Porous-coated Acetabular Component Research Articles

Tissue Growth Into Porous-Coated Acetabular Components in 42 Patients Effects of Adjunct Fixation

Histologic examination was performed on 42 uncemented, porous-coated acetabular components removed for reasons not related to fixation. Included were 20 devices that had fixed pegs or spikes to aid in initial fixation and 22 devices that used screws through the component. The diagnoses and patient ages at insertion, times in situ, and reasons for removal were comparable for the two groups. Bone ingrowth was observed in 28 of the 42 acetabular components (67%). Of the 20 components with pegs or spikes, nine had no bone ingrowth, six had minimal bone ingrowth, four had moderate ingrowth, and one had extensive bone ingrowth. Of the 22 components with screws, five had no bone ingrowth, six had minimal bone ingrowth, six had moderate bone ingrowth, and five had extensive bone ingrowth. Two of the devices with screws also had external threads on the metallic shell; neither had any bone ingrowth, and the two accounted for two of the five devices having no bone ingrowth in this group. Bone ingrowth occurred more frequently, in greater amounts and was more evenly distributed anatomically in cups using screws for initial adjunct fixation. Roentgenographic and clinical findings were unreliable in predicting ingrowth of bone.

The Harris-Galante porous-coated acetabular component with screw fixation. Radiographic analysis of eighty-three primary hip replacements at a minimum of five years.

The results of eighty-three consecutive primary total hip arthroplasties in which a Harris-Galante porous-coated acetabular component had been used were reviewed after a minimum of five years. In all patients, the stated diameter of the acetabular component (the diameter printed on the packaging for the implant) used was equal to the stated diameter of the reamer (the diameter printed on the reamer) that had been used last in the preparation of the acetabulum. As there was little or no press-fit stability, stability was obtained initially with multiple transfixing screws. No component was revised because of loosening, and none were radiographically loose at an average of sixty-eight months and a maximum of seven years after the operation. There was no evidence of disruption of the titanium porous mesh, and no screw had bent or broken. Two sockets, however, had been revised because of failure of the liner-locking mechanism as well as disassociation of the polyethylene liner from the titanium-alloy shell. Lysis of bone occurred in only one patient, around one screw. Areas of non-contact (gaps) between the porous mesh at the periphery of the acetabular component and the bone were seen on the immediate postoperative radiographs of nearly half of the patients. New areas of radiolucency, which had not been seen immediately postoperatively, were identified at two years in forty-nine hips. These radiolucent lines were never wider than one millimeter and were most frequently located in zone 3 and, less frequently, in zone 1. At the time of the most recent follow-up evaluation, a progressive radiolucent line was identified around twenty-two components and a discontinuous radiolucent line was present in all three zones around eleven components. No continuous radiolucent line was identified at the mesh-bone interface of any component. These results are superior to our results with cemented acetabular components after a similar period of follow-up. A longer period of follow-up is needed before the importance of these thin radiolucent lines can be determined, but experience with cemented acetabular components indicates that progressive or extensive radiolucent lines, or both, may represent resorption of bone at the porous mesh-bone interface and this can lead to loosening of the component. Our data suggest that the technique used for implantation may be important not only for the initial fixation and ingrowth of bone, but also for the long-term durability of the fixation of a porous-coated acetabular component.(ABSTRACT TRUNCATED AT 400 WORDS)

The fate of massive allografts in total hip acetabular revision surgery

A series of 23 major load-bearing acetabular allografts done in conjunction with revision total hip arthroplasty were prospectively evaluated. This study includes cases with a minimum 2-year follow-up period. The procedures were performed using noncemented porous-coated acetabular components with pegs. In seven acetabula there was no change in cup position when compared with the initial postoperative roentgenogram (35%). Six acetabula migrated 3–5 mm during the first 2 years, then became stable without further progression (28.6%). In six cases (30%) gross loosening and migration occurred, requiring revision to a larger cup. One case required exchange arthroplasty for infection (5%). All biopsies taken at the time of the revision for failure showed viable bone replacing allograft. If the criteria for success of major superior acetabular allografts include incorporation of the graft and long-term stability of the implant, then the success rate in this series is very low. Only 7 of 20 hips were successful over a relatively short time period. However, if expectations are lowered, and the procedure is considered successful if adequate bone stock is restored to the acetabulum to allow reconstruction with a cementless cup firmly fixed in viable bone, then all but three revisions were successful.

Bead Loosening From a Porous-Coated Acetabular Component

Beaded porous-coated implants are commonly used in total joint arthroplasty. In this study, the authors extended the follow-up period for the Davey and Harris study of bead loosening in beaded cementless acetabular components. When 56 primary total hip arthroplasties were first reviewed, at an average of 2.5 years after surgery, the incidence of bead loosening was 8.9%. Reevaluation at a mean of 4.5 years after surgery revealed that the incidence of loosening had increased to 19.6%. Bead loosening was associated with acetabular migration in one component and a broken screw in a second. In the absence of loose beads, there were no broken fixation screws or socket migration. Radiolucencies at the bone-implant interface were seen in association with loose beads in only one case. Although long-term implications of bead loosening are not clear, bead migration may increase the possibility of macrophage response to metallic debris.

