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Mechanical properties of nasal fascia and periosteum
Clinical Biomechanics 18 (2003) 760–764 www.elsevier.com/locate/clinbiomech
Mechanical properties of nasal fascia and periosteum Yan-Jun Zeng
a,b,*
, Xiao-peng Sun b, Jian Yang b, Wei-hua Wu c, Xiao-hu Xu a, Yi-ping Yan d a
b
Medical School, Shantou University, Shantou, PR China Biomechanics and Medical Information Institute, Biomedical Engineering Center, Beijing Polytechnic University, Beijing 100022, PR China c Hangzhou Orthopedic Hospital, Hangzhou, PR China d Plastic Surgery Hospital of Chinese Academy of Medical Sciences, Beijing, PR China Received 1 July 2002; accepted 11 June 2003
Abstract Objective. To determine under which layer the silicone implants should be inserted into, the biomechanical properties of fascia and periosteum were investigated. Design. Biomechanical testing of cadaveric tissues. Background. In silicone augmentation rhinoplasty, most complications are closely related to the depth of implant and the mechanical character of the tissue surrounding the implant. Methods. Biomechanical properties of human nasal periosteum and fascia were studied, including tensile strength, stress–strain relationship and stress relaxation under uniaxial elongation. Result. Although with less failure strain, the periosteum has more tensile strength than fascia. The slope of the linear part of stress–strain curve of the periosteum is bigger than that of fascia, which indicates the periosteum is stiffer than fascia. The stressrelaxation slope of periosteum is smaller than that of fascia. Conclusion. In the view of biomechanics, the periosteum is thicker, stronger and stiffer than fascia. Under periosteum the silicone implants are easier to be fixed at desired position, thus periosteum is more suitable for covering silicone implants. Relevance The periosteum is more suitable than fascia for covering silicone implants in augmentation rhinoplasty. 2003 Elsevier Ltd. All rights reserved. Keywords: Augmentation rhinoplasty; Stress–strain relationship; Tensile strength; Stress relaxation
1. Introduction With the rapid development of aesthetic plastic surgery, augmentation rhinoplasty has become one of the most popular plastic surgery procedures in China. Silicone implant augmentation rhinoplasty is used to correct congenital saddle-nose and flat nose (Rozner et al., 1980; Lovice et al., 1999; Deva et al., 1998). The increasing number of patients requesting this operation is linked with improvement of technique and more demand on beauty. It is frequent to see patients asking for
* Corresponding author. Address: Biomechanics and Medical Information Institute, Biomedical Engineering Center, Beijing Polytechnic University, Beijing 100022, PR China. E-mail address: [email protected] (Y.-J. Zeng).
0268-0033/$ - see front matter 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0268-0033(03)00136-0
correction of minor defects. The operation is simple and makes people look better, more beautiful, and more vibrant (Ercolani and Baldaro, 1999). But the results of our follow-up indicate that many problems in rhinoplasty stem not only from the technique of the surgeon but also from the layer that silicone implants was inserted into. According to our clinical experience, silicone implants can be inserted into one of three anatomical layers of the nasal dorsum: subcutaneous, subperiosteal or subfascial (Lovice et al., 1999; Deva et al., 1998) (Fig. 1). Many postoperative complications, such as drifting of the plastic frame, step-like deformity at the nasal bridge, maldirected silicone implants, changing in skin color, abnormal sensation and the silicone implants protruding through nasal skin, occur when the silicone implants are inserted into subcutaneous or subfascial
Y.-J. Zeng et al. / Clinical Biomechanics 18 (2003) 760–764
761
tion cycles is dependent on the tissue and the method of preparation. Preconditioning was continued until a reproducible, identical curve was obtained over several cycles. Load versus elongation was saved and plotted simultaneously on the computer screen for immediate verification. 2.1. Tensile strength For this test, the specimen is carefully cut into dumbbell shape in order to produce rupture at the center. The area in the middle is carefully measured again. The engineering stress was measured as the load normalized for the area and defined as T ¼
L tw
ð1Þ
Fig. 1. Anatomic structure of nasan dorsum.
shallow layers (classical rhinoplasty). According to our clinic experience, these complications can be greatly reduced if the silicone implants are implanted deeper. But the mechanism is not clear. Therefore the biomechanical properties of human nasal periosteum and fascia, including their tensile strength, stress–strain relationship and stress-relaxation characters under uniaxial elongation were investigated.
