Fixation of cementless acetabular cups: A radiographic 4-8-year study of 102 porous-coated components

We studied fixation changes over time in 113 porous-coated Howmedica (PCA) cementless acetabular cups inserted in 90 patients 1984-1988. The mean follow-up was 5 years. Radiographic fixation was classified as stable, fibrous-stable, or unstable. 9 cups, 3 in neutral position and 6 vertical, were revised. At follow-up, 40/75 neutral cups were stable versus 7/27 vertical cups. Most stable cups and two thirds of the unstable cups were clinically good. After the first 2 years, 28/75 neutral cups and 10/27 vertical cups changed their fixation: 12 had improved fixation and 26 had a worse one.     

Analysis of retrieved uncemented porous-coated acetabular components in patients with and without pelvic osteolysis

Retrieved polyethylene liners and femoral heads from a consecutive series of revision components of one design were examined. All patients had Long-Term Stable Fixation (OsteoTechnology International, Timonium, Md) total hip arthroplasties (THAs) implanted between 1987 and 1992. The retrieved femoral heads and liners from patients with osteolysis were compared to those without osteolysis. Patients with osteolysis had significantly thinner polyethylene (5.1 mm versus 7.4 mm, P<.01 ) and a higher linear wear rate (0.5 mm/y versus 0.3 mm/y, P=.05). The average femoral head surface roughness also was significantly greater in patients with osteolysis (67 nm versus 35 nm, P<.05). Patients with osteolysis had more total volumetric wear, total linear wear, and volumetric wear rate compared to patients without osteolysis. Age, obesity index, time in situ, and cup inclination were not different between the two groups. Excessive polyethylene wear, probably accelerated by surface roughness of the femoral heads, was associated with pelvic osteolysis in these patients.     

Revision of failure acetabular components with cementless acetabular components

Outcomes of cemented acetabular components show unacceptably high rates of loosening over the short-term, and increased failure over the long term. The use of uncemented acetabular components with porous coatings and supplemental screw fixation has improved the success rates of revision surgery with bone loss. Intermediate follow-up results of uncemented acetabular components for revision surgery suggest excellent outcomes with superior fixation compared with cemented components. Use of large components that rely on the posterior column and acetabular dome for fixation appear to function satisfactorily, even in a significantly bone deficient acetabulum.     

Postmortem analysis of consecutively retrieved asymmetric porous-coated tibial components

The objective of this investigation was to conduct a postmortem analysis of 8 porous-coated asymmetric tibial components to measure the extent of radiolucencies and bone ingrowth. With the use of radiographic, electron microscope, and histologic analysis techniques, a quantitative postmortem study of 8 consecutively retrieved porous-coated tibial components was conducted. Time in situ averaged 47 ± 36 months. The components were secured with 4 pegs and 2 screws. Autograft bone chips were applied to the resected tibia during implantation. Contact radiographs of an average of 8 3-mm sections from each implant revealed that 73% ± 17% of the porous coating had no apparent radiolucencies present between the host bone and porous coating for the series. Backscattered electron imaging showed that the bone ingrowth averaged 6% ± 2%. Histologic analysis was unable to demonstrate any adverse cellular response. The analysis suggested that this asymmetric implant design is stable and biocompatible and has potential for long-term clinical durability.     

Histologic analysis of retrieved human porous-coated total joint components

A histologic and microradiographic analysis was performed on 90 retrieved human noncemented porous-coated total joint implants recovered from 58 patients. The specimens included 62 total knee components from 34 patients and 28 total hip components from 24 patients. All components were inserted without the use of bone cement, and in no case was the retrieved component removed due to clinically or roentgenographically apparent loosening. Approximately 92% of the total knee components and 93% of the total hip components had been in situ at least six weeks; 70% of the knee components and more than 50% of the hip components had been functional for at least nine months. The histologic sections and microradiographs revealed varying amounts of bone growth into or in apposition to the porous coatings. In approximately one third of the components, no bone ingrowth or apposition was observed. No component had greater than 10% of the available porous material ingrown with bone. No relationship between the degree of bone ingrowth and the length of time in situ was noted. In all components, the majority of the porous coating contained fibrous tissue that in some cases displayed orientation indicating evidence of load transmission capability. The adherence of bony tissue at the time of removal, a positive roentgenographic evaluation, or a positive clinical presentation was not found to be a definite prognosticator of bone ingrowth. It appears that the combination of limited bone ingrowth and extensive fibrous tissue ingrowth is adequate for implant fixation.     

