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allograft prosthetic composite by finite element analysis
Applied Surface Science 255 (2008) 276–278
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
The biomechanical behavior on the interface of tumor arthrosis/allograft prosthetic composite by finite element analysis H.Z. Chen a, W. Jiang a, W. Zou a, J.M. Luo a,*, J.Y. Chen a, C.Q. Tu b, B.B. Xing b, Z.W. Gu a, X.D. Zhang a a b
Engineering Research Centre in Biomaterials, Sichuan University, Chengdu 610064, China Department of Orthopaedic Surgery, the West China Hospital, Sichuan University, Chengdu 610041, China
A R T I C L E I N F O
A B S T R A C T
Article history:
The biomechanical behavior of the uniting interface between the allograft bone and the autogenetic bone plays an important role in the treatment of the proximal femur massive defects with artificial tumor arthrosis/allograft prosthetic composite (TAAPC). According to the CT data of a patient, a 3D medical treatment model of TAAPC was established. Under the loads of 1.5 and 2.5 times standard body weight (70 kg), the mechanical behavior of the treatment model was analyzed by finite element analysis (FEA) for three typical healing periods. The results show that there are significant differences in the stress values and distribution in different healing periods. With healing of osteotomy, the hardness of the tissue of the uniting interface increases, the stress in uniting area was increased greatly and the stress concentration decreased. After cured the stress almost reached the level of normal bone. In the initial stage of healing, the healing training is not encouraged because there is an obvious risk of fracture of prosthesis and bone cement. In addition, porous hydroxyapatite (HA) ceramic used as bone tissue scaffold for this case, not only facilitates the generation of new bone, but also can avoid this risk caused by the non-uniting interface. ß 2008 Elsevier B.V. All rights reserved.
Available online 3 July 2008 PACS: 68.35.Gy 46.70.LK Keywords: Tumor arthrosis APC Interface Stress FEA HA ceramic
1. Introduction Currently, there are more and more clinical cases of proximal femur massive defects due to disease, accidents and elderly osteoporosis. The several clinical methods including allograft hip joint transplant, customization metal hip joint implant and allograft prosthetic composite [1–3] have been applied to reconstruct the proximal femur massive defects. Allograft hip joint reconstruction has been abandoned for the unreliable fixation and other reasons [4,5]. With custom metal hip joint implant, there is massive bone loss which can not be rebuilt, and it is difficult for the soft tissue to reconstruct around femur. Then, the metal hip joint may loosen and go down, and lead to failure [6,7]. Tumor arthrosis/allograft prosthetic composite (TAAPC) is a comparatively better method to treat these clinical cases [8,9], could overcome some shortage above. But clinical results indicate that over 10% of the uniting interface non-union cases take place after treatment [8]. Of course the mechanical behavior of uniting interface between allograft and autogenetic bone is one of the
* Corresponding author. Tel.: +86 28 85410563; fax: +86 28 85410246. E-mail address: [email protected] (J.M. Luo). 0169-4332/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2008.06.163
important factors, but until now, there is lack of investigation in experiment and theoretical analysis. The purpose of this work is to achieve the biomechanical behavior of TAAPC and the uniting interface. The analyzed results would provide the biomechanical data for the design of composite hip joints, and be profitable to improve the successful rate of operation. 2. Materials and methods A three dimensional model was reconstructed based on the CT data, which were colleted from a patient with sarcoma in his left proximal femur, as shown in Fig. 1. According to the specific situation of the patient, a 2-mm cut was made in proximal diaphysis, 100 mm away from the middle point of the line between the greater and lesser trochanter [10]. Accordingly the femur model was divided into three segments. The far femur was autogenetic bone, the proximal femur was replaced by allograft bone and the middle was the uniting interface of allograft and autogenetic bone. The medical assembly model consisted of the stainless steel tumor hip joint, 2-mm thickness bone cement which linked the hip joint and the femur, allograft bone, autogenetic bone and the uniting interface between the allograft and autogenetic bones, as shown in Fig. 2. Soft tissue, bone
H.Z. Chen et al. / Applied Surface Science 255 (2008) 276–278
277
Table 1 The mechanical properties of materials
Fig. 1. CT image and CAD model of femur.
