Management of Wear and Osteolysis





CASE STUDY


A 49-year-old man presented with left groin pain that began insidiously and had been getting progressively worse over the past few months. He had previously been pain free. Eleven years earlier, he had primary total hip arthroplasty to treat the effects of osteoarthritis caused by acetabular dysplasia.


Physical examination confirmed a mild Trendelenburg lurch, a mildly antalgic gait related to his right lower extremity, and groin pain with a straight leg raise. Radiographs ( Fig. 69.1 ) revealed well-fixed, cementless implants; eccentricity of the femoral head; and pelvic osteolysis. The erythrocyte sedimentation rate and C-reactive protein values were normal. He was classified as having a type I acetabular defect. Treatment consisted of socket and stem retention, head and liner exchange, and débridement and grafting of the osteolytic lesions.




FIGURE 69.1


Preoperative ( A and B ) and 2-year postoperative ( C and D ) radiographs show a type III acetabular defect treated with socket revision, débridement of the osteolytic granuloma, and grafting.




Algorithms







This diagram shows the treatment algorithm for management of osteolysis around osseointegrated femoral components.





This diagram shows the treatment algorithm for management of osteolysis around osseointegrated acetabular components.




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Chapter Synopsis


Periprosthetic osteolysis remains a common cause of late failure after total hip arthroplasty (THA). This failure mechanism is particularly important for younger, active patients, who will undoubtedly challenge the durability of modern bearing surfaces in the future. Good midterm results with retention of the implants have been achieved in certain cases. Cases that do not meet the strict criteria for implant retention outlined in this chapter should be treated with full revision of the implants.


Important Points





  • Treatment is indicated for patients with osseointegrated, cementless sockets when osteolytic lesions of the pelvis progress over a 3- to 6-month period.



  • Severe polyethylene wear may justify a lower threshold for treatment, because it is better to intervene before the head wears through the liner and engages the shell.



Clinical/Surgical Pearls





  • Factors that determine whether the well-fixed shell can be retained include the ability to exchange the liner, extent of osseointegration, position of the socket, and the type of fixation surface (i.e., three-dimensional ingrowth versus two-dimensional ongrowth pattern).



  • In cases of femoral osteolysis, operative treatment is indicated for progressive lesions, diaphyseal osteolysis, impending fracture, and pain.



  • Factors that determine whether the osseointegrated femoral component can be retained include location of the lesion, exchangeability of the femoral head, and extent of osseointegration.



Clinical/Surgical Pitfalls





  • Although implant retention and grafting is appropriate in certain cases, surgeons must be prepared to revise the implants if the strict criteria outlined in this chapter are not met.





Introduction


Aseptic loosening from periprosthetic osteolysis is a common cause of late failure after total hip arthroplasty (THA). Data from the 2010 Annual Report of the Swedish Hip Arthroplasty Register revealed that the percentage of all revisions performed for aseptic loosening or osteolysis declined slightly to 55%. This decline is encouraging, but the rate remains four times greater than the next leading cause of revision: dislocation (13.6%). In the United States in 2006, 24.7% of 51,345 hip revisions were performed for mechanical loosening and bearing surface wear. In this chapter, we propose a strategy for managing periprosthetic osteolysis in the setting of well-fixed implants.


Osteolysis was first described by Harris and colleagues in 1976. At the time, it was attributed to “cement disease.” Initially seen around cemented femoral components, osteolysis was later observed around cemented acetabular components that failed due to aseptic loosening. Cementless sockets were designed to mitigate the failures seen with cemented fixation. Over time, osteolysis also was seen around cementless implants. The processes around cemented and cementless implants were found to be histologically similar. Osteolysis appears to be driven by the biologic response to particulate wear debris generated at articulating surfaces and bone–cement interfaces.


The natural history of osteolysis in cemented and cementless fixation is different. In cemented fixation, osteolysis involving the bone–cement interface typically leads to aseptic loosening. Surgical management in this situation is revision of the whole implant. Timing depends on the severity of bone loss and the patient’s symptoms. In cementless fixation, osteolysis more commonly involves the periprosthetic bone, and the implants may remain osseointegrated despite massive bone loss. Revision of the entire implant and bearing exchange with débridement of the osteolytic granuloma and bone grafting are viable options in this setting.




Indications and Contraindications


Pain is often the chief complaint of patients who develop osteolysis around cemented acetabular components. The radiographic pattern of osteolysis tends to be linear and progresses to involve the entire bone–cement interface. When the whole bone–cement interface is involved, the cup becomes loose. The linear pattern precludes grafting, and there is no prophylactic surgical treatment that is practical. Pain is the indication for operative treatment of these patients. The timing of intervention should be commensurate with symptoms, because many patients with loose, cemented sockets report only mild pain that does not warrant surgical intervention immediately.


