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Complications and surgical revision for failed disc arthroplasty
The Spine Journal 4 (2004) 289S–291S
Complications and surgical revision for failed disc arthroplasty John P. Kostuik, MD* Department of Orthopaedic Surgery, The Johns Hopkins University School of Medicine, 601 North Caroline Street, Suite 5006, Baltimore, MD 21287, USA
Abstract
This review will outline the indications and options for revision of failed disc arthroplasty. Such indications may include implant loosening, malposition, displacement, early wear, and infection. Each indication will likely require different preoperative planning, testing, and strategies. 쑖 2004 Elsevier Inc. All rights reserved.
Keywords:
Complications; Failed disc arthroplasty; Revision surgery
Introduction Despite all the research and development that has already been conducted, it is unknown what the failure rate for disc arthroplasty will be once spine surgeons begin widespread use of the technique. Numerous studies investigating multiple intervertebral implant systems have been underway in Europe for several years. The reported satisfaction rate in the European literature for improvements in patient pain and function has been relatively high and typically greater than 70% [1–3]. Unfortunately, the closely controlled inclusion groups, relatively small study populations and lack of extensive long-term follow-up have provided limited insight into the incidence of mechanical failure, infection rates and other potential complications. The intent of this article is to outline the indications and options for revision of failed intervertebral disc arthroplasty.
Indications The primary indications for surgical revision should include 1) patients with continued pain secondary to implant loosening, malposition or displacement; 2) patients with continued pain of unknown etiology; 3) surgical site infection, particularly late infections that involve the implant system. FDA device/drug status: not applicable. Nothing of value received from a commercial entity related to this research. * Corresponding author. Department of Orthopaedic Surgery, The Johns Hopkins University, School of Medicine, 601 North Caroline Street, Suite 5006, Baltimore, MD 21287, USA. Tel.: (410) 614-1451; fax: (410) 955-1795. E-mail address: [email protected] (J.P. Kostuik) 1529-9430/04/$ – see front matter doi:10.1016/j.spinee.2004.07.021
쑖 2004 Elsevier Inc. All rights reserved.
The effects of wear debris are well reported in the total joint replacement population and are associated with osteolysis as well as concerns about systemic debris deposition [4– 6]. By comparison the data on spinal arthroplasty remain somewhat scanty. Debris created from disc replacement implants result in an inflammatory response similar to that commonly seen in total joint arthroplasty [7]. However, the long-term effects of wear debris in the spinal arthroplasty population remain unknown. To this end, an article within this publication discusses the findings and effects of wear debris in the spinal setting. Unknown at this time is whether wear debris of either metallic or polymer nature will have an effect on spinal arthroplasty, such as the aseptic loosening seen in joint replacement. Long-term mechanical failures of disc arthroplasty implants, although theoretically possible, are not anticipated. An exception may be the long-term results seen with polymers as high-density polyethylene may demonstrate cold flow and/or breakage after years of use after implantation. Mechanical testing to this point would indicate, however, that the likelihood of mechanical failure of either polymers or metals remains highly unlikely.
Surgical revision for failed disc arthroplasty Few articles comment on the direct complications of artificial disc replacement. Van Ooij et al. [8] have reported on 27 patients who had failed Charite´ disc (DePuy Spine, Raynham, MA) replacement. The initial placements of these patients’ implants had all been performed at other institutions. All replacements had been at either the L4–L5 or L5–S1 level. The mean age of the patients was 40 years, ranging from 30 to 67 years at the time of operation. The patients presented an average of 53 months (range, 11 to 127
290S
J.P. Kostuik / The Spine Journal 4 (2004) 289S–291S
months) after initial disc replacement surgery. Two patients required early removal and two late removal of the prosthesis. In 11 patients, a second spinal reconstructive salvage procedure was performed. Early complications included an anterior luxation of the prosthesis 1 week after surgery requiring urgent removal and an attempted arthrodesis, which failed. A second patient who had undergone replacement at both L4–L5 and L5–S1 needed removal of the L5– S1 prosthesis 12 months after implantation after it dislocated anteriorly 9 months earlier (at 3 months after surgery). Four patients experienced an abdominal wall hematoma. In addition, neurologic injuries occurred in two patients: one developed retrograde ejaculation as a result, and the other had difficulty obtaining an erection. Twelve patients experienced a temporary benefit from their arthroplasty, and 14 patients reported no benefit. For the patient group noted here, the major cause of persistent complaints was pain. The causes of the pain were noted to be adjacent level degeneration for 14 patients, prosthesis subsidence in 16 