J Plast Surg Hand Surg, 2013; 47: 484–488 © 2013 Informa Healthcare ISSN: 2000-656X print / 2000-6764 online DOI: 10.3109/2000656X.2012.738422
ORIGINAL ARTICLE
Not only “nurture”, but also “nature”, influence the outcome of zygoma repair Tomohisa Nagasao1, Tomoki Itamiya2, Yoshiaki Sakamoto1, Yusuke Shimizu1, Hisao Ogata1, Hua Jiang3, Kazuo Kishi1 & Tsuyoshi Kaneko4 1
Department of Plastic and Reconstructive Surgery, School of Medicine, Keio University, Tokyo, Japan, 2Design Faculty, Tokyo University of Technology, Tokyo, Japan, 3Department of Plastic Surgery, ChangZheng Hospital, Second Military Medical University, Shanghai, PR China, 4 Department of Plastic and Reconstructive Surgery, Japanese National Center of Child Health and Development, Tokyo, Japan Abstract The present study aims to elucidate the relationship between preoperative deviation patterns of fractured zygomas and treatment outcomes. Fortyfive randomly selected patients with tri-pod type zygoma fractures were classified into a medial rotation group and a lateral rotation group, depending on preoperative deviation patterns. A minimum of 6 months after the operation, symmetry of the cheek was evaluated by three plastic surgeons using a VAS system. The evaluated scores were compared between the two groups. Furthermore, simulation of postoperative secondary deformity was performed by applying hypothetically defined relapse forces on CAD models produced by referring to the CT data of 20 patients. The deviation values obtained by the simulation were compared between the two groups. The results demonstrate that VAS scores were higher for the lateral rotation group than for the medial rotation group and that the deviation values were higher for the medial rotation group than for the lateral rotation group. It is concluded that treatment outcomes of zygoma fractures are affected by preoperative deviation patterns. Cases with medial rotation are likely to present poorer outcomes than those with lateral rotation. Key Words: Zygoma, fracture, repair, trauma, relapse
Introduction “Nature or nurture” has been a theme commonly discussed throughout human history. This theme concerns whether or not two persons with different genetic backgrounds can equally achieve social prosperity when they are raised in the same way. Some argue they can, because they are given the same chance; others argue they cannot, because they are not equally talented. After a zygoma fracture, the zygoma presents various deviation patterns. Analogising the preoperative condition of the zygoma and surgical treatment to the nature and nurture of a zygoma fracture case, respectively, we can produce mutually exclusive hypotheses, as follows. The first hypothesis assumes that no matter in which direction and to what degree zygomas deviate preoperatively, the treatment results should be the same if they are treated in the same way, since the condition is reset after the deviated zygomas are returned to their correct positions and fixed there. Based on this hypothesis, there should be no correlations between preoperative deviation patterns of fractured zygomas and their treatment outcomes (Figure 1). The second hypothesis assumes that, once fracture occurs, zygomas acquire a tendency to re-dislocate from their correct positions to the dislocated positions resultant from fracture. Based on this hypothesis, treatment outcomes should differ for zygoma fracture cases depending on the direction and degree of the dislocations the fractured zygomas present in preoperative conditions, even if they are treated exactly in the same way (Figure 2).
The aim of the present study was to elucidate which of these two hypotheses is correct. To achieve this purpose, clinical cases treated by the authors were evaluated; in the latter part of the study, computer models simulating skulls with zygoma fractures were produced, and biomechanical behaviours the zygomas can present as secondary deformity after fixation were studied using computer models. Patients, materials, and methods Evaluation of clinical cases Evaluation of clinical cases was conducted as a multicentre study by Keio University Hospital, Sano Hospital of the Japanese Agriculture Association, Yamato Municipal Hospital, Tokyo, Japan, and Shanghai Second Military Hospital, China. Among the patients treated for tri-pod type fractures at these hospitals, 45 patients (30 men and 15 women) for whom the zygoma was fixed at the frontal process were randomly selected for a retrospective study. In the Knight and North [1] classification system, fractures with rotation are classified into medial rotation type and lateral rotation type. According to this classification, the 45 collected cases were classified into groups presenting with medial rotation (Medial Rotation Group) or lateral rotation (Lateral Rotation Group). The Medial Rotation Group consisted of 24 patients (16 men and eight women); The Lateral Rotation Group consisted of 21 patients (14 men and seven women). Example cases for Medial and Lateral Rotation Groups are shown in Figure 3. In the surgical correction, fractured zygomas were returned to the correct position and were fixed at the frontal process using miniplates and screws. By
Correspondence: Tomohisa Nagasao, MD, PhD, Department of Plastic and Reconstructive Surgery, Keio University Hospital, Shinjuku-Ward, Shinanomachi 35, Tokyo, Japan. Tel: +81 3 5363 3814. Fax: +81 3 3352-1054. E-mail: [email protected] (Accepted 8 April 2012)
“Nature or nurture?” in zygoma repair 485 Major dislocation
Reposition & fixation
Same outcome
Minor dislocation
Reposition & fixation
Same outcome
Figure 1. The first hypothesis. Irrespective of the degree of preoperative dislocation, the same outcome is achieved as long as the fractured zygoma is repositioned and fixed with the same methods.
