with the shoulder at full elevation, elbow at full extension, forearm neutral, and both arms overhead. DICOM (Digital Imaging and Communications in Medicine) data were sent to a workstation (Dell Precision Workstation 390; Dell, Round Rock, TX, USA).
1646 Table I
E. Kim et al. Demographic and clinical data of patients with plastic bowing deformity of ulna
Type
Case
Sex
Age (y)
Time from injury to assessment (mo)
Initial treatment
Symptoms
Radial head dislocation
1 2 3 4 5 6 7 8 9 10
Female Female Male Male Male Male Male Male Female Female
9 13 12 7 19 9 16 13 12 15
4 1 3 10 38 8 6 9 24 26
Open reduction Closed reduction Closed reduction Closed reduction Cast Pinning Pinning Cast Pinning Cast
Limitation of motion Limitation of motion Limitation of motion Limitation of motion Limitation of motion Limitation of motion Limitation of motion Limitation of motion Limitation of motion, pain Limitation of motion, cosmetic problem
Malunited radius
First, we used commercially available software (Bone Viewer; Orthree, Osaka, Japan) to construct 3-dimensional surface models of the entire bilateral radii and ulnae by applying 3-dimensional generation of the surface of the cortex without a marker19,21 using 1.25-mm slice digital data. The proximal part of the affected bone was superimposed onto its mirror image of the contralateral normal bone. The same procedure was applied to the distal part followed by semiautomatic adjustment with use of independent implementation of an interactive closest-point algorithm for surface-based registration,4 which was performed with software (Bone Simulator; Orthree). The accuracy of this surface-based registration technique is 1.7 in rotation and 0.2 mm in translation.14 The technique’s interobserver reliability is over 0.9.29 Second, the amount of 3-dimensional displacement of the distal part of the affected side relative to the mirror image of the normal side was quantified with 6 df in Euler angles as proposed by the International Society of Biomechanics.35 In the ulna, the origin of the axis, Yu, intersects the approximate center of the tubular bone along the principal axis of inertia, which in the distal ulna is at the level of the dome of the ulnar head and in the proximal ulna is at the level of the coronoid process. Xu is the line perpendicular to the Yu axis and along a vector passing through the tip of the coronoid process. Zu is the common line perpendicular to the Xu and Yu axes (Fig. 2). In the radius, the origin of the axis, Yr, crosses at the ridge between the radioscaphoid fossa and radiolunate fossa to the depression of the radial head. Zr is the line perpendicular to Yr and parallel to the plane between the radial styloid process and the base of concavity of the sigmoid notch. Xr is the line perpendicular to Yr and Zr.35 When the rotational angles of the distal parts of the ulna and radius matched their mirror images, this was considered to indicate the deformity angle in 3 directions. We quantified bending deformity of extension (þ) or flexion (–) in the sagittal plane (XY), bending deformity of valgus (þ) or varus (–) in the coronal plane (YZ), and internal (þ, clockwise) or external (–, counterclockwise) rotational deformity in the axial plane (XZ) in Euler angle space (Fig. 3). We compared the differences in these 3 kinds of deformity between the group of patients with radial head dislocation and the group with malunited radial shaft, and differences among the 3 kinds of deformity angles in each group were also compared. Absolute values of deformity angles of the 2 groups were compared. Furthermore, we conducted analyses to detect correlations between the deformity angles of the ulna and radius in the malunited radial shaft group.
Figure 2 Anatomic coordinate system of 3-dimensional deformity in Euler angle space proposed by International Society of Biomechanics. The deformed ulna is superimposed onto the mirror image of the normal side (semi-lucent ulna).
Statistical analysis Statistical software (SPSS 19.0; IBM, Armonk, NY, USA) was used for all analyses. Results are expressed as the median (interquartile range). Differences between the 2 groups were analyzed by Mann-Whitney U tests, and linear correlations were assessed by the Spearman r coefficient. The results were considered significant if P < .05.
