The significance of stem-cement loosening of grit-blasted femoral components

This study analyzed 15 patients who underwent revision for loosening at the stem-cement interface. The femoral components were from the same manufacturer and had grit-blast roughened surfaces. An apparent radiographic deficiency in the cement mantle was present in at least one zone in 1 3 patients. In 9 of 12 patients with localized osteolysis, the osteolysis developed in a zone with an apparent radiographic cement mantle defect. Loosening occurred due to tension failure of the stem-cement interface followed by axial subsidence and movement into relative retroversion. Motion between the stem and the cement mantle fueled an abrasive wear mechanism between the roughened metal surface and the cement mantle, generating excessive metal and cement particles that gained access to endosteal bone via defects in the cement mantle and resulting in localized osteolysis. Although the roughened surface played a central role in these failures, it is unlikely the layer of polymethylmethacrylate (precoat) played a role in the mechanism of failure. In some cases, debonding occurred as a result of tension failure of the metal-precoat interface. In others, tension failure occurred within the cement mantle, leaving the precoat and some cement from the mantle on the stems. There was no difference in the mechanism of failure of stems with precoat proximally compared to stems with precoat proximally and distally. One stem had no precoat; findings in this patient were indistinguishable from the others. The significance of debonding depends on the surface roughness of the stem. Debonding carries a poorer prognosis with a rougher stem surface because of abrasive wear with the generation of numerous metal and cement particulates, which can lead to rapid osteolysis if there are cement mantle defects. Stems with a higher metal-cement bond strength may require a higher quality cement mantle for long-term success.     

Early failure of modern cemented stems

In the late 1970s, improved cement technique was introduced in an attempt to address the problem of early cemented stem loosening. Subsequently, numerous centers reported stem survival rates of >95% beyond 10 years. Long-term cemented stem fixation was believed widely to be consistently obtainable in most patients. Despite the widespread clinical success of these early cemented stems, numerous changes were introduced in stem design and cement technique. In more recent years, a surprising number of series of early failures of cemented stems have been reported. Some designs consistently have had a high early failure rate. Others have failed infrequently, but the failures have occurred early and with extensive osteolysis. Numerous causes have been proposed, including poor cement technique, undersized broaches, increased stem offset, decreased stem length, rough surface finish, and circular stem cross-section. Failures often are multifactorial and defy a simple explanation based on a single parameter. Results of cemented stems are more variable than previously appreciated. There are nuances of cemented stem design, cement technique, and patient selection that can lead to early failure and that are not understood completely at present. Given the availability of many cemented designs with proven records of clinical success, new design features should be introduced prudently with extensive premarket testing, limited clinical release, and careful postmarket surveillance.     

Total hip arthroplasty with a cemented, polished, collared femoral stem and a cementless acetabular component. A follow-up study at a minimum of ten years

BACKGROUND: Recent studies have suggested that cemented femoral components with a polished surface may provide superior long-term fixation when compared with femoral components with a roughened surface. The purpose of this study was to evaluate the results of total hip arthroplasty with a cemented femoral component with a polished surface finish and compare them with the results of total hip arthroplasty performed with a similar design of cemented femoral component with a rougher surface finish. METHODS: We retrospectively reviewed a consecutive group of 132 patients (149 hips) in whom primary total hip arthroplasty had been performed by one surgeon using a cemented collared femoral component with a polished (0.1-microm Ra) surface finish and a cementless acetabular component. Ninety-eight patients (115 hips) were followed for a minimum of ten years. We compared the survivorship of this prosthesis with that of a femoral component of similar design but with rougher surfaces (matte or grit-blasted). RESULTS: No polished stems were revised because of aseptic loosening or demonstrated radiographic evidence of loosening; however, eight hips (5.4%) with a polished stem demonstrated osteolysis distal to the greater or lesser tro-chanter. In contrast, six stems (2.0%) with a matte surface finish of 0.8-microm Ra were revised because of aseptic loosening, and an additional five stems were seen to be loose radiographically. Eleven stems (9.2%) with a grit-blasted surface finish of 2.1-microm Ra were revised because of aseptic loosening, and an additional four stems were seen to be loose radiographically. The difference in the prevalence of revision due to aseptic loosening between the group with the 0.1-microm Ra surface and the group with the 2.1-microm Ra surface was significant (p = 0.001), as was the difference between the prevalence of revision due to aseptic loosening between the group with the 0.8-microm Ra surface and the group with the 2.1-microm Ra surface (p = 0.001). No cups were revised because of aseptic loosening, and one hip had radiographic signs of acetabular loosening. CONCLUSIONS: This study demonstrated excellent durability of a prosthesis consisting of a cemented, collared, polished femoral component and a cementless acetabular component. While no hips were revised because of aseptic loosening, distal femoral osteolysis was observed in eight hips (5.4%), a higher prevalence than has been reported by others after similar durations of follow-up of tapered, collarless, polished femoral components.     