performing CT scan examination on the first postoperative day, it was confirmed that the zygomas were placed back to their correct positions in all cases. At a minimum of 6 months after the surgical correction, the symmetry of the faces of the patients was evaluated by three plastic surgeons using a Visual Analogue Scaling (VAS) system ranging from 0–100 (high scores indicating good symmetry). The VAS scores for Medial and Lateral Rotation Groups were compared using the Mann-Whitney U-test. P-values less than 0.05 were considered to be statistically significant. Theoretical experiment Production of analysis model. Ten patients were randomly selected from each group. Referring to the preoperative computed tomography (CT) data of the patients, threedimensional computer-aided-design models (CAD models) were produced simulating the patients’ fractured skulls. Details of the model production process are provided in our previously published papers [2–5]. Representative models for the Medial Rotation Group and the Lateral Rotation Group are shown in Figure 4.
Minor dislocation
Reposition & fixation
Figure 3. Representative cases for the Medial Rotation Group (left) and the Lateral Rotation Group (right).
Simulation of surgical treatment. With the CAD models simulating the preoperative conditions of the patients, the dislocated zygomas were placed back to their correct positions (Figure 5). The zygomas were then connected to their respective frontal processes with titanium screws and plates, simulating fixation of the fractured zygomas. Thus, produced CAD models were divided into 128,000–186,000 elements using ANSYS (ANSYS Co., Canonsburg, PA, USA) software developed for structural analyses. As material properties for each part of the CAD models, values shown in Table I were assigned [6]. Hypothetical quantification of relapse forces Zygomas receive external forces from the surrounding tissues as contracture occurs over time. The external forces work to dislocate the repositioned zygomas to their preoperative positions. We defined the external forces as Relapse Forces. Thirtytwo marking points were set for the zygoma. For each of these marking points, a Relapse Force was hypothetically quantified and applied (Figure 5). The direction and magnitude of the hypothetical Relapse Forces were assigned following two rules. First, the greater the preoperative deviation of a marking point from its correct position, the greater the Relapse Force working on the point should be. Second, the Relapse Force should work in the direction that pulls the repaired zygoma to its preoperative position. To meet these conditions, a Relapse Force was set for each marking point as a vector starting at the corrected position (postoperative position) and ending at the dislocated position (preoperative position) of the marking point. Specific explanation for this method of definition is given in Figure 6. The preoperative position of the zygoma is indicated with solid lines
Good outcome Lateral rotation case
Major dislocation
Reposition & fixation
Poor outcome Medial rotation case
Figure 2. The second hypothesis. The degree of preoperative dislocation affects the degree of secondary deformity. For cases with minor dislocation, optimal results can be achieved; for cases with major dislocation, the outcomes tend to be poor.
Figure 4. Examples of CAD models for cases of the Lateral Rotation Group (above) and Medial Rotation Group (below).
486 T. Nagasao et al. Preoperative Modeling
B′ Lateral rotation
Postoperative
A′ Da
Medial rotation
Fa
A Fb
Db C′ Reposition & fixation
B Dc Fc C Fa = rDa Fb = rDb Fc = rDc
Loading
Figure 5. For each CAD model (upper row), deviated zygomas were placed back to their correct positions (middle row). Thereafter, hypothetical loads simulating relapse forces were applied (lower row).
for the left figure (preoperative) and with dotted lines for the right figure (postoperative). When fracture occurs, points A, B, and C dislocate to A, B, and C, respectively. When the dislocated zygoma is returned to the correct position, relapse forces work on A, B, and C, potentially causing secondary deformity. The directions of the relapse forces working on A, B, and C are assumed to be parallel to the vectors connecting points A and A(Da), B and B (Db), and C and C(Dc), since relapse forces work on each point to return it to its preoperative position. The intensity of the relapse forces should be in proportion to the lengths of Da, Db, and Dc, since the greater a point’s dislocation is in the preoperative condition, the greater the relapse force should be after repositioning. Therefore, relapse forces working on each point were set as vectors parallel to those connecting the postoperative and preoperative positions of each point. For instance, when relapse forces working on A, B, and C were defined as Fa, Fb, and Fc, these vectors were defined as rFa, rFb, and rFc., where r is a constant. The constant r – indicating the intensity of contracture force – can be set arbitrarily. In the present study, r was set as 0.01. Calculation of deviation in response to hypothetical relapse forces The values of the deviation the zygoma presented in response to the hypothetical relapse forces were calculated using finite element structural analysis. Evaluation The calculated values were compared between the Medial Rotation Group and the Lateral Rotation Group using the
Table I. Material properties. Cortical bone Cancellous bone Titanium
Figure 6. Da, Db, and Dc are three-dimensional vectors indicating the dislocations of A, B, and C, respectively. Fa, Fb, and Fc are the forces that work on A, B, and C after repair. Fa, Fb, and Fc have the same directions as Da, Db, and Dc, respectively; the lengths of Fa, Fb, and Fc are in proportion to Da, Db, and Dc, respectively.