patients and facet joint arthrosis for 11 patients. Clearly, the clinical impression was that some patients had more than one source contributing to their persistent pain. Slow anterior migration of the prosthesis was observed in two cases, with compression of the iliac vessels resulting in one case. Polyethylene wear was obvious in one patient’s implant, but it remains unclear whether the worn implant was a Charite´ III disc or one of its less technologically advanced precursors. Eight patients underwent posterior fusion with pedicle screw instrumentation for more definitive fixation. An additional two patients underwent circumferential fusion after late removal of their prostheses. All patients covered in this report demonstrated some degree of optimal long-term results. This was because, in the authors’ clinical opinion, the majority of the problems appeared to develop as a result of adjacent disc segment degeneration, facet joint arthrosis at the same or other levels or subsidence of the prosthesis. Diagnosis of continuing pain Continuing pain of an unknown etiology could be identified in disc arthroplasty patients. Diagnosis would rely primarily on the delineation of whether the new pain resembles or significantly differs from the pain for which the patient was originally treated with disc replacement. This diagnostic approach—coupled with careful history taking and, at minimum, the use of normal radiographs, flexionextension films and both axial and sagittal computed tomography (CT) scans—should be used to elucidate a mechanism for the patient’s ongoing pain. Should these fail to reveal any underlying pathology, then the diagnostic algorithm should include injection of local anesthetic and radiosensitive dye into the periprosthetic area to determine if that alleviates the pain. Repeat radiographs should be taken before and after local anesthetic injection, as well as during flexion and extension of the affected area.
The use of additional diagnostic and therapeutic modalities, such as facet blocks at the level of arthroplasty, may also prove beneficial. It is important to rule out other sources of pain, particularly in those patients who did not undergo preoperative discography. The use of discography at the levels adjacent to the arthroplasty may be of diagnostic value as well. The patient who develops new pain or continues to have pain that is secondary to loosening, malposition or displacement of the intervertebral implant should also undergo a similar diagnostic algorithm. Again, this would include radiographs, including flexion-extension views, CT scans in at least the axial and sagittal planes and injection studies, including the use of local anesthetic injected with dye periprosthetically to identify any alleviation of pain. If pain is in fact relieved after local anesthetic injection, one could assume that the pain is related to loosening, malposition or displacement. Failures resulting from infections Periprosthetic loosening resulting from infection may prove to be difficult to differentiate from loosening resulting from other causes. Classic laboratory values associated with infection, such as leukocytosis, an elevated erythrocyte sedimentation rate (ESR) and high C-reactive protein value, may be a helpful starting point for diagnosis. Aspiration of fluid from the periprosthetic area and injection of saline with reaspiration are of value in determining if the surgical site shows indications of infection. Evidence of bone resorption on CT scans may also be helpful but are not specifically diagnostic of infection. In the setting of presumed periprosthetic infection, empiric antibiotic therapy should be initiated once suitable aspirates and cultures have been collected. Identification of a specific infective agent with culture and sensitivity reports will subsequently lead to the question of appropriate management. Specifically, the question will be whether nonsurgical management with appropriately targeted antibiotics will be sufficient to eradicate the infection. Antibiotics in the presence of such a bulky implant are unlikely to be of any long-term value. Indeed, in the presence of continuing infection or recurrent infection unresponsive to antibiotic therapy, surgical intervention is indicated. The surgical technique for management of infection would consist of implant removal, careful debridement and irrigation of soft tissues, followed by fusion. In this author’s opinion, fusion is best achieved with a structural autograft rather than allograft. Some surgeons may question whether supplementation of the anterior procedure with anterior fixation is required. Because the presence of infection provides the indication for surgical revision, additional instrumentation near the infected site is not advised. Rather, consideration should be given to a posterior procedure with instrumentation and bone grafting about 1 week after the prosthesis removal and debridement operation. An additional question
J.P. Kostuik / The Spine Journal 4 (2004) 289S–291S
may arise as to whether the posterior procedure is necessary. Consider that a thin patient who can be fitted with a securely fitted clamshell orthosis or body spica may be sufficiently managed without posterior instrumentation. The vast majority of patients, however, will require anterior and posterior procedures, and dependent on infection, this is best accomplished in a staged manner.