Analysis of 16 retrieved proximally cemented femoral stems

Sixteen proximally cemented, collared, and distally splined, Bridge Hip femoral stems with a matte proximal surface and smooth distal surface were retrieved because of loosening. Electron microscopy, with correlated elemental analysis, identified titanium particulate embedded in the internal surface of the cement mantle. Data supported the observations that loosening of the femoral stems was related to proximal debonding at the cement-implant interface, loosening at the proximal cement-bone interface, and inherent rotational instability. Cement-implant interface debonding resulted in the proximally matte femoral stem surface abrading with the opposing cement mantle, resulting in particulate and osteolysis in some cases. Careful consideration of implant design and clinically relevant biomechanical testing protocols should be considered before the clinical introduction of future proximally cemented femoral stems.     

Early failure of precoated femoral components in primary total hip arthroplasty

BACKGROUND: In an effort to decrease the rate of aseptic loosening, certain cemented femoral components were designed to have a roughened or textured surface with a methylmethacrylate precoating. Reports differ as to whether this step has increased or decreased the rate of failure. This study was designed to evaluate this issue. METHODS: Five hundred and fourteen hips treated with a cemented Harris Precoat stem (Zimmer, Warsaw, Indiana) were evaluated clinically and radiographically and compared with 254 hips treated with an uncoated Harris Design-2 stem (Howmedica, East Rutherford, New Jersey). Prostheses that had been removed at revision were examined. The cementing and surgical techniques were identical and the population demographics were similar for these two groups. RESULTS: The mean durations of follow-up were 8.4 and 13.5 years for the Precoat and uncoated Design-2 stems, respectively. At those times, at least forty-nine (9.5%) of the 514 Precoat components and at least ten (3.9%) of the 254 uncoated Design-2 stems had failed (p = 0.006). Five Precoat stems fractured, and no uncoated Design-2 stems fractured. Component failure was associated with use in young, active, heavy men with a diagnosis of avascular necrosis and generally with the use of smaller components. The cementing technique was satisfactory in the majority of the patients, and there were no qualitative differences in cementing technique between the hips that failed and those that did not. The mechanisms of failure of the Precoat prostheses included bone-cement loosening, focal osteolysis, stem fracture, and prosthesis-cement debonding. Fractures of smaller components occurred as a result of fatigue failure and were associated with good distal fixation but proximal stem loosening. CONCLUSIONS: The rate of failure of roughened, precoated, cemented femoral components was considerably higher and occurred earlier than that of femoral components that were neither textured nor precoated with methylmethacrylate. Younger patients with avascular necrosis had a higher risk of failure; however, this factor alone did not completely explain the differences in outcome between these two components. The causes of aseptic loosening are multifactorial and may be related to component design and size as well as to precoating and surface finish.     