Mann-Whitney U-test. P-values less than 0.05 were considered to be statistically significant. Results Evaluation of clinical cases VAS scores were higher for the Lateral Rotation Group than for the Medial Rotation Group, indicating treatment outcomes are better for the Lateral Rotation Group than for the Medial Rotation Group (Table II). Theoretical experiment The deviation of the zygoma responding to the hypothetical relapse forces is greater for the Medial Rotation Group than for the Lateral Rotation Group, indicating that secondary relapse is more likely to occur for the Medial Rotation Group than for the Lateral Rotation Group (Table III). Examples of hypothetical relapse for the two groups are shown in Figure 7. Discussion Zygoma fracture is one of the traumas most commonly encountered in the practice of plastic surgery [7–9]. Because zygoma fracture is common, substantial numbers of studies have been performed regarding its treatment [10–14]. Despite the popularity of zygoma fracture as a research theme, little is known about the relationship between preoperative deviation patterns and postoperative outcomes. This is probably because it is taken for granted that once fractured zygomas are repaired, they never move from the corrected position. However, fractured zygomas do move to some extent, even after they are repaired, causing secondary deformity [15]. The authors have felt that longterm treatment outcomes present variations between cases, even if the fracture is treated with exactly the same method. They have been searching for reasons that can explain this Table II. VAS scores for clinical cases.
Young’s Modulus (MPa)
Poisson’s ratio
1,500 150 10,640
0.33 0.3 0.34
Average (range) Medial rotation group Lateral rotation group
60 (34–80) 65 (53–99)
Statistical significance of difference p = 0.05
“Nature or nurture?” in zygoma repair 487 Table III. Theoretically calculated secondary deformity.
Medial rotation group Lateral rotation group
Average (range) in millimetres
Statistical significance of difference
4.4 (0.8–7.2) 2.8 (0.8–4.5)
p = 0.031
phenomenon. This phenomenon is explainable referring to the concept of plasticity. Plasticity – a term in physics – means the propensity of a material to undergo permanent deformation under loading. For instance, when a wooden stick is bent to make a bow, the bent stick hardly returns to its original straight shape, even if the bow is forcibly compressed. This is due to the plasticity of the wood (Figure 8). If this theory of plasticity also holds with zygoma fractures, preoperative dislocation patterns should affect postoperative behaviours of zygomas, giving a reason for treatment outcomes to vary in cases, even if they are treated with the same method. Taking this pathway of thought, the authors designed the present study. The authors combined two approaches – evaluation of clinical cases and theoretical experiment – for the following reasons. Merely to examine the relationship between preoperative dislocation patterns and postoperative outcomes, the simplest study design would be to examine the postoperative zygoma positions by referring to CT data. However, postoperative CT examination for the purpose of long-term checkups is rarely conducted, because fixed zygomas adhere to the surrounding bones and become immovable in a few months. The stability of the situation makes additional radio-invasive examination generally unnecessary to the patients. Hence, outcomes of treatment were evaluated by referring to the patients’ appearances in pictures. Although the evaluation was performed by three plastic surgeons to secure the objectivity of the examination, the results are not so strong that a scientific law can be derived merely depending on them. To make up for the methodological weakness of the evaluation of clinical cases, the authors also performed the theoretical experiment. The theoretical experiment demonstrated that secondary deformity is more likely to occur for the Medial Rotation Group than for the Lateral Rotation Group. This phenomenon can be explained as follows. As shown in Figure 9, the body of the
Medial rotation 0
Lateral rotation 4 mm
Figure 7. Examples of theoretical relapse for cases of the Medial Rotation Group and Lateral Rotation Group.
Figure 8. Once a wood stick is transformed into a bow, it is difficult to re-straighten it, because of the plasticity of the wood.