Revision of the acetabular component with an uncemented Harris-Galante porous-coated prosthesis.

One hundred and forty revisions for loosening of the acetabular component were performed in 124 patients, with the use of an uncemented Harris-Galante acetabular prosthesis. A component was considered loose if there was a change in its position or vertical or horizontal migration, or both, of four millimeters or more, as demonstrated on serial radiographs. All patients were followed prospectively for a mean of forty-one months (range, twenty-four to seventy-six months). Bone-grafting was performed at the time of the revision in 127 of the hips. Identifiable failure of fixation of the acetabular component occurred in only two hips (1 per cent), which had both severe acetabular bone loss and pelvic discontinuity. In one of these hips, fixation of the component could not be achieved during the revision, and the component subsequently migrated. No other components migrated. Only one patient had a revision of the index acetabular operation. A continuous radiolucency developed at the bone-mesh interface of five acetabular components, and in one other hip a small portion of the mesh separated. This hip was reoperated on for a problem with the femur, and the socket was found to be rigidly fixed. No other evidence of loosening was identified. All of the bone grafts united, but partial resorption of the graft occurred in thirty-nine hips. Although there were substantial osseous defects that necessitated major bone-grafting, revision with the uncemented Harris-Galante porous-coated acetabular component provided superior fixation compared with that reported in other series in which cemented acetabular components were used for revision. Of the 140 hips, eighty-nine (64 per cent) had a postoperative score of good or excellent, according to the Harris hip-rating system. Twenty-eight (70 per cent) of the forty hips that had revision of the acetabular component alone were rated as good or excellent.

Current Status of Acetabular Fixation in Primary Total Hip Arthroplasty

Factors that influence the outcome of acetabular replacement are design materials, means of fixation, operative technique, and patient-related parameters (e.g., etiology of osteoarthrosis). Whereas improved cementing techniques have produced a marked reduction in the rate of femoral component loosening, the incidence of acetabular loosening has been only slightly influenced by such improvements. Presently, uncemented porous-coated acetabular components represent the state of the art in total hip arthroplasty. Experimental and clinical data have shown in histologic, radiologic, clinical, and survivorship studies that hemispheric cups are superior to other designs and that primary stability can be better maintained by creating "intrinsic" stability (e.g., "oversized cup") rather than by screw fixation. Threaded cups have failed to demonstrate any improvement in results and have been virtually abandoned in the United States. The idea of metal backing has some obvious theoretical advantages. However, metal backing has failed to provide any improvement with respect to cemented cups. There are great reservations concerning metal backing in cementless fixation. Although there is some enthusiasm about hydroxyapatite, a "wait-and-see" attitude is justified because of the brittleness of the material, its questionable strength of bonding to substrate, and its unproven long-term behavior in vivo. Polyethylene as a bearing surface remains problematic, and the future will show whether new technologies are able to solve the problems encountered with metal-to-metal combinations. For the size of the femoral head, a compromise between smaller (22 mm) and larger (32 mm) components seems to be most effective.

Mechanical stability of porous-coated acetabular components in total hip arthroplasty

Five different porous-coated acetabular prosthetic configurations underwent in vitro testing to assess mechanical stability in embalmed cadaver hemipelves: Harris Galante II cup with three cancellous screws, Biomet Universal cup, Whiteside cup with peripheral pegs, Whiteside cup with two cancellous screws, and plain Whiteside cup. Following implantation in a neutral frame, cyclic load testing was done using 33 specimens at 100-kg load for 100,000 cycles using an MTS machine (MTS Systems Corp., Minneapolis, MN). Subsequently, static load-to-failure testing was done in all specimens. Subsidence and micromovement were determined for each specimen using linear variable differential transformers. With cyclic testing, overall cup subsidence revealed a significant increase, from 500 to 100,000 cycles. Overall cup micromovement revealed a significant decrease, and all cup groups demonstrated less than 125 μm (125 mm) of average mean micromotion at the completion of cyclic testing. The best cup configuration was a 1-mm, oversized, press-fit cup using two 6.5 cancellous screws for additional fixation, which revealed an average mean of 60 μm (.06 mm) of micromovement. Static load testing revealed unacceptable micromovement over 150 μm (.150 mm) in most cups with 300-kg loads

Porous-coated Acetabular Component Quantitative Assessment of Normal Radiophosphate Uptake as a Function of Implant Age

A computer-assisted quantitative analysis was undertaken of normal radiophosphate bone uptake adjacent to the porous-coated acetabular component in asymptomatic patients. Implants ranged from 1.6 to 49 months of age. In 62 hips, it was found that implants newer than 12 months of age had uptakes that were significantly greater than those 12 months or older. Between 12 and 49 months, there was no correlation with age, indicating a stabilization of the remodeling process.