Options The options for any failure of disc arthroplasty include 1) posterior fusion, 2) revision replacement and 3) anterior fusion (interbody). Posterior fusion In the absence of life, limb or organ-system–threatening complications, such as infection, neurovascular compromise or significant prosthesis displacement, the use of posterior arthrodesis at the level of arthroplasty may be sufficient to alleviate symptoms of pain. Evidence of gross loosening during dynamic radiography (flexion-extension films) or CT scans may predict an unsuccessful result with posterior fusion alone. Ultimately, an anterior procedure or a combined anterior/posterior procedure may be required to provide complete pain relief. Revision replacement The presence of minor prosthetic loosening or minor malposition or displacement should lead to the consideration of revision arthroplasty. This can be a somewhat perilous procedure and is not to be considered lightly, because the previous anterior approach can be heavily scarred and difficult to visualize and access. This concept is particularly significant at the L4–L5 level, where significant retraction of the great vessels was likely necessary at the primary procedure and where the loss of typical anatomic landmarks may have catastrophic consequences. The approach for L5– S1 level revision is typically inferior to the bifurcation of the aorta, but the risk of a venous tear is not insignificant. Surgeons should be prepared for this possibility with sufficient blood products and the use of a cell saver available. The replacement arthroplasty will, in all likelihood, require a larger height size prosthesis. Careful preparation of the bed will be necessary with the removal of all interbody scar tissue. Of significant concern with regard to revision arthroplasty is the likelihood of prosthesis subsidence. This development may be distinctly possible because the destruction of the bony vertebral end plates during implant and scar tissue removal. Additionally, the surgeon must question why the initial arthroplasty procedure failed in order to avoid similar problems in revision.
291S
In the absence of neurological complications causing radicular pain or radicular signs, the use of preoperative magnetic resonance imaging or CT myelography is, in all likelihood, unnecessary. Anterior interbody fusion Anterior interbody fusion will be necessary in cases of infection as well as significant prosthesis displacement, loosening or malposition. The latter indications will require anterior fusion if they are not amenable to revision arthroplasty. In the absence of infection, after the anterior removal of the implant and preparation of a vascularized bony bed, the use of allograft should suffice for attaining a stable fusion. If rigid fixation is obtainable through the use of a plate, retention screws or a screw/rod system, this may preclude a posterior arthrodesis. However, if significant anterior stability is not obtainable, then a same-day posterior arthrodesis at the level of the arthroplasty may be necessary. As noted when considering revision arthroplasty, the risks of anterior interbody fusion for revision surgery may be further scarring and vascular, neurologic or ureteral injury. At this time the strategies for revision arthroplasty remain relatively speculative because there is no wealth of experience. At least 5 years of routine use and follow-up with intervertebral disc arthroplasty will likely be necessary before one might reach reasonable conclusions about prosthesis loosening, displacement and malposition, in addition to the problems related to continued, undiagnosed pain. The European literature on the experience with the Charite´-Link disc was not done prospectively. In part because of this lack of prospective scope because this prosthesis has undergone a number of revisions over the years, the data, at best, are sparse. Future experience will point in the direction our further efforts and studies will need to go. References [1] Griffith SL, Shelokov AP, Buttner-Janz K, et al. A multicenter retrospective study of the clinical results of the LINK SB Charite´ intervertebral prosthesis. The initial European experience. Spine 1994;19:1842–9. [2] Cinotti G, David T, Postacchini F. Results of disc prosthesis after a minimum follow-up period of 2 years. Spine 1996;21:995–1000. [3] Zeegers WS, Bohnen LM, Laaper M, et al. Artificial disc replacement with the modular type SB Charite´ III: 2-year results in 50 prospectively studied patients. Eur Spine J 1999;8:210–7. [4] Chan FW, Bobyn JD, Medley JB, Krygier JJ, Yue S, Tanzer M. Engineering issues and wear performance of metal on metal hip implants. Clin Orthop 1996;333:96–107. [5] Kobayashi A, Freeman MAR, Bonfield W, et al. Number of polyethylene particles and osteolysis in total joint replacements. A quantitative study using a tissue-digestion method. J Bone Joint Surg Br 1997; 79:844–8. [6] Wagner M, Wagner H. Medium-term results of a modern metal-onmetal system in total hip replacement. Clin Orthop 2000;379:123–33. [7] Hallab NJ, Cunningham BW, Jacobs JJ. Spinal implant debris-induced osteolysis. Spine 2003;28:S125–38. [8] van Ooij A, Oner FC, Verbout AJ. Complications of artificial disc replacement: a report of 27 patients with SB Charite´ disc. J Spinal Dis Tech 2003;16(4):369–83.