The Exeter Universal stem: a minimum ten-year review from an independent centre

We reviewed 142 consecutive primary total hip replacements implanted into 123 patients between 1988 and 1993 using the Exeter Universal femoral stem. A total of 74 patients (88 hips) had survived for ten years or more and were reviewed at a mean of 12.7 years (10 to 17). There was no loss to follow-up. The rate of revision of the femoral component for aseptic loosening and osteolysis was 1.1% (1 stem), that for revision for any cause was 2.2% (2 stems), and for re-operation for any cause was 21.6% (19 hips). Re-operation was because of failure of the acetabular component in all but two hips. All but one femoral component subsided within the cement mantle to a mean of 1.52 mm (0 to 8.3) at the final follow-up. One further stem had subsided excessively (8 mm) and had lucent lines at the cement-stem and cement-bone interfaces. This was classified as a radiological failure and is awaiting revision. One stem was revised for deep infection and one for excessive peri-articular osteolysis. Defects of the cement mantle (Barrack grade C and D) were found in 28% of stems (25 hips), associated with increased subsidence (p = 0.01), but were not associated with endosteal lysis or failure. Peri-articular osteolysis was significantly related to the degree of polyethylene wear (p < 0.001), which was in turn associated with a younger age (p = 0.01) and male gender (p < 0.001). The use of the Exeter metal-backed acetabular component was a notable failure with 12 of 32 hips (37.5%) revised for loosening. The Harris-Galante components failed with excessive wear, osteolysis and dislocation with 15% revised (5 of 33 hips). Only one of 23 hips with a cemented Elite component (4%) was revised for loosening and osteolysis. Our findings show that the Exeter Universal stem implanted outside the originating centre has excellent medium-term results.     

Direct compression molded polyethylene for total hip and knee replacements.

Direct compression molded polyethylene is a process of creating a net-shaped component with finished articular surfaces from ultrahigh molecular weight polyethylene by applying heat and pressure to the raw resin (usually Hi-fax 1900) with the use of fixed geometry metallic tools. The final product has no machining or finishing. Sterilization was by gamma radiation in air. Between 1974 and 1978, there were 378 cemented T-28 stems (321 patients) and 171 cemented TR-28 stems (158 patients) articulating with a cemented direct compression molded acetabular component. Radiographically, linear wear was 0.06 mm per year for the T-28 stem and 0.05 mm for the TR-28 stems. The revision rates for the acetabulum were 9.5% and 7.9%, respectively with only two acetabula having osteolysis. On the femoral side, the revision rates were 11.1% and 12.8%, with 11 cases and one case of osteolysis, respectively. Between 1983 and 1996, 4583 AGC cemented total knee replacements were done with direct compression molded nonmodular tibial components. There was no osteolysis seen in these nonmodular compression molded total knee replacements even with 0.1% failure of the femoral components and 0.4% failure of the tibial components. Failure of all of the hip and knee implants was because of poor cement technique, instability, or both. Wear and osteolysis were minimal. Direct compression molded polyethylene has stood the test of time and is a good choice among the currently available polyethylenes.     

Primary hybrid total hip arthroplasty with a roughened femoral stem: integrity of the stem-cement interface

One hundred and two consecutive cemented femoral stems were evaluated in 92 patients at an average 9-year follow-up and a minimum 5-year follow-up (range, 5-14 years). The stem used was cobalt chromium with a collar, normalization steps, and a roughened surface (Ra 40); the stem was inserted using contemporary cementing techniques. This series demonstrated a femoral component aseptic loosening rate of 2.0% and a femoral component survivorship of 97.2 +/- 2.0% at 10 years. One of 2 failed stems was revised at 95 months for failure at the cement-bone interface. The second failed stem showed failure at the cement-bone interface with incomplete debonding radiographically at 65 months. The remaining femoral components did not demonstrate any evidence of debonding at the stem-cement interface. These results compare favorably with other series of cemented femoral stems, as well as with those with a polished surface.     

Effects of femoral neck length, stem size, and body weight on strains in the proximal cement mantle