Osteolysis in cemented versus cementless acetabular components

A prospective, randomized, double-blind, clinical trial comparing cemented with cementless total hip arthroplasty was performed to compare the prevalence and pattern of acetabular osteolysis. Both groups were similar before surgery. Acetabular components were metal-backed, titanium implants. Twenty-eight-millimeter modular femoral heads with titanium femoral stems were used. At a minimum 2-year and mean 4-year follow-up period (range, 2–6 years), 224 patients had clinical and radiographic data available. There was no significant difference in the prevalence of acetabular osteolysis between cemented (5%) and cementless (9%) fixation. With or without cement, the use of a titanium femoral head led to osteolysis within a relatively short period after surgery in almost all of the cases, although this was not significant. The pattern of acetabular osteolysis was different. Progressive osteolysis occurred predominantly in acetabular zone 1 in the cemented group and zone 2 in the cementless group. Cementless fixation of acetabular components has been advocated in an attempt to minimize osteolysis that may occur in cemented total hip arthroplasty. This study found no difference in the prevalence of acetabular osteolysis between the two groups.     

Impingement in total hip arthroplasty a study of retrieved acetabular components

Impingement can damage the acetabular liner, create polyethylene wear, and cause dislocation. We determined the prevalence of impingement, its relation with dislocation, and the influence of patient, surgical, and design factors in 162 components randomly selected from a larger group retrieved between 1990 and 1999. Impingement arc, severity, and wear damage were measured; patient data were obtained from medical records, and component position was determined from radiographs. More than half (56%) showed impingement, including 94% of those removed for dislocation. The occurrence of impingement was significantly increased if the revision diagnosis was dislocation, if the component had a large outer diameter or an elevated rim, and if the femoral component had an extended flanged neck. Implant design, in particular head/neck ratio, can help reduce the prevalence of impingement.     

The mechanism of loosening of cemented acetabular components in total hip arthroplasty. Analysis of specimens retrieved at autopsy.

Late aseptic loosening of cemented acetabular components is governed by the progressive, three-dimensional resorption of the bone immediately adjacent to the cement mantle. This process begins circumferentially at the intraarticular margin and progresses toward the dome of the implant. Evidence of bone resorption at the cement-bone interface was present even in the most well-fixed implants before the appearance of lucent lines on standard roentgenographic views. The mechanical stability of the implant was determined by the three-dimensional extent of bone resorption and membrane formation at the cement-bone interface. The leading edge of the membrane is a transition zone from regions of membrane interposition between the cement and the bone to regions of intimate cement-bone contact. Histologic analysis revealed that progressive bone resorption is fueled by small particles of high density polyethylene (HDP) migrating along the cement-bone interface and bone resorption occurs as a result of the macrophage inflammatory response to the particulate HDP. Evidence in support of a mechanical basis for failure of fixation was lacking. The mechanism of late aseptic loosening of a cemented acetabular component is therefore biologic in nature, not mechanical. This is exactly opposite to the mechanism of loosening on the femoral side of a cemented total hip replacement, which is mechanical in nature.     

A comparison of bone remodelling around hydroxyapatite-coated, porous-coated and grit-blasted hip replacements retrieved at post-mortem

