- Email: [email protected]
Femoral head–neck modularity: Curtain calls and caveats
SE
M I N A R S I N
A
R T H R O P L A S T Y
27 (2016) 232–234
Available online at www.sciencedirect.com
www.elsevier.com/locate/sart
Femoral head–neck modularity: Curtain calls and caveats Thomas P. Schmalzried, MD Joint Replacement Institute, St. Vincent Medical Center, 2200 W. Third St, Suite 400, Los Angeles, CA 90057
article info
abstract
Keywords:
There are practical and fiscal benefits of head–neck modularity. Taper corrosion occurs
Taper corrosion
with all head sizes and rarely necessitates revision. The role of design and manufacturing
Modularity
variables continues to be investigated and debated. The utilization of ceramic heads has
Total hip
increased but the cost–utility ratio needs scrutiny. Changes in surgical practice, including
Assembly
smaller incisions and the increased use of cementless, tapered titanium stems are challenges to consistent and adequate taper assembly. Surgical taper assembly is variable and important regardless of the head material. Standardization of surgical taper assembly is desirable for all head materials: taper assembly has been implicated in ceramic head fracture as well as in fretting and corrosion. & 2016 Published by Elsevier Inc.
1.
The benefits of head–neck modularity
Modularity at the head–neck junction in total hip arthroplasty (THA) was developed in the 1970s to accommodate ceramic heads and became popular in the 1980s. The benefits include decreasing stem inventory, adjustment of leg length and offset, and allowing a choice of different head materials and diameters. In a consecutive series of 100 primary cementless total hip arthroplasties, the neck length chosen for the broach trial reduction was compared with the final neck length chosen after the actual femoral component had been impacted. In 19%, the neck length was changed after insertion of the femoral component. The ability to adjust neck length after stem insertion has both practical and fiscal value [1].
2.
Complications of head–neck modularity
Taper design and manufacturing are not standardized, and there are more than 30 head–neck tapers in use worldwide [2]. A femoral head with an incompatible taper bore can (inadvertently) be assembled onto a modular femur. The “mis-fit” may E-mail address: [email protected] http://dx.doi.org/10.1053/j.sart.2017.03.004 1045-4527/& 2016 Published by Elsevier Inc.
not be apparent to the naked eye. The surgeon and surgical staff should take due care to avoid this. Other complications include disassociation [3], and fretting and corrosion [4–6]. In the 1980s and early 1990s, corrosion of the head–neck junction occasionally necessitated revision. The incidence was not definitively established. Such corrosion could rarely lead to neck fracture [7] or a significant adverse local tissue reaction (ALTR). In 1988, Svensson et al. [8] reported the formation of a fulminant soft tissue pseudotumor associated with a cementless cast cobalt–chromium (CoCr) total hip stem and a modular CoCr head articulating with a polyethylene acetabular bearing. Grossly, necrotic bone and soft tissue were seen at revision. The histology showed extensive necrosis, fibrosis, and inflammation consistent with what was later termed aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) by Willert et al. [9]. This tissue reaction occurs only in association with CoCr alloys. The most salient finding on implant retrieval analysis was extensive corrosion of the modular head–neck taper. A multi-center retrieval analysis of 231 modular hip implants found that (1) fretting and corrosion scores were correlated, (2) the scores tended to be higher for heads than
SE
M I N A R S I N
AR
T H R O P L A S T Y
necks, (3) significantly higher for mixed alloy versus similar alloy couples, (4) longer implantation time, and (5) flexibility of the neck were both positively correlated with head and neck corrosion. The results suggest that such taper deterioration is due to mechanically assisted crevice corrosion. The authors note that larger diameter necks (stiffer) may reduce interface fretting and subsequent corrosion, but would reduce range of motion and joint stability [6]. Improvements in taper design and manufacturing reduced the occurrence of clinically significant taper corrosion. However, several more recent reports have demonstrated fretting and corrosion of this modular junction associated with clinical failure (revision), occurring more commonly in association with larger diameter (432 mm) metal-on-metal (MoM) bearings [2]. Such interface degradation can also occur with smaller CoCr heads on polyethylene: retrieval analysis indicates that taper fretting and corrosion is not affected by head size [10]. In 2012, Cooper et al. [11] reported on ten patients (eight women) with a metal-on-polyethylene THA, from three different manufacturers, who underwent revision surgery for ALTR due to corrosion at the modular head–neck junction: 3 were 28 mm, 5 were 32 mm, and 2 were 36 mm. Seven had a CoCr stem and CoCr head. Distinct from the intended wear of a MoM bearing where the cobalt and chromium ion levels are roughly equivalent, with a corrosive mechanism the systemic cobalt level is usually substantially higher than the chromium level. These procedures represented 1.8% of 569 THA revisions performed at that institution. In another retrieval study, fretting and corrosion scores were lower for stems with a ceramic head. The mechanism of mechanically assisted crevice corrosion was similar for both ceramic and CoCr heads although with ceramic femoral heads, only the male metal taper engages in the oxide abrasion and re-passivation process. The results suggest that with a ceramic femoral head, fretting and corrosion from the modular head–neck taper may be mitigated but not eliminated [12]. The utilization of ceramic heads has steadily increased. It should be noted, however, in the 2016 Australian National Joint Registry with up to 13 years follow-up, there is no difference in the cumulative percent revision for metal or ceramic heads on cross-linked polyethylene (XLPE) [13]. Carnes et al. [14] used decision modeling to compare the cost-effectiveness of ceramic versus metal heads on XLPE. The ability to recoup the initial increased expenditure of ceramic heads through a diminished lifetime revision cost is dependent on the price premium for ceramic and the age of the patient. They concluded that a wholesale switch to ceramic bearings regardless of age or cost differential may result in an economic burden to the health system.
