Orthopedics

Lysis in the Well-Fixed Shell: “Hold ‘Em” or “Fold ‘Em”

Edwin P. Su, MD

  • Orthopedics. 2010;33(9)
  • Posted September 1, 2010

Abstract

Periacetabular osteolysis is the greatest challenge for longevity of total hip arthroplasty. The generation of wear debris from the bearing surface is inevitably going to cause bone loss around the implants. The challenges for the arthroplasty surgeon in managing this problem are: detection, knowing when to intervene surgically, and choosing the best reconstructive option. From a surgical standpoint, the options for addressing osteolysis are: (1) liner exchange with or without bone grafting of lytic lesions; or (2) complete component revision. The advantages of “holding ‘em” include a faster surgery, no bony disruption, a quicker recovery for the patient, and cost. The downside of isolated liner exchange is that there is a high rate of instability, there may be incomplete access to the lytic lesions, and the limitations of the existing component. There have been techniques developed to provide access to the retroacetabular lesions, particularly superolaterally via a trap-door technique. Alternatively, other surgeons have advocated injection of bone graft substitutes in the retroacetabular regions to fill osteolytic defects. However, one may not be able to take advantage of newer bearing materials, larger head sizes, or component reposition to improve stability and wear properties. The advantages of a complete component revision are access to lytic lesions, and the ability to modify component position and take advantage of newer technologies. The disadvantages are cost, a longer recovery, and bony disruption. Each method of addressing acetabular osteolysis has compelling reasons to use it; individual patient factors such as component type, size of lesion, and remaining bone will play a role in selecting the treatment.

Once the decision has been made to surgically intervene in a patient with acetabular osteolysis, the goals of operative treatment should be to: (1) arrest the osteolytic process; (2) debulk the biological response via a complete synovectomy and removal of wear debris; (3) replenish bone stock; and (4) exchange the bearing surfaces. Another potential goal of surgical intervention can be to take advantage of newer bearing materials to hopefully delay this process.

The 2 major strategies to deal with osteolysis of the periacetabular bone are: (1) “hold ‘em”: to retain a well-fixed shell; or (2) “fold ‘em”: to remove the well-fixed shell and perform a complete acetabular revision.

The advantages to retaining a well-fixed acetabular component are numerous. First, there is a shorter operative time and less blood loss. Furthermore, there is no bone disruption, and as such, patients will generally recover more quickly because of the ability to immediately bear weight. Finally, the economics of retaining the shell are advantageous because of a lower implant cost, shorter operative time and hospitalization, and a quicker recovery. However, one major disadvantage of isolated liner exchange is that there may be incomplete access to retroacetabular lesions—it can be difficult to debride the areas of osteolysis while the component is present. Furthermore, several studies have documented a high rate of dislocation with isolated liner exchange. To compound this problem, the component cannot be repositioned if the acetabular implant is retained. Finally, due to constraints of the existing implant, one may not be able to take advantage of newer bearing materials, or larger head sizes.

The advantage of removing a well-fixed acetabular component is to give complete access to the osteolytic lesions, allowing for debridement of the wear granuloma and placement of bone graft. Furthermore, one can reposition the component into a more optimal position to aid in the stability of the hip joint, as well as to upsize the femoral head. Unfortunately this strategy does introduce another variable, namely the healing of host bone to the new implant; as such, the patients must…

Abstract

Periacetabular osteolysis is the greatest challenge for longevity of total hip arthroplasty. The generation of wear debris from the bearing surface is inevitably going to cause bone loss around the implants. The challenges for the arthroplasty surgeon in managing this problem are: detection, knowing when to intervene surgically, and choosing the best reconstructive option. From a surgical standpoint, the options for addressing osteolysis are: (1) liner exchange with or without bone grafting of lytic lesions; or (2) complete component revision. The advantages of “holding ‘em” include a faster surgery, no bony disruption, a quicker recovery for the patient, and cost. The downside of isolated liner exchange is that there is a high rate of instability, there may be incomplete access to the lytic lesions, and the limitations of the existing component. There have been techniques developed to provide access to the retroacetabular lesions, particularly superolaterally via a trap-door technique. Alternatively, other surgeons have advocated injection of bone graft substitutes in the retroacetabular regions to fill osteolytic defects. However, one may not be able to take advantage of newer bearing materials, larger head sizes, or component reposition to improve stability and wear properties. The advantages of a complete component revision are access to lytic lesions, and the ability to modify component position and take advantage of newer technologies. The disadvantages are cost, a longer recovery, and bony disruption. Each method of addressing acetabular osteolysis has compelling reasons to use it; individual patient factors such as component type, size of lesion, and remaining bone will play a role in selecting the treatment.