zygoma sinks downward when medial rotation occurs. On the other hand, with lateral rotation, although the zygomatic arch sinks in the medial direction, the anterior part of the zygoma flips up and protrudes. Relapse forces work to reproduce these initial dislocation patterns. For zygomas presenting with medial rotation preoperatively, the relapse forces work to push the zygoma backward after they are repaired; for zygomas presenting with lateral rotation preoperatively, the relapse forces work to twist the zygoma. The effects of these relapse forces are easily understood by referring to models where the zygoma is simplified as a cross (Figure 10). The legs of the cross indicate the zygomatic arch (ZA), zygomatico-maxillary buttress (ZMB), inferior orbital rim (IOR), and frontal process (FP). The effect of the relapse forces for the Medial Rotation Group can be analogised to the situation where the central part of the cross is pushed downward. The effect of the relapse forces for the Lateral Rotation Group can be analogised to the situation where the cross is twisted. It is intuitively understandable that the degree of secondary relapse is smaller for the latter. The evaluation of clinical cases showed better treatment outcomes for the Lateral Rotation Group than for the Medial Rotation Group. Furthermore, the validity of this result was reinforced by the theoretical experiment. These findings indicate
Medial rotation
Lateral rotation
Figure 9. With the Medial Rotation Group, the zygoma body shifts backward (left). With the Lateral Rotation Group, the zygoma rotates just like a revolving door, centering on the axis connecting the frontal process and the zygomatico-maxillary buttress (right).
488 T. Nagasao et al. FP
References
FP ZA
ZA
IOR IOR ZMB
ZMB
FP
FP
Figure 10. (Above) The zygoma is simulated as a cross. (Below left) With the Medial Rotation Group, the relapse forces work to push the center of the zygoma inward. (Below right) With the Lateral Rotation Group, the relapse forces work to twist the zygoma.
that, even if treated with the same method, outcomes can differ in zygoma fractures, depending on the preoperative deviation of the zygoma. Therefore, if we go back to the argument of “nature or nurture” given in the introduction, the answer is “nature” can affect treatment outcomes. The fact that treatment outcomes can differ depending on the preoperative dislocation pattern is important information for clinicians, as it means that the direction in which the zygoma dislocated preoperatively needs to be taken into consideration in selecting treatment methods. For cases where the zygoma presents lateral rotation, optimal results can be achieved with relatively simple fixation. However, for cases with medial rotation, special care is needed to prevent secondary deformity. Specifically, fixation of the zygoma at an overcorrected (protruded) position with plural sites is recommended. By taking these measures, treatment outcomes can be improved. Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
[1] Knight JS, North JF. The classification of malar fractures: an analysis of displacement as a guide to treatment. Br J Plast Surg 1961;13:325–9. [2] Nagasao T, Nakajima T, Kimura N, et al. The dynamic role of buttress reconstruction after maxillectomy. Plast Reconstr Surg 2005;115:1328–41. [3] Nagasao T, Miyamoto J, Nagasao M, et al. The effect of striking angle on the buckling mechanism in blowout fracture. Plast Reconsrt Surg 2006;117:2373–81. [4] Nagasao M, Nagasao T, Imanishi Y, et al. Experimental evaluation of relapse-risks in operated zygoma fractures. Auris Nasus Larynx 2009;36:168–75. [5] Nagasao T, Tamada I, Miyamoto J, et al. Effectiveness of additional transmalar Kirschner wire fixation for a zygoma fracture. Plast Reconstr Surg 2007;119:1010–19. [6] Nagasao T, Miyamoto J, Tamaki T, et al. Combined fixation with plates and transmalar Kirschner wires for zygomatic fractures. Scand J Plast Reconstr Surg Hand Surg 2009;43:270–8. [7] Hollier LH, Thornton J, Pazmino P, Stal S. The management of orbitozygomatic fractures. Plast Reconstr Surg 2003;111: 2386–92. [8] Czerwinski M, Martin M, Lee C. Quantitative comparison of open reduction and internal fixation versus the Gillies method in the treatment of orbitozygomatic complex fractures. Plast Reconstr Surg 2005;115:1848–57. [9] Westendorff C, Gulicher D, Dammann F, et al. Computerassisted surgical treatment of orbitozygomatic fractures. J Craniofac Surg 2006;17:837–42. [10] Davidson J, Nickerson D, Nickerson B. Zygomatic fractures: comparison of methods of internal fixation. Plast Reconstr Surg 1990;86:25–32. [11] O’Hara DE, DelVecchio DA, Barlett SP, Whitaler LA. The role of microfixation in malar fractures: a quantitative biophysical study. Plast Reconstr Surg 1996;97:345–53. [12] Rohner D, Tay A, Chung S, et al. The sphenozygomatic suture as a key site for osteosynthesis of the orbitozygomatic complex in panfacial fractures: a biomechanical study in human cadavers based on clinical practice. Plast Reconstr Surg 2002; 110:1463–71. [13] Deveci M, Eski M, Gurse S, et al. Biomechanical analysis of the rigid fixation of zygoma fractures: an experimental study. J Craniofac Surg 2004;15:595–602. [14] Hanemann MJ, Simmons O, Jain S, et al. A comparison of combinations of titanium and resorbable plating systems for repair of isolated zygomatic fractures in the adult: a quantitative biomechanical study. Ann Plast Surg 2005;54:402–8. [15] Barry CP, Ryan WJ, Stassen LF. Anatomical study of factors contributing to zygomatic complex fracture instability in human cadavers. Plast Reconstr Surg 2007;119:637–41.
