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Metal-on-Metal Resurfacing Arthroplasty
The Journal of Arthroplasty Vol. 20 No. 4 Suppl. 2 2005
Metal-on-Metal Resurfacing Arthroplasty No Way Under the Sun!—In Opposition Thomas P. Schmalzried, MD
Abstract: The functional demands and the longevity of hip arthroplasty patients are increasing. High volumetric wear and osteolysis limit the durability of metalultra high molecular weight polyethylene resurfacing. Cemented femoral hemiresurfacing components (no acetabular component) do not develop osteolysis and rarely loosen. Consistent long-term fixation has been demonstrated with hemispherical cementless acetabular components. Metal-metal bearings have demonstrated low wear and rare osteolysis over 3 decades of use. These facts form foundation for total hip resurfacing with metal-metal bearings. Key words: metalmetal bearings, total hip resurfacing, arthroplasty. n 2005 Elsevier Inc. All rights reserved.
Total hip resurfacing has long been conceptually attractive to both surgeons and patients. However, historical experience has been plagued by limited durability and acetabular bone loss. There is evidence that cementless fixation and more wear-resistant bearings can favorably affect the outcomes of total hip resurfacing and that it is reasonable to give this old concept another try with new embodiments.
diameter of the resurfacing components (38-54 mm) produces a volumetric wear that is 4 to 10 times higher than that of a 28-mm bearing couple [1]. Osteolysis with completely intracapsular fixation surfaces is a prime example of the adverse effects of polyethylene wear particles in the effective joint space [2]. Acetabular bone loss was often substantial from the insertion of a cemented component and additional loss caused by osteolysis, thus violating the conservative premise of the procedure.
Failure of Total Hip Resurfacing With Polyethylene
Eliminate Polyethylene and Eliminate Osteolysis
Although circulatory compromise of the proximal femoral bone may play a role in some failures, several retrieval studies indicate that osteolysis (inflammatory bone resorption) is responsible for most failures. When mated to a conventional polyethylene acetabular component, the large
A cemented femoral resurfacing component articulating against acetabular cartilage (no acetabular component) has been used in the treatment of Ficat stage III and early stage IV osteonecrosis. In contrast to the osteolytic failures of total resurfacing with a polyethylene acetabular component, osteolysis has not been observed and loosening is rare with such hemiresurfacing. The clinical success of this procedure has been limited by less complete and less predicable pain relief [3]. The experience with cemented femoral hemiresurfacing suggests, however, that fixation and periarticular bone could be maintained in total resurfacing if periprosthetic inflammation could be reduced.
From the Joint Replacement Institute at Orthopedic Hospital, Los Angeles, California. No benefits or funds were received in support of the study. Reprint requests: Thomas P. Schmalzried, MD, Joint Replacement Institute, Orthopedic Hospital, 2400 S. Flower St, Los Angeles, CA 90007. n 2005 Elsevier Inc. All rights reserved. 0883-5403/05/2004-2020$30.00/0 doi:10.1016/j.arth.2005.03.007
70
Metal-on-Metal Resurfacing Arthroplasty ! Thomas P. Schmalzried
Cementless Acetabular Components Cementless, porous-coated, hemispherical acetabular components have demonstrated durable fixation, even in young and active patients. The limitation of these components has been periprosthetic osteolysis caused by wear of the polyethylene bearing. With such cementless acetabular components, the bone loss is localized and generally does not result in loosening, although reoperation may be needed to treat progressive osteolysis [4].
Metal-Metal Bearings In long-term studies, the volumetric wear of the McKee-Farrar (41 mm) metal-on-metal hip has been documented to be 20 to 100 times lower than that of a 28-mm metal-on-polyethylene hip. Furthermore, frictional torque has not been demonstrated to play a role in the initiation of either femoral or acetabular loosening. Although osteolysis has been reported in association with a metalmetal bearing, the occurrence is much lower than with conventional polyethylene. Concerns remain regarding the potential adverse effects of metal particles and ions [5]. It is possible to manufacture cementless, monoblock cobalt-chromium resurfacing acetabular components with a wall thickness of less than 5 mm. Such a component occupies about the same space as the total hip acetabular component for the same patient [6].