Once the decision has been made to surgically intervene in a patient with acetabular osteolysis, the goals of operative treatment should be to: (1) arrest the osteolytic process; (2) debulk the biological response via a complete synovectomy and removal of wear debris; (3) replenish bone stock; and (4) exchange the bearing surfaces. Another potential goal of surgical intervention can be to take advantage of newer bearing materials to hopefully delay this process.

The 2 major strategies to deal with osteolysis of the periacetabular bone are: (1) “hold ‘em”: to retain a well-fixed shell; or (2) “fold ‘em”: to remove the well-fixed shell and perform a complete acetabular revision.

The advantages to retaining a well-fixed acetabular component are numerous. First, there is a shorter operative time and less blood loss. Furthermore, there is no bone disruption, and as such, patients will generally recover more quickly because of the ability to immediately bear weight. Finally, the economics of retaining the shell are advantageous because of a lower implant cost, shorter operative time and hospitalization, and a quicker recovery. However, one major disadvantage of isolated liner exchange is that there may be incomplete access to retroacetabular lesions—it can be difficult to debride the areas of osteolysis while the component is present. Furthermore, several studies have documented a high rate of dislocation with isolated liner exchange. To compound this problem, the component cannot be repositioned if the acetabular implant is retained. Finally, due to constraints of the existing implant, one may not be able to take advantage of newer bearing materials, or larger head sizes.

The advantage of removing a well-fixed acetabular component is to give complete access to the osteolytic lesions, allowing for debridement of the wear granuloma and placement of bone graft. Furthermore, one can reposition the component into a more optimal position to aid in the stability of the hip joint, as well as to upsize the femoral head. Unfortunately this strategy does introduce another variable, namely the healing of host bone to the new implant; as such, the patients must protect weight bearing, leading to a slower recovery. Furthermore, a full revision is more costly due to the additional expense of the acetabular shell.

Factors to Consider: Acetabular Component Condition, Fixation & Position

A careful visual inspection of the acetabular component must be conducted at the time of revision surgery. If the socket is malpositioned, this is a definite indication for complete revision; an isolated liner exchange is likely to lead to instability or a rapid recurrence of the process that led to the revision in the first place. Furthermore, if the implant is damaged, particularly at the locking mechanism of the liner, one should consider complete revision. If the locking mechanism for the polyethylene liner is not competent, the liner may disengage or lead to backside wear.

Fixation of the acetabular component may be difficult to assess, particularly when facing large areas of retroacetabular osteolysis (Figure 1). Keep in mind that in post-mortem retrieval studies of well-functioning components, the amount of bone ingrowth only averaged about 30%,1 so it is possible that such a socket is well-fixed. In any case, the component should be tested to the surgeon’s satisfaction to ensure stable fixation; if there is any question of stability, then clearly, it must be revised.

Figure 1: This component was well-fixed
Figure 1: This component was well-fixed, despite the large areas of retroacetabular osteolysis.

Access to Lesions

The ability to successfully remove the granulomatous membrane and bone graft the osteolytic lesions should also influence the decision for liner exchange vs full revision. If the socket has multiple screw holes that would allow access to these retro-acetabular lesions, then shell-retention is a reasonable choice. If the existing component is solid, however, then a trap-door may need to be made in the iliac bone to provide access. A complete revision will give unfettered access to these lesions. Once exposed, bone grafting may be performed. I prefer to use particulate fresh-frozen corticocancellous chips for their ability to be directed through screw holes if necessary. Occasionally I may use injectable calcium phosphates to fill hard-to-reach areas. Engh et al2 have demonstrated that these injectables can reach approximately 50% of lesions.

Component Size & Availability of Liners

One must always know what type and manufacture of component is in vivo when attempting to retain the shell. Most manufacturers stock and manufacture polyethylene inserts for their acetabular implants. At times, the manufacturer may have improved the materials used in their liners with highly cross-linked polyethylene. However, if the component has been discontinued, the polyethylene liner may not be readily available. Furthermore, a long shelf-life of >5 years is not acceptable because of the possibility of oxidative degradation. If new liners are not available for the existing acetabular component, then other strategies must be entertained.

If the component is large enough, a new polyethylene liner may be cemented into the existing shell using the technique described by Haft et al.3 The existing shell needs to be large enough to accommodate both the new liner and a reasonable cement mantle. Furthermore, the inner surface must be amenable to cemented fixation by having screw holes or a roughened surface.

Component size will also influence the ability to increase femoral head size. If small, then a complete revision would allow a greater flexibility to enlarge the bearing diameter.