Results Table II shows the 3 deformity angles of the distal part relative to the proximal part for each patient in Euler angle space. The radial head dislocation group had extended sagittal angulation (10.4 7.0 ), whereas the radial shaft malunion group had flexed sagittal angulation (–6.3 5.6 ) (P < .05). No difference was found in coronal angulation between the 2 groups (P ¼ .7). All 4 cases with anterior dislocations of the radial head had a mean of 18.7 17.4 of external rotation (–) without internal
Plastic bowing deformity of ulna
1647
Figure 3 Three kinds of deformed angles in Euler angle space. The deformed ulna is superimposed onto the mirror image of the normal side (semi-lucent ulna) in the sagittal plane for extended or flexed angulation (YX) (A) in the coronal plane for valgus or varus angulation (YZ) (B) and in the axial plane for rotational angulation (XZ) (C).
rotation. In the 6 cases of ulnar bowing deformity with malunited radial shaft fracture, there was a mean of 12.5 12.7 of internal rotation (þ) of the ulna (P < .05), with 1 case showing almost no rotational deformity (case 7) (Table II). Rotational deformities of each group were statistically larger than their sagittal or coronal deformities (P < .05). Furthermore, the mean absolute value of rotational deformity in the axial plane of all 10 cases was 15.1 13.9 , which was significantly greater than the mean values of coronal deformity (8.7 5.2 ) and sagittal deformity (4.0 4.4 ) (P < .05). There was no linear correlation among sagittal, coronal, and axial deformity of the ulna in Monteggia-equivalent cases. In addition, no linear correlation was found between deformities of the ulna and radial deformities in patients with malunion of the radius (r < 0.7). In terms of the radial deformities in the malunited radial shaft fractures, most of the patients had internal rotational deformities, which were significantly greater than the bending deformities (P < .05).
Discussion Fractures or dislocations of the radius in children often occur because of falls from heights onto outstretched hands. Among these very common injuries of the forearm, plastic bowing deformities are considered to be relatively rare. A biomechanical study of plastic deformation proposed that compressive, longitudinal force exceeding the zone of elastic deformation but not the point of fracture during the plastic phase allows bowing.8 The forearm is vulnerable to plastic deformity because of its 2 naturally curved bones, but plastic deformity commonly takes place in a single bone rather than in both the radius and the ulna.2,6
Moreover, plastic deformity of the ulna is more prevalent2,3,5 than that of the radius.34 The flexibility of the ulna in children allows for bowing without fracture and dislocation of the radial head.5,12 Evans12 suggested that rotational force at the wrist causes rupture of the annular ligament and then dislocates the radial head. Tompkins32 mentioned hyperextension of the elbow as being responsible for bowing and dislocation, but rotational force in addition to axial force seems to be more related to plastic bowing and dislocation. Therefore it is reasonable to hypothesize that considerable rotational stress around the forearm axis would be produced. However, the factor that determines whether external or internal rotation occurs was uncertain. Several biomechanical studies about rotational deformity of the forearm showed a change in the range of motion. In vitro studies that produced artificial malunions of the ulna caused decreased range of rotational movement of the forearm.11,30,33,36 Recently, in vivo kinematic studies have also been reported.20,31 A few 3-dimensional analyses of malunion21 and the importance of rotational deformity in corrective osteotomy9 have been reported, but to our knowledge, there are no studies concerning 3-dimensional analysis of plastic bowing of the forearm in children. We believe that 3-dimensional assessment of plastic bowing deformity gave important information about torque and the direction of force of the initial injuries, which could yield presumptions regarding the mechanism of the injury. On the basis of the results of our study, anterior radial head dislocation appeared to be caused by external rotational deformities of the ulna as well as sagittal extension deformity. Almost all radial shaft fractures had internal rotational deformities with sagittal flexion deformity, except for 1 case with almost no rotational deformity (case 7) (Table II). Therefore we suggest the following mechanism of injury in forearm bones: During falling injuries, the
1648 Table II Type
E. Kim et al. Data of 3-dimensional angular deformity of radius and ulna Case Deformity of ulna ( ))
Radial head dislocation
Radial shaft malunion
)
1 2 3 4 Mean SD 5 6 7 8 9 10 Mean SD
Sagittal extension
Coronal valgus angulation
4.51 4.24 17.72 15.00 10.37 7.01 4.93 4.83 13.35 3.10 7.94 10.06 6.33 5.64
4.91 1.75 3.21 0.34 1.68 2.96 0.03 0.55 3.14 14.42 4.60 7.83 5.09 5.38
Axial internal rotation 8.32) 8.27 44.44 13.81 18.71 17.35 34.61 17.17 0.91 4.73 13.87 5.28 12.46 12.69
Deformity of radius ( )) Sagittal extension
Coronal valgus angulation
Axial internal rotation
18.93 29.06 8.18 19.83 22.51 30.37 8.08 21.25
5.75 5.81 1.19 4.80 0.06 1.64 1.58 4.18
2.72 37.18 15.07 45.20 8.66 20.28 15.74 22.42
A minus signs means opposite direction of data in same column.
