This review article on cementless acetabular components will address two issues: the problem that generated interest in the concept of a cementless acetabular component, namely, the loss of fixation of cemented acetabular components; and the long-term results of the more successful cementless designs relative to three subsets of patients requiring total hip arthroplasty (THA), namely, primary THA in older patients, primary THA in young patients, and acetabular revisions.
The overriding problem that led to the need for cementless acetabular reconstructions was failure of fixation. In older patients, during the first decade after THA, radiolucencies at the cement-bone interface did not interfere with the success of the operations. At 8 years, Charnley 13 reported that the total percent of loose sockets in his entire study was 0.58% and in the 547 patients with current radiographs, it was 0.36%. However, when reassessed between 12 and 15 years after insertion, the incidence of Grade III (continuous radiolucent lines at the interface) demarcation was 14%, and 11% had migrated. 14 Therefore, radiolucent zones around the acetabular component had taken on a more sinister implication. In addition, balloon-type osteolysis was being recognized in the pelvis. Additional experience also showed that cemented acetabular components had distinctly less satisfactory records in the younger patients and even less satisfactory records in patients having revision surgery.
Schmalzried et al showed that the histologic features of the radiolucent zones parallels the macrophage response to particulate debris that underlies femoral endosteal erosion and balloon type osteolysis. 29 Because of this, loss of fixation of cemented acetabular components proved to be primarily an issue of periprosthetic osteolysis. In revision cases, this etiology also was compounded by the increased difficulty of obtaining sound fixation using cement because of the bone loss.
Followup studies of Charnley prostheses in the older age group beyond 12 to 15 years showed an additional increase in radiographic loosening and acetabular revisions for aseptic loosening. A series of Charnley THAs was reported with a minimum 20-year followup. 31 Twenty-two percent of the sockets were loose, with 8% being revised for aseptic loosening. When rereviewed at 25 years, 15% of the acetabular components had been revised for aseptic loosening. 11
Fixation of cemented acetabular components in the younger patients has a worse record. At 12 years, Barrack et al 3 reported that 44% of the cemented acetabular components in patients who were 50 years and younger became loose. In Sullivan et al’s 32 series of Charnley THA in patients younger than 50 years followed up for an average of 18 years, 13% of the sockets in the patients who were alive were revised for aseptic loosening and 50% of the sockets were either loose by radiographic criterion or revised for aseptic loosening. When the followup was extended to an average of 23 years, 12 23% of the sockets had required revision for aseptic loosening.
Among the many reports on cemented acetabular revisions, the study of Raut et al 27 warrants specific attention because this report reflects the outcomes from an experienced total hip surgeon skilled in the use of cement. Among 387 cemented acetabular revisions done for aseptic loosening, by 5.5 years, 20.8% were loose. In the subsets of patients in whom the bone stock had been compromised more extensively, radiographic failure of fixation was 51%. In patients who had multiple acetabular revisions treated with a cemented socket, the results were even less satisfactory. 35
Among younger patients (55 years or younger) with osteoarthritis in whom the cemented Charnley socket was used for revision because of aseptic loosening, after 6 years, 32% of the sockets were loose. 28 Among hips with the worst bone stock, 51% had loosening. Thirty-eight percent of patients with rheumatoid arthritis with a Charnley implant for revision of a loose aseptic socket had loosening by 7 years 4 months. 26 Clearly, these rates of failure of fixation were unacceptable.
From the vantage point of approximately 20 years of experience, the most appropriate design for a cementless acetabular component seems to be a hemispheric design (or nearly hemispheric) with a continuous or nearly continuous exterior surface of suitable porous materials, either press-fit or fixed with screws. 22,34
In patients younger than 50 years (average age, 37 years) treated with a primary THR using the HG cementless socket, Berger et al 5 reported that among the 72 sockets in patients who were followed up for 7 to 11 years, none were revised for aseptic loosening and none were loose radiographically. Two liners were exchanged for wear and one pelvic lytic area was grafted with retention of the shell. These data are remarkable in terms of fixation, compared with the failure of fixation noted above for cemented sockets in the younger age group. Cementless hemispheric sockets seem preferable for young patients having primary THA. The experience of the hemispheric cementless sockets in the primary THA in the older age group also registers a positive difference compared with cemented sockets. Clohisy and Harris 15 reported that in a matched pair series all done by the same surgeon 33% of the cemented acetabular components were loose radiographically or by revision surgery, but none of the cementless were loose at 9 to 12 years.
Revision surgery with cementless sockets has been the most outstanding use of cementless components as compared with cemented sockets for revision. One hundred twenty-two of 188 consecutive hips with acetabular revisions in which the HG cementless component was the only technique used were available for followup at an average of 12.5 years postoperative. 20 The average age of the patients was 54 years. Fifty-eight had high hip centers (arbitrarily defined as at least 35 mm above the teardrop line), and 13 had jumbo cups (arbitrarily defined as 65 mm in diameter or greater). Femoral head penetration (also called linear wear) into the polyethylene averaged 0.11 mm per year. Five acetabular components were rerevised for aseptic loosening (4%) and the incidence of periprosthetic osteolysis was 9.6%.