Component Track Record/Locking Mechanism

The track record of the existing component should also be known, if possible. A component such as the porous coated anatomic (PCA; Stryker Howmedica Osteonics, Mahwah, New Jersey) has shown a high failure rate in the intermediate term due to loss of fixation.4,5 An isolated liner exchange in this situation, with a higher-than-expected failure rate of the existing component, is likely to result in another operation in short order. Therefore, it would be advantageous to perform a complete acetabular revision if the existing component does not have a good long-term history.

The history of the locking mechanism may also influence the decision to revise or retain the socket. At the very least, it can change the way the new liner is inserted. For example, the Harris-Galante 2 component (Zimmer, Inc, Warsaw, Indiana) has been shown to have a high rate of locking mechanism breakage and liner dislodgement.6 Therefore, when performing a revision of a Harris Galante 2 cup, I always cement in a new liner or revise the shell, rather than relying on the original locking mechanism.

Available Bone

It is important to preoperatively imagine the periacetabular bone available if the socket is to be removed. If, once the socket is explanted, the bone would not support a standard hemispherical socket, a well-fixed shell should be retained. It would be senseless to disrupt a well-fixed component only to have large defects that would not support a standard, hemispherical revision socket. Some preoperative clues that this may occur are extensive osteolysis of the ischium, which often indicates involvement of the posterior column, and penetration of the medial wall. In such cases, if the well-fixed socket is removed, a reconstruction cage may be needed.

In Vivo Performance

It is important to consider how the implant performed in this particular patient. If there is extensive osteolysis after only a short implantation time, then one must suspect a problem with component position or materials. For example, if a revision for osteolysis is necessary after only 5 years, we are less apt to perform an isolated liner exchange because without a complete revision, another surgery is highly likely in another 5 years. Careful preoperative planning must be performed to assess what factors may have played a role in the rapid development of osteolysis in order to avoid its recurrence.

Results

Lie et al7 compared the results of isolated liner exchange with those of complete acetabular revision, using the Norwegian Hip Register. Interestingly, the group that had isolated liner exchange had a 1.8× higher risk for a re-revision when compared to the group that had a complete revision. Most of these re-revisions were performed to address instability (28%) and subsequent loosening (11%) at a mean of 7.3 years after the liner exchange. Therefore, a complete acetabular revision may decrease the risk of re-revision in the intermediate term.

Boucher et al8 also demonstrated a high rate of instability following isolated liner exchange. Out of 24 patients, 25% experienced dislocation after an average follow-up of 4.5 years. One can imagine that the high rate of dislocation may be related to the complete synovectomy and excision of soft tissues that is performed. Furthermore, as many patients are asymptomatic preoperatively, they may recover quickly, with little postoperative pain after isolated liner exchange, and forget about their dislocation precautions.

Discussion

It is obviously a balance of factors when considering these two options to address osteolysis in the setting of a well-fixed socket. Does one perform a less-invasive procedure (liner exchange) with a quicker recovery, possibly subjecting the patient to future surgery for instability or loosening? Or does one perform a more invasive, definitive procedure with a complete acetabular revision? This can be a difficult decision, particularly in light of the fact that most patients are asymptomatic.

Other factors that may play a role are the medical condition of the patient, age, and rehabilitation potential. The more comorbidities that a patient has, the more reasonable an isolated liner exchange would be. The younger a patient is, the more important it is to reconstitute bone stock and improve the bearing surfaces and the more likely I would perform a complete revision.

A variety of factors influence the decision to “hold ‘em” or “fold ‘em”; the decision must be individualized for each patient. A few case examples are provided to demonstrate this thought process.

Patient 1

A 35-year-old woman underwent left total hip replacement (THR) 12 years prior for posttraumatic arthritis. Note the retroacetabular osteolysis (Figure 2). The socket was in an acceptable position. However, on close inspection, the head was sitting eccentrically within the socket, and intraoperative assessment indicated complete wear through of the liner, damaging the metal shell. Furthermore, there were no transacetabular screw holes through which to perform bone-grafting, so access to the lesions was deemed poor. Finally, component position was small due to the thick walls (Figure 3), so cementing a new liner was not an option. Thus, a complete revision was performed, allowing for a larger head size and newer bearing materials (Figure 4).

Figure 2: Eccentric polyethylene wear after 12 years Figure 3: Complete polyethylene wear-through
Figure 2: Eccentric polyethylene wear after 12 years of implantation, with evidence of retroacetabular osteolysis. Figure 3: Complete polyethylene wear-through, leading to acetabular shell damage. Note also the thick walls and small inner diameter of the component.