BACKGROUND: Several studies have shown that certain cemented total hip replacement femoral stems have been associated with the complications of early debonding, loosening, and osteolysis. Some authors have suggested that these failures may be related to the surface finish of the stems. We developed an in vitro biomechanical experiment characterized by simulated stair-climbing to investigate the multiple factors involved in loosening of cemented femoral stems. In this study, we measured the effects of stem neck length, body weight, stem size, and calcar-collar contact on the torsional stability, as reflected by the strains in the proximal cement mantle, of one design of cemented femoral stem. METHODS: Eight Centralign femoral stems (Zimmer, Warsaw, Indiana) were cemented into eight cadaver femora with use of contemporary cementing techniques. Prior to insertion, fifteen strain-gauge rosettes were mounted around the proximal portion of the stem. The stems were loaded on a jig that simulated static peak loading during stair-climbing. Loading was repeated for each stem with three different joint reaction forces and for three different neck lengths. Calcar loading by the collar was then eliminated by removing a 0.5-mm slice of bone beneath the collar, and all loadings were then repeated. RESULTS: The peak principal tensile strains in the proximal cement increased linearly with both body weight (r (2) > 0.95) and neck length (r (2) > 0.75). Increasing body weight affected the peak cement strains far more than did increasing neck length. During simulated stair-climbing, calcar-collar contact reduced peak strains in the proximal cement by a factor of 1.5 to two. Peak principal tensile strains in the proximal cement often exceeded 1000 me when the smaller stems were used. CONCLUSIONS: In this stair-climbing test model, the peak proximal cement strains were increased more by changes in body weight than they were by changes in neck length. Even during stair-climbing, calcar-collar contact reduced peak cement strains.     

Surface finish mechanics explain different clinical survivorship of cemented femoral stems for total hip arthroplasty

The ability of bone cement to adhere to the implant surface is dependent on the surface finish. Stems with a rough surface finish require greater force to disrupt their interface with the cement than do stems with a smooth or polished surface. However, if micromotion occurs at the cement-metal interface, the fretting of a smoother surface implant results in less cement and metallic abrasion than an implant with a rough surface finish. Today, surgeons implant femoral stems with a wide variety of surface finish and textures that are supported by the previously mentioned contrasting philosophy of fixation. This article presents the micro and macro surface finish mechanics, history, and rationale for changes in surface finish, the clinical and operative implications of changes in surface finish, the retrieval analysis, and the clinical evidence that examine the consequences of changes in surface finish in the outcome of cemented femoral stems for total hip arthroplasty. Current data and our own experience support the use of cemented femoral stems with a smooth or polished surface finish.     

Total hip arthroplasty with satin finish, tapered stems

Subsidence of femoral hip prostheses with a rough surface has been associated with osteolysis and loosening. However, recent evidence has suggested that smooth-finish tapered stems may not incur these problems. An experimental monobloc satin finish, tapered femoral component was designed to subside within the cement. There were 49 femoral components implanted, and patients averaged a 1.8-mm subsidence at the prosthesis-cement interface with a follow-up of 6.76 years. There were no failures attributable to aseptic loosening at the cement-bone interface. This study supports the use of a satin finish, tapered femoral component in cemented total hip arthroplasty.     

The effect of surface finish and of vertical ribs on the stability of a cemented femoral stem: an in vitro stair climbing test

The search for improved femoral fixation in cemented total hip arthroplasty is ongoing. Two design variables, surface finish and stem contour, were evaluated. Sixteen titanium femoral stems of one design were cemented into fiberglass femora. One half of the components had a polished surface and the rest had a roughened finish. Within each group, 4 stems had vertically oriented ribs on the proximal portion and 4 did not. Micromotion was measured in a stair climbing simulator with loading to a joint reaction force of 200 kg for 6 million cycles. Micromotion increased throughout the course of the experiment. Stems with a polished surface had significantly higher micromotion. Although stems with ribs had less micromotion compared with those without ribs, this difference was not statistically significant.     

Clinical and biological assessment of cemented titanium femoral stems: an 11-year experience

This study prospectively assessed the outcome of 134 cemented titanium stems and serum ion levels. The stems were polished (0.1 μm Ra) with circular cross section. At the end point, only one stem revision was performed for aseptic loosening, and two were planned due to subsidence greater than 5 mm. Non-progressive radiolucencies in zones 1 and 7 were observed in 16 hips at the cement-bone interface without osteolysis. Median serum titanium concentrations were below the detection limit (30 nmol/l) except in patients with failed stems. The overall stem survival rate was 97.7% at nine years, which is comparable to other series of cemented stems. The protective layer of titanium oxide coating the stem and a thick cement mantle may help resist aseptic loosening. In addition, satisfactory monitoring of the stem