3.
27 (2016) 232–234
233
Figure 1 – Intraoperative view of total hip arthroplasty performed through a posterior approach with a smaller incision. The taper is encompassed by posterior soft tissue, making it more difficult to keep clean and deliver an axial impaction blow 20 years, there has been an evolution of surgical practice. Incisions/exposures have gotten smaller while patients have gotten larger (higher average BMI), and femoral heads are also larger. This makes “clean” head–neck taper assembly, and getting an axial impaction force, more challenging (Fig. 1). Impaction force and number are both highly variable. Further, the most commonly used femoral component today is a cementless tapered (collarless), titanium alloy, which have been associated with acute proximal femoral fractures [15] (Fig. 2). The rare case of clinically significant taper fretting and corrosion may simply be due to inadequate surgical taper assembly. Additional studies are needed to analyze the role of taper assembly compared with design,
The role of surgical technique
It is appropriate to investigate the role of design and manufacturing variables in taper fretting and corrosion. For example, there has been a trend toward thinner (more flexible) necks to increase range of motion and joint stability. There are, however, other factors that could play a role in the occurrence of taper fretting and corrosion. Over the past 10–
Figure 2 – Postoperative radiograph of a proximal femur fracture associated with a cementless, tapered titanium stem. Could vigorous impaction of the head onto the taper contribute to this outcome in some cases?
234
SE
M I N A R S I N
AR
T H R O P L A S T Y
manufacturing, and other implant variables. Standardization of surgical taper assembly is desirable for all head materials: taper assembly has been implicated in ceramic head fracture as well as in fretting and corrosion [16]. “Squeezing” the head onto the taper may allow a more consistent assembly force than impaction. In summary, there are practical and fiscal benefits of head– neck modularity. Taper corrosion occurs with all head sizes and rarely necessitates revision. The role of design and manufacturing variables continues to be investigated and debated. The utilization of ceramic heads has increased but the cost–utility ratio needs scrutiny. Changes in surgical practice, including smaller incisions and the use of cementless, tapered titanium stems are challenges to consistent and adequate taper assembly. Surgical taper assembly is variable and important regardless of the head material. Standardization of surgical taper assembly is desirable for all head materials: taper assembly has been implicated in ceramic head fracture as well as in fretting and corrosion.
r e f e r e n c e s
[1] Hozack WJ, Mesa JJ, Rothman RH. Head-neck modularity for total hip arthroplasty. Is it necessary? The Journal of Arthroplasty 1996;11:397–9. [2] Wassef AJ, Schmalzried TP. Femoral taperosis. An Accident waiting to happen? The Bone & Joint Journal 2013;95-B(11 Suppl A):3–6. [3] Barrack RL, Burke DW, Cook SD, et al. Complications related to modularity of total hip components. The Journal of Bone and Joint Surgery 1993;75-B:688–92. [4] Collier JR, et al. Corrosion at the interface of cobalt-alloy heads on titanium-alloy stems. Clinical Orthopaedics and Related Research 1991;271:305–12.