2. Methods Periosteum and fascia were removed from 15 adult cadavers (aged from 17 to 49) within 48 h postmortem. Periosteum and fascia were separated, placed on microscopic slides (Mutou et al., 1975), covered with saline moistened gauze and stored in refrigerator at 4 C before experiment. Their width and thickness were measured with optic magnifying scale. Mechanical test was performed with a hydraulically powered uniaxial elongation machine, (Instron Limited, Buckinghamshire, UK) under room temperature. An ultrasound moistener was used to keep the tissues moist. Tensile strength, stress–strain relationship were performed at extension rates of 10 mm/min. Specimens around 5 mm · 3 mm were cut from the fascia and periosteum. During test, two ends of each specimen was placed between two self-made clamps. The bottom clamp is fixed on a fastened lower grip on the Instron desktop, whereas the top clamp could move at a specified speed in the vertical direction. The gauge length of the tissue between the clamps was measured and was considered to be the original length l0 . Preconditioning was performed in stress–strain test and stress-relaxation test in order to get repeatable result. This is necessary because data on preconditioned specimens are less variable than unpreconditioned specimens. The number of precondi-
where T is stress in megapascals. L (Newton) is the load recorded by the load cell. The t (mm) and w (mm) are the initial thickness and width of the tissue specimen in the middle cross-section. Engineering strain was defined as e¼
l l0 ¼k1 l0
ð2Þ
where e is the strain. l is the length and l0 is the gauge length of the specimen at zero load. k is the stretch ratio. 2.2. Stress–strain relationship A specimen was stretched at a constant speed (10 mm/min) until the pulling force, L, reached a specific value. Then the specimen was unloaded at the same speed. The computer plotted the L–Dl curve of the specimen automatically. The phenomenon of hysteresis can be observed in both periosteums and fascias. The difference in the loading and unloading process indicate the energy is dissipated. In this case, three cycles of preconditioning was needed before the stable stress– strain relation could be achieved. The stress and strain of periosteum and fascia are determined under the assumption that the tissues are incompressible. According to the theory of large deformation, the EulerÕs stress and GreenÕs strain must be used. The EulerÕs stress r¼
L L ¼ k ¼ Tk A A0
ð3Þ
and GreenÕs strain E¼
k2 1 2
ð4Þ
where engineering stress T ¼ L=A0 , L ¼ load, A ¼ crosssectional area, A0 ¼ t w, original area. Fig. 2 shows the typical stress–strain relationship of the periosteums and fascias.
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Y.-J. Zeng et al. / Clinical Biomechanics 18 (2003) 760–764
Fig. 3. Curves of stress relaxation, a, b, c, d––periosteum, e, f, g, h–– fascia. Fig. 2. The stress–strain relation of the periosteum and fascia (a, b, c, d––periosteum, e, f, g, h––fascia).
The power function was used to fit the stress–strain curves of the specimens (Fu et al., 1997; Huang et al., 1998; Zeng et al., 2001a) r ¼ aEb
ð5Þ
where a and b are coefficients to be determined. 2.3. Stress relaxation If the tissue is loaded to a finite strain and then its length held constant, it exhibits the phenomenon of stress relaxation. In this study, elongation speed was 125 mm/min. When it reached the stretch force 2 N, the upper clamp stopped and the stretched length was maintained for 600 s while the absolute tension on samples was monitored. In this study, three preconditioning cycles were conducted before the formal test. The reduced relaxation function GðtÞ was used to normalize relaxation (Fig. 3, the same number represent the same person). Stress relaxation was plotted as a percent of stress remaining versus time (Fung, 1993; Zeng et al., 2001b). The percent stress remaining was calculated as following: T ðtÞ Percentage stress remaining ¼ 100% ð6Þ T ð0Þ where T ðtÞ and T ð0Þ were the engineering stresses measured at time t and relaxation beginning time (t ¼ 0 is
defined that the maximum force was reached) respectively. A linear regression line was fitted to the curve in the time range from 100 to 600 s.
