In vivo construction of a metal-backed, high-molecular-weight polyethylene cup during McKee-Farrar revision total joint arthroplasty. A case report

The need for revision total hip arthroplasty after metal-to-metal articulating prostheses is well known. An alternative to conventional acetabular revision in the clinical circumstance of isolated femoral component loosening is in vivo construction of a metal-backed, high-molecular-weight polyethylene (HMWPE) acetabular component. This surgical approach reduces the likelihood of intraoperative acetabular bone loss, should minimize subsequent loosening, and virtually eliminates the source of metallic wear debris. Follow-up evaluation after 3 years revealed maintenance of the acetabular component position and a satisfactory clinical result. In vivo construction of a metal-backed HMWPE acetabular component is an effective alternative in the management of this potentially difficult orthopedic problem.     

Fracture of a metal-backed acetabular component in total hip arthroplasty. A case report

Metal-backed acetabular components offer the advantage of a lower incidence of loosening. The case of a 33-year-old man emphasizes the potential problem of fracture of both the polyethylene and metal-backed structures. Although this case report may represent an unusual and infrequent occurrence, it emphasizes a potential failure mode for acetabular components with metal backing. While fracture of the polyethylene has been previously reported, little thought has been given to the further potential of fracture of metal-backed support. The clinical profile as well as the roentgenographic appearance of such a phenomenon is presented for further sophistication of the surgeon when dealing in the challenging area of hip arthroplasty.     

Total hip arthroplasty in patients less than 40 years old with avascular necrosis of the femoral head. A 5 to 19-year follow-up study

We evaluated 34 total hip arthroplasties (THA) for avascular necrosis of the femoral head in 26 patients who were younger than 40 years at the time of the index operation. The average age at the time of THA was 283 (17-38) years. The mean follow-up was 10.9 (5-19) years. We used 6 cemented and 28 cementless acetabular components and a cemented polished tapered stem in all hips. The mean Charnley modified Merle d' Aubigné Postel score was 8.9 points preoperatively and 16.6 points at final follow-up. Two cemented metal-backed cups were revised because of aseptic loosening at 10 years, one cemented polyethylene cup failed at 12 years and 2 more all polyethylene cups had pending failure. The metal-backed cemented cups and the all polyethylene cups had a longer follow-up than the uncemented cups. Therefore and because of the proven unfavourable long-term outcome of the cemented metal-backed Exeter cup we are not able to draw any firm conclusions regarding the preferred choice between cemented and uncemented cups in this particular group of patients. On the femoral site none of the stems had to be revised. Our results show that a cemented polished tapered femoral component has an excellent survival in primary total hip replacement in young patients with avascular necrosis of the femoral head.     

Polyethylene liner dissociation in Harris-Galante acetabular components: a report of 7 cases.

Harris-Galante modular acetabular components (Zimmer, Warsaw, IN) have been used widely for primary and revision total hip arthroplasties. The survivorship of this implant has been well documented in the literature. Failure of the liner locking mechanism and subsequent dissociation of the polyethylene liner from the metal-backed shell is a potential cause of failure, however. We report 7 cases of liner dissociation and propose the mode of failure. The result in all cases was a well-fixed metal acetabular shell with a failed locking mechanism, which usually is managed by revision of the entire component. This procedure may be accompanied by the potential loss of acetabular bone stock, which should be replenished.     

Loading of the acetabulum by polyethylene and all-ceramic inserts in metal-backed acetabular cups

Both static and dynamic loads were applied to metal-backed acetabular cups with ceramic or polyethylene inserts and the resulting load transmissions at a simulated bone interface were determined. Perfect fit and under-sized and over-sized cavities were prepared in simulated bone substrates, lined with Fuji pressure sensitive film, and acetabular cups inserted with physiological loads. The magnitude and location of contact forces between the cup and bone were measured. These cups were then subjected to a controlled impact load and the intensity and frequency of the loads transmitted to the substrate were determined. The results suggest that a polyethylene backing for ceramics is not necessary as there were no major differences in the static and dynamic stresses transmitted to the cup-bone interface with all polyethylene or ceramic inserts.     

