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Well-fixed acetabular component retention or replacement: The whys and the wherefores
The Journal of Arthroplasty Vol. 17 No. 4 Suppl. 1 2002
Well-Fixed Acetabular Component Retention or Replacement The Whys and the Wherefores J. David Blaha, MD
Abstract: Occasionally the adult reconstructive surgeon is faced with a well-fixed acetabular component that is associated with an arthroplasty problem that ordinarily would require removal and replacement of the cup. Removal of a well-fixed cup is associated with considerable morbidity in bone loss, particularly in the medial wall of the acetabulum. In such a situation, retention of the cup with exchange only of the polyethylene liner may be possible. As preparation for a prospective study, I informally reviewed my experience of cup retention or replacement in revision total hip arthroplasty. An algorithm for retaining or revising a well-fixed acetabular component is presented here. Key words: acetabular cup, total hip arthroplasty (THA), revision. Copyright 2002, Elsevier Science (USA). All rights reserved.
There is a continuing problem in total hip arthroplasty (THA) patients with debris-induced osteolysis. The rapid wearing of (in most but not all cases) polyethylene leads to lesions of bone loss in areas where the debris-laden joint fluid can be pumped toward the interface. Near the acetabulum, these lesions can be large with the access gained through screw holes in the cup or around the cup at its periphery. It is frequently the case, however, that despite these large osteolytic lesions, the cup itself is still well fixed through osseointegration [1]. In such a case, the surgeon is faced with the problem of the well-fixed acetabular socket with a worn polyethylene liner and significant periacetabular osteolysis.
Another problem that can lead to consideration of retaining a well-fixed cup is that of malpositioning of a cup that is leading to chronic dislocation. In such a situation, it can be preferable to replace the polyethylene liner with one that can correct the malpositioning through specific augments (eg, a lipped liner). Removal of the cup is not always an easy task and can be associated with significant bone loss. Because of the problems encountered in trying to replace an acetabular component when there has been bone loss, surgeons have begun retaining the well-fixed component in situ by exchanging the polyethylene liner while attempting to encourage bone formation through grafting the defects with bone or bone substitutes. I reviewed my experiences of revision THAs in which a decision was made either to remove or to retain the acetabular component. This article presents my conclusions after this review.
From the Department of Orthopedics, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia. No benefits or funds were received in support of this study. Reprint requests: J. David Blaha, MD, Department of Orthopedics, Robert C. Byrd Health Sciences Center, HSS Box 9196, 1 Medical Center Drive, West Virginia University, Morgantown, WV 26506-9196. E-mail: [email protected] Copyright 2002, Elsevier Science (USA). All rights reserved. 0883-5403/02/1704-1042$35.00/0 doi:10.1054/arth.2002.33301
Clinical Material and Results Between 1981 and 2001, 460 revision THAs during which a decision was made about retention or
157
158 The Journal of Arthroplasty Vol. 17 No. 4 Suppl. 1 June 2002 removal of the acetabular component were done. In preparing a protocol for a prospective study of the treatment of well-fixed acetabular components, I reviewed the operative notes and final outcomes of the revision THAs. In 32 of the 460 cases, a wellfixed acetabular component was retained in situ. In none of those cases was a second revision operation necessary for loosening of the acetabular component. Based on the morbidity associated with removing a well-fixed acetabular component, the success of the cases in which a well-fixed component was left in place, and the results of a literature review, I constructed an algorithm (Fig. 1) for replacement or retention of a well-fixed acetabular component for a prospective study. Figs. 2 and 3 are case examples from my experience.
Fig. 2. This patient had bilateral worn-through THA sockets. The right socket was revised to this expansion cup with a good functional result. The left socket was pending revision.
Preoperative Decisions In contrast to the common situation in adult reconstructive surgery in which the patient’s symp-
Fig. 1. Algorithm for retaining a well-fixed cementless THA cup.
Fig. 3. This patient fell and fractured her pelvis on the right and displaced the acetabular component. This stable shift of the cup proved to be pain-free and stable after the healing of the pelvic fracture. The left hip was treated by cementing a new polyethylene liner into the well-fixed shell and filling the osteolytic cavity with a combination of demineralized bone matrix and calcium sulfate. Both hips are doing well, but there was considerably less morbidity in the treatment of the left hip with socket retention.