3. Results 3.1. Tensile strength Table 1 gives the comparison of tensile strength (engineering stress) and failure strain (engineering strain) of the periosteum and fascia, The tensile strength of the periosteum is greater than that of the fascia, but the failure strain is much less. Although having bigger tensile strength, periosteum has less deformation under failure strain so they are less extensible than fascia. This explains why it is so easy to lacerate the periosteum when it is separated to insert silicone implants. 3.2. Stress–strain relationship The stress–strain curves vary greatly due to individual difference. However, in the same person, the curve of the periosteum is always on the left side of the curve for the fascia, indicating that the periosteum is less extensible than fascia. The best fit values of a, b of the curves are listed in Table 2. From the tables, we found that the value of a for a periosteum specimen was much larger than that of
Table 1 Comparison of tensile strength and the failure strain of the periosteum and fascia Periosteum samples
Tensile strength (MPa)
Failure strain (%)
Fascia samples
Tensile strength (MPa)
Failure strain (%)
n1gs n2gs n3gs n4gs n5gs n6gs
4.020 3.764 4.036 3.993 3.662 3.790
19.61 21.92 34.76 19.84 22.50 30.40
n1js n2js n3js n4js n5js n6js
3.101 2.648 2.875 2.951 1.831 2.803
49.35 65.04 51.37 54.66 46.38 49.92
Y.-J. Zeng et al. / Clinical Biomechanics 18 (2003) 760–764 Table 2 The stress–strain relation of the periosteum and fasciaÕs coefficients a and b a
b
A. periosteum n1gs n3gs n9gs n10gs
397.11 764.00 108.06 118.68
2.89 3.29 2.67 2.34
Mean (SD)
346.96 (267.22)
2.79 (0.34)
B. fascia n1js n3js n9js n10js
25.69 38.63 45.80 16.85
2.40 2.69 2.55 1.99
Mean (SD)
31.75 (11.22)
2.40 (0.26)
facia, which shows that the linear parts in curves of the periosteum specimens have greater slopes than those of facia. The value of b does not vary so much. Because the periosteum shows some elasticity and is less extensible than fascia, we think that silicone implants being inserted into the periosteum have better fixation result. 3.3. Stress relaxation The relaxation curves of the periosteum and fascia of different people vary greatly. However, for the same person, the curve of periosteum is always higher than that of the fascia. The results for the stress-relaxation slopes are presented in Table 3. Significant differences in the relaxation slopes were observed between perioteum and fascia. The relaxation slope of periosteum is much smaller than that of fascia. Stress relaxation is a very important viscoelastic character in biomaterials, it also has a very important clinical implication. After the silicon implant is inserted, the tissue around it will be ex-
Table 3 Stress-relaxation slopes Specimen
763
tended and yield more stress, the stress will reduce with time, which is the process of stress relaxation. In rhinoplasty, the stress value remained in the tissue surrounding the implant is very important for the fixation result.
4. Discussion According to our clinical investigation, the site of implantation plays an important role in the success of rhinoplasty. Our research on biomechanical properties of human nasal periosteum and fascia provides strong evidence that periosteum is less extensible than fascia and has less stress relaxation, thus more suitable for implant fixation. In clinical practice, the silicone implant are sculptured into the shape of part of the nose before it is implanted. In an additional experiment, we have studied mechanical properties of implant silicone, and found it is a very elastic material. The tensile stress is about 2.44 ± 0.48 MPa, failure strain around 0.94 ± 0.22, the stress–strain curve is more like a linear one than a exponential one, very little stress relaxation with the slope after 100 s is 6 · 105 /s. The elastic character of this material indicates that the fixation character of adjacent host tissue is very important. In the same time, we have tried subperiosteal implantation in 22 cases in order to reduce the complications of classical rhinoplasty, and obtained satisfactory results with no complications. In view of previous clinical research and experience, subperiosteal separation was difficult to perform because the periosteum is easy torn when being separated from the underlying bone. However, special rhinoplasty surgical instruments have been invented to make the separation easier. A complete or relatively complete subperiosteal cavity may now be established which could not be done previously with ordinary surgical knives and scissors. If the subperiosteal operation can be carried out without breaking the periosteum, it would be a good solution, for periosteum is both thicker, stronger and stiffer than fascia, and shows less stress relaxation, thus providing a better fixation result.