27 (2016) 232–234
[5] Collier JR, et al. Corrosion between the components of modular femoral hip prostheses. The Journal of Bone and Joint Surgery 1992;74-B:511–7. [6] Goldberg JR, Gilbert JL, Jacobs JJ, Bauer TW, Paprosky W, Leurgans S. A multicenter retrieval study of the taper interfaces of modular hip prostheses. Clinical Orthopaedics and Related Research 2002;401:149–61. [7] Gilbert JL, et al. Intergranular corrosion-fatigue failure of cobalt alloy femoral stems. The Journal of Bone and Joint Surgery 1994;76-A:110–5. [8] Svensson O, Mathiesen EB, Reinholt FP, Blomgren G. Formation of a fulminant soft-tissue pseudotumor after uncemented hip arthroplasty: a case report. The Journal of Bone and Joint Surgery 1988;70-A:1238–42. [9] Willert HG, et al. Metal-on-metal bearings and hypersensitivity in patients with artificial hip joints: a clinical and histomorphological study. The Journal of Bone and Joint Surgery 2005;87-A:28–36. [10] Triantafyllopoulos GK, et al. Otto Aufranc award: large heads do not increase damage at the head-neck taper of metal-onpolyethylene total hip arthroplasties. Clinical Orthopaedics and Related Research 2016;474:330–8. [11] Cooper HJ, et al. Corrosion at the head-neck taper as a cause for adverse local tissue reactions after total hip arthroplasty. The Journal of Bone and Joint Surgery 2012;94-A:1655–61. [12] Kurtz SM, Kocagöz SB, Hanzlik JA, et al. Do ceramic femoral heads reduce taper fretting corrosion in hip arthroplasty? A retrieval study. Clinical Orthopaedics and Related Research 2013;471(10):3270–82. [13] AOA National Joint Replacement Registry. https://aoanjrr. sahmri.com/annual-reports-2016. [14] Carnes KJ, et al. Cost analysis of ceramic heads in primary total hip arthroplasty. The Journal of Bone and Joint Surgery. American Volume 2016;98-A:1794–800. [15] Abdel MP, et al. Epidemiology of periprosthetic fracture of the femur in 32 644 primary total hip arthroplasties: a 40year experience. The Bone & Joint Journal 2016;98-B:461–7. [16] Massin P, et al. Does Biolox Delta ceramic reduce the rate of component fractures in total hip replacement? Orthopaedics and Traumatology, Surgery and Research 2014;100(6 Suppl.):S317–21.
M I N A R S I N
A
R T H R O P L A S T Y
27 (2016) 232–234
Available online at www.sciencedirect.com
www.elsevier.com/locate/sart
Femoral head–neck modularity: Curtain calls and caveats Thomas P. Schmalzried, MD Joint Replacement Institute, St. Vincent Medical Center, 2200 W. Third St, Suite 400, Los Angeles, CA 90057
article info
abstract
Keywords:
There are practical and fiscal benefits of head–neck modularity. Taper corrosion occurs
Taper corrosion
with all head sizes and rarely necessitates revision. The role of design and manufacturing
Modularity
variables continues to be investigated and debated. The utilization of ceramic heads has
Total hip
increased but the cost–utility ratio needs scrutiny. Changes in surgical practice, including
Assembly
smaller incisions and the increased use of cementless, tapered titanium stems are challenges to consistent and adequate taper assembly. Surgical taper assembly is variable and important regardless of the head material. Standardization of surgical taper assembly is desirable for all head materials: taper assembly has been implicated in ceramic head fracture as well as in fretting and corrosion. & 2016 Published by Elsevier Inc.
1.
The benefits of head–neck modularity
Modularity at the head–neck junction in total hip arthroplasty (THA) was developed in the 1970s to accommodate ceramic heads and became popular in the 1980s. The benefits include decreasing stem inventory, adjustment of leg length and offset, and allowing a choice of different head materials and diameters. In a consecutive series of 100 primary cementless total hip arthroplasties, the neck length chosen for the broach trial reduction was compared with the final neck length chosen after the actual femoral component had been impacted. In 19%, the neck length was changed after insertion of the femoral component. The ability to adjust neck length after stem insertion has both practical and fiscal value [1].
2.