Ehhancement of fixation of porous-coated implants in the presence of interface gaps when treated with autograft, freeze dried allograft and fibrin glue

This study examined the long-term outcome of a single institution’s experience with 4,289 primary total hip arthroplasties using hemispheric porous-coated cups. Initial fixation was achieved with spikes (255 AML TriSpike cups), by press-fitting with rim screws (427 Arthropor cups) or by press-fitting the component (83 Harris-Galante, 391 ACS Triloc+, 2,537 Duraloc, and 596 Pinnacle cups). Among 203 revised hips, only 18 cups were found to be loose at the time of revision. Using revision for any reason as an end point, 15-year survivorship was 82.9% ± 5.6% (95% confidence interval) for spiked components, 71.6% ± 8.5% for press-fit cups with adjunctive rim screws, and 72.0% ± 12.6% for press-fit components (P<.001, log rank). Using revision for aseptic loosening as an end point, 15-year survivorship was 94.7% ± 3.4% for spiked cups, 98.4% ± 1.9% for press-fit cups with screws and 100% ± 0.1% for press-fit cups. Despite an increasing incidence of polyethylene wear-related revisions, porous-coated acetabular components have demonstrated excellent long-term fixation.

Cementless total hip arthroplasty with femoral head bone grafting for hip dysplasia

Femoral head bone grafting was required to augment acetabular bone stock in 19 cases of hip dysplasia treated with cementless total hip arthroplasty. All acetabular grafts provided mechanical support for the cementless acetabular component. Radiographic evaluation of the fixation of the femoral components at an average of 3 years after surgery revealed an optimum appearance in all cases. All porous-coated acetabular components remained stable, but only one of six (17%) nonporous threaded acetabular components maintained stability. One threaded acetabular component has been revised for symptomatic loosening. Acetabular graft healing was suspected in 18 of 19 cases (95%). Significant graft resorption was observed only in the cases with unstable threaded acetabular components. The clinical scores were high. Cementless total hip arthroplasty with structural acetabular grafting and porous acetabular components appears to produce satisfactory short-term results.

Measuring the volume fraction of bone ingrowth: A comparison of three techniques

The need for quick, accurate, and reproducible methods to measure the amount of bone within porous metals has increased as the use of these materials has become more common within orthopedics. The purpose of this paper is to compare measurements of bone ingrowth using microradiography, stained histology, and backscattered electron imaging-scanning electron microscopy (BEI-SEM) in cementless, porous-coated acetabular components retrieved from human patients. BEI-SEM of bone ingrowth into porous metal provided excellent images for quantitative analysis. The stained sections and BEI-SEM images provided very comparable results, while microradiography consistently underestimated the porosity of the porous coating and overestimated the amount of bone ingrowth.

In vitro initial fixation of porous-coated acetabular total hip components: A biomechanical comparative study

Two-phase in vitro testing was performed to determine the initial mechanical stability of uncemented but fixed porous coated acetabular components. Six each of three-screw fixation, two-peg fixation, and three-spike fixation porous acetabular components were implanted into fresh and embalmed human cadaver acetabula. Measurement of prosthesis-bone displacement at a load of 100 kg did not show a significant difference among the three methods of fixation. However, torque testing showed that three-screw fixation failed at significantly higher loads (46 N-m) than two-peg fixation (32 N-m) or three-spike fixation (32 N-m).

A Preliminary Report of the Use of a Cementless Acetabular Component With a Cemented Femoral Component

A clinical and roentgenographic study was done on 52 primary total hip arthroplasties (THAs) in which all patients were treated with hip reconstruction with a combination of a cementless, porous-coated acetabular component and a cemented femoral component. The operations were performed between November 1982 and May 1984, and the patients were followed for an average of 31 months (range, 24-40 months). The average age of the patients (55 years) was younger than in many THA series. At the last follow-up assessment, 50 hips were classified as good or excellent, one as fair, and one as a poor result. No total hip component required revision. No acetabular components had migrated as judged by conventional roentgenographic examination, and only one hip had progressive radiolucencies around the acetabular component. No femoral component was rated definitely loose or probably loose, and only one was rated possibly loose. If long-term follow-up study confirms these preliminary results, the combination of a cemented femoral component with a cementless socket may prove to be of value for selected patients requiring THA.

Loosening of Cobalt Chrome Beads from a Porous-Coated Acetabular Component

Seventy consecutive total hip arthroplasties were performed using a porous-coated acetabular component consisting of a cobalt chrome substrate to which cobalt chrome beads were sintered. Fifty-six were primary arthroplasties and 14 were revisions. The authors analyzed the immediate postoperative roentgenographs of all 70 hips and the follow-up roentgenographs of the 66 hips that were followed for a minimum of two years, the average follow-up period being 30 months. Loose cobalt chrome beads were diagnosed in ten of the 70 hips (14.3%), five (8.9%) in the primary arthroplasties, and five (35.7%) in the revision arthroplasties. In two of the primary arthroplasties and three of the revision arthroplasties, the loose beads were observed on the immediate postoperative roentgenographs. None of the acetabular components appeared loose by other roentgenographic criteria. The sintering technique used in the manufacture of these implants did not prevent loosening of cobalt chrome beads from porous-coated cobalt chrome acetabular components. A longer follow-up period is required to assess fully the clinical significance.