Complications and surgical revision for failed disc arthroplasty John P. Kostuik, MD* Department of Orthopaedic Surgery, The Johns Hopkins University School of Medicine, 601 North Caroline Street, Suite 5006, Baltimore, MD 21287, USA
Abstract
This review will outline the indications and options for revision of failed disc arthroplasty. Such indications may include implant loosening, malposition, displacement, early wear, and infection. Each indication will likely require different preoperative planning, testing, and strategies. 쑖 2004 Elsevier Inc. All rights reserved.
Keywords:
Complications; Failed disc arthroplasty; Revision surgery
Introduction Despite all the research and development that has already been conducted, it is unknown what the failure rate for disc arthroplasty will be once spine surgeons begin widespread use of the technique. Numerous studies investigating multiple intervertebral implant systems have been underway in Europe for several years. The reported satisfaction rate in the European literature for improvements in patient pain and function has been relatively high and typically greater than 70% [1–3]. Unfortunately, the closely controlled inclusion groups, relatively small study populations and lack of extensive long-term follow-up have provided limited insight into the incidence of mechanical failure, infection rates and other potential complications. The intent of this article is to outline the indications and options for revision of failed intervertebral disc arthroplasty.
Indications The primary indications for surgical revision should include 1) patients with continued pain secondary to implant loosening, malposition or displacement; 2) patients with continued pain of unknown etiology; 3) surgical site infection, particularly late infections that involve the implant system. FDA device/drug status: not applicable. Nothing of value received from a commercial entity related to this research. * Corresponding author. Department of Orthopaedic Surgery, The Johns Hopkins University, School of Medicine, 601 North Caroline Street, Suite 5006, Baltimore, MD 21287, USA. Tel.: (410) 614-1451; fax: (410) 955-1795. E-mail address: [email protected] (J.P. Kostuik) 1529-9430/04/$ – see front matter doi:10.1016/j.spinee.2004.07.021
쑖 2004 Elsevier Inc. All rights reserved.
The effects of wear debris are well reported in the total joint replacement population and are associated with osteolysis as well as concerns about systemic debris deposition [4– 6]. By comparison the data on spinal arthroplasty remain somewhat scanty. Debris created from disc replacement implants result in an inflammatory response similar to that commonly seen in total joint arthroplasty [7]. However, the long-term effects of wear debris in the spinal arthroplasty population remain unknown. To this end, an article within this publication discusses the findings and effects of wear debris in the spinal setting. Unknown at this time is whether wear debris of either metallic or polymer nature will have an effect on spinal arthroplasty, such as the aseptic loosening seen in joint replacement. Long-term mechanical failures of disc arthroplasty implants, although theoretically possible, are not anticipated. An exception may be the long-term results seen with polymers as high-density polyethylene may demonstrate cold flow and/or breakage after years of use after implantation. Mechanical testing to this point would indicate, however, that the likelihood of mechanical failure of either polymers or metals remains highly unlikely.
Surgical revision for failed disc arthroplasty Few articles comment on the direct complications of artificial disc replacement. Van Ooij et al. [8] have reported on 27 patients who had failed Charite´ disc (DePuy Spine, Raynham, MA) replacement. The initial placements of these patients’ implants had all been performed at other institutions. All replacements had been at either the L4–L5 or L5–S1 level. The mean age of the patients was 40 years, ranging from 30 to 67 years at the time of operation. The patients presented an average of 53 months (range, 11 to 127
290S
J.P. Kostuik / The Spine Journal 4 (2004) 289S–291S
months) after initial disc replacement surgery. Two patients required early removal and two late removal of the prosthesis. In 11 patients, a second spinal reconstructive salvage procedure was performed. Early complications included an anterior luxation of the prosthesis 1 week after surgery requiring urgent removal and an attempted arthrodesis, which failed. A second patient who had undergone replacement at both L4–L5 and L5–S1 needed removal of the L5– S1 prosthesis 12 months after implantation after it dislocated anteriorly 9 months earlier (at 3 months after surgery). Four patients experienced an abdominal wall hematoma. In addition, neurologic injuries occurred in two patients: one developed retrograde ejaculation as a result, and the other had difficulty obtaining an erection. Twelve patients experienced a temporary benefit from their arthroplasty, and 14 patients reported no benefit. For the patient group noted here, the major cause of persistent complaints was pain. The causes of the pain were noted to be adjacent level degeneration for 14 patients, prosthesis subsidence in 16 patients and facet joint arthrosis for 11 patients. Clearly, the clinical