Copyright of Journal of Plastic Surgery & Hand Surgery is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
ORIGINAL ARTICLE
Not only “nurture”, but also “nature”, influence the outcome of zygoma repair Tomohisa Nagasao1, Tomoki Itamiya2, Yoshiaki Sakamoto1, Yusuke Shimizu1, Hisao Ogata1, Hua Jiang3, Kazuo Kishi1 & Tsuyoshi Kaneko4 1
Department of Plastic and Reconstructive Surgery, School of Medicine, Keio University, Tokyo, Japan, 2Design Faculty, Tokyo University of Technology, Tokyo, Japan, 3Department of Plastic Surgery, ChangZheng Hospital, Second Military Medical University, Shanghai, PR China, 4 Department of Plastic and Reconstructive Surgery, Japanese National Center of Child Health and Development, Tokyo, Japan Abstract The present study aims to elucidate the relationship between preoperative deviation patterns of fractured zygomas and treatment outcomes. Fortyfive randomly selected patients with tri-pod type zygoma fractures were classified into a medial rotation group and a lateral rotation group, depending on preoperative deviation patterns. A minimum of 6 months after the operation, symmetry of the cheek was evaluated by three plastic surgeons using a VAS system. The evaluated scores were compared between the two groups. Furthermore, simulation of postoperative secondary deformity was performed by applying hypothetically defined relapse forces on CAD models produced by referring to the CT data of 20 patients. The deviation values obtained by the simulation were compared between the two groups. The results demonstrate that VAS scores were higher for the lateral rotation group than for the medial rotation group and that the deviation values were higher for the medial rotation group than for the lateral rotation group. It is concluded that treatment outcomes of zygoma fractures are affected by preoperative deviation patterns. Cases with medial rotation are likely to present poorer outcomes than those with lateral rotation. Key Words: Zygoma, fracture, repair, trauma, relapse
Introduction “Nature or nurture” has been a theme commonly discussed throughout human history. This theme concerns whether or not two persons with different genetic backgrounds can equally achieve social prosperity when they are raised in the same way. Some argue they can, because they are given the same chance; others argue they cannot, because they are not equally talented. After a zygoma fracture, the zygoma presents various deviation patterns. Analogising the preoperative condition of the zygoma and surgical treatment to the nature and nurture of a zygoma fracture case, respectively, we can produce mutually exclusive hypotheses, as follows. The first hypothesis assumes that no matter in which direction and to what degree zygomas deviate preoperatively, the treatment results should be the same if they are treated in the same way, since the condition is reset after the deviated zygomas are returned to their correct positions and fixed there. Based on this hypothesis, there should be no correlations between preoperative deviation patterns of fractured zygomas and their treatment outcomes (Figure 1). The second hypothesis assumes that, once fracture occurs, zygomas acquire a tendency to re-dislocate from their correct positions to the dislocated positions resultant from fracture. Based on this hypothesis, treatment outcomes should differ for zygoma fracture cases depending on the direction and degree of the dislocations the fractured zygomas present in preoperative conditions, even if they are treated exactly in the same way (Figure 2).
The aim of the present study was to elucidate which of these two hypotheses is correct. To achieve this purpose, clinical cases treated by the authors were evaluated; in the latter part of the study, computer models simulating skulls with zygoma fractures were produced, and biomechanical behaviours the zygomas can present as secondary deformity after fixation were studied using computer models. Patients, materials, and methods Evaluation of clinical cases Evaluation of clinical cases was conducted as a multicentre study by Keio University Hospital, Sano Hospital of the Japanese Agriculture Association, Yamato Municipal Hospital, Tokyo, Japan, and Shanghai Second Military Hospital, China. Among the patients treated for tri-pod type fractures at these hospitals, 45 patients (30 men and 15 women) for whom the zygoma was fixed at the frontal process were randomly selected for a retrospective study. In the Knight and North [1] classification system, fractures with rotation are classified into medial rotation type and lateral rotation type. According to this classification, the 45 collected cases were classified into groups presenting with medial rotation (Medial Rotation Group) or lateral rotation (Lateral Rotation Group). The Medial Rotation Group consisted of 24 patients (16 men and eight women); The Lateral Rotation Group consisted of 21 patients (14 men and seven women). Example cases for Medial and Lateral Rotation Groups are shown in Figure 3. In the surgical correction, fractured zygomas were returned to the correct position and were fixed at the frontal process using miniplates and screws. By
Correspondence: Tomohisa Nagasao, MD, PhD, Department of Plastic and Reconstructive Surgery, Keio University Hospital, Shinjuku-Ward, Shinanomachi 35, Tokyo, Japan. Tel: +81 3 5363 3814. Fax: +81 3 3352-1054. E-mail: [email protected] (Accepted 8 April 2012)
“Nature or nurture?” in zygoma repair 485 Major dislocation
Reposition & fixation
Same outcome
Minor dislocation
Reposition & fixation
Same outcome
Figure 1. The first hypothesis. Irrespective of the degree of preoperative dislocation, the same outcome is achieved as long as the fractured zygoma is repositioned and fixed with the same methods.