Figure 4: Complete acetabular revision Figure 5: Extensive osteolysis after 15 years of implantation
Figure 4: Complete acetabular revision allowed for complete access to lytic lesions as well as component reorientation, larger head size, and use of newer bearing materials. Figure 5: Extensive osteolysis after 15 years of implantation.

Patient 2

A 75-year-old man underwent right THR 15 years prior. There was extensive retro-acetabular osteolysis involving the entire socket, extending to the medial wall (Figure 5). The cup position was felt to be adequate; the cup was tested to be stable, despite the lysis (Figure 1). The available bone, if the cup was to be removed, was judged to be poor because of the extension to the medial wall. Furthermore, a new socket would likely lead to medialization of the center of rotation which could not be adequately compensated for by the existing stem (note the valgus neck). Access to the lesions was good via the lytic lesions posterosuperiorly; there was available polyethylene and an intact locking mechanism. These factors all contributed to the decision to retain this well-fixed shell (Figure 6).

Figure 6: Retention of the well-fixed shell Figure 7: Extensive retroacetabular lysis after 12 years
Figure 6: Radiograph showing retention of the well-fixed shell, bone-grafting, and liner exchange. Figure 7: Extensive retroacetabular lysis after 12 years of implantation of a THR for posttraumatic hip arthritis.

Patient 3

A 36-year-old man underwent right THR 11 years prior for posttraumatic arthritis. Preoperative radiographs demonstrated a large retroacetabular lesion and retained periacetabular plates (Figure 7). Although his cup position was judged to be acceptable, it was noted to be a PCA socket, which has been shown to have a relatively high failure rate in the mid- to long-term.4,5 Access to the lesions was not sufficient without the presence of multiple screw holes. Finally, because of the patient’s young age and desire to update the bearing surface to highly cross-linked polyethylene, a full revision was performed (Figure 8).

Figure 8: Complete revision was performed
Figure 8: Complete revision was performed to provide access for bone grafting and use newer bearing materials.

References

  1. Engh CA, Zettl-Schaffer KF, Kukita Y, Sweet D, Jasty M, Bragdon C. Histological and radiographic assessment of well functioning porous-coated acetabular components. A human postmortem retrieval study. J Bone Joint Surg Am. 1993; 75(6):814-824.
  2. Engh CA Jr, Egawa H, Beykirch SE, Hopper RH Jr, Engh CA. The quality of osteolysis grafting with cementless acetabular component retention. Clin Orthop Relat Res. 2007; (465):150-154.
  3. Haft GF, Heiner AD, Dorr LD, Brown TD, Callaghan JJ. A biomechanical analysis of polyethylene liner cementation into a fixed metal acetabular shell. J Bone Joint Surg Am. 2003; 85(6):1100-1110.
  4. Little BS, Wixson RL, Stulberg SD. Total hip arthroplasty with the porous-coated anatomic hip prosthesis: results at 11 to 18 years. J Arthroplasty. 2006; 21(3):338-343.
  5. Ferrell MS, Browne JA, Attarian DE, Cook C, Bolognesi MP. Cementless porous-coated anatomic total hip arthroplasty at Duke: 18- to 24-year follow-up. J Surg Orthop Adv. 2009; 18(3):150-154.
  6. Gonzalez della Valle A, Ruzo PS, Li S, Pellicci P, Sculco TP, Salvati EA. Dislodgment of polyethylene liners in first and second-generation Harris-Galante acetabular components. A report of eighteen cases. J Bone Joint Surg Am. 2001; 83(4):553-559.
  7. Lie SA, Hallan G, Furnes O, Havelin LI, Engesaeter LB. Isolated acetabular liner exchange compared with complete acetabular component revision in revision of primary uncemented acetabular components: a study of 1649 revisions from the Norwegian Arthroplasty Register. J Bone Joint Surg Br. 2007; 89(5):591-594.
  8. Boucher HR, Lynch C, Young AM, Engh CA Jr, Engh C Sr. Dislocation after polyethylene liner exchange in total hip arthroplasty. J Arthroplasty. 2003; 18(5):654-657.

Author

Dr Su is from the Department of Adult Reconstruction and Joint Replacement, Hospital for Special Surgery, New York, New York.

Dr Su has no relevant financial relationships to disclose.

Presented at Current Concepts in Joint Replacement 2009 Winter Meeting; December 9-12, 2009; Orlando, Florida.

Correspondence should be addressed to: Edwin P. Su, MD, Hospital for Special Surgery, 535 E 70th St, New York, NY 10021 (sue@hss.edu).

doi: 10.3928/01477447-20100722-47

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