We investigated the implant-bone interface around one design of femoral stem, proximally coated with either a plasma-sprayed porous coating (plain porous) or a hydroxyapatite porous coating (porous HA), or which had been grit-blasted (Interlok). Of 165 patients implanted with a Bimetric hip hemiarthroplasty (Biomet, Bridgend, UK) specimens were retrieved from 58 at post-mortem. We estimated ingrowth and attachment of bone to the surface of the implant in 21 of these, eight plain porous, seven porous HA and six Interlok, using image analysis and light morphometric techniques. The amount of HA coating was also quantified. There was significantly more ingrowth (p = 0.012) and attachment of bone (p < 0.05) to the porous HA surface (mean bone ingrowth 29.093 +/- 2.019%; mean bone attachment 37.287 +/- 2.489%) than to the plain porous surface (mean bone ingrowth 21.762 +/- 2.068%; mean bone attachment 18.9411 +/- 1.971%). There was no significant difference in attachment between the plain porous and Interlok surfaces. Bone grew more evenly over the surface of the HA coating whereas on the porous surface, bone ingrowth and attachment occurred more on the distal and medial parts of the coated surface. No significant differences in the volume of HA were found with the passage of time. This study shows that HA coating increases the amount of ingrowth and attachment of bone and leads to a more even distribution of bone over the surface of the implant. This may have implications in reducing stress shielding and limiting osteolysis induced by wear particles.     

Late loosening of press-fit cementless acetabular components

Between January 1987 and September 1990, 67 consecutive cementless total hip arthroplasties were implanted in 59 patients by one surgeon. The mean age of the patients at surgery was 57 years (range, 23-80 years). All acetabular components were plasma-sprayed titanium hemispheric cups with four peripheral rim fins, but additional screw fixation was not used. The mean followup was 10.4 years (range, 8.8-12.5 years). With revision as the endpoint, the failure rate of this acetabular component at a mean of 10.4 years was 28% (19/67). Of the 56 patients (56 hips) with radiographic followup, loosening of the acetabular shell occurred in 10 hips in 10 patients (18%). Seventy percent of these loosened cups failed by tilt which occurred in a rapid manner; all of the patients required revision surgery. We examined the manner of loosening of a press-fit acetabular component after early (5-year) results showed high hip scores and a low failure rate.     

Acetabular preparation and insertion of cementless acetabular components

acetabular preparation is of critical importance for the long term success of cernentless acetabular components.The goals of this preparation are to provide intimate bony prosthesis contact and initial component stability. Technical aspects of the procedure including osteophyte removal, component positioning, controversies concerning on line versus underrearning of the acetabulum, and screw and component insertion are outlined.     

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 comparative study on medium-term results of cementless acetabular components with metal-on-metal and metal-on-polyethylene articulations

The purpose of this study was to evaluate the medium-term clinical and radiological outcomes of two metal-backed acetabular cups with metal-on-metal and metal-on-polyethylene joint couples, in patients unselected for age. Seventy-five metal-on-polyethylene CLS expansion cups were implanted in 70 patients and 66 metal-on-metal Fitek cups were implanted in 65 patients. The average age at surgery in the two groups was 63 years (range, 25 to 72 years) and 58 years (range, 32 to 68 years), respectively. Data regarding 64 of 75 CLS cups (85%) and 58 of 66 Fitek cups (88%) were collected at a minimum 36-month and maximum 144-month follow-up. The Harris hip score showed excellent results in 86% of the CLS cups, good results in 7%, and fair results in 7%. No poor results were recorded. For metal-on-metal acetabular components, excellent results were recorded in 84% of the cups, good results in 8%, fair results in 5%, and poor results in 3%. Fifty-five patients with 57 of 64 CLS cups (89%) and 50 patients with 51 of 58 Fitek cups (88%) were fully satisfied with their prosthesis. No acetabular reconstructions were revised for aseptic loosening. No radiolucent lines greater than 2 mm were observed, either about CLS or Fitek cups, and low incidence of osteolysis and polyethylene wear was noted in metal-on-polyethylene articulations. Post-operative three-phase bone scanning was obtained in 51 patients and this examination did not show increased uptake in blood pool or bone phase indicating aseptic loosening of CLS and Fitek cups. In conclusion, we found similar rates of excellent and good results using two acetabular components with different bearing surfaces, in patients of unselected age. Therefore, the less expensive implant should be selected for total hip arthroplasty in elderly or low-demand patients. Received: 25 January 2002/Accepted: 18 February 2002     

Hydroxyapatite-coated femoral stems. Histological analysis of components retrieved at autopsy.