Cementation of a polyethylene liner into a metal shell

As the number of revision hip arthroplasties continues to increase, alternative reconstructive options may be necessary. Cementation of a polyethylene liner into a well-fixed metal acetabular shell has previously been reported to save bone stock and enhance the pullout strength. This study analyzed whether cementation of various types of mechanically modified or nonmodified liners into a metal shell altered wear characteristics when compared with noncemented modular liners. The authors used nonirradiated and highly cross-linked polyethylene liners that were mechanically modified or left unmodified. Wear in both nonirradiated and highly cross-linked liners was not affected by the cementing process. Wear of the highly cross-linked polyethylene liners was significantly less when compared with the nonirradiated liners. This laboratory study provides quantitative data supporting previous qualitative studies of cementing a polyethylene liner into a metal-backed acetabular shell. Based on this study, cementation of a mechanically modified liner did not affect wear in this study, which simulated 3 years of activity.     

Fracture of a metal-backed acetabular cup. A case report

In this case of fracture of a metal-backed polyethylene acetabular component after a total hip arthroplasty, there was no history of difficulties prior to the component fracture and no history of trauma.     

Metal-backed acetabular cups in total hip arthroplasty

Metal backing for the acetabular component of a total hip replacement, initially designed to allow replacement of the polyethylene liner, has since been universally accepted as a means of decreasing peak stresses at the interfaces of bone and cement. We studied the results of 238 total hip replacements that had been performed between 1980 and 1983 and that differed only in that 138 of the acetabular components had a metal backing and 100 were made of polyethylene only. Kaplan-Meier survival analysis, with three different modes of failure (radiolucency, loosening, and revision), showed a significant increase in the rate of failure of the metal-backed acetabular cup compared with the all-polyethylene cup: radiolucency, 39 compared with 23 per cent (p less than 0.0001); loosening, 4 compared with 2 per cent (p less than 0.0001); and revision, 6 compared with 2 per cent (p less than 0.0034). It was concluded that metal backing cannot be recommended for a cemented acetabular component of a total hip-replacement system.     

Cementing acetabular sockets into metal-backed acetabular components and antiprotrusio cages: a technical tip

Cementing a polyethylene socket or acetabular liner into a well-fixed metal-backed acetabular shell has become a useful procedure in selected complex primary and revision hip arthroplasties. Polyethylene sockets are frequently cemented into antiprotrusio cages as well. Frequently, these metallic devices are fixed to host bone with acetabular screws. Unfortunately, when polyethylene sockets are cemented into such devices, the cement fills the recess within the screw head and makes subsequent screw removal extremely difficult should the device need to be removed or revised. The author describes a technique of filling the screw heads with bone wax and gel foam before cementation. This keeps the recess within the screw head relatively patent and allows easier removal of the screw in the future should it become necessary.     

Survivorship analysis of cemented total hip arthroplasty acetabular components implanted with second-generation techniques

The clinical and radiographic results of primary cemented total hip arthroplasty performed by a single surgeon, with particular emphasis on the performance of acetabular components implanted with so-called second-generation cement techniques, were studied. Seventy hips with 48 metal-backed and 22 polyethylene acetabular components were followed for a mean of 9 years (range, 5–11.5 years). The clinical results were evaluated using a recognized hip score. The fixation status of the cemented acetabular component was evaluated using two methods of measuring radiolucent lines at 5 years and at the last evaluation. Acetabular component loosening was defined as a circumferential radiolucent line, component migration, or revision for loosening. This study was unable to confirm the findings of others that demonstrated higher failure rates with cemented metal-backed components when compared with all-polyethylene components. The survival of cemented acetabular components with 28-mm head femoral prostheses was worse than the survival of cemented acetabular components with 22-mm femoral heads in other published reports, despite advances in cement techniques. Because of the high rate of loosening of cemented 28-mm-inner-diameter acetabular components at 5 and 10 years, the authors no longer use these cemented components for acetabular reconstruction.     

Results of cemented metal-backed acetabular components: A 10-year-average follow-up study

The clinical and radiographic results of 86 primary total hip arthroplasties performed in 74 patients from 1983 to 1987 with a cemented metal-backed acetabular component and a cemented collared straight femoral stem with a 32-mm head were reviewed at a mean follow-up of 10.1 years. Seven patients (9.2%) underwent acetabular component revision at a mean of 9.0 years after implantation; an additional 24 components (31.6%) demonstrated evidence of radiographic loosening, resulting in a total failure rate of 40.8%. Periacetabular radiolucencies were noted in Charnley zones at the following rates: 34.2% in zone I, 18.4% in zone II, and 27.6% in zone III. In addition, 18.4% and 38.2% of implants demonstrated evidence of migration and excessive polyethylene wear. Excessively vertical cup placement (>49° inclination) at the time of initial arthroplasty was statistically correlated with polyethylene wear, implant migration, and fixation failure. A trend of increasing implant failure was also noted with decreasing polyethylene liner thickness. Periacetabular cement mantle thickness was not statistically correlated with subsequent component loosening or failure. Results of Kaplan-Meier survivorship analysis using revision as an endpoint showed 93.6% survivorship at 10 years and 88.4% at 12 years. The mean modified Harris hip scores were 46.9 preoperatively and 81.8 at final follow-up. The significant overall rates of radiographic loosening, migration, polyethylene wear, and implant revision confirm the suspected trend of increasing failure rates of cemented metal-backed acetabular components over time.     