scab, cortex bone and hydroxyapatite (HA) ceramic were used to simulate different healing periods and operation methods. In accordance with the medical statistics, 1.5 and 2.5 times standard body weight (70 kg) were loaded on the femoral head of the hip joint at the physical axial direction of the femur [11]. All parts in FE models experienced small strain, and could be considered to be linear, elastic and isotropic. The mechanical properties of parts used in the model are listed in Table 1. In the calculation, 1.2 million elements were meshed, and it took over 3 h for a computer with an Intel EN6300 processor, 2G memory and 64-bit operating system to get a result. 3. Results Fig. 3(a) shows the von Mises stress distribution of assembly model, and Fig. 3(b) plots von Mises stress of the uniting interface treated by HA ceramics under the load of 1.5 times standard body weight. The stress ranges from 0.6 MPa to 28.3 MPa. Maximal stress (MX) positions at the outside of the HA ceramics, and the internal side is a tensile stress and the external side is a compress stress. The contour plots of von Mises stress distribution of bone cement, autogenetic bone and hip joint reveal similar stress distribution features, the outside is tensile stress, the internal side is compressive stress, and the maximum stress of the three components are 6.5 MPa, 37.373 MPa and 143.4 MPa, respectively. When the uniting interface was simulated by other materials, and the model calculated at the load of 2.5 times body weight, the contour plots of von Mises stress distributions are similar, but are of different stress values. Under 1.5 times body weight load, simulating the uniting interface by soft tissue, the MX of the hip joint positioned at its
Fig. 2. The assembly FEA model.
Material
Elastic modulus (Pa)
Poisson’s ratio
Strength (MPa)
Cortex bone Bone cement Hip joint Soft tissue Bone scab HA ceramic
1.55E10 2.07E9 2.1E11 5E4 3E9 3.1E10
0.28 0.35 0.30 0.23 0.3 0.31
196 14 310 8.6 57.4 10.5
middle near the internal side of uniting interface is 298.28 MPa. The MX of bone cement is about 16 MPa positioned at the interface among uniting interface, autogenetic bone and bone cement. When the uniting interface was simulated by three other materials – bone scab, mature cortex bone and HA – with increased modulus, the MX of the hip joint and bone cement decreased slightly. The MX of hip joint positioned at the internal side of femur 40–50 mm away from the distant side of the hip joint, and the corresponding MX values are 143.74 MPa, 143.75 MPa and 143.361 MPa. The MXs of bone cement are 5.60 MPa, 5.58 MPa and 6.05 MPa. In order to plot the axial stress distribution of the femur, two paths were chosen, shown in Fig. 3a, at the internal side and external side respectively, from point A (located in the proximal of allograft bone), to point B and C (located in the interfaces between allograft and autogenetic bone), and point D (located in the proximal of autogenetic bone). The path-von Mises stresses of internal and external sides of femur under the load of 1.5 times body weight are displayed in Fig. 4. The curves M1, M2, M3 and M4 represented stress distribution of the uniting interface simulated by soft tissue, bone scab, cortex bone and HA ceramic, and the vertical dashed lines corresponded to the four specific points A, B, C, D in Fig. 3(a). From Fig. 4 it is apparent that the materials with different elastic modulus in the uniting interface have obvious effect on the value and distribution of stress of the femur. When the material in the uniting interface was cortex bone, curve M3 shows that the stresses of autogenetic bone, allograft bone and uniting interface slowly and smoothly decrease from proximal side to distal side, and the stress in uniting is uniform and shows little change. When the simulated material has lower elastic modulus than that of autogenetic bone, soft tissue or bone scab (curve M1 or M2 in Fig. 4), either reveals that the stresses of the femur decrease obviously. And a sharp decrease of stress is found in the uniting interface and minimum stress is located in the uniting interface.
Fig. 3. The von Mises stress distribution of TAAPC and the uniting interface (1.5 times body weight load).
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H.Z. Chen et al. / Applied Surface Science 255 (2008) 276–278
Fig. 4. The stress curves of femur.