The indications for operative treatment of osteolysis around cementless acetabular components are less well defined. Patients with loose cementless sockets have pain, and the indication for revision is straightforward. Controversy exists regarding the timing of operative intervention when the socket remains well fixed and patients are pain free. The issue becomes one of operating on asymptomatic patients. A few small areas of osseointegration can keep cups well fixed, and patients can remain pain free despite expansile lesions. Most experts agree that osteolytic lesions that progress over a 3- to 6-month period warrant operative intervention. Severe polyethylene wear may justify a lower threshold for treatment, because it is better to intervene before the head wears through the liner and engages the shell. Prompt operative treatment is warranted when the head has worn through the liner, because this situation generates metallosis and an intense local inflammatory response to the metal and polyethylene debris. The importance of early intervention in these cases cannot be overstated, because massive periarticular metallosis may be impossible to débride completely without incurring significant functional loss.


Patients with femoral osteolysis usually remain asymptomatic until they have extensive synovitis and an impending fracture, except when the osteolysis is associated with femoral component loosening. As on the acetabular side, the timing for surgical intervention is controversial. Indications for operative treatment in cases of femoral osteolysis include progressive lesions, diaphyseal osteolysis, impending fracture, and pain.




Preoperative Considerations


Femoral Treatment


Several key factors must be addressed when treating osteolysis around cementless femoral components. First, stem stability must be determined. Although the surgeon should have an accurate prediction of stability based on the interpretation of preoperative radiographs, intraoperative assessment is essential for corroboration. Second, the extent of osseointegration should be assessed. The surgeon must be confident that the remaining bony apposition to the fixation surface is sufficient to provide long-term implant stability. Third, the location of the lesion is important, because well-fixed stems with metaphyseal lesions may be retained in many cases. Diaphyseal lesions indicate a connection between the joint space and the distal endosteum. These lesions are difficult to access, and stem revision may be required in the setting of lesion progression or impending fracture. Fourth, the exchangeability of the femoral head should be considered. For nonmodular implants, the head must be in good condition and of sufficient size, and the offset and length must be appropriate to ensure adequate hip stability.


A classification system has been devised to guide surgeons in the treatment of osteolytic lesions around cementless femoral components (see “Algorithms”). In type I cases, lesions are predominantly metaphyseal, and the extent of stem osseointegration is sufficient to ensure long-term stability. In this situation, we recommend stem retention, grafting of contained lesions, and exchange of the femoral head. Relative contraindications to stem retention and head exchange include a fixed femoral head that is damaged or insufficient in size or length to provide hip stability, a limited area of osseointegration, diaphyseal osteolysis, appropriate head that is unavailable, and a severely corroded taper. Taper corrosion generates biologically active particulate debris that can lead to third-body wear. It can also weaken the stem and cause implant fracture. In type II cases, the stem is osseointegrated, but there is significant diaphyseal osteolysis, an insufficient extent of osseointegration, or the femoral head is fixed and damaged. In these cases, we recommend revision of the femoral stem. In type III cases, revision is required to address the loose stem.


Acetabular Treatment


The central issue in treating acetabular osteolysis in the setting of a well-fixed shell is whether to retain the cup. Several early reports recommended removing the entire shell to allow for adequate access to the lesion. The drawback to this approach is that the reconstruction after cup removal is likely to be complex, especially for lesions with a compromised posterior column. Key factors in determining whether the shell can be retained include exchangeability of the liner, osseointegration, and the type of fixation surface (i.e., two-dimensional ongrowth versus three-dimensional ingrowth type).


A classification system has been developed to guide surgeons in the treatment of pelvic osteolysis with cementless acetabular components (see “Algorithms”). A type 1 socket is well positioned, has an ingrowth fixation surface, has a modular liner, and has acceptable survivorship. These cases can be addressed with débridement of the lesion and bone grafting at the surgeon’s discretion. Relative contraindications to liner exchange include a damaged shell or locking mechanism and unavailability of liners with adequate thickness, head size, or highly cross-linked polyethylene construction. An undamaged locking mechanism is a relative contraindication because it is safe to cement a liner into an appropriate shell. Unfortunately, there are no data regarding how much shell damage is permissible. Ongrowth fixation surfaces are a relative contraindication to liner exchange because the tensile strength between bone and the socket is weaker than the same interface with an ingrowth surface.