In a second study of 109 hips receiving the HG socket in revision for aseptic loosening the Kaplan-Meier survival at 11.5 years was 98% with no hip having rerevision of the shell for aseptic loosening. 23
In a third study, there were 32 of 61 hips in patients who were living at 12.9 years with an HG socket used for acetabular revision for aseptic loosening. 33 None of these shells were revised for aseptic loosening, two were loose radiographically, and eight required liner exchanges. Pelvic osteolysis was present in 13%.
The aggregate from these three studies of acetabular revisions with followup between 7 and 15 years was 263 hips. Only five hips had rerevision for aseptic loosening (2%) and 9% had periprosthetic pelvic osteolysis.
These numbers show much improved results compared with the 20.8% loose cemented cups in revision at only 5.5 years postoperative noted previously. Remarkably, using the cementless hemispheric acetabular component for revision, neither age, gender, initial diagnosis, or body mass index were associated with failure.
Difficult Acetabular Reconstructions
One severe test of acetabular reconstruction is cases done for difficult congenital dysplastic hips. Anderson and Harris 1 reported on 20 hips in patients who had an average age of 52 years with severe dysplasia or total developmental dislocation of the hip who received the HG acetabular component. In only three hips were bulk grafts added to support the socket. At 7 years, none of the 20 hips had loosening, migration, rerevision, or pelvis osteolysis. Moreover, in some CDH hips in which the deficient acetabular bone stock had required a femoral head allograft, revascularization of the graft often permits a subsequent revision with a porous-coated acetabular hemispheric socket. 2
Bellabarba et al 4 used a cementless acetabular component in 30 hips in patients who averaged 51 years with arthritis after acetabular fractures. Ninety percent of patients had good or excellent results 6 years postoperative and the Kaplan-Meier curve for 10-year survival, with revision or radiographic loosening as the end point was 97%.
The two innovative conceptual aspects that the hemispheric cementless acetabular component supported, namely the cementless high hip center and the jumbo socket also have proven to be useful. If the only intact, viable host bone remaining is proximal, the cementless component must be placed at a high hip center to be in contact with viable host bone. Dearborn and Harris 16 reported on the 10-year followup of a series of 36 hips in patients alive with the implant in place in whom the hip center was placed at least 35-mm above the interteardrop line. In that group one hip was loose. Of the entire initial group of 44 such hips, two became loose. Jumbo cementless sockets have been helpful in certain patients with major concentric bone loss. 17
This review was a summary documentation of the data, defining examples of the failure rates of cemented acetabular reconstructions in three subsets of patients, those in the younger group with primary THA, those in the older age group with primary THA, and those with acetabular revision THA.
This was followed by the results, generally at 10 years or more, of the use of hemispheric porous-coated cementless acetabular components. The aggregated results showed clear advantages of cementless hemispheric acetabular components over the use of cemented acetabular components in all three categories.
There are a few important limitations to the use of hemispheric cementless sockets. Success has not been achieved in treating ON of the pelvis. Some hips with massive bone loss will not permit the use of a hemispheric socket. Sometimes bilobed cementless sockets are useful. 8 The impaction grafting technique of Schreurs et al 30 with a cemented cup can solve some of these problems. Pelvic dissociation sometimes can be treated using reconstruction plates to restore the continuity of the acetabular bone and then an acetabular hemispheric shell fixed with screws can be implanted. 6 In other hips with severe bone loss an acetabular cage must be used. 7 Another limitation to the early designs of hemispheric cementless acetabular components was difficulty with the locking mechanisms for the polyethylene lines. All manufacturers have substantially eliminated that problem in the current designs.
Osteolysis and Dislocation
Despite the improvement with fixation with hemispheric cementless sockets, there are two serious problems, which are periprosthetic osteolysis and dislocation. With cementless hemispheric sockets the problem of wear and lysis can be manifested somewhat differently than with cemented cups. Osteolysis may be a linear process leading to loosening, but more commonly is a balloon lysis, which at times requires grafting or revision of the shell. Therefore, even though the pattern of osteolysis differs somewhat from cemented sockets, a need still exists to reduce particle generation. The alternative articulation surfaces available for the reduction of the particulate burden are metal-on-metal articulations, 18 ceramic-on-ceramic articulations, 21 and the use of highly cross-linked polyethylene. 24,25 These articulation couples give hope for a substantial reduction of periprosthetic osteolysis in the future.
The prevalence of dislocation can be reduced by using larger femoral heads. 10 All three alternate bearing surfaces permit the use of larger femoral heads. Component-to-component impingement can be eliminated with head sizes greater than 32 mm. 10 The use of a constrained acetabular component can solve many cases of recurrent dislocation. 9,19
Hemispheric cementless acetabular components represent one of the most important advances in THA since 1962. A review of cementless acetabular components 20 years after their introduction has shown that fixation failure with hemispheric cementless acetabular components has been substantially improved for primary THR in patients younger than 50 years, in revisions, and even in primary THR in older patients. The two major problems of periprosthetic osteolysis and dislocations now are being addressed using alternate bearing surfaces, innovative designs, and larger head sizes.
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