Acetabular Component Retention or Replacement • J. David Blaha
toms drive the decision to operate, an acetabular component with obvious wear and significant bone loss from osteolysis should be considered more urgent. Although there is some evidence that alendronate [2] can retard bone destruction in an animal model, in clinical experience it seems that once the osteolytic process has begun, it continues. If the lesions progress far enough, the integrity of the bony socket becomes compromised, and this in turn compromises the end result of any reconstruction. A patient with significant bone loss should be cautioned about heavy activity and should be encouraged strongly to seek a revision arthroplasty at the soonest convenient opportunity. If the patient declines surgery or if the general health of the patient precludes an operation, frequent follow-up should be done with radiographs and continued discussion with the patient. A classification system has been proposed for the retention of acetabular components based on the stability of the acetabular shell and the exchangeability of the polyethylene liner [3]. Type I cases have a stable osseointegrated shell that has an exchangeable polyethylene liner. Type II cases have a stable shell, but the liner is not exchangeable. Type III cases have a loose metal shell that must be removed [4]. If it is suspected from the preoperative radiographs (and other imaging studies, such as computed tomography scan) that the cup is loose (type III), a more typical revision operation should be planned. The surgeon should be prepared to be surprised, however, and be ready to retain a wellfixed acetabular component if it is stable. If it is evident from the preoperative evaluation that the cup is broken, it should be revised. Preoperative sedimentation rate and C-reactive protein should be obtained, and if the results are suspicious, an aspiration of the joint should be done searching for infection. If infection is found, in virtually every case the cup should be revised. To prepare for possible cup retention, as much information as possible about the previous surgery should be obtained, specifically the types of components used. The manufacturer’s representative should be contacted about the possibility of getting a new polyethylene liner for the cup. The quality of the locking mechanism for the polyethylene should be investigated. In some instances, the locking mechanism will have been proved to be ineffective so that any new liner would have to be placed with alternative fixation— usually with bone– cement. The operating room should have instruments (eg, special polyethylene removing instruments or a high-speed bur with metal cutting bits) that can be
159
used to remove and replace a liner or for scoring the surface of a metal shell and the polyethylene so that good interlocking of the cement and good fixation can be achieved.
Intraoperative Decisions Preoperative evaluation and planning, based on the history, physical examination, and imaging studies, are essential to be prepared for the revision operation. Because the best of preoperative evaluations are imprecise, however, the surgeon needs to be ready to alter course of the operation based on the circumstances found at surgery. A loose cup, broken cup, or infection (found through Gram stain or frozen section analysis of the periarticular tissues) alters a preoperative plan that expected to retain a well-fixed cup. The back table and the equipment available near the operating room must be prepared for any change in plan occasioned by the findings at surgery. Malposition When the acetabulum is exposed fully so that the relationship between the bone confines of the acetabulum can be compared with the component itself, the surgeon may find that a cup is in a position that can lead to dislocation or impingement. Specific patterns of wear on the polyethylene (eg, an impression of the neck of the femoral component in the liner) can lead to the conclusion that the cup is positioned incorrectly. It may be possible to exchange the polyethylene liner in the cup for one that can correct the position (eg, a cup with slightly more lateral placement of the center of rotation and an appropriately placed lip). If the malposition cannot be corrected, the component must be removed and a new one placed in the proper position. The polyethylene liner generally can be removed by a purpose-built device from the manufacturer, by prying (with a small osteotome) the liner out of place, or by a screw (placed through the cup into the metal back below) that is used to back the cup out of the liner. Wear In most cases, the penetration of the head into the polyethylene has been noted on preoperative imaging studies, and the surgeon is prepared to remove and replace a polyethylene liner into a well-fixed cup. The amount of wear can be assessed in the operating room by direct observation of the polyethylene surface or by placing an
