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Structural characteristics of impaction allografting for revision total hip arthroplasty
Clinical Biomechanics 20 (2005) 853–855 www.elsevier.com/locate/clinbiomech
Structural characteristics of impaction allografting for revision total hip arthroplasty Marcus C. Robinson
a,b
, Go¨ran Fernlund b, R.M. Dominic Meek c, Bassam A. Masri c, Clive P. Duncan c, Thomas R. Oxland a,*
a
c
Division of Orthopaedic Engineering Research, 566-828, West 10th Avenue, The University of British Columbia, Vancouver, B.C., Canada V5Z 1L8 b Department of Materials Engineering, The University of British Columbia, Vancouver, B.C., Canada Division of Lower Limb Reconstruction and Oncology, Department of Orthopaedics, The University of British Columbia, Vancouver, B.C., Canada Received 12 February 2004; accepted 6 May 2005
Abstract Background. The impaction allografting procedure for treatment of failed hip reconstructions has shown promising but variable results. The objective of this study was to compare the structural characteristics of revision total hip arthroplasty constructs with impaction allografting (cement + morsellized bone) with all-cement and all-morsellized bone constructs. Methods. Uniaxial cyclic compression was applied to a simplified uniaxial, parallel, aluminum tube model to simulate normal gait. Applied force and axial stem displacement were recorded to determine stem subsidence and construct stiffness. Findings. Introduction of a small amount of cement into the bone graft, as suggested in an impaction allografting procedure previously reported, makes the construct behave structurally more similar to an all-cemented construct than to an all-bone graft construct. Interpretation. The results suggest that the structural properties achieved in an impaction allografting construct are sensitive to the amount of cement in the graft and that care should be taken clinically to achieve consistent constructs. 2005 Elsevier Ltd. All rights reserved. Keywords: Hip; Impaction allografting; Biomechanics; Revision
1. Introduction Gie et al. (1993) outlined a procedure for the revision of the femoral component of a primary total hip arthroplasty (THA) known as impaction allografting that provides an initially rigid construct and the opportunity for bony reconstitution by using a combination of morsellized bone and polymethylmethacrylate (PMMA) cement. The procedure involves the creation of a neomedullary canal with impacted morsellized bone and *
Corresponding author. E-mail address: [email protected] (T.R. Oxland).
0268-0033/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.clinbiomech.2005.05.013
then implanting the stem with an intermediary cement layer. The variability in the clinical results of the impaction allografting procedure suggests that the extent to which individual factors such as amount of cement and cement penetration into the graft affect the success of the procedure is not well known. In vivo stem subsidence has been reported to vary from zero (Gie et al., 1993) to more than 10 mm (Eldridge et al., 1997; Meding et al., 1997; Piccaluga et al., 2002). The objective of this study was to compare the structural characteristics (subsidence and stiffness) of revision THA constructs with impaction allografting (cement + morsellized bone) to all-cement and all-morsellized bone
854
M.C. Robinson et al. / Clinical Biomechanics 20 (2005) 853–855
constructs in order to assess the effect of cement on the structural properties of the construct.