Slope (105 /s)
A. periosteum n25gr n23gr n24gr n22gr
5.33 8.00 9.35 5.33
Mean (SD)
7.00 (2.01)
B. fascia n25jr n24jr n23jr n22jr
12.01 13.35 13.88 16.02
Mean (SD)
13.82 (1.67)
Acknowledgement This work was supported by the Chinese National Nature Science Foundation.
References Deva, A.K., Merten, S., Chang, L., 1998. Silicone in nasal augmentation rhinoplasty: a decade of clinical experience. Plast. Reconstr. Surg. 102, 1230–1237.
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Y.-J. Zeng et al. / Clinical Biomechanics 18 (2003) 760–764
Ercolani, M., Baldaro, B., 1999. Short-term outcome of rhinoplasty for medical or cosmetic indication. J. Psychosom. Res. 47, 277– 281. Fu, G.Y., Zeng, Y.J., et al., 1997. Biorheological features of some soft tissues under a surgical tissue expansion procedure. Biorheology 34, 281–293. Fung, Y.C., 1993. Bioviscoelastic solids. In: Fung, Y.C. (Ed.), Biomechanics: Mechanical Properties of Living Tissues, second ed. Springer-Verlag, New York, pp. 242–251. Huang, K., Zeng, Y.J., et al., 1998. Alteratons in the biorheological features of some soft tissues after limb lengthening. Biorheology 35, 355–363.
Lovice, D.B., Mingrone, M.D., Toriumi, D.M., 1999. Grafts and implants in rhinoplasty and nasal reconstruction. Otolaryngol. Clin. North Am. 32, 113–141. Mutou, Y., 1975. The complications of augmentation rhinoplasty in orientals. Br. J. Plast. Surg. 28, 160–163. Rozner, L. et al., 1980. Augmentation rhinoplasty British. J. Plast. Surg. 33, 377–382. Zeng, Y., Yang, J., Huang, K., et al., 2001a. A Comparison of biomechanical properties between human and porcine cornea. J. Biomech. 34, 533–538. Zeng, Y., Huang, K., et al., 2001b. Biorheological characteristics of skin after expansion. Biorheology 38, 367–378.
Mechanical properties of nasal fascia and periosteum Yan-Jun Zeng
a,b,*
, Xiao-peng Sun b, Jian Yang b, Wei-hua Wu c, Xiao-hu Xu a, Yi-ping Yan d a
b
Medical School, Shantou University, Shantou, PR China Biomechanics and Medical Information Institute, Biomedical Engineering Center, Beijing Polytechnic University, Beijing 100022, PR China c Hangzhou Orthopedic Hospital, Hangzhou, PR China d Plastic Surgery Hospital of Chinese Academy of Medical Sciences, Beijing, PR China Received 1 July 2002; accepted 11 June 2003
Abstract Objective. To determine under which layer the silicone implants should be inserted into, the biomechanical properties of fascia and periosteum were investigated. Design. Biomechanical testing of cadaveric tissues. Background. In silicone augmentation rhinoplasty, most complications are closely related to the depth of implant and the mechanical character of the tissue surrounding the implant. Methods. Biomechanical properties of human nasal periosteum and fascia were studied, including tensile strength, stress–strain relationship and stress relaxation under uniaxial elongation. Result. Although with less failure strain, the periosteum has more tensile strength than fascia. The slope of the linear part of stress–strain curve of the periosteum is bigger than that of fascia, which indicates the periosteum is stiffer than fascia. The stressrelaxation slope of periosteum is smaller than that of fascia. Conclusion. In the view of biomechanics, the periosteum is thicker, stronger and stiffer than fascia. Under periosteum the silicone implants are easier to be fixed at desired position, thus periosteum is more suitable for covering silicone implants. Relevance The periosteum is more suitable than fascia for covering silicone implants in augmentation rhinoplasty. 2003 Elsevier Ltd. All rights reserved. Keywords: Augmentation rhinoplasty; Stress–strain relationship; Tensile strength; Stress relaxation
1. Introduction With the rapid development of aesthetic plastic surgery, augmentation rhinoplasty has become one of the most popular plastic surgery procedures in China. Silicone implant augmentation rhinoplasty is used to correct congenital saddle-nose and flat nose (Rozner et al., 1980; Lovice et al., 1999; Deva et al., 1998). The increasing number of patients requesting this operation is linked with improvement of technique and more demand on beauty. It is frequent to see patients asking for
* Corresponding author. Address: Biomechanics and Medical Information Institute, Biomedical Engineering Center, Beijing Polytechnic University, Beijing 100022, PR China. E-mail address: [email protected] (Y.-J. Zeng).