Discussion More durable fixation and more wear-resistant bearings have improved the outcomes of total hip arthroplasty [5]. Total hip arthroplasty clearly meets the needs of many patients. However, patient demands and longevity are both increasing. What is the next limitation of conventional (with intramedullary fixation) total hip arthroplasty? Fatigue failure of substrates (ie, stem fracture) may ultimately limit the longevity. Advances in fixation and bearings have implications for total hip resurfacing. Considering the issues summarized above, it is reasonable to combine a femoral resurfacing shell with a cementless cobalt-chromium acetabular component. If the walls of the acetabular component are less than 5 mm, acetabular reaming for the
71
surface arthroplasty is no greater than for a conventional total hip component [6]. Thus, the operation is conservative on both the femoral and acetabular sides. If the wear of the bearing is as low as expected, periprosthetic osteolysis is also likely to be low. Patient selection is important. The risk of femoral-side failure of metal-metal surface arthroplasty has been associated with female sex, a femoral head cyst greater than 1 cm, shorter patients, smaller component size (in men), relative varus positioning, and extensive osteonecrosis. Of note, high survivorship has been seen in large men [7]. Dense bone and a large fixation area are the best foundation for resurfacing. Resurfaced hips can be lengthened up to 1 cm. Femoral offset after resurfacing is essentially equal to that of the same hip preoperatively but less than the offset of the normal contralateral hip. These results indicate that proximal femoral morphology should be considered in the selection of patients for resurfacing and that those with a relatively low offset or limb length discrepancy of more than 1 cm may be better served by a conventional total hip [6].
References 1. Schmalzried TP, Callaghan JJ. Wear in total hip and knee replacements. J Bone Joint Surg Am 1999; 81-A:115. 2. Schmalzried TP, Jasty M, Harris WH. Periprosthetic bone loss in total hip arthroplasty: the role of polyethylene wear debris and the concept of the effective joint space. J Bone Joint Surg Am 1992; 74-A:849. 3. Beaule P, et al. Risk factors affecting early outcome of metal on metal surface arthroplasty of the hip in patients 40 years old and younger. Clin Orthop 2004; 418:80. 4. Hartley WT, McAuley JP, Culpepper WJ, et al. Osteonecrosis of the femoral head treated with cementless total hip arthroplasty. J Bone Joint Surg Am 2000;82-A:1408. 5. Heisel C, Silva M, Schmalzried TP. Bearing surface options for total hip replacement in young patients. J Bone Joint Surg Am 2003;85-A:1366. 6. Silva M, et al. The biomechanical results of total hip resurfacing arthroplasty. J Bone Joint Surg Am 2004;86-A:40. 7. Amstutz HC, et al. Metal-on-metal hybrid surface arthroplasty: two to six-year follow-up study. J Bone Joint Surg Am 2004;86-A:28.
Metal-on-Metal Resurfacing Arthroplasty No Way Under the Sun!—In Opposition Thomas P. Schmalzried, MD
Abstract: The functional demands and the longevity of hip arthroplasty patients are increasing. High volumetric wear and osteolysis limit the durability of metalultra high molecular weight polyethylene resurfacing. Cemented femoral hemiresurfacing components (no acetabular component) do not develop osteolysis and rarely loosen. Consistent long-term fixation has been demonstrated with hemispherical cementless acetabular components. Metal-metal bearings have demonstrated low wear and rare osteolysis over 3 decades of use. These facts form foundation for total hip resurfacing with metal-metal bearings. Key words: metalmetal bearings, total hip resurfacing, arthroplasty. n 2005 Elsevier Inc. All rights reserved.
Total hip resurfacing has long been conceptually attractive to both surgeons and patients. However, historical experience has been plagued by limited durability and acetabular bone loss. There is evidence that cementless fixation and more wear-resistant bearings can favorably affect the outcomes of total hip resurfacing and that it is reasonable to give this old concept another try with new embodiments.
diameter of the resurfacing components (38-54 mm) produces a volumetric wear that is 4 to 10 times higher than that of a 28-mm bearing couple [1]. Osteolysis with completely intracapsular fixation surfaces is a prime example of the adverse effects of polyethylene wear particles in the effective joint space [2]. Acetabular bone loss was often substantial from the insertion of a cemented component and additional loss caused by osteolysis, thus violating the conservative premise of the procedure.
Failure of Total Hip Resurfacing With Polyethylene
Eliminate Polyethylene and Eliminate Osteolysis
Although circulatory compromise of the proximal femoral bone may play a role in some failures, several retrieval studies indicate that osteolysis (inflammatory bone resorption) is responsible for most failures. When mated to a conventional polyethylene acetabular component, the large
A cemented femoral resurfacing component articulating against acetabular cartilage (no acetabular component) has been used in the treatment of Ficat stage III and early stage IV osteonecrosis. In contrast to the osteolytic failures of total resurfacing with a polyethylene acetabular component, osteolysis has not been observed and loosening is rare with such hemiresurfacing. The clinical success of this procedure has been limited by less complete and less predicable pain relief [3]. The experience with cemented femoral hemiresurfacing suggests, however, that fixation and periarticular bone could be maintained in total resurfacing if periprosthetic inflammation could be reduced.