elbow is extended with the wrist pronated and extended. While the body shifts laterally around the forearm after contacting the ground, both axial and external rotational stresses are produced on the forearm. This force produces external rotation and posterior bowing of the ulna. At the same time, the radius is pushed by the ulna, and the radial head is compressed forward, causing an anterior dislocation of the radial head. In other cases, when the body shifts medially around the forearm, axial and internal rotational stress is produced on the forearm, which produces internal rotational bowing of the ulna. The pronated distal radius bends dorsally, and the radial head is compressed posteriorly. This force breaks the radial shaft and produces a dorsally angulated fracture of the radial shaft rather than dislocation (Fig. 4). Although some reports have shown good results of ulnar corrective osteotomy in chronic Monteggia-equivalent lesions,15 many complications have been reported, such as redislocation of the radial head and limited motion of the elbow and forearm.7,16,18,23,25 The causes were not clearly explained. Our hypothesis may explain the poor results of treatment of chronic radial head dislocations. In addition, our results indicate the importance of rotational correction because rotational deformities were larger than bowing deformities in our patients. To apply the 3-dimensional corrective osteotomy in the surgical field, a set of marker pins were inserted on the distal and proximal ulnae, and the 2 sets of pins were twisted at deformed rotational degrees to each other. Correction was considered complete when the surgeon rotated the distal fragment until these 2 sets of pins became parallel after osteotomy. Furthermore, the surgeon can predict the rotational deformity by comparing the distal and proximal slices of the CT scans of both arms without using a special computer program such as the program that we used for precise analysis of 3-dimensional deformities.
Figure 4 Suggested mechanism of Monteggia-equivalent lesion and radial shaft fracture. (A) Bowed ulna with radial head dislocation. (B) Bowed ulna with radial shaft fracture. The large arrows indicate the direction of the loading force of the injuries, the small arrows indicate the direction of force to the radial head, and the curved arrows indicate the rotational direction of the forearms. The curved lines and lightning bolt show the direction of the curvature caused by the plastic deformity and the breaking force. The outside force to the body causes external rotation of the forearm, and the inside force results in internal rotation.
One of the limitations of this study was the small number of subjects. Although cases of traumatic bowed bones rarely present clinically, the inclusion of more cases would yield greater confidence in our conclusions. The other limitation was that this study still could not give us the exact correlation between rotational deformity and limitation of motion of the elbow or forearm. The data we report were calculated in the hypothetical coordinate system, so they could not quantify what deformity would have been present in the real surgical field.
Plastic bowing deformity of ulna In future studies, it will be necessary to report surgical outcomes after long-term follow-up and also to evaluate larger numbers of cases. More accurate surgical application of analyzed data, such as the use of a surgical navigation system, should be developed. In addition, biomechanical studies performed to seek the correlation between rotational deformity and limited motion of the elbow and forearm are needed to overcome the limitations of our study and validate our hypothesis.
Conclusion Traumatic plastic bowing deformity of the ulna included external rotational deformity in patients with radial head dislocation of Monteggia-equivalent lesions and internal rotational deformity in patients with radial shaft fractures rather than bending deformities. External rotational and axial stress on the ulna was suspected to result in radial head dislocation and internal rotational and axial stress was suspected to result in radial shaft fracture during injury involving falling onto an outstretched arm. Therefore rotational deformity should be considered in treatment strategies.
Acknowledgments We thank Ryoji Nakao and Sumika Ikemoto, Department of Orthopaedic Surgery, Osaka University Graduate School of Medicine, for development of software and assistance in simulation work.
Disclaimer Tsuyoshi Murase, MD, PhD, and Eugene Kim, MD, PhD, received a grant from the Japan Science and Technology Agency (No. 1810), and Eugene Kim, MD, PhD, was partially supported by the National Research Foundation grant funded by the Korean government (MEST) (No. 2010-0027294).
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