0268-0033/$ - see front matter 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0268-0033(03)00136-0
correction of minor defects. The operation is simple and makes people look better, more beautiful, and more vibrant (Ercolani and Baldaro, 1999). But the results of our follow-up indicate that many problems in rhinoplasty stem not only from the technique of the surgeon but also from the layer that silicone implants was inserted into. According to our clinical experience, silicone implants can be inserted into one of three anatomical layers of the nasal dorsum: subcutaneous, subperiosteal or subfascial (Lovice et al., 1999; Deva et al., 1998) (Fig. 1). Many postoperative complications, such as drifting of the plastic frame, step-like deformity at the nasal bridge, maldirected silicone implants, changing in skin color, abnormal sensation and the silicone implants protruding through nasal skin, occur when the silicone implants are inserted into subcutaneous or subfascial
Y.-J. Zeng et al. / Clinical Biomechanics 18 (2003) 760–764
761
tion cycles is dependent on the tissue and the method of preparation. Preconditioning was continued until a reproducible, identical curve was obtained over several cycles. Load versus elongation was saved and plotted simultaneously on the computer screen for immediate verification. 2.1. Tensile strength For this test, the specimen is carefully cut into dumbbell shape in order to produce rupture at the center. The area in the middle is carefully measured again. The engineering stress was measured as the load normalized for the area and defined as T ¼
L tw
ð1Þ
Fig. 1. Anatomic structure of nasan dorsum.
shallow layers (classical rhinoplasty). According to our clinic experience, these complications can be greatly reduced if the silicone implants are implanted deeper. But the mechanism is not clear. Therefore the biomechanical properties of human nasal periosteum and fascia, including their tensile strength, stress–strain relationship and stress-relaxation characters under uniaxial elongation were investigated.
2. Methods Periosteum and fascia were removed from 15 adult cadavers (aged from 17 to 49) within 48 h postmortem. Periosteum and fascia were separated, placed on microscopic slides (Mutou et al., 1975), covered with saline moistened gauze and stored in refrigerator at 4 C before experiment. Their width and thickness were measured with optic magnifying scale. Mechanical test was performed with a hydraulically powered uniaxial elongation machine, (Instron Limited, Buckinghamshire, UK) under room temperature. An ultrasound moistener was used to keep the tissues moist. Tensile strength, stress–strain relationship were performed at extension rates of 10 mm/min. Specimens around 5 mm · 3 mm were cut from the fascia and periosteum. During test, two ends of each specimen was placed between two self-made clamps. The bottom clamp is fixed on a fastened lower grip on the Instron desktop, whereas the top clamp could move at a specified speed in the vertical direction. The gauge length of the tissue between the clamps was measured and was considered to be the original length l0 . Preconditioning was performed in stress–strain test and stress-relaxation test in order to get repeatable result. This is necessary because data on preconditioned specimens are less variable than unpreconditioned specimens. The number of precondi-
where T is stress in megapascals. L (Newton) is the load recorded by the load cell. The t (mm) and w (mm) are the initial thickness and width of the tissue specimen in the middle cross-section. Engineering strain was defined as e¼
l l0 ¼k1 l0
ð2Þ
where e is the strain. l is the length and l0 is the gauge length of the specimen at zero load. k is the stretch ratio. 2.2. Stress–strain relationship A specimen was stretched at a constant speed (10 mm/min) until the pulling force, L, reached a specific value. Then the specimen was unloaded at the same speed. The computer plotted the L–Dl curve of the specimen automatically. The phenomenon of hysteresis can be observed in both periosteums and fascias. The difference in the loading and unloading process indicate the energy is dissipated. In this case, three cycles of preconditioning was needed before the stable stress– strain relation could be achieved. The stress and strain of periosteum and fascia are determined under the assumption that the tissues are incompressible. According to the theory of large deformation, the EulerÕs stress and GreenÕs strain must be used. The EulerÕs stress r¼
L L ¼ k ¼ Tk A A0
ð3Þ
and GreenÕs strain E¼
k2 1 2
ð4Þ
where engineering stress T ¼ L=A0 , L ¼ load, A ¼ crosssectional area, A0 ¼ t w, original area. Fig. 2 shows the typical stress–strain relationship of the periosteums and fascias.