performing CT scan examination on the first postoperative day, it was confirmed that the zygomas were placed back to their correct positions in all cases. At a minimum of 6 months after the surgical correction, the symmetry of the faces of the patients was evaluated by three plastic surgeons using a Visual Analogue Scaling (VAS) system ranging from 0–100 (high scores indicating good symmetry). The VAS scores for Medial and Lateral Rotation Groups were compared using the Mann-Whitney U-test. P-values less than 0.05 were considered to be statistically significant. Theoretical experiment Production of analysis model. Ten patients were randomly selected from each group. Referring to the preoperative computed tomography (CT) data of the patients, threedimensional computer-aided-design models (CAD models) were produced simulating the patients’ fractured skulls. Details of the model production process are provided in our previously published papers [2–5]. Representative models for the Medial Rotation Group and the Lateral Rotation Group are shown in Figure 4.
Minor dislocation
Reposition & fixation
Figure 3. Representative cases for the Medial Rotation Group (left) and the Lateral Rotation Group (right).
Simulation of surgical treatment. With the CAD models simulating the preoperative conditions of the patients, the dislocated zygomas were placed back to their correct positions (Figure 5). The zygomas were then connected to their respective frontal processes with titanium screws and plates, simulating fixation of the fractured zygomas. Thus, produced CAD models were divided into 128,000–186,000 elements using ANSYS (ANSYS Co., Canonsburg, PA, USA) software developed for structural analyses. As material properties for each part of the CAD models, values shown in Table I were assigned [6]. Hypothetical quantification of relapse forces Zygomas receive external forces from the surrounding tissues as contracture occurs over time. The external forces work to dislocate the repositioned zygomas to their preoperative positions. We defined the external forces as Relapse Forces. Thirtytwo marking points were set for the zygoma. For each of these marking points, a Relapse Force was hypothetically quantified and applied (Figure 5). The direction and magnitude of the hypothetical Relapse Forces were assigned following two rules. First, the greater the preoperative deviation of a marking point from its correct position, the greater the Relapse Force working on the point should be. Second, the Relapse Force should work in the direction that pulls the repaired zygoma to its preoperative position. To meet these conditions, a Relapse Force was set for each marking point as a vector starting at the corrected position (postoperative position) and ending at the dislocated position (preoperative position) of the marking point. Specific explanation for this method of definition is given in Figure 6. The preoperative position of the zygoma is indicated with solid lines
Good outcome Lateral rotation case
Major dislocation
Reposition & fixation
Poor outcome Medial rotation case
Figure 2. The second hypothesis. The degree of preoperative dislocation affects the degree of secondary deformity. For cases with minor dislocation, optimal results can be achieved; for cases with major dislocation, the outcomes tend to be poor.
Figure 4. Examples of CAD models for cases of the Lateral Rotation Group (above) and Medial Rotation Group (below).
486 T. Nagasao et al. Preoperative Modeling
B′ Lateral rotation
Postoperative
A′ Da
Medial rotation
Fa
A Fb
Db C′ Reposition & fixation
B Dc Fc C Fa = rDa Fb = rDb Fc = rDc
Loading
Figure 5. For each CAD model (upper row), deviated zygomas were placed back to their correct positions (middle row). Thereafter, hypothetical loads simulating relapse forces were applied (lower row).
for the left figure (preoperative) and with dotted lines for the right figure (postoperative). When fracture occurs, points A, B, and C dislocate to A, B, and C, respectively. When the dislocated zygoma is returned to the correct position, relapse forces work on A, B, and C, potentially causing secondary deformity. The directions of the relapse forces working on A, B, and C are assumed to be parallel to the vectors connecting points A and A(Da), B and B (Db), and C and C(Dc), since relapse forces work on each point to return it to its preoperative position. The intensity of the relapse forces should be in proportion to the lengths of Da, Db, and Dc, since the greater a point’s dislocation is in the preoperative condition, the greater the relapse force should be after repositioning. Therefore, relapse forces working on each point were set as vectors parallel to those connecting the postoperative and preoperative positions of each point. For instance, when relapse forces working on A, B, and C were defined as Fa, Fb, and Fc, these vectors were defined as rFa, rFb, and rFc., where r is a constant. The constant r – indicating the intensity of contracture force – can be set arbitrarily. In the present study, r was set as 0.01. Calculation of deviation in response to hypothetical relapse forces The values of the deviation the zygoma presented in response to the hypothetical relapse forces were calculated using finite element structural analysis. Evaluation The calculated values were compared between the Medial Rotation Group and the Lateral Rotation Group using the
Table I. Material properties. Cortical bone Cancellous bone Titanium
Figure 6. Da, Db, and Dc are three-dimensional vectors indicating the dislocations of A, B, and C, respectively. Fa, Fb, and Fc are the forces that work on A, B, and C after repair. Fa, Fb, and Fc have the same directions as Da, Db, and Dc, respectively; the lengths of Fa, Fb, and Fc are in proportion to Da, Db, and Dc, respectively.