160 The Journal of Arthroplasty Vol. 17 No. 4 Suppl. 1 June 2002 appropriate-sized head into the cup and observing the opposing defect in the cup. Knowledge of the quality of the polyethylene (eg, sterilization method, storage medium, shelf life, service life) can help decide whether a slightly worn cup should be replaced with the bias of the decision toward revision of the polyethylene component. If the quality of the polyethylene cannot be determined, it is better to assume that the quality of the polyethylene is poor and to replace the liner. I replace virtually all polyethylene liners encountered at revision. If the problem cannot be solved with the liner exchange (eg, the liner cannot be disassociated from the metal back), the cup must be replaced. Osteolysis Usually significant periacetabular osteolysis is associated with marked polyethylene wear so that the problems of wear and osteolysis are addressed together. Assuming that it is reasonable to replace the polyethylene liner, the surgeon must assess critically the stability of the metal back of the cup. All edges of the component should be fully visualized. If possible, the surgeon should observe directly an area of ingrowth or ongrowth surface and look for macroscopic soft tissue at the interface. Firm pressure should be placed on the cup first through its central axis, then through its periphery while observing the interface for motion or for the expression of bloody fluid from the interface. Either of these findings implies that the component is not well fixed and that it should be exchanged. Grasping the cup with a clamp through screw holes and twisting it is another method to assess the stability. Osteolytic cavities may be approached through the holes in the cup or through a trapdoor that allows access to the lesion. Bone grafting with autogenous bone, allograft bone, demineralized bone matrix, calcium sulfate, combinations of these, and other materials has been reported with satisfactory results [5].
adequate to hold a liner firmly, the liner can be cemented into the retained metal back. A liner should be chosen that is smaller than the inside diameter of the retained metal back. The ideal of a 2-mm cement mantle [6] can be achieved only if the cup is 4 mm smaller than the inside diameter of the cup—a situation that is not always attainable. The difference in diameter between the outside of the liner and inside of the cup should be at least 1 mm. Scoring of the cup and polyethylene liner with furrows cut with a highspeed bur should be done to increase the interdigitation and the thickness of the cement to improve the durability of the fixation. After packing the osteolytic defects with graft material, the cup should be cleaned and dried as is appropriate for any surface to be cemented, and interdigitation of the cement with the screw holes should be ensured to improve the fixation of the liner to the retained metal back.
Conclusion ● Careful preoperative evaluation and planning are essential. ● As much information as possible about the components in place and consultation with the manufacturer’s representative about the components and insertion and removal equipment are essential parts of the preoperative evaluation and planning. ● Intraoperative assessment must be thorough and must drive the decision about retaining or removing an acetabular metal back. ● Careful de´bridement of osteolytic lesions and grafting of the lesions is probably important for the long-term success of the reconstruction. ● Attention to good cement technique, including using a high-speed bur for ensuring interdigitation, is essential for firm fixation of the polyethylene liner when it is cemented to a well-fixed metal back.
Considerations for Replacing a Polyethylene Liner
References
Ideally the liner exchanged fits the metal back exactly and engages the locking mechanism of the cup. In situations in which an appropriate polyethylene liner is no longer available from the manufacturer or the locking mechanism of the cup is known to be poor and would not likely be
1. Zicat B, Engh CA, Gocken E: Patterns of osteolysis around total hip components inserted with and without cement. J Bone Joint Surg Am 77:432, 1995 2. Shanbhag AS, Hasselman CT, Rubash HE: Inhibition of wear debris mediated osteolysis in a canine total hip arthroplasty model. Clin Orthop 344:33, 1997 3. Rubash HE, Sinha RK, Engh CA, et al: A new classifi-
Acetabular Component Retention or Replacement • J. David Blaha cation system for the management of acetabular osteolysis after total hip arthroplasty. Instr Course Lect 48:37, 1999 4. Maloney WJ: The revision acetabulum: Dealing with bone loss. Socket retention: Staying in place. Orthopedics 23:65, 2000
161
5. Schmalzried TP, Fowble VA, Amstutz HC: The fate of pelvic osteolysis after reoperation: No recurrence with lesional treatment. Clin Orthop 350:128, 1998 6. Bensen CV, Del Schutte H Jr, Weaver KD: Mechanical stability of polyethylene liners cemented into acetabular shells. Crit Rev Biomed Eng 28:7, 2000
Well-Fixed Acetabular Component Retention or Replacement The Whys and the Wherefores J. David Blaha, MD
Abstract: Occasionally the adult reconstructive surgeon is faced with a well-fixed acetabular component that is associated with an arthroplasty problem that ordinarily would require removal and replacement of the cup. Removal of a well-fixed cup is associated with considerable morbidity in bone loss, particularly in the medial wall of the acetabulum. In such a situation, retention of the cup with exchange only of the polyethylene liner may be possible. As preparation for a prospective study, I informally reviewed my experience of cup retention or replacement in revision total hip arthroplasty. An algorithm for retaining or revising a well-fixed acetabular component is presented here. Key words: acetabular cup, total hip arthroplasty (THA), revision. Copyright 2002, Elsevier Science (USA). All rights reserved.