762
Y.-J. Zeng et al. / Clinical Biomechanics 18 (2003) 760–764
Fig. 3. Curves of stress relaxation, a, b, c, d––periosteum, e, f, g, h–– fascia. Fig. 2. The stress–strain relation of the periosteum and fascia (a, b, c, d––periosteum, e, f, g, h––fascia).
The power function was used to fit the stress–strain curves of the specimens (Fu et al., 1997; Huang et al., 1998; Zeng et al., 2001a) r ¼ aEb
ð5Þ
where a and b are coefficients to be determined. 2.3. Stress relaxation If the tissue is loaded to a finite strain and then its length held constant, it exhibits the phenomenon of stress relaxation. In this study, elongation speed was 125 mm/min. When it reached the stretch force 2 N, the upper clamp stopped and the stretched length was maintained for 600 s while the absolute tension on samples was monitored. In this study, three preconditioning cycles were conducted before the formal test. The reduced relaxation function GðtÞ was used to normalize relaxation (Fig. 3, the same number represent the same person). Stress relaxation was plotted as a percent of stress remaining versus time (Fung, 1993; Zeng et al., 2001b). The percent stress remaining was calculated as following: T ðtÞ Percentage stress remaining ¼ 100% ð6Þ T ð0Þ where T ðtÞ and T ð0Þ were the engineering stresses measured at time t and relaxation beginning time (t ¼ 0 is
defined that the maximum force was reached) respectively. A linear regression line was fitted to the curve in the time range from 100 to 600 s.
3. Results 3.1. Tensile strength Table 1 gives the comparison of tensile strength (engineering stress) and failure strain (engineering strain) of the periosteum and fascia, The tensile strength of the periosteum is greater than that of the fascia, but the failure strain is much less. Although having bigger tensile strength, periosteum has less deformation under failure strain so they are less extensible than fascia. This explains why it is so easy to lacerate the periosteum when it is separated to insert silicone implants. 3.2. Stress–strain relationship The stress–strain curves vary greatly due to individual difference. However, in the same person, the curve of the periosteum is always on the left side of the curve for the fascia, indicating that the periosteum is less extensible than fascia. The best fit values of a, b of the curves are listed in Table 2. From the tables, we found that the value of a for a periosteum specimen was much larger than that of
Table 1 Comparison of tensile strength and the failure strain of the periosteum and fascia Periosteum samples
Tensile strength (MPa)
Failure strain (%)
Fascia samples
Tensile strength (MPa)
Failure strain (%)
n1gs n2gs n3gs n4gs n5gs n6gs
4.020 3.764 4.036 3.993 3.662 3.790
19.61 21.92 34.76 19.84 22.50 30.40
n1js n2js n3js n4js n5js n6js
3.101 2.648 2.875 2.951 1.831 2.803
49.35 65.04 51.37 54.66 46.38 49.92
Y.-J. Zeng et al. / Clinical Biomechanics 18 (2003) 760–764 Table 2 The stress–strain relation of the periosteum and fasciaÕs coefficients a and b a
b
A. periosteum n1gs n3gs n9gs n10gs
397.11 764.00 108.06 118.68
2.89 3.29 2.67 2.34
Mean (SD)
346.96 (267.22)
2.79 (0.34)
B. fascia n1js n3js n9js n10js
25.69 38.63 45.80 16.85
2.40 2.69 2.55 1.99
Mean (SD)
31.75 (11.22)
2.40 (0.26)
facia, which shows that the linear parts in curves of the periosteum specimens have greater slopes than those of facia. The value of b does not vary so much. Because the periosteum shows some elasticity and is less extensible than fascia, we think that silicone implants being inserted into the periosteum have better fixation result. 3.3. Stress relaxation The relaxation curves of the periosteum and fascia of different people vary greatly. However, for the same person, the curve of periosteum is always higher than that of the fascia. The results for the stress-relaxation slopes are presented in Table 3. Significant differences in the relaxation slopes were observed between perioteum and fascia. The relaxation slope of periosteum is much smaller than that of fascia. Stress relaxation is a very important viscoelastic character in biomaterials, it also has a very important clinical implication. After the silicon implant is inserted, the tissue around it will be ex-
Table 3 Stress-relaxation slopes Specimen
763
tended and yield more stress, the stress will reduce with time, which is the process of stress relaxation. In rhinoplasty, the stress value remained in the tissue surrounding the implant is very important for the fixation result.