Compared with the curve M2, curve M1 has lower stress level, indicating that materials with lower modulus elasticity such as soft tissue led to a great decrease in stress level and stress concentration. Curve M4 shows the stress distribution of the femur when the HA ceramics with elastic modulus 3.1 GPa were used in the uniting interface. The results show that the stresses distribution in autogenetic bone and allograft bone are similar to that of curve M3, but a 10–20% increase in stress in the uniting interface appeared and a maximum stress existed in the uniting interface. 4. Discussion In an ideal treatment procedure, post-operation of the healing process manifested as change of tissues. In uniting interface with 2 mm width, bone scab generated first, then bone tissue rebuilt and regenerated, finally cortex bone filled in. The autogenetic bone and allograft bone were united by the new bone. From the aspect of mechanics, the rebuilding process is thought of tissues changing from soft to hard, and from hard tissue to mature cortex bone [12]. In order to simulate this process, the biomechanical data of soft tissue, bone scab and cortex bone are used in calculation of biomechanical behavior by finite element analysis (FEA). In the initial healing period, the hip joint showed an MX stress in the middle of uniting interface, and the value of MX is 298.2 MPa, is slightly less than the compressive strength 310 MPa of stainless steel. When loaded with 2.5 times physiologic loading, the results reveal that there are serious stress concentration in the interface among the uniting interface, autogenetic bone and allograft bone. The maximal value in the cement is about 16.5 MPa, is higher than the compressive limit strength 14 MPa. Therefore, the patient is advised not to do intensive health training. The path plots of stress distribution along internal side of femur reveal obvious difference when different materials are used in the uniting interface for simulation of cure procedure. In the initial healing period, the modulus of the soft tissue is greatly smaller than that of the cortex bone, and the stress is bore by the hip joint, there is serious stress shielding in the autogenetic bone and allograft bone. With the maturing of bone scab, the hardness of the tissue in the uniting interface increases, and the stress shielding becomes weak. When the bone scab grows mature, the stress shielding in the autogenetic bone and allograft is not obvious (the curve M2 in Fig. 4), and the MXs of hip joint and bone cement are 238.9 MPa and 10.1 MPa, respectively. These values are within the safe stress range. It has been demonstrated that HA porous ceramics has excellent bioactivity and permit bone ingrowths [13]. By controlling the porosity of HA, it could be manufactured to exhibit suitable
mechanical properties. When HA ceramics are used in the uniting interface, the FEA results reveal that it can promote the bony union between allograft and autogenetic bone, the MXs of hip joint and bone cement are far lower than their compressive strength, the path plots of stress distribution in Fig. 4 show that there is a stress increase of 10–20% in the uniting interface, and is higher than that of the autogenetic bone and allograft bone, which benefit the bone to rebuild and to grow from the point view of biomechanics. Therefore, HA porous ceramic material used in the uniting interface, has two advantages, it could facilitate osteogenesis and more importantly it may prevent the potential risk in case of non-union between autogenetic bone and allograft bone. 5. Conclusion The following results are achieved: in post-operation period, the 1.5 times body weight loading may lead to the failure of bone cement, so the patient is not suitable to do healing training; with the growth of bone scab in the uniting interface, the mechanical strength of uniting interface was gradually reinforced, and the stress shielding near uniting interface is relaxed, proper training enabled bone reconstruction and renewal. HA porous ceramics are used as the bone scaffold to unite the autogenetic bone and allograft bone, can greatly improve the mechanical behavior of TAAPC. It is believed that porous HA ceramics with properly higher elastic modulus than that of femur bone will promote bone reconstruction and conducting, and it also can reduce the risk caused by bony non-union. Acknowledgements This study was financially supported by Natural Science Foundation of China (No. 30471758). And thanks for the help of Prof. X.D. Li. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
E.N. Zeegen, L.A. Aponte-Tinao, F.J. Hornicek, et al. J. Clin. Northup 420 (2004) 239. J. Kimberly, M.D. Templeton, J. Curr. Opin. Orthop. 13 (2002) 71. D. Donati, S. Giacomini, E. Gozzi, et al. J. Clin. Northup 394 (2002) 192. C.J. Della-Valle, W.J. Paprosky, J. Clin. Northup 420 (2004) 55. D. Donati, M.D. Liddo, M. Zavatta, et al. J. Clin. Northup 377 (2000) 186. C.M. Ogilvie, J.S. Wunder, P.C. Ferguson, et al. J. Clin. Northup 426 (2004) 44. J.J. Eckardt, J.M. Kabo, C.M. Kelly, et al. J. Clin. Northup 415 (2003) 254. F.M. Wodajo, J. Bickels, J. Wittig, et al. J. Curr. Opin. Oncol. 15 (2003) 304. P.P. Farid, V.O. Lin, Lewis, et al. J. Clin. Northup 442 (2006) 223. J.L. Lewis, M.J. Askew, R.L. Wixson, et al. J. Bone Joint Surg. 66-A (1984) 283. L.A. Lim, et al. J. Anat. Rec. 257 (1999) 110 (New ANAT). M.G. Go´mez-Benitoa, J.M. Garcı´a-Aznara, et al. J. Theor. Biol. 235 (2005) 105. J. Chris, J. Arts, et al. J. Biomater. 27 (2006) 1110.