Mann-Whitney U-test. P-values less than 0.05 were considered to be statistically significant. Results Evaluation of clinical cases VAS scores were higher for the Lateral Rotation Group than for the Medial Rotation Group, indicating treatment outcomes are better for the Lateral Rotation Group than for the Medial Rotation Group (Table II). Theoretical experiment The deviation of the zygoma responding to the hypothetical relapse forces is greater for the Medial Rotation Group than for the Lateral Rotation Group, indicating that secondary relapse is more likely to occur for the Medial Rotation Group than for the Lateral Rotation Group (Table III). Examples of hypothetical relapse for the two groups are shown in Figure 7. Discussion Zygoma fracture is one of the traumas most commonly encountered in the practice of plastic surgery [7–9]. Because zygoma fracture is common, substantial numbers of studies have been performed regarding its treatment [10–14]. Despite the popularity of zygoma fracture as a research theme, little is known about the relationship between preoperative deviation patterns and postoperative outcomes. This is probably because it is taken for granted that once fractured zygomas are repaired, they never move from the corrected position. However, fractured zygomas do move to some extent, even after they are repaired, causing secondary deformity [15]. The authors have felt that longterm treatment outcomes present variations between cases, even if the fracture is treated with exactly the same method. They have been searching for reasons that can explain this Table II. VAS scores for clinical cases.
Young’s Modulus (MPa)
Poisson’s ratio
1,500 150 10,640
0.33 0.3 0.34
Average (range) Medial rotation group Lateral rotation group
60 (34–80) 65 (53–99)
Statistical significance of difference p = 0.05
“Nature or nurture?” in zygoma repair 487 Table III. Theoretically calculated secondary deformity.
Medial rotation group Lateral rotation group
Average (range) in millimetres
Statistical significance of difference
4.4 (0.8–7.2) 2.8 (0.8–4.5)
p = 0.031
phenomenon. This phenomenon is explainable referring to the concept of plasticity. Plasticity – a term in physics – means the propensity of a material to undergo permanent deformation under loading. For instance, when a wooden stick is bent to make a bow, the bent stick hardly returns to its original straight shape, even if the bow is forcibly compressed. This is due to the plasticity of the wood (Figure 8). If this theory of plasticity also holds with zygoma fractures, preoperative dislocation patterns should affect postoperative behaviours of zygomas, giving a reason for treatment outcomes to vary in cases, even if they are treated with the same method. Taking this pathway of thought, the authors designed the present study. The authors combined two approaches – evaluation of clinical cases and theoretical experiment – for the following reasons. Merely to examine the relationship between preoperative dislocation patterns and postoperative outcomes, the simplest study design would be to examine the postoperative zygoma positions by referring to CT data. However, postoperative CT examination for the purpose of long-term checkups is rarely conducted, because fixed zygomas adhere to the surrounding bones and become immovable in a few months. The stability of the situation makes additional radio-invasive examination generally unnecessary to the patients. Hence, outcomes of treatment were evaluated by referring to the patients’ appearances in pictures. Although the evaluation was performed by three plastic surgeons to secure the objectivity of the examination, the results are not so strong that a scientific law can be derived merely depending on them. To make up for the methodological weakness of the evaluation of clinical cases, the authors also performed the theoretical experiment. The theoretical experiment demonstrated that secondary deformity is more likely to occur for the Medial Rotation Group than for the Lateral Rotation Group. This phenomenon can be explained as follows. As shown in Figure 9, the body of the
Medial rotation 0
Lateral rotation 4 mm
Figure 7. Examples of theoretical relapse for cases of the Medial Rotation Group and Lateral Rotation Group.
Figure 8. Once a wood stick is transformed into a bow, it is difficult to re-straighten it, because of the plasticity of the wood.
zygoma sinks downward when medial rotation occurs. On the other hand, with lateral rotation, although the zygomatic arch sinks in the medial direction, the anterior part of the zygoma flips up and protrudes. Relapse forces work to reproduce these initial dislocation patterns. For zygomas presenting with medial rotation preoperatively, the relapse forces work to push the zygoma backward after they are repaired; for zygomas presenting with lateral rotation preoperatively, the relapse forces work to twist the zygoma. The effects of these relapse forces are easily understood by referring to models where the zygoma is simplified as a cross (Figure 10). The legs of the cross indicate the zygomatic arch (ZA), zygomatico-maxillary buttress (ZMB), inferior orbital rim (IOR), and frontal process (FP). The effect of the relapse forces for the Medial Rotation Group can be analogised to the situation where the central part of the cross is pushed downward. The effect of the relapse forces for the Lateral Rotation Group can be analogised to the situation where the cross is twisted. It is intuitively understandable that the degree of secondary relapse is smaller for the latter. The evaluation of clinical cases showed better treatment outcomes for the Lateral Rotation Group than for the Medial Rotation Group. Furthermore, the validity of this result was reinforced by the theoretical experiment. These findings indicate
Medial rotation
Lateral rotation
Figure 9. With the Medial Rotation Group, the zygoma body shifts backward (left). With the Lateral Rotation Group, the zygoma rotates just like a revolving door, centering on the axis connecting the frontal process and the zygomatico-maxillary buttress (right).