2. Methods An in vitro axisymmetric straight structural model was developed (Fig. 1), based on that outlined by Gross and Abel (2001). The conical stems used in this study were modeled after the commonly used Exeter stem, and the cement (Surgical Simplex P, Howmedica, Rutherford NJ USA) and bone graft were prepared as they are intraoperatively. The bone graft was made by passing 15 · 15 · 40 mm sections of fresh-frozen femoral heads and femoral condyles through a bone mill (Lere Bone Mill, DePuy Inc., Warsaw IN USA). Bone particles ranged in size from 0.6 mm to 4.0 mm. The aluminum tubes (3.34 cm OD · 2.84 cm ID) were cut into lengths of 5.27 cm and the inside surfaces were roughened with a surgical high-speed cutter to achieve an interfacial strength between the aluminum tube and bone cement similar to that of the interfacial strength between a cadaveric femur and bone cement, based on laboratory tests. The inner diameter and the stiffness of the aluminum tubes in the axial and hoop directions were matched to that of cortical bone. An experienced orthopaedic surgeon performed the impaction allografting procedure on 14 tube models, varying the filler material from all-morsellized bone graft, all-cement, to a mixture of both materials as used in a standard impaction allografting procedure (Table 1). A uniform 2 mm cement mantle in the impaction allografting constructs produced a graft:cement ratio of approximately 80:20 by volume. Successive uniaxial cyclic compression was applied to the tube models at 1 Æ body weight (750 N) for 250 cycles, 2 Æ body weight (1500 N) for 250 cycles, and
Table 1 Test matrix showing the number of specimens (n) with different treatments Filler material
Number of specimens
Impaction allografting (IA) All-cement (CE) All-morsellized bone (MB)
7 3 4
3 Æ body weight (2250 N) for 500 cycles using a servohydraulic load frame (model 8874, Instron Corp., Canton MA USA), representing a progression from aided to full weight-bearing walking. Force–displacement data from the load frame were used to determine subsidence and stiffness of the constructs. Subsidence was defined as the non-recoverable distal migration of the stem, when the load was completely removed at the end of the test. Stiffness was calculated as the maximum force in a cycle (e.g., 750, 1500, or 2250 N) divided by the recoverable displacement during the cycle, i.e. the displacement at maximum load in the cycle minus the displacement at zero load in the same cycle, and was calculated at the 100th cycle of each loading regime. Radiographs were taken of all specimens before and after testing in an attempt to assess the location of subsidence.
3. Results When cyclic compressive loads were applied at 1 Æ body weight (750 N), 2 Æ body weight (1500 N), and 3 Æ body weight (2250 N), corresponding regions of successively increasing displacement were observed in the displacement–time curves (Fig. 2). Note that within each loading regime (1, 2, and 3 Æ body weight), the specimen is subject to a large number of load cycles ranging from zero to maximum load. The ‘‘thickness’’ of the displacement–time curves represents the recoverable displacement during each load cycle, which is substantially less
CE
Displacement (mm)
0
IA
-5 -10
Subsidence
-15 MB -20 1·BW
2·BW
3·BW
-25 0
200
400
600
800
1000
1200
Time (s)
Fig. 1. Schematic of in vitro model used to examine the structural behaviour of impaction allografting constructs. Strain gauge results are not presented in this study (BW = body weight).
Fig. 2. Typical stem displacement curves for impaction allografting (IA), all-cement (CE), and all-morsellized bone (MB) (BW = body weight).
M.C. Robinson et al. / Clinical Biomechanics 20 (2005) 853–855
than the non-recoverable displacement (subsidence), especially for the impaction allografting and morsellized bone constructs. The morsellized bone constructs exhibited substantially more stem subsidence at the end of the third load cycle (average = 21.8, range: 15.6–24.9 mm, n = 4) than the impaction allografting constructs (average = 1.21, range: 0.64–1.81 mm, n = 7) or the cement constructs (average = 0.24, range: 0.17–0.35 mm, n = 3). The stiffness (load/recoverable displacement in the 100th cycle in each load regime) was much more similar for the different constructs, with no statistically significant difference between them (Fig. 3). Note that the recoverable displacement at 3 Æ body weight is of the order of 0.2 mm for all constructs, which should be contrasted with the non-recoverable displacement numbers just presented. 20000 18000
Cement (n=3) Impaction allografting (n=7) Morsellized bone (n=4)
Stiffness (N/mm)
16000 14000 12000 10000 8000 6000 4000 2000 0 1·BW
2·BW
3·BW
Fig. 3. Average stiffness (load/recoverable displacement) of the model constructs as a function of filler material composition: impaction allografting (IA), all-cement (CE), and all-morsellized bone (MB). (BW = body weight). Error bars represent ±one standard deviation.
855
Radiographic results suggest that subsidence in the morsellized bone constructs is a consequence of stemmorsellized bone interface slippage and morsellized bone consolidation (Fig. 4). While the migration of the stem with respect to the tube was clearly observable, there was no indication in any of the morsellized bone specimens that there was slippage at the morsellized bone–tube interface. The stem subsidence of the impaction allografting and cement constructs was less than 2 mm, and the resolution of the imaging system did not allow determination of the source of non-recoverable deformation in these constructs.