Contents lists available at ScienceDirect
Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc
The biomechanical behavior on the interface of tumor arthrosis/allograft prosthetic composite by finite element analysis H.Z. Chen a, W. Jiang a, W. Zou a, J.M. Luo a,*, J.Y. Chen a, C.Q. Tu b, B.B. Xing b, Z.W. Gu a, X.D. Zhang a a b
Engineering Research Centre in Biomaterials, Sichuan University, Chengdu 610064, China Department of Orthopaedic Surgery, the West China Hospital, Sichuan University, Chengdu 610041, China
A R T I C L E I N F O
A B S T R A C T
Article history:
The biomechanical behavior of the uniting interface between the allograft bone and the autogenetic bone plays an important role in the treatment of the proximal femur massive defects with artificial tumor arthrosis/allograft prosthetic composite (TAAPC). According to the CT data of a patient, a 3D medical treatment model of TAAPC was established. Under the loads of 1.5 and 2.5 times standard body weight (70 kg), the mechanical behavior of the treatment model was analyzed by finite element analysis (FEA) for three typical healing periods. The results show that there are significant differences in the stress values and distribution in different healing periods. With healing of osteotomy, the hardness of the tissue of the uniting interface increases, the stress in uniting area was increased greatly and the stress concentration decreased. After cured the stress almost reached the level of normal bone. In the initial stage of healing, the healing training is not encouraged because there is an obvious risk of fracture of prosthesis and bone cement. In addition, porous hydroxyapatite (HA) ceramic used as bone tissue scaffold for this case, not only facilitates the generation of new bone, but also can avoid this risk caused by the non-uniting interface. ß 2008 Elsevier B.V. All rights reserved.
Available online 3 July 2008 PACS: 68.35.Gy 46.70.LK Keywords: Tumor arthrosis APC Interface Stress FEA HA ceramic
1. Introduction Currently, there are more and more clinical cases of proximal femur massive defects due to disease, accidents and elderly osteoporosis. The several clinical methods including allograft hip joint transplant, customization metal hip joint implant and allograft prosthetic composite [1–3] have been applied to reconstruct the proximal femur massive defects. Allograft hip joint reconstruction has been abandoned for the unreliable fixation and other reasons [4,5]. With custom metal hip joint implant, there is massive bone loss which can not be rebuilt, and it is difficult for the soft tissue to reconstruct around femur. Then, the metal hip joint may loosen and go down, and lead to failure [6,7]. Tumor arthrosis/allograft prosthetic composite (TAAPC) is a comparatively better method to treat these clinical cases [8,9], could overcome some shortage above. But clinical results indicate that over 10% of the uniting interface non-union cases take place after treatment [8]. Of course the mechanical behavior of uniting interface between allograft and autogenetic bone is one of the
* Corresponding author. Tel.: +86 28 85410563; fax: +86 28 85410246. E-mail address: [email protected] (J.M. Luo). 0169-4332/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2008.06.163
important factors, but until now, there is lack of investigation in experiment and theoretical analysis. The purpose of this work is to achieve the biomechanical behavior of TAAPC and the uniting interface. The analyzed results would provide the biomechanical data for the design of composite hip joints, and be profitable to improve the successful rate of operation. 2. Materials and methods A three dimensional model was reconstructed based on the CT data, which were colleted from a patient with sarcoma in his left proximal femur, as shown in Fig. 1. According to the specific situation of the patient, a 2-mm cut was made in proximal diaphysis, 100 mm away from the middle point of the line between the greater and lesser trochanter [10]. Accordingly the femur model was divided into three segments. The far femur was autogenetic bone, the proximal femur was replaced by allograft bone and the middle was the uniting interface of allograft and autogenetic bone. The medical assembly model consisted of the stainless steel tumor hip joint, 2-mm thickness bone cement which linked the hip joint and the femur, allograft bone, autogenetic bone and the uniting interface between the allograft and autogenetic bones, as shown in Fig. 2. Soft tissue, bone
H.Z. Chen et al. / Applied Surface Science 255 (2008) 276–278
277
Table 1 The mechanical properties of materials
Fig. 1. CT image and CAD model of femur.