There is a continuing problem in total hip arthroplasty (THA) patients with debris-induced osteolysis. The rapid wearing of (in most but not all cases) polyethylene leads to lesions of bone loss in areas where the debris-laden joint fluid can be pumped toward the interface. Near the acetabulum, these lesions can be large with the access gained through screw holes in the cup or around the cup at its periphery. It is frequently the case, however, that despite these large osteolytic lesions, the cup itself is still well fixed through osseointegration [1]. In such a case, the surgeon is faced with the problem of the well-fixed acetabular socket with a worn polyethylene liner and significant periacetabular osteolysis.
Another problem that can lead to consideration of retaining a well-fixed cup is that of malpositioning of a cup that is leading to chronic dislocation. In such a situation, it can be preferable to replace the polyethylene liner with one that can correct the malpositioning through specific augments (eg, a lipped liner). Removal of the cup is not always an easy task and can be associated with significant bone loss. Because of the problems encountered in trying to replace an acetabular component when there has been bone loss, surgeons have begun retaining the well-fixed component in situ by exchanging the polyethylene liner while attempting to encourage bone formation through grafting the defects with bone or bone substitutes. I reviewed my experiences of revision THAs in which a decision was made either to remove or to retain the acetabular component. This article presents my conclusions after this review.
From the Department of Orthopedics, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia. No benefits or funds were received in support of this study. Reprint requests: J. David Blaha, MD, Department of Orthopedics, Robert C. Byrd Health Sciences Center, HSS Box 9196, 1 Medical Center Drive, West Virginia University, Morgantown, WV 26506-9196. E-mail: [email protected] Copyright 2002, Elsevier Science (USA). All rights reserved. 0883-5403/02/1704-1042$35.00/0 doi:10.1054/arth.2002.33301
Clinical Material and Results Between 1981 and 2001, 460 revision THAs during which a decision was made about retention or
157
158 The Journal of Arthroplasty Vol. 17 No. 4 Suppl. 1 June 2002 removal of the acetabular component were done. In preparing a protocol for a prospective study of the treatment of well-fixed acetabular components, I reviewed the operative notes and final outcomes of the revision THAs. In 32 of the 460 cases, a wellfixed acetabular component was retained in situ. In none of those cases was a second revision operation necessary for loosening of the acetabular component. Based on the morbidity associated with removing a well-fixed acetabular component, the success of the cases in which a well-fixed component was left in place, and the results of a literature review, I constructed an algorithm (Fig. 1) for replacement or retention of a well-fixed acetabular component for a prospective study. Figs. 2 and 3 are case examples from my experience.
Fig. 2. This patient had bilateral worn-through THA sockets. The right socket was revised to this expansion cup with a good functional result. The left socket was pending revision.
Preoperative Decisions In contrast to the common situation in adult reconstructive surgery in which the patient’s symp-
Fig. 1. Algorithm for retaining a well-fixed cementless THA cup.
Fig. 3. This patient fell and fractured her pelvis on the right and displaced the acetabular component. This stable shift of the cup proved to be pain-free and stable after the healing of the pelvic fracture. The left hip was treated by cementing a new polyethylene liner into the well-fixed shell and filling the osteolytic cavity with a combination of demineralized bone matrix and calcium sulfate. Both hips are doing well, but there was considerably less morbidity in the treatment of the left hip with socket retention.