Assessment of polyethylene wear in total hip replacement

The three-dimensional technique is a method for the measurement of polyethylene wear in patients with total hip joint replacement. Application of image processing technology allows automation of point selection from digital images of radiographs scanned into the computer. Validation of image processing modifications reveals a three-fold increase in accuracy and a 40-fold increase in reproducibility compared with manual input of points from a digitizer during bench testing. A review of three-dimensional technique application to clinical patients gives information on the factors that influence polyethylene wear. Increasing age, activity level, femoral head size, decreasing polyethylene thickness, and insertion of total hip prostheses without cement all increase polyethylene wear. Restoration of femoral offset during total hip replacement seems to decreases polyethylene wear. No apparent difference in polyethylene wear rate could be found between two groups of patients, one group had a stainless steel-polyethylene articulation and the other had a ceramic-polyethylene articulation. Measurement of the serial polyethylene wear of individual patients reveals a high rate of femoral head penetration during the first 2 years after total hip replacement using metal-backed acetabular components inserted without cement. Interpretation of this femoral head penetration as true polyethylene wear may be erroneous, however, because creep of the polyethylene and acetabular liner movement within its metal shell cannot be measured.     

Dissociation of a metal-backed polyethylene acetabular component. A case report

A case of early failure of a total hip arthroplasty presenting as a dislocation is discussed. After failed attempts at closed reduction, an open procedure revealed that the polyethylene insert of the acetabulum had separated from its metal backing. The increasing use of metal-backed acetabular components in total hip arthroplasty produces another mechanical interface that may fail: the metal-polyethylene interface. surgeons should consider this possibility in dislocations of total hip prostheses that cannot be reduced by closed means.     

Periacetabular Stress Distributions After Joint Replacement with Subchondral Bone Retention

Two-dimensional finite element stress analyses were conducted of the acetabular region after total joint replacement. The effect of subchondral bone retention was evaluated for both conventional and metal-backed acetabular components. Stresses in the bone, cement and acetabular cup were significantly reduced when subchondral bone was retained for both component types. The results indicate that the most favorable stress conditions are created when a metal-backed acetabular component is implanted with subchondral bone retention.     

Separation of the polyethylene liner from acetabular cup metal backing. A report of three cases.

In three young patients with cementless Porous Coated Anatomic (PCA) total hip prostheses implanted two to four years previously, the polyethylene liner separated from metal backing. These cups were of the original PCA design, manufactured and packaged as single assembled components, rather than the more recent two-piece components packaged with interchangeable liners separate from the metal backing. Each case of separation was associated with the failure of the thin outer polyethylene rim and central polyethylene peg on the back of the liner that secures it to the metal backing. Cup liners should be securely attached to the metal backing. The possibility of polyethylene failure is considerable when cementless metal-backed acetabular cups are used in active young patients.     

Further follow-up on socket fixation using a metal-backed acetabular component for total hip replacement. A minimum ten-year follow-up study

In 1982, Harris and White reported the data after a minimum five-year follow-up of fifty-three total hip replacements in forty-seven patients in whom a cemented metal-backed acetabular component had been used. There actually had been fifty-four total hip replacements in fifty-three hips, as in one hip a revision was done for a traumatic disruption of the initial acetabular component that occurred two months after the first insertion. Six of the fifty-four operations did not qualify for inclusion in this ten-year follow-up study, including four operations in three patients who had died before that time. The remaining forty-eight hips have been followed for ten to 13.5 years (mean, 11.3 years). With one exception, the ages of the patients at the time of the index operation ranged from seventeen to fifty years (mean, forty-one years). Six (12.5 per cent) of the forty-eight hips required revision because of symptomatic aseptic loosening of the acetabular component. In addition, two acetabular components, although they were not loose, were revised concomitantly with revision of the femoral component because of the presence of radiolucent lines at the cement-bone interface of the acetabular implant. One other acetabular component that was not loose was revised because of unexplained pain, one was removed because of sepsis, and for one only the polyethylene liner was exchanged because of damage to the polyethylene when the weld holding the femoral head to the femoral neck failed. Nine additional hips (19 per cent), although they were not revised, showed radiographic evidence of migration, and one (2 per cent) showed radiographic evidence of impending failure.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of polymerization of methylmethacrylate on metal-backed and non-metal-backed acetabular components.