4. Discussion The conclusions from this simplified tube model study are that although constructs of all-morsellized bone may be favourable for bone reconstitution they do not provide sufficient structural support for the stem. Introduction of a small amount of cement, as in the impaction allografting technique proposed by Gie et al. (1993), makes the construct behave more like an all-cemented construct than an all-morsellized bone construct from a structural point of view. The results suggest that stem subsidence and other structural properties of the construct are sensitive to the amount of cement used and the achieved cement penetration into the graft. Thus care has to be taken during the surgical procedure to ensure that consistent impaction allografting constructs are achieved.
Acknowledgements We thank NSERC and CIHR for financial support of the research and DePuy, Stryker-Howmedica, and Zimmer for providing materials. References
Fig. 4. Radiographs of a typical morsellized bone construct before (left) and after (right) compressive testing. Though the stem subsided nearly 25 mm, the morsellized bone–tube interface remained intact.
Eldridge, J.D., Smith, E.J., Hubble, M.J., Whitehouse, S.L., Learmonth, I.D., 1997. Massive early subsidence following femoral impaction grafting. J. Arthroplasty 12, 535–540. Gie, G.A., Linder, L., Ling, R.S., Simon, J.P., Slooff, T.J., Timperley, A., 1993. Impacted cancellous allografts and cement for revision total hip arthroplasty. J. Bone Joint Surg. Br. 75, 14–21. Gross, S., Abel, E.W., 2001. A finite element analysis of hollow stemmed hip prostheses as a means of reducing stress shielding of the femur. J. Biomech. 34, 995–1003. Meding, J.B., Ritter, M.A., Keating, E.M., Faris, P.M., 1997. Impaction bone-grafting before insertion of a femoral stem with cement in revision total hip arthroplasty. A minimum two-year follow-up study. J. Bone Joint Surg. Am. 79, 1834–1841. Piccaluga, F., Gonzalez, Della, V., Encinas Fernandez, J.C., Pusso, R., 2002. Revision of the femoral prosthesis with impaction allografting and a Charnley stem. A 2- to 12-year follow-up. J. Bone Joint Surg. Br. 84, 544–549.
Structural characteristics of impaction allografting for revision total hip arthroplasty Marcus C. Robinson
a,b
, Go¨ran Fernlund b, R.M. Dominic Meek c, Bassam A. Masri c, Clive P. Duncan c, Thomas R. Oxland a,*
a
c
Division of Orthopaedic Engineering Research, 566-828, West 10th Avenue, The University of British Columbia, Vancouver, B.C., Canada V5Z 1L8 b Department of Materials Engineering, The University of British Columbia, Vancouver, B.C., Canada Division of Lower Limb Reconstruction and Oncology, Department of Orthopaedics, The University of British Columbia, Vancouver, B.C., Canada Received 12 February 2004; accepted 6 May 2005
Abstract Background. The impaction allografting procedure for treatment of failed hip reconstructions has shown promising but variable results. The objective of this study was to compare the structural characteristics of revision total hip arthroplasty constructs with impaction allografting (cement + morsellized bone) with all-cement and all-morsellized bone constructs. Methods. Uniaxial cyclic compression was applied to a simplified uniaxial, parallel, aluminum tube model to simulate normal gait. Applied force and axial stem displacement were recorded to determine stem subsidence and construct stiffness. Findings. Introduction of a small amount of cement into the bone graft, as suggested in an impaction allografting procedure previously reported, makes the construct behave structurally more similar to an all-cemented construct than to an all-bone graft construct. Interpretation. The results suggest that the structural properties achieved in an impaction allografting construct are sensitive to the amount of cement in the graft and that care should be taken clinically to achieve consistent constructs. 2005 Elsevier Ltd. All rights reserved. Keywords: Hip; Impaction allografting; Biomechanics; Revision
1. Introduction Gie et al. (1993) outlined a procedure for the revision of the femoral component of a primary total hip arthroplasty (THA) known as impaction allografting that provides an initially rigid construct and the opportunity for bony reconstitution by using a combination of morsellized bone and polymethylmethacrylate (PMMA) cement. The procedure involves the creation of a neomedullary canal with impacted morsellized bone and *
Corresponding author. E-mail address: [email protected] (T.R. Oxland).