4. Discussion According to our clinical investigation, the site of implantation plays an important role in the success of rhinoplasty. Our research on biomechanical properties of human nasal periosteum and fascia provides strong evidence that periosteum is less extensible than fascia and has less stress relaxation, thus more suitable for implant fixation. In clinical practice, the silicone implant are sculptured into the shape of part of the nose before it is implanted. In an additional experiment, we have studied mechanical properties of implant silicone, and found it is a very elastic material. The tensile stress is about 2.44 ± 0.48 MPa, failure strain around 0.94 ± 0.22, the stress–strain curve is more like a linear one than a exponential one, very little stress relaxation with the slope after 100 s is 6 · 105 /s. The elastic character of this material indicates that the fixation character of adjacent host tissue is very important. In the same time, we have tried subperiosteal implantation in 22 cases in order to reduce the complications of classical rhinoplasty, and obtained satisfactory results with no complications. In view of previous clinical research and experience, subperiosteal separation was difficult to perform because the periosteum is easy torn when being separated from the underlying bone. However, special rhinoplasty surgical instruments have been invented to make the separation easier. A complete or relatively complete subperiosteal cavity may now be established which could not be done previously with ordinary surgical knives and scissors. If the subperiosteal operation can be carried out without breaking the periosteum, it would be a good solution, for periosteum is both thicker, stronger and stiffer than fascia, and shows less stress relaxation, thus providing a better fixation result.
Slope (105 /s)
A. periosteum n25gr n23gr n24gr n22gr
5.33 8.00 9.35 5.33
Mean (SD)
7.00 (2.01)
B. fascia n25jr n24jr n23jr n22jr
12.01 13.35 13.88 16.02
Mean (SD)
13.82 (1.67)
Acknowledgement This work was supported by the Chinese National Nature Science Foundation.
References Deva, A.K., Merten, S., Chang, L., 1998. Silicone in nasal augmentation rhinoplasty: a decade of clinical experience. Plast. Reconstr. Surg. 102, 1230–1237.
764
Y.-J. Zeng et al. / Clinical Biomechanics 18 (2003) 760–764
Ercolani, M., Baldaro, B., 1999. Short-term outcome of rhinoplasty for medical or cosmetic indication. J. Psychosom. Res. 47, 277– 281. Fu, G.Y., Zeng, Y.J., et al., 1997. Biorheological features of some soft tissues under a surgical tissue expansion procedure. Biorheology 34, 281–293. Fung, Y.C., 1993. Bioviscoelastic solids. In: Fung, Y.C. (Ed.), Biomechanics: Mechanical Properties of Living Tissues, second ed. Springer-Verlag, New York, pp. 242–251. Huang, K., Zeng, Y.J., et al., 1998. Alteratons in the biorheological features of some soft tissues after limb lengthening. Biorheology 35, 355–363.
Lovice, D.B., Mingrone, M.D., Toriumi, D.M., 1999. Grafts and implants in rhinoplasty and nasal reconstruction. Otolaryngol. Clin. North Am. 32, 113–141. Mutou, Y., 1975. The complications of augmentation rhinoplasty in orientals. Br. J. Plast. Surg. 28, 160–163. Rozner, L. et al., 1980. Augmentation rhinoplasty British. J. Plast. Surg. 33, 377–382. Zeng, Y., Yang, J., Huang, K., et al., 2001a. A Comparison of biomechanical properties between human and porcine cornea. J. Biomech. 34, 533–538. Zeng, Y., Huang, K., et al., 2001b. Biorheological characteristics of skin after expansion. Biorheology 38, 367–378.