488 T. Nagasao et al. FP
References
FP ZA
ZA
IOR IOR ZMB
ZMB
FP
FP
Figure 10. (Above) The zygoma is simulated as a cross. (Below left) With the Medial Rotation Group, the relapse forces work to push the center of the zygoma inward. (Below right) With the Lateral Rotation Group, the relapse forces work to twist the zygoma.
that, even if treated with the same method, outcomes can differ in zygoma fractures, depending on the preoperative deviation of the zygoma. Therefore, if we go back to the argument of “nature or nurture” given in the introduction, the answer is “nature” can affect treatment outcomes. The fact that treatment outcomes can differ depending on the preoperative dislocation pattern is important information for clinicians, as it means that the direction in which the zygoma dislocated preoperatively needs to be taken into consideration in selecting treatment methods. For cases where the zygoma presents lateral rotation, optimal results can be achieved with relatively simple fixation. However, for cases with medial rotation, special care is needed to prevent secondary deformity. Specifically, fixation of the zygoma at an overcorrected (protruded) position with plural sites is recommended. By taking these measures, treatment outcomes can be improved. Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
[1] Knight JS, North JF. The classification of malar fractures: an analysis of displacement as a guide to treatment. Br J Plast Surg 1961;13:325–9. [2] Nagasao T, Nakajima T, Kimura N, et al. The dynamic role of buttress reconstruction after maxillectomy. Plast Reconstr Surg 2005;115:1328–41. [3] Nagasao T, Miyamoto J, Nagasao M, et al. The effect of striking angle on the buckling mechanism in blowout fracture. Plast Reconsrt Surg 2006;117:2373–81. [4] Nagasao M, Nagasao T, Imanishi Y, et al. Experimental evaluation of relapse-risks in operated zygoma fractures. Auris Nasus Larynx 2009;36:168–75. [5] Nagasao T, Tamada I, Miyamoto J, et al. Effectiveness of additional transmalar Kirschner wire fixation for a zygoma fracture. Plast Reconstr Surg 2007;119:1010–19. [6] Nagasao T, Miyamoto J, Tamaki T, et al. Combined fixation with plates and transmalar Kirschner wires for zygomatic fractures. Scand J Plast Reconstr Surg Hand Surg 2009;43:270–8. [7] Hollier LH, Thornton J, Pazmino P, Stal S. The management of orbitozygomatic fractures. Plast Reconstr Surg 2003;111: 2386–92. [8] Czerwinski M, Martin M, Lee C. Quantitative comparison of open reduction and internal fixation versus the Gillies method in the treatment of orbitozygomatic complex fractures. Plast Reconstr Surg 2005;115:1848–57. [9] Westendorff C, Gulicher D, Dammann F, et al. Computerassisted surgical treatment of orbitozygomatic fractures. J Craniofac Surg 2006;17:837–42. [10] Davidson J, Nickerson D, Nickerson B. Zygomatic fractures: comparison of methods of internal fixation. Plast Reconstr Surg 1990;86:25–32. [11] O’Hara DE, DelVecchio DA, Barlett SP, Whitaler LA. The role of microfixation in malar fractures: a quantitative biophysical study. Plast Reconstr Surg 1996;97:345–53. [12] Rohner D, Tay A, Chung S, et al. The sphenozygomatic suture as a key site for osteosynthesis of the orbitozygomatic complex in panfacial fractures: a biomechanical study in human cadavers based on clinical practice. Plast Reconstr Surg 2002; 110:1463–71. [13] Deveci M, Eski M, Gurse S, et al. Biomechanical analysis of the rigid fixation of zygoma fractures: an experimental study. J Craniofac Surg 2004;15:595–602. [14] Hanemann MJ, Simmons O, Jain S, et al. A comparison of combinations of titanium and resorbable plating systems for repair of isolated zygomatic fractures in the adult: a quantitative biomechanical study. Ann Plast Surg 2005;54:402–8. [15] Barry CP, Ryan WJ, Stassen LF. Anatomical study of factors contributing to zygomatic complex fracture instability in human cadavers. Plast Reconstr Surg 2007;119:637–41.
Copyright of Journal of Plastic Surgery & Hand Surgery is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