Plasma-sprayed coating of hydroxyapatite are biocompatible and, because of their osteoconductive properties, may contribute to the early fixation of total joint prostheses. To evaluate this interface, we histologically analyzed five hydroxyapatite-coated femoral stems which, along with the surrounding bone, were retrieved from three humans at autopsy. The five femoral components had been in situ for a mean duration of twelve months (range, almost five to twenty-five months) and had been inserted for osteonecrosis (two), osteoarthrosis (two), and as an uncermented revision for failure of a cemented stem. The three patients had had a good or excellent clinical result and had died of causes unrelated to the joint arthroplasty. A coating of hydroxyapatite was identified on each stem. There was a variable amount of apposition of bone (32 to 78 per cent of available surface per section). The deposition of bone was most prominent on the surface of the prosthesis that was close to the endosteal surface of the bone, especially in areas that are predicted by Wolff's law (anterior and medial aspects of the implant, and at lateral-oblique corners). There were occasional foci of bone-remodeling around the implant, including osteoclast-mediated removal of the coating of hydroxyapatite along with adjacent bone. Occasional particles of ceramic were present within macrophages in the adjacent bone marrow. Other areas showed formation of new bone with a few areas of bone directly against the metal substrate. The over-all histological features suggest mechanically stable implants with bone-remodeling at the surface of the bone-implant interface.     

Are cementless acetabular components contra-indicated in the elderly?

The long-term success of primary total hip arthroplasty in elderly patients has been well documented. In addition, the use of uncemented acetabular components in younger patients has been well established. However, as yet, there has not been widespread use of uncemented acetabular components in older patients. This study reviews a single surgeon series of 179 consecutive primary total hip replacements using an uncemented acetabular component. Patients were followed up clinically, radiologically and by means of a postal questionnaire. Patients were divided into under-70 years (n = 80) and 70 years and older (n = 99). There were 88 males and 91 females who were followed up to a mean of 24.1 months. There were no significant differences between the groups with respect to the need for additional screw fixation, post-operative complications or implant loosening. Functionally, no differences were recorded in terms of pain, limp, mobility or ability to put on shoes and socks post-operatively. There was no significant difference between the two groups in the levels of satisfaction reported. These results justify the use of uncemented acetabular components in older patients.     

Clinical and radiographic results and wear performance in different generations of a cementless porous-coated acetabular cup

We compared clinical results and wear performance in two different generations of a cementless porous-coated cup, analysing the long-term results of 83 uncemented Harris-Galante I cups (32-mm femoral head) and 93 uncemented Harris-Galante II cups (28-mm femoral head). All polyethylene liners were gamma irradiated in air. Polyethylene linear wear was estimated using a software package. The minimum follow-up was 10 years. Nine Harris-Galante I cups and two Harris-Galante II cups were revised due to aseptic loosening or polyethylene problems. The mean femoral head penetration at 6 weeks after surgery was 0.15 ± 0.05 mm for the Harris-Galante I cups and 0.12 ± 0.03 for the Harris-Galante II cups (p < 0.001);but mean wear was 0.13 ± 0.23 mm per year for the Harris-Galante I cups and 0.11 ± 0.10 for the Harris-Galante II cups (p = 0.740). Most of the metallic shells in both groups showed stable fixation. The so-called second-generation cups had lower initial polyethylene wear that resulted in less polyethylene wear at the latest the follow-up, but the overall wear rate was similar in both groups despite the different femoral head sizes and the improved locking mechanism.

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Résumé Nous avons analysé les résultats cliniques et l’usure portant sur deux types de cupules sans ciment différentes. 83 patients ont bénéficié d’une cupule sans ciment type Harris-Galante I (diamètre de la tête 32 mm) et, 93 patients d’une cupule sans ciment type Harris-Galante II (diamètre de la tête 28 mm). Tous les inserts en polyéthylène ont été irradiés aux rayons gamma en atmosphère d’air. L’usure du polyéthylène a été analysée par un logiciel informatique. Le suivi moyen a été de 10 ans. 9 cupules de type Harris-Galante I et 2 cupules de type Harris-Galante II ont été révisées pour un descellement aseptique ou pour des problèmes au niveau du polyéthylène. La pénétration moyenne de la tête fémorale, six semaines après l’intervention a été de 0,15±0,05 mm pour la Harris-Galante I et de 0,12±0,03 mm pour la Harris-Galante II (p < 0,001). L’usure moyenne a été de 0,13 ± 0,23 mm par an pour la cupule Harris-Galante I et de 0,11 ± 0,10 pour la cupule Harris-Galante II (p = 0,740). La plupart des inserts mécaniques n’ont pas présenté de défauts de stabilité. Ces cupules de deuxième génération ont une usure initiale du polyéthylène inférieure à celle de première génération par contre, l’usure moyenne est identique dans les deux groupes au plus long suivi quel que soit le diamètre de la tête fémorale et l’amélioration du mécanisme de fixation de l’insert PE.