Acetabular Component Retention or Replacement • J. David Blaha
toms drive the decision to operate, an acetabular component with obvious wear and significant bone loss from osteolysis should be considered more urgent. Although there is some evidence that alendronate [2] can retard bone destruction in an animal model, in clinical experience it seems that once the osteolytic process has begun, it continues. If the lesions progress far enough, the integrity of the bony socket becomes compromised, and this in turn compromises the end result of any reconstruction. A patient with significant bone loss should be cautioned about heavy activity and should be encouraged strongly to seek a revision arthroplasty at the soonest convenient opportunity. If the patient declines surgery or if the general health of the patient precludes an operation, frequent follow-up should be done with radiographs and continued discussion with the patient. A classification system has been proposed for the retention of acetabular components based on the stability of the acetabular shell and the exchangeability of the polyethylene liner [3]. Type I cases have a stable osseointegrated shell that has an exchangeable polyethylene liner. Type II cases have a stable shell, but the liner is not exchangeable. Type III cases have a loose metal shell that must be removed [4]. If it is suspected from the preoperative radiographs (and other imaging studies, such as computed tomography scan) that the cup is loose (type III), a more typical revision operation should be planned. The surgeon should be prepared to be surprised, however, and be ready to retain a wellfixed acetabular component if it is stable. If it is evident from the preoperative evaluation that the cup is broken, it should be revised. Preoperative sedimentation rate and C-reactive protein should be obtained, and if the results are suspicious, an aspiration of the joint should be done searching for infection. If infection is found, in virtually every case the cup should be revised. To prepare for possible cup retention, as much information as possible about the previous surgery should be obtained, specifically the types of components used. The manufacturer’s representative should be contacted about the possibility of getting a new polyethylene liner for the cup. The quality of the locking mechanism for the polyethylene should be investigated. In some instances, the locking mechanism will have been proved to be ineffective so that any new liner would have to be placed with alternative fixation— usually with bone– cement. The operating room should have instruments (eg, special polyethylene removing instruments or a high-speed bur with metal cutting bits) that can be
159
used to remove and replace a liner or for scoring the surface of a metal shell and the polyethylene so that good interlocking of the cement and good fixation can be achieved.
Intraoperative Decisions Preoperative evaluation and planning, based on the history, physical examination, and imaging studies, are essential to be prepared for the revision operation. Because the best of preoperative evaluations are imprecise, however, the surgeon needs to be ready to alter course of the operation based on the circumstances found at surgery. A loose cup, broken cup, or infection (found through Gram stain or frozen section analysis of the periarticular tissues) alters a preoperative plan that expected to retain a well-fixed cup. The back table and the equipment available near the operating room must be prepared for any change in plan occasioned by the findings at surgery. Malposition When the acetabulum is exposed fully so that the relationship between the bone confines of the acetabulum can be compared with the component itself, the surgeon may find that a cup is in a position that can lead to dislocation or impingement. Specific patterns of wear on the polyethylene (eg, an impression of the neck of the femoral component in the liner) can lead to the conclusion that the cup is positioned incorrectly. It may be possible to exchange the polyethylene liner in the cup for one that can correct the position (eg, a cup with slightly more lateral placement of the center of rotation and an appropriately placed lip). If the malposition cannot be corrected, the component must be removed and a new one placed in the proper position. The polyethylene liner generally can be removed by a purpose-built device from the manufacturer, by prying (with a small osteotome) the liner out of place, or by a screw (placed through the cup into the metal back below) that is used to back the cup out of the liner. Wear In most cases, the penetration of the head into the polyethylene has been noted on preoperative imaging studies, and the surgeon is prepared to remove and replace a polyethylene liner into a well-fixed cup. The amount of wear can be assessed in the operating room by direct observation of the polyethylene surface or by placing an