scab, cortex bone and hydroxyapatite (HA) ceramic were used to simulate different healing periods and operation methods. In accordance with the medical statistics, 1.5 and 2.5 times standard body weight (70 kg) were loaded on the femoral head of the hip joint at the physical axial direction of the femur [11]. All parts in FE models experienced small strain, and could be considered to be linear, elastic and isotropic. The mechanical properties of parts used in the model are listed in Table 1. In the calculation, 1.2 million elements were meshed, and it took over 3 h for a computer with an Intel EN6300 processor, 2G memory and 64-bit operating system to get a result. 3. Results Fig. 3(a) shows the von Mises stress distribution of assembly model, and Fig. 3(b) plots von Mises stress of the uniting interface treated by HA ceramics under the load of 1.5 times standard body weight. The stress ranges from 0.6 MPa to 28.3 MPa. Maximal stress (MX) positions at the outside of the HA ceramics, and the internal side is a tensile stress and the external side is a compress stress. The contour plots of von Mises stress distribution of bone cement, autogenetic bone and hip joint reveal similar stress distribution features, the outside is tensile stress, the internal side is compressive stress, and the maximum stress of the three components are 6.5 MPa, 37.373 MPa and 143.4 MPa, respectively. When the uniting interface was simulated by other materials, and the model calculated at the load of 2.5 times body weight, the contour plots of von Mises stress distributions are similar, but are of different stress values. Under 1.5 times body weight load, simulating the uniting interface by soft tissue, the MX of the hip joint positioned at its
Fig. 2. The assembly FEA model.
Material
Elastic modulus (Pa)
Poisson’s ratio
Strength (MPa)
Cortex bone Bone cement Hip joint Soft tissue Bone scab HA ceramic
1.55E10 2.07E9 2.1E11 5E4 3E9 3.1E10
0.28 0.35 0.30 0.23 0.3 0.31
196 14 310 8.6 57.4 10.5
middle near the internal side of uniting interface is 298.28 MPa. The MX of bone cement is about 16 MPa positioned at the interface among uniting interface, autogenetic bone and bone cement. When the uniting interface was simulated by three other materials – bone scab, mature cortex bone and HA – with increased modulus, the MX of the hip joint and bone cement decreased slightly. The MX of hip joint positioned at the internal side of femur 40–50 mm away from the distant side of the hip joint, and the corresponding MX values are 143.74 MPa, 143.75 MPa and 143.361 MPa. The MXs of bone cement are 5.60 MPa, 5.58 MPa and 6.05 MPa. In order to plot the axial stress distribution of the femur, two paths were chosen, shown in Fig. 3a, at the internal side and external side respectively, from point A (located in the proximal of allograft bone), to point B and C (located in the interfaces between allograft and autogenetic bone), and point D (located in the proximal of autogenetic bone). The path-von Mises stresses of internal and external sides of femur under the load of 1.5 times body weight are displayed in Fig. 4. The curves M1, M2, M3 and M4 represented stress distribution of the uniting interface simulated by soft tissue, bone scab, cortex bone and HA ceramic, and the vertical dashed lines corresponded to the four specific points A, B, C, D in Fig. 3(a). From Fig. 4 it is apparent that the materials with different elastic modulus in the uniting interface have obvious effect on the value and distribution of stress of the femur. When the material in the uniting interface was cortex bone, curve M3 shows that the stresses of autogenetic bone, allograft bone and uniting interface slowly and smoothly decrease from proximal side to distal side, and the stress in uniting is uniform and shows little change. When the simulated material has lower elastic modulus than that of autogenetic bone, soft tissue or bone scab (curve M1 or M2 in Fig. 4), either reveals that the stresses of the femur decrease obviously. And a sharp decrease of stress is found in the uniting interface and minimum stress is located in the uniting interface.
Fig. 3. The von Mises stress distribution of TAAPC and the uniting interface (1.5 times body weight load).
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H.Z. Chen et al. / Applied Surface Science 255 (2008) 276–278
Fig. 4. The stress curves of femur.