     

Hydroxyapatite-coated acetabular components. Histological and histomorphometric analysis of six cups retrieved at autopsy between three and seven years after successful implantation.

BACKGROUND: Important questions remain regarding the use of hydroxyapatite-coated acetabular components in total hip arthroplasty. What is the relation of resorption of the hydroxyapatite coating to enduring fixation? Will unresorbed or dislodged hydroxyapatite particles cause adverse tissue reactions? Retrieval studies of clinically well-functioning acetabular components should help to answer these questions. METHODS: We examined six clinically successful hydroxyapatite-coated cementless acetabular components that were retrieved at autopsy between 3.3 and 6.6 years after implantation. All components were of the same design. The prostheses and the surrounding bone were prepared for qualitative histological and quantitative histomorphometric analysis. The percentage of bone growth onto the implant, the relative bone area around the implant, the extent of residual hydroxyapatite coating, and the coating thickness were measured. RESULTS: All of the cups showed bone ongrowth, with a mean bone-implant contact (and standard deviation) of 36.5% +/- 13.5%. The contact area was the same in all three zones delineated by DeLee and Charnley. The extent and thickness of the hydroxyapatite layer were much reduced in the specimens from older patients and in those associated with a longer duration of implantation. Degradation of the hydroxyapatite coating by osteoclasts was observed. We did not observe loose hydroxyapatite granules far from the coating, nor did we note any adverse tissue reaction to these granules. In contrast, polyethylene debris was noted in approximately half of the empty screw-holes. CONCLUSIONS: Cell-mediated hydroxyapatite resorption seems to be the main reason for loss of hydroxyapatite coating. The area of bone ongrowth was within a certain range (20% to 50%) of the measured surfaces, and it was independent of the amount of hydroxyapatite residue. The hydroxyapatite coating showed a slow rate of resorption with time, without any adverse tissue reactions.     

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 microns (.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 microns (.06 mm) of micromovement. Static load testing revealed unacceptable micromovement over 150 microns (.150 mm) in most cups with 300-kg loads.     

High placement of porous-coated acetabular components in complex total hip arthroplasty

The authors retrospectively evaluated the results of 56 hips in 51 patients with an acetabular deficiency who had a total hip arthroplasty with a porous-coated, cementless acetabular component implanted at a high hip center. Forty-nine cases were revisions and seven were primary operations. The mean height of the hip center was 43 mm above the interteardrop line compared to 14 mm for the anatomic center, threefold higher than normal. In contrast, the mean horizontal locus was reduced compared to normal (33 vs 37 mm for the anatomic center). Sixteen acetabular components were small (46–48 mm o.d.) and eight were miniature (40–44 mm o.d.). Despite superior placement of the acetabular component, 32 limbs were lengthened by the procedure. The mean preoperative Harris hip score was 51 (range, 28–93). At a mean follow-up period of 40 months (range, 24–64 months), the mean Harris hip score was 86 (range, 36–100). In 23 hips no radiolucent lines were present at the interface of the bone to the porous mesh, and 33 hips had a thin (0.5 mm), nonprogressive radiolucent line in one or more zones. No acetabular component had migrated and no problems occurred with the screws. Four hips (3 revisions and 1 primary operation) had a complete radiolucent line on one oblique view of the acetabulum. No acetabular component has been revised for loosening. These short-term data suggest that under circumstances in which the acetabulum cannot be reconstructed at the anatomic level without a major structural bone-graft, superior placement of the porous-coated acetabular component against viable host-bone at a higher level than normal may be an acceptable alternative.