160 The Journal of Arthroplasty Vol. 17 No. 4 Suppl. 1 June 2002 appropriate-sized head into the cup and observing the opposing defect in the cup. Knowledge of the quality of the polyethylene (eg, sterilization method, storage medium, shelf life, service life) can help decide whether a slightly worn cup should be replaced with the bias of the decision toward revision of the polyethylene component. If the quality of the polyethylene cannot be determined, it is better to assume that the quality of the polyethylene is poor and to replace the liner. I replace virtually all polyethylene liners encountered at revision. If the problem cannot be solved with the liner exchange (eg, the liner cannot be disassociated from the metal back), the cup must be replaced. Osteolysis Usually significant periacetabular osteolysis is associated with marked polyethylene wear so that the problems of wear and osteolysis are addressed together. Assuming that it is reasonable to replace the polyethylene liner, the surgeon must assess critically the stability of the metal back of the cup. All edges of the component should be fully visualized. If possible, the surgeon should observe directly an area of ingrowth or ongrowth surface and look for macroscopic soft tissue at the interface. Firm pressure should be placed on the cup first through its central axis, then through its periphery while observing the interface for motion or for the expression of bloody fluid from the interface. Either of these findings implies that the component is not well fixed and that it should be exchanged. Grasping the cup with a clamp through screw holes and twisting it is another method to assess the stability. Osteolytic cavities may be approached through the holes in the cup or through a trapdoor that allows access to the lesion. Bone grafting with autogenous bone, allograft bone, demineralized bone matrix, calcium sulfate, combinations of these, and other materials has been reported with satisfactory results [5].
adequate to hold a liner firmly, the liner can be cemented into the retained metal back. A liner should be chosen that is smaller than the inside diameter of the retained metal back. The ideal of a 2-mm cement mantle [6] can be achieved only if the cup is 4 mm smaller than the inside diameter of the cup—a situation that is not always attainable. The difference in diameter between the outside of the liner and inside of the cup should be at least 1 mm. Scoring of the cup and polyethylene liner with furrows cut with a highspeed bur should be done to increase the interdigitation and the thickness of the cement to improve the durability of the fixation. After packing the osteolytic defects with graft material, the cup should be cleaned and dried as is appropriate for any surface to be cemented, and interdigitation of the cement with the screw holes should be ensured to improve the fixation of the liner to the retained metal back.
Conclusion ● Careful preoperative evaluation and planning are essential. ● As much information as possible about the components in place and consultation with the manufacturer’s representative about the components and insertion and removal equipment are essential parts of the preoperative evaluation and planning. ● Intraoperative assessment must be thorough and must drive the decision about retaining or removing an acetabular metal back. ● Careful de´bridement of osteolytic lesions and grafting of the lesions is probably important for the long-term success of the reconstruction. ● Attention to good cement technique, including using a high-speed bur for ensuring interdigitation, is essential for firm fixation of the polyethylene liner when it is cemented to a well-fixed metal back.
Considerations for Replacing a Polyethylene Liner
References
Ideally the liner exchanged fits the metal back exactly and engages the locking mechanism of the cup. In situations in which an appropriate polyethylene liner is no longer available from the manufacturer or the locking mechanism of the cup is known to be poor and would not likely be
1. Zicat B, Engh CA, Gocken E: Patterns of osteolysis around total hip components inserted with and without cement. J Bone Joint Surg Am 77:432, 1995 2. Shanbhag AS, Hasselman CT, Rubash HE: Inhibition of wear debris mediated osteolysis in a canine total hip arthroplasty model. Clin Orthop 344:33, 1997 3. Rubash HE, Sinha RK, Engh CA, et al: A new classifi-
Acetabular Component Retention or Replacement • J. David Blaha cation system for the management of acetabular osteolysis after total hip arthroplasty. Instr Course Lect 48:37, 1999 4. Maloney WJ: The revision acetabulum: Dealing with bone loss. Socket retention: Staying in place. Orthopedics 23:65, 2000
161
5. Schmalzried TP, Fowble VA, Amstutz HC: The fate of pelvic osteolysis after reoperation: No recurrence with lesional treatment. Clin Orthop 350:128, 1998 6. Bensen CV, Del Schutte H Jr, Weaver KD: Mechanical stability of polyethylene liners cemented into acetabular shells. Crit Rev Biomed Eng 28:7, 2000