0268-0033/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.clinbiomech.2005.05.013
then implanting the stem with an intermediary cement layer. The variability in the clinical results of the impaction allografting procedure suggests that the extent to which individual factors such as amount of cement and cement penetration into the graft affect the success of the procedure is not well known. In vivo stem subsidence has been reported to vary from zero (Gie et al., 1993) to more than 10 mm (Eldridge et al., 1997; Meding et al., 1997; Piccaluga et al., 2002). The objective of this study was to compare the structural characteristics (subsidence and stiffness) of revision THA constructs with impaction allografting (cement + morsellized bone) to all-cement and all-morsellized bone
854
M.C. Robinson et al. / Clinical Biomechanics 20 (2005) 853–855
constructs in order to assess the effect of cement on the structural properties of the construct.
2. Methods An in vitro axisymmetric straight structural model was developed (Fig. 1), based on that outlined by Gross and Abel (2001). The conical stems used in this study were modeled after the commonly used Exeter stem, and the cement (Surgical Simplex P, Howmedica, Rutherford NJ USA) and bone graft were prepared as they are intraoperatively. The bone graft was made by passing 15 · 15 · 40 mm sections of fresh-frozen femoral heads and femoral condyles through a bone mill (Lere Bone Mill, DePuy Inc., Warsaw IN USA). Bone particles ranged in size from 0.6 mm to 4.0 mm. The aluminum tubes (3.34 cm OD · 2.84 cm ID) were cut into lengths of 5.27 cm and the inside surfaces were roughened with a surgical high-speed cutter to achieve an interfacial strength between the aluminum tube and bone cement similar to that of the interfacial strength between a cadaveric femur and bone cement, based on laboratory tests. The inner diameter and the stiffness of the aluminum tubes in the axial and hoop directions were matched to that of cortical bone. An experienced orthopaedic surgeon performed the impaction allografting procedure on 14 tube models, varying the filler material from all-morsellized bone graft, all-cement, to a mixture of both materials as used in a standard impaction allografting procedure (Table 1). A uniform 2 mm cement mantle in the impaction allografting constructs produced a graft:cement ratio of approximately 80:20 by volume. Successive uniaxial cyclic compression was applied to the tube models at 1 Æ body weight (750 N) for 250 cycles, 2 Æ body weight (1500 N) for 250 cycles, and
Table 1 Test matrix showing the number of specimens (n) with different treatments Filler material
Number of specimens
Impaction allografting (IA) All-cement (CE) All-morsellized bone (MB)
7 3 4
3 Æ body weight (2250 N) for 500 cycles using a servohydraulic load frame (model 8874, Instron Corp., Canton MA USA), representing a progression from aided to full weight-bearing walking. Force–displacement data from the load frame were used to determine subsidence and stiffness of the constructs. Subsidence was defined as the non-recoverable distal migration of the stem, when the load was completely removed at the end of the test. Stiffness was calculated as the maximum force in a cycle (e.g., 750, 1500, or 2250 N) divided by the recoverable displacement during the cycle, i.e. the displacement at maximum load in the cycle minus the displacement at zero load in the same cycle, and was calculated at the 100th cycle of each loading regime. Radiographs were taken of all specimens before and after testing in an attempt to assess the location of subsidence.
3. Results When cyclic compressive loads were applied at 1 Æ body weight (750 N), 2 Æ body weight (1500 N), and 3 Æ body weight (2250 N), corresponding regions of successively increasing displacement were observed in the displacement–time curves (Fig. 2). Note that within each loading regime (1, 2, and 3 Æ body weight), the specimen is subject to a large number of load cycles ranging from zero to maximum load. The ‘‘thickness’’ of the displacement–time curves represents the recoverable displacement during each load cycle, which is substantially less
CE
Displacement (mm)
0
IA
-5 -10
Subsidence
-15 MB -20 1·BW
2·BW
3·BW
-25 0
200
400
600
800
1000
1200
Time (s)
Fig. 1. Schematic of in vitro model used to examine the structural behaviour of impaction allografting constructs. Strain gauge results are not presented in this study (BW = body weight).