Complications of head–neck modularity
Taper design and manufacturing are not standardized, and there are more than 30 head–neck tapers in use worldwide [2]. A femoral head with an incompatible taper bore can (inadvertently) be assembled onto a modular femur. The “mis-fit” may E-mail address: [email protected] http://dx.doi.org/10.1053/j.sart.2017.03.004 1045-4527/& 2016 Published by Elsevier Inc.
not be apparent to the naked eye. The surgeon and surgical staff should take due care to avoid this. Other complications include disassociation [3], and fretting and corrosion [4–6]. In the 1980s and early 1990s, corrosion of the head–neck junction occasionally necessitated revision. The incidence was not definitively established. Such corrosion could rarely lead to neck fracture [7] or a significant adverse local tissue reaction (ALTR). In 1988, Svensson et al. [8] reported the formation of a fulminant soft tissue pseudotumor associated with a cementless cast cobalt–chromium (CoCr) total hip stem and a modular CoCr head articulating with a polyethylene acetabular bearing. Grossly, necrotic bone and soft tissue were seen at revision. The histology showed extensive necrosis, fibrosis, and inflammation consistent with what was later termed aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) by Willert et al. [9]. This tissue reaction occurs only in association with CoCr alloys. The most salient finding on implant retrieval analysis was extensive corrosion of the modular head–neck taper. A multi-center retrieval analysis of 231 modular hip implants found that (1) fretting and corrosion scores were correlated, (2) the scores tended to be higher for heads than
SE
M I N A R S I N
AR
T H R O P L A S T Y
necks, (3) significantly higher for mixed alloy versus similar alloy couples, (4) longer implantation time, and (5) flexibility of the neck were both positively correlated with head and neck corrosion. The results suggest that such taper deterioration is due to mechanically assisted crevice corrosion. The authors note that larger diameter necks (stiffer) may reduce interface fretting and subsequent corrosion, but would reduce range of motion and joint stability [6]. Improvements in taper design and manufacturing reduced the occurrence of clinically significant taper corrosion. However, several more recent reports have demonstrated fretting and corrosion of this modular junction associated with clinical failure (revision), occurring more commonly in association with larger diameter (432 mm) metal-on-metal (MoM) bearings [2]. Such interface degradation can also occur with smaller CoCr heads on polyethylene: retrieval analysis indicates that taper fretting and corrosion is not affected by head size [10]. In 2012, Cooper et al. [11] reported on ten patients (eight women) with a metal-on-polyethylene THA, from three different manufacturers, who underwent revision surgery for ALTR due to corrosion at the modular head–neck junction: 3 were 28 mm, 5 were 32 mm, and 2 were 36 mm. Seven had a CoCr stem and CoCr head. Distinct from the intended wear of a MoM bearing where the cobalt and chromium ion levels are roughly equivalent, with a corrosive mechanism the systemic cobalt level is usually substantially higher than the chromium level. These procedures represented 1.8% of 569 THA revisions performed at that institution. In another retrieval study, fretting and corrosion scores were lower for stems with a ceramic head. The mechanism of mechanically assisted crevice corrosion was similar for both ceramic and CoCr heads although with ceramic femoral heads, only the male metal taper engages in the oxide abrasion and re-passivation process. The results suggest that with a ceramic femoral head, fretting and corrosion from the modular head–neck taper may be mitigated but not eliminated [12]. The utilization of ceramic heads has steadily increased. It should be noted, however, in the 2016 Australian National Joint Registry with up to 13 years follow-up, there is no difference in the cumulative percent revision for metal or ceramic heads on cross-linked polyethylene (XLPE) [13]. Carnes et al. [14] used decision modeling to compare the cost-effectiveness of ceramic versus metal heads on XLPE. The ability to recoup the initial increased expenditure of ceramic heads through a diminished lifetime revision cost is dependent on the price premium for ceramic and the age of the patient. They concluded that a wholesale switch to ceramic bearings regardless of age or cost differential may result in an economic burden to the health system.
3.
27 (2016) 232–234
233
Figure 1 – Intraoperative view of total hip arthroplasty performed through a posterior approach with a smaller incision. The taper is encompassed by posterior soft tissue, making it more difficult to keep clean and deliver an axial impaction blow 20 years, there has been an evolution of surgical practice. Incisions/exposures have gotten smaller while patients have gotten larger (higher average BMI), and femoral heads are also larger. This makes “clean” head–neck taper assembly, and getting an axial impaction force, more challenging (Fig. 1). Impaction force and number are both highly variable. Further, the most commonly used femoral component today is a cementless tapered (collarless), titanium alloy, which have been associated with acute proximal femoral fractures [15] (Fig. 2). The rare case of clinically significant taper fretting and corrosion may simply be due to inadequate surgical taper assembly. Additional studies are needed to analyze the role of taper assembly compared with design,
The role of surgical technique
It is appropriate to investigate the role of design and manufacturing variables in taper fretting and corrosion. For example, there has been a trend toward thinner (more flexible) necks to increase range of motion and joint stability. There are, however, other factors that could play a role in the occurrence of taper fretting and corrosion. Over the past 10–
Figure 2 – Postoperative radiograph of a proximal femur fracture associated with a cementless, tapered titanium stem. Could vigorous impaction of the head onto the taper contribute to this outcome in some cases?