Aseptic loosening of the acetabular component has been identified as the main cause of failure of cemented total hip arthroplasty in the long term. Wear of the high-density polyethylene has been implicated as a major contributory factor to loosening. The etiology of wear is multifactorial. The exothermic phase of polymerization of polymethylmethacrylate is associated with a 5.9% volume expansion. Using double-exposure holographic interferometry, the authors examined the influence of polymerization of cement on the internal geometry of a metal-backed cup and two non-metal-backed cups (Charnley 22 mm, Muller 32 mm). The non-metal-backed cups exhibited marked heat concentration points and disrupted fringe patterns, indicating distortion of the internal geometry of the cup. In contradistinction, the metal-backed cup showed good heat dissipation and regular fringe patterns, indicating minimal internal distortion. The differences were not quantified but were visually dramatic. The authors believe this may be an important contributory factor to cup wear in cemented total hip arthroplasty.     

Cementless acetabular replacement in the young. A 5- to 10-year prospective study

This article presents a prospective clinical and radiologic review of 55 total hip replacements in 50 patients in which the cementless Harris-Galante porous-coated acetabular component was used. All patients were 50 years of age or younger. The cups were inserted by 15 different surgeons. The minimum followup was 5 years, with a mean of 7 years. No acetabular component has been revised for loosening, and none have migrated. Three (5.5%) cups have progressive bone-component radiolucent lines, two (3.6%) of which are complete. Six (10.9%) acetabular liners have been replaced for excessive polyethylene wear, and an additional four (7.3%) show sufficient wear to produce obvious radiographic eccentricity of the femoral head. All of the revised liners had 32-mm femoral heads and an initial polyethylene thickness of less than 6 mm. Although the results reflect excellent fixation of this component in the medium term, the incidence of exchange of the polyethylene liner for excessive wear is unacceptably high. The reduction in polyethylene thickness associated with the use of a metal-backed component and a 32-mm articulation was one of the factors contributing to the accelerated wear patterns seen in this series.     

A stress analysis of acetabular reconstruction in protrusio acetabuli

We are reporting the results of a finite-element analysis of acetabular reconstruction for total hip replacement in the presence of protrusio acetabuli. In a protruded acetabulum, cortical bone stresses on the medial part of the pelvic wall increase with medial placement of the acetabular component, while normal placement of the component (more lateral placement) reduces these stresses. Metal backing of a polyethylene acetabular component causes a reduction in the peak cement and trabecular-bone stresses. A metal protrusio ring about only the periphery of the acetabular component increases stress levels within the lateral part of the pelvic cortex and has little effect on stresses in the medial part of the pelvic wall. A complete metal protrusio cup increases stresses in the lateral part of the pelvic cortex while decreasing substantially the stresses in the medial part of the cortex and the trabecular bone. Prosthetic reinforcement of the medial part of the acetabular wall has little effect on stress patterns in the acetabular region. Clinical Relevance: The major long-term problem with cemented total hip prostheses is loosening. Loosening is probably related in part to the stress state in the cement and surrounding bone. The protruded acetabulum is particularly difficult to reconstruct in a manner that ensures longevity of the total hip replacement. In patients with protrusio acetabuli, the prosthetic acetabulum should be placed in a normal and not in a protruded position. A metal-backed acetabular component or a complete metal cup incorporated within the cement reduces stress levels within the medial aspect of the pelvic bone and thus may reduce the incidence of loosening.     

A comparison of the outcome of cemented all-polyethylene and cementless metal-backed acetabular sockets in primary total hip arthroplasty

We compared, after a 10-year-minimum follow-up, the outcome of 50 cemented all-polyethylene Charnley acetabular sockets with that of 51 cementless metal-backed sockets in 2 comparable cohorts of young patients. Although the revision rate for the cemented and cementless group was 28% and 35%, respectively, the revision rate for aseptic loosening was 28% for the cemented and 12% for the cementless group. The mean polyethylene wear was 0.112 and 0.114 mm/y, respectively, for the 2 groups. Linear osteolysis was observed in 18 of 50 cemented sockets. Expansile osteolysis presented in 10 of 51 cementless sockets and only in one of the cemented sockets. In conclusion, cementless components had more durable fixation than cemented components. However, they presented more aggressive expansile osteolysis caused by the coexistence of polyethylene and metal debris.