impression was that some patients had more than one source contributing to their persistent pain. Slow anterior migration of the prosthesis was observed in two cases, with compression of the iliac vessels resulting in one case. Polyethylene wear was obvious in one patient’s implant, but it remains unclear whether the worn implant was a Charite´ III disc or one of its less technologically advanced precursors. Eight patients underwent posterior fusion with pedicle screw instrumentation for more definitive fixation. An additional two patients underwent circumferential fusion after late removal of their prostheses. All patients covered in this report demonstrated some degree of optimal long-term results. This was because, in the authors’ clinical opinion, the majority of the problems appeared to develop as a result of adjacent disc segment degeneration, facet joint arthrosis at the same or other levels or subsidence of the prosthesis. Diagnosis of continuing pain Continuing pain of an unknown etiology could be identified in disc arthroplasty patients. Diagnosis would rely primarily on the delineation of whether the new pain resembles or significantly differs from the pain for which the patient was originally treated with disc replacement. This diagnostic approach—coupled with careful history taking and, at minimum, the use of normal radiographs, flexionextension films and both axial and sagittal computed tomography (CT) scans—should be used to elucidate a mechanism for the patient’s ongoing pain. Should these fail to reveal any underlying pathology, then the diagnostic algorithm should include injection of local anesthetic and radiosensitive dye into the periprosthetic area to determine if that alleviates the pain. Repeat radiographs should be taken before and after local anesthetic injection, as well as during flexion and extension of the affected area.
The use of additional diagnostic and therapeutic modalities, such as facet blocks at the level of arthroplasty, may also prove beneficial. It is important to rule out other sources of pain, particularly in those patients who did not undergo preoperative discography. The use of discography at the levels adjacent to the arthroplasty may be of diagnostic value as well. The patient who develops new pain or continues to have pain that is secondary to loosening, malposition or displacement of the intervertebral implant should also undergo a similar diagnostic algorithm. Again, this would include radiographs, including flexion-extension views, CT scans in at least the axial and sagittal planes and injection studies, including the use of local anesthetic injected with dye periprosthetically to identify any alleviation of pain. If pain is in fact relieved after local anesthetic injection, one could assume that the pain is related to loosening, malposition or displacement. Failures resulting from infections Periprosthetic loosening resulting from infection may prove to be difficult to differentiate from loosening resulting from other causes. Classic laboratory values associated with infection, such as leukocytosis, an elevated erythrocyte sedimentation rate (ESR) and high C-reactive protein value, may be a helpful starting point for diagnosis. Aspiration of fluid from the periprosthetic area and injection of saline with reaspiration are of value in determining if the surgical site shows indications of infection. Evidence of bone resorption on CT scans may also be helpful but are not specifically diagnostic of infection. In the setting of presumed periprosthetic infection, empiric antibiotic therapy should be initiated once suitable aspirates and cultures have been collected. Identification of a specific infective agent with culture and sensitivity reports will subsequently lead to the question of appropriate management. Specifically, the question will be whether nonsurgical management with appropriately targeted antibiotics will be sufficient to eradicate the infection. Antibiotics in the presence of such a bulky implant are unlikely to be of any long-term value. Indeed, in the presence of continuing infection or recurrent infection unresponsive to antibiotic therapy, surgical intervention is indicated. The surgical technique for management of infection would consist of implant removal, careful debridement and irrigation of soft tissues, followed by fusion. In this author’s opinion, fusion is best achieved with a structural autograft rather than allograft. Some surgeons may question whether supplementation of the anterior procedure with anterior fixation is required. Because the presence of infection provides the indication for surgical revision, additional instrumentation near the infected site is not advised. Rather, consideration should be given to a posterior procedure with instrumentation and bone grafting about 1 week after the prosthesis removal and debridement operation. An additional question
J.P. Kostuik / The Spine Journal 4 (2004) 289S–291S
may arise as to whether the posterior procedure is necessary. Consider that a thin patient who can be fitted with a securely fitted clamshell orthosis or body spica may be sufficiently managed without posterior instrumentation. The vast majority of patients, however, will require anterior and posterior procedures, and dependent on infection, this is best accomplished in a staged manner.