Hydroxyapatite-coated and macrotextured cups are examples of sockets that should not be classified as type I. Type II sockets are well fixed but do not meet the criteria for a type I socket. Some type II sockets in which the locking mechanism has been damaged can be retained if the contemporary liner can be cemented into the metal shell. The socket should be large enough to place a liner with an adequate cement mantle while increasing the head size to maximize stability. Numerous reports have described the clinical success with cementing into a metal shell. If cementation of a liner is not feasible, type II sockets should be removed, and residual bone defects should be managed accordingly. Type III sockets are loose and should be revised.




Equipment


Careful preoperative planning is essential. If retention of implants is considered, the surgeon must verify the implants to ensure that the appropriate replacements parts are available. We recommend obtaining the implant labels (i.e., stickers) for verification rather than relying on the surgeon’s operative report. If the proper parts are not available, cementing a liner into a well-fixed shell is an option that has shown reliable midterm results.




Surgical Techniques


Anatomy and Approaches


The surgical approach should allow wide exposure of the acetabulum, femur, and periprosthetic bone. This ensures adequate visualization for testing socket and stem stability and for débridement of the osteolytic granuloma and bone grafting. Prior skin incisions may dictate the approach. The surgeon should use the approach that he or she is most comfortable with. If the femoral component is to be retained, the surgeon can consider performing a gluteus maximus tenotomy if the posterior approach is used. This facilitates retraction of the proximal femur anteriorly. Special care must be taken to protect the trunnion after the femoral head has been removed. The finger of a glove works well for this.


Examination and Imaging


Plain radiographs usually underestimate the size of osteolytic lesions. In addition to the standard anteroposterior pelvis, anteroposterior hip, and cross-table lateral views, Judet views (i.e., 45-degree obturator and iliac oblique views) can provide additional information regarding the extent of involvement of the anterior and posterior columns. Helical computed tomography (spiral CT) with metal artifact suppression can provide the most accurate representation of the size and anatomy of osteolytic lesions. Magnetic resonance imaging is also useful for the evaluation of periprosthetic osteolysis.


Procedure


After the fibrous tissue has been removed from the periphery of the socket, the liner can be removed. The surgeon should have information about the manufacturer and type of locking mechanism so that the appropriate extraction tool can be used to facilitate removal of the liner without damaging the shell and locking mechanism. If a specialized extraction tool does not exist or is unavailable, other methods can be used. Osteotomes and screwing the liner out by drilling a screw through the liner can achieve the same goal with relatively little damage to the lock detail and shell.


Socket stability can be tested after the screws are removed. Many techniques have been described to test socket stability. If available, the cup inserter can provide a long lever arm. A bone tamp can be used to press on the rim of the cup. If the rim is proud, a heavy needle driver can be used to dislodge the shell from the surrounding bone.


After socket stability has been confirmed, the next step is to gain access to the osteolytic lesions for débridement and bone grafting. Several methods can accomplish this, and the technique used depends on the location of the lesions. Lesions of the anterior column and symphysis pubis often are not grafted because of difficulty with accessibility. Dome lesions can be grafted through existing screw holes. Due to the difficulty of placing instruments through screw holes, special instruments and bone graft substitutes have been designed to facilitate this process. Specially designed trumpets with a plunger allow effective and efficient placement of up to several cubic centimeters of allograft bone chips. If screw holes are not available, a trap door can be made in the ilium to access the dome. The surgeon may consider limiting weight bearing postoperatively if a trap door approach is used.


Lesions of the posterior column are readily accessible if a posterior approach is used. Although several bone-void fillers are available, there are no data regarding the efficacy of allograft bone chips or other substitutes in this application.


The technique for grafting femoral lesions is relatively intuitive. After the fibrous tissue has been removed from the proximal femoral orifice, the location and size of the lesion are assessed. The granuloma is then débrided, and contained defects are amenable to bone grafting. After the osteolytic lesions have been treated, a trial is performed to assess hip stability, offset restoration, and leg length. Different liner options can be used if the hip offset, leg length, or implant position is not optimal. Face-changing and lipped liners may increase joint stability. Lateralized liners can increase the leg length and offset to increase the tension within the articulation. Larger heads should be considered to maximize stability. If larger heads are not available for the current construct, use of newer dual-mobility technology may be an option for upsizing the femoral head.


The technique to cement a liner into the metal shell includes full exposure of the shell. The undersurface of the shell should be roughened with a bur tip to increase surface area. The surface of the liner backside should also be scored with the bur. A trial liner should be placed within the socket to ensure that the cement mantle is adequate. The liner is then cemented into place. Constant pressure is maintained to ensure optimal fixation.

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May 29, 2019 | Posted by in ORTHOPEDIC | Comments Off on Management of Wear and Osteolysis
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