Compared with the curve M2, curve M1 has lower stress level, indicating that materials with lower modulus elasticity such as soft tissue led to a great decrease in stress level and stress concentration. Curve M4 shows the stress distribution of the femur when the HA ceramics with elastic modulus 3.1 GPa were used in the uniting interface. The results show that the stresses distribution in autogenetic bone and allograft bone are similar to that of curve M3, but a 10–20% increase in stress in the uniting interface appeared and a maximum stress existed in the uniting interface. 4. Discussion In an ideal treatment procedure, post-operation of the healing process manifested as change of tissues. In uniting interface with 2 mm width, bone scab generated first, then bone tissue rebuilt and regenerated, finally cortex bone filled in. The autogenetic bone and allograft bone were united by the new bone. From the aspect of mechanics, the rebuilding process is thought of tissues changing from soft to hard, and from hard tissue to mature cortex bone [12]. In order to simulate this process, the biomechanical data of soft tissue, bone scab and cortex bone are used in calculation of biomechanical behavior by finite element analysis (FEA). In the initial healing period, the hip joint showed an MX stress in the middle of uniting interface, and the value of MX is 298.2 MPa, is slightly less than the compressive strength 310 MPa of stainless steel. When loaded with 2.5 times physiologic loading, the results reveal that there are serious stress concentration in the interface among the uniting interface, autogenetic bone and allograft bone. The maximal value in the cement is about 16.5 MPa, is higher than the compressive limit strength 14 MPa. Therefore, the patient is advised not to do intensive health training. The path plots of stress distribution along internal side of femur reveal obvious difference when different materials are used in the uniting interface for simulation of cure procedure. In the initial healing period, the modulus of the soft tissue is greatly smaller than that of the cortex bone, and the stress is bore by the hip joint, there is serious stress shielding in the autogenetic bone and allograft bone. With the maturing of bone scab, the hardness of the tissue in the uniting interface increases, and the stress shielding becomes weak. When the bone scab grows mature, the stress shielding in the autogenetic bone and allograft is not obvious (the curve M2 in Fig. 4), and the MXs of hip joint and bone cement are 238.9 MPa and 10.1 MPa, respectively. These values are within the safe stress range. It has been demonstrated that HA porous ceramics has excellent bioactivity and permit bone ingrowths [13]. By controlling the porosity of HA, it could be manufactured to exhibit suitable
mechanical properties. When HA ceramics are used in the uniting interface, the FEA results reveal that it can promote the bony union between allograft and autogenetic bone, the MXs of hip joint and bone cement are far lower than their compressive strength, the path plots of stress distribution in Fig. 4 show that there is a stress increase of 10–20% in the uniting interface, and is higher than that of the autogenetic bone and allograft bone, which benefit the bone to rebuild and to grow from the point view of biomechanics. Therefore, HA porous ceramic material used in the uniting interface, has two advantages, it could facilitate osteogenesis and more importantly it may prevent the potential risk in case of non-union between autogenetic bone and allograft bone. 5. Conclusion The following results are achieved: in post-operation period, the 1.5 times body weight loading may lead to the failure of bone cement, so the patient is not suitable to do healing training; with the growth of bone scab in the uniting interface, the mechanical strength of uniting interface was gradually reinforced, and the stress shielding near uniting interface is relaxed, proper training enabled bone reconstruction and renewal. HA porous ceramics are used as the bone scaffold to unite the autogenetic bone and allograft bone, can greatly improve the mechanical behavior of TAAPC. It is believed that porous HA ceramics with properly higher elastic modulus than that of femur bone will promote bone reconstruction and conducting, and it also can reduce the risk caused by bony non-union. Acknowledgements This study was financially supported by Natural Science Foundation of China (No. 30471758). And thanks for the help of Prof. X.D. Li. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13]
E.N. Zeegen, L.A. Aponte-Tinao, F.J. Hornicek, et al. J. Clin. Northup 420 (2004) 239. J. Kimberly, M.D. Templeton, J. Curr. Opin. Orthop. 13 (2002) 71. D. Donati, S. Giacomini, E. Gozzi, et al. J. Clin. Northup 394 (2002) 192. C.J. Della-Valle, W.J. Paprosky, J. Clin. Northup 420 (2004) 55. D. Donati, M.D. Liddo, M. Zavatta, et al. J. Clin. Northup 377 (2000) 186. C.M. Ogilvie, J.S. Wunder, P.C. Ferguson, et al. J. Clin. Northup 426 (2004) 44. J.J. Eckardt, J.M. Kabo, C.M. Kelly, et al. J. Clin. Northup 415 (2003) 254. F.M. Wodajo, J. Bickels, J. Wittig, et al. J. Curr. Opin. Oncol. 15 (2003) 304. P.P. Farid, V.O. Lin, Lewis, et al. J. Clin. Northup 442 (2006) 223. J.L. Lewis, M.J. Askew, R.L. Wixson, et al. J. Bone Joint Surg. 66-A (1984) 283. L.A. Lim, et al. J. Anat. Rec. 257 (1999) 110 (New ANAT). M.G. Go´mez-Benitoa, J.M. Garcı´a-Aznara, et al. J. Theor. Biol. 235 (2005) 105. J. Chris, J. Arts, et al. J. Biomater. 27 (2006) 1110.