Options The options for any failure of disc arthroplasty include 1) posterior fusion, 2) revision replacement and 3) anterior fusion (interbody). Posterior fusion In the absence of life, limb or organ-system–threatening complications, such as infection, neurovascular compromise or significant prosthesis displacement, the use of posterior arthrodesis at the level of arthroplasty may be sufficient to alleviate symptoms of pain. Evidence of gross loosening during dynamic radiography (flexion-extension films) or CT scans may predict an unsuccessful result with posterior fusion alone. Ultimately, an anterior procedure or a combined anterior/posterior procedure may be required to provide complete pain relief. Revision replacement The presence of minor prosthetic loosening or minor malposition or displacement should lead to the consideration of revision arthroplasty. This can be a somewhat perilous procedure and is not to be considered lightly, because the previous anterior approach can be heavily scarred and difficult to visualize and access. This concept is particularly significant at the L4–L5 level, where significant retraction of the great vessels was likely necessary at the primary procedure and where the loss of typical anatomic landmarks may have catastrophic consequences. The approach for L5– S1 level revision is typically inferior to the bifurcation of the aorta, but the risk of a venous tear is not insignificant. Surgeons should be prepared for this possibility with sufficient blood products and the use of a cell saver available. The replacement arthroplasty will, in all likelihood, require a larger height size prosthesis. Careful preparation of the bed will be necessary with the removal of all interbody scar tissue. Of significant concern with regard to revision arthroplasty is the likelihood of prosthesis subsidence. This development may be distinctly possible because the destruction of the bony vertebral end plates during implant and scar tissue removal. Additionally, the surgeon must question why the initial arthroplasty procedure failed in order to avoid similar problems in revision.
291S
In the absence of neurological complications causing radicular pain or radicular signs, the use of preoperative magnetic resonance imaging or CT myelography is, in all likelihood, unnecessary. Anterior interbody fusion Anterior interbody fusion will be necessary in cases of infection as well as significant prosthesis displacement, loosening or malposition. The latter indications will require anterior fusion if they are not amenable to revision arthroplasty. In the absence of infection, after the anterior removal of the implant and preparation of a vascularized bony bed, the use of allograft should suffice for attaining a stable fusion. If rigid fixation is obtainable through the use of a plate, retention screws or a screw/rod system, this may preclude a posterior arthrodesis. However, if significant anterior stability is not obtainable, then a same-day posterior arthrodesis at the level of the arthroplasty may be necessary. As noted when considering revision arthroplasty, the risks of anterior interbody fusion for revision surgery may be further scarring and vascular, neurologic or ureteral injury. At this time the strategies for revision arthroplasty remain relatively speculative because there is no wealth of experience. At least 5 years of routine use and follow-up with intervertebral disc arthroplasty will likely be necessary before one might reach reasonable conclusions about prosthesis loosening, displacement and malposition, in addition to the problems related to continued, undiagnosed pain. The European literature on the experience with the Charite´-Link disc was not done prospectively. In part because of this lack of prospective scope because this prosthesis has undergone a number of revisions over the years, the data, at best, are sparse. Future experience will point in the direction our further efforts and studies will need to go. References [1] Griffith SL, Shelokov AP, Buttner-Janz K, et al. A multicenter retrospective study of the clinical results of the LINK SB Charite´ intervertebral prosthesis. The initial European experience. Spine 1994;19:1842–9. [2] Cinotti G, David T, Postacchini F. Results of disc prosthesis after a minimum follow-up period of 2 years. Spine 1996;21:995–1000. [3] Zeegers WS, Bohnen LM, Laaper M, et al. Artificial disc replacement with the modular type SB Charite´ III: 2-year results in 50 prospectively studied patients. Eur Spine J 1999;8:210–7. [4] Chan FW, Bobyn JD, Medley JB, Krygier JJ, Yue S, Tanzer M. Engineering issues and wear performance of metal on metal hip implants. Clin Orthop 1996;333:96–107. [5] Kobayashi A, Freeman MAR, Bonfield W, et al. Number of polyethylene particles and osteolysis in total joint replacements. A quantitative study using a tissue-digestion method. J Bone Joint Surg Br 1997; 79:844–8. [6] Wagner M, Wagner H. Medium-term results of a modern metal-onmetal system in total hip replacement. Clin Orthop 2000;379:123–33. [7] Hallab NJ, Cunningham BW, Jacobs JJ. Spinal implant debris-induced osteolysis. Spine 2003;28:S125–38. [8] van Ooij A, Oner FC, Verbout AJ. Complications of artificial disc replacement: a report of 27 patients with SB Charite´ disc. J Spinal Dis Tech 2003;16(4):369–83.