From the Joint Replacement Institute at Orthopedic Hospital, Los Angeles, California. No benefits or funds were received in support of the study. Reprint requests: Thomas P. Schmalzried, MD, Joint Replacement Institute, Orthopedic Hospital, 2400 S. Flower St, Los Angeles, CA 90007. n 2005 Elsevier Inc. All rights reserved. 0883-5403/05/2004-2020$30.00/0 doi:10.1016/j.arth.2005.03.007
70
Metal-on-Metal Resurfacing Arthroplasty ! Thomas P. Schmalzried
Cementless Acetabular Components Cementless, porous-coated, hemispherical acetabular components have demonstrated durable fixation, even in young and active patients. The limitation of these components has been periprosthetic osteolysis caused by wear of the polyethylene bearing. With such cementless acetabular components, the bone loss is localized and generally does not result in loosening, although reoperation may be needed to treat progressive osteolysis [4].
Metal-Metal Bearings In long-term studies, the volumetric wear of the McKee-Farrar (41 mm) metal-on-metal hip has been documented to be 20 to 100 times lower than that of a 28-mm metal-on-polyethylene hip. Furthermore, frictional torque has not been demonstrated to play a role in the initiation of either femoral or acetabular loosening. Although osteolysis has been reported in association with a metalmetal bearing, the occurrence is much lower than with conventional polyethylene. Concerns remain regarding the potential adverse effects of metal particles and ions [5]. It is possible to manufacture cementless, monoblock cobalt-chromium resurfacing acetabular components with a wall thickness of less than 5 mm. Such a component occupies about the same space as the total hip acetabular component for the same patient [6].
Discussion More durable fixation and more wear-resistant bearings have improved the outcomes of total hip arthroplasty [5]. Total hip arthroplasty clearly meets the needs of many patients. However, patient demands and longevity are both increasing. What is the next limitation of conventional (with intramedullary fixation) total hip arthroplasty? Fatigue failure of substrates (ie, stem fracture) may ultimately limit the longevity. Advances in fixation and bearings have implications for total hip resurfacing. Considering the issues summarized above, it is reasonable to combine a femoral resurfacing shell with a cementless cobalt-chromium acetabular component. If the walls of the acetabular component are less than 5 mm, acetabular reaming for the
71
surface arthroplasty is no greater than for a conventional total hip component [6]. Thus, the operation is conservative on both the femoral and acetabular sides. If the wear of the bearing is as low as expected, periprosthetic osteolysis is also likely to be low. Patient selection is important. The risk of femoral-side failure of metal-metal surface arthroplasty has been associated with female sex, a femoral head cyst greater than 1 cm, shorter patients, smaller component size (in men), relative varus positioning, and extensive osteonecrosis. Of note, high survivorship has been seen in large men [7]. Dense bone and a large fixation area are the best foundation for resurfacing. Resurfaced hips can be lengthened up to 1 cm. Femoral offset after resurfacing is essentially equal to that of the same hip preoperatively but less than the offset of the normal contralateral hip. These results indicate that proximal femoral morphology should be considered in the selection of patients for resurfacing and that those with a relatively low offset or limb length discrepancy of more than 1 cm may be better served by a conventional total hip [6].
References 1. Schmalzried TP, Callaghan JJ. Wear in total hip and knee replacements. J Bone Joint Surg Am 1999; 81-A:115. 2. Schmalzried TP, Jasty M, Harris WH. Periprosthetic bone loss in total hip arthroplasty: the role of polyethylene wear debris and the concept of the effective joint space. J Bone Joint Surg Am 1992; 74-A:849. 3. Beaule P, et al. Risk factors affecting early outcome of metal on metal surface arthroplasty of the hip in patients 40 years old and younger. Clin Orthop 2004; 418:80. 4. Hartley WT, McAuley JP, Culpepper WJ, et al. Osteonecrosis of the femoral head treated with cementless total hip arthroplasty. J Bone Joint Surg Am 2000;82-A:1408. 5. Heisel C, Silva M, Schmalzried TP. Bearing surface options for total hip replacement in young patients. J Bone Joint Surg Am 2003;85-A:1366. 6. Silva M, et al. The biomechanical results of total hip resurfacing arthroplasty. J Bone Joint Surg Am 2004;86-A:40. 7. Amstutz HC, et al. Metal-on-metal hybrid surface arthroplasty: two to six-year follow-up study. J Bone Joint Surg Am 2004;86-A:28.