Fig. 2. Typical stem displacement curves for impaction allografting (IA), all-cement (CE), and all-morsellized bone (MB) (BW = body weight).
M.C. Robinson et al. / Clinical Biomechanics 20 (2005) 853–855
than the non-recoverable displacement (subsidence), especially for the impaction allografting and morsellized bone constructs. The morsellized bone constructs exhibited substantially more stem subsidence at the end of the third load cycle (average = 21.8, range: 15.6–24.9 mm, n = 4) than the impaction allografting constructs (average = 1.21, range: 0.64–1.81 mm, n = 7) or the cement constructs (average = 0.24, range: 0.17–0.35 mm, n = 3). The stiffness (load/recoverable displacement in the 100th cycle in each load regime) was much more similar for the different constructs, with no statistically significant difference between them (Fig. 3). Note that the recoverable displacement at 3 Æ body weight is of the order of 0.2 mm for all constructs, which should be contrasted with the non-recoverable displacement numbers just presented. 20000 18000
Cement (n=3) Impaction allografting (n=7) Morsellized bone (n=4)
Stiffness (N/mm)
16000 14000 12000 10000 8000 6000 4000 2000 0 1·BW
2·BW
3·BW
Fig. 3. Average stiffness (load/recoverable displacement) of the model constructs as a function of filler material composition: impaction allografting (IA), all-cement (CE), and all-morsellized bone (MB). (BW = body weight). Error bars represent ±one standard deviation.
855
Radiographic results suggest that subsidence in the morsellized bone constructs is a consequence of stemmorsellized bone interface slippage and morsellized bone consolidation (Fig. 4). While the migration of the stem with respect to the tube was clearly observable, there was no indication in any of the morsellized bone specimens that there was slippage at the morsellized bone–tube interface. The stem subsidence of the impaction allografting and cement constructs was less than 2 mm, and the resolution of the imaging system did not allow determination of the source of non-recoverable deformation in these constructs.
4. Discussion The conclusions from this simplified tube model study are that although constructs of all-morsellized bone may be favourable for bone reconstitution they do not provide sufficient structural support for the stem. Introduction of a small amount of cement, as in the impaction allografting technique proposed by Gie et al. (1993), makes the construct behave more like an all-cemented construct than an all-morsellized bone construct from a structural point of view. The results suggest that stem subsidence and other structural properties of the construct are sensitive to the amount of cement used and the achieved cement penetration into the graft. Thus care has to be taken during the surgical procedure to ensure that consistent impaction allografting constructs are achieved.
Acknowledgements We thank NSERC and CIHR for financial support of the research and DePuy, Stryker-Howmedica, and Zimmer for providing materials. References
Fig. 4. Radiographs of a typical morsellized bone construct before (left) and after (right) compressive testing. Though the stem subsided nearly 25 mm, the morsellized bone–tube interface remained intact.
Eldridge, J.D., Smith, E.J., Hubble, M.J., Whitehouse, S.L., Learmonth, I.D., 1997. Massive early subsidence following femoral impaction grafting. J. Arthroplasty 12, 535–540. Gie, G.A., Linder, L., Ling, R.S., Simon, J.P., Slooff, T.J., Timperley, A., 1993. Impacted cancellous allografts and cement for revision total hip arthroplasty. J. Bone Joint Surg. Br. 75, 14–21. Gross, S., Abel, E.W., 2001. A finite element analysis of hollow stemmed hip prostheses as a means of reducing stress shielding of the femur. J. Biomech. 34, 995–1003. Meding, J.B., Ritter, M.A., Keating, E.M., Faris, P.M., 1997. Impaction bone-grafting before insertion of a femoral stem with cement in revision total hip arthroplasty. A minimum two-year follow-up study. J. Bone Joint Surg. Am. 79, 1834–1841. Piccaluga, F., Gonzalez, Della, V., Encinas Fernandez, J.C., Pusso, R., 2002. Revision of the femoral prosthesis with impaction allografting and a Charnley stem. A 2- to 12-year follow-up. J. Bone Joint Surg. Br. 84, 544–549.