234
SE
M I N A R S I N
AR
T H R O P L A S T Y
manufacturing, and other implant variables. Standardization of surgical taper assembly is desirable for all head materials: taper assembly has been implicated in ceramic head fracture as well as in fretting and corrosion [16]. “Squeezing” the head onto the taper may allow a more consistent assembly force than impaction. In summary, there are practical and fiscal benefits of head– neck modularity. Taper corrosion occurs with all head sizes and rarely necessitates revision. The role of design and manufacturing variables continues to be investigated and debated. The utilization of ceramic heads has increased but the cost–utility ratio needs scrutiny. Changes in surgical practice, including smaller incisions and the use of cementless, tapered titanium stems are challenges to consistent and adequate taper assembly. Surgical taper assembly is variable and important regardless of the head material. Standardization of surgical taper assembly is desirable for all head materials: taper assembly has been implicated in ceramic head fracture as well as in fretting and corrosion.
r e f e r e n c e s
[1] Hozack WJ, Mesa JJ, Rothman RH. Head-neck modularity for total hip arthroplasty. Is it necessary? The Journal of Arthroplasty 1996;11:397–9. [2] Wassef AJ, Schmalzried TP. Femoral taperosis. An Accident waiting to happen? The Bone & Joint Journal 2013;95-B(11 Suppl A):3–6. [3] Barrack RL, Burke DW, Cook SD, et al. Complications related to modularity of total hip components. The Journal of Bone and Joint Surgery 1993;75-B:688–92. [4] Collier JR, et al. Corrosion at the interface of cobalt-alloy heads on titanium-alloy stems. Clinical Orthopaedics and Related Research 1991;271:305–12.
27 (2016) 232–234
[5] Collier JR, et al. Corrosion between the components of modular femoral hip prostheses. The Journal of Bone and Joint Surgery 1992;74-B:511–7. [6] Goldberg JR, Gilbert JL, Jacobs JJ, Bauer TW, Paprosky W, Leurgans S. A multicenter retrieval study of the taper interfaces of modular hip prostheses. Clinical Orthopaedics and Related Research 2002;401:149–61. [7] Gilbert JL, et al. Intergranular corrosion-fatigue failure of cobalt alloy femoral stems. The Journal of Bone and Joint Surgery 1994;76-A:110–5. [8] Svensson O, Mathiesen EB, Reinholt FP, Blomgren G. Formation of a fulminant soft-tissue pseudotumor after uncemented hip arthroplasty: a case report. The Journal of Bone and Joint Surgery 1988;70-A:1238–42. [9] Willert HG, et al. Metal-on-metal bearings and hypersensitivity in patients with artificial hip joints: a clinical and histomorphological study. The Journal of Bone and Joint Surgery 2005;87-A:28–36. [10] Triantafyllopoulos GK, et al. Otto Aufranc award: large heads do not increase damage at the head-neck taper of metal-onpolyethylene total hip arthroplasties. Clinical Orthopaedics and Related Research 2016;474:330–8. [11] Cooper HJ, et al. Corrosion at the head-neck taper as a cause for adverse local tissue reactions after total hip arthroplasty. The Journal of Bone and Joint Surgery 2012;94-A:1655–61. [12] Kurtz SM, Kocagöz SB, Hanzlik JA, et al. Do ceramic femoral heads reduce taper fretting corrosion in hip arthroplasty? A retrieval study. Clinical Orthopaedics and Related Research 2013;471(10):3270–82. [13] AOA National Joint Replacement Registry. https://aoanjrr. sahmri.com/annual-reports-2016. [14] Carnes KJ, et al. Cost analysis of ceramic heads in primary total hip arthroplasty. The Journal of Bone and Joint Surgery. American Volume 2016;98-A:1794–800. [15] Abdel MP, et al. Epidemiology of periprosthetic fracture of the femur in 32 644 primary total hip arthroplasties: a 40year experience. The Bone & Joint Journal 2016;98-B:461–7. [16] Massin P, et al. Does Biolox Delta ceramic reduce the rate of component fractures in total hip replacement? Orthopaedics and Traumatology, Surgery and Research 2014;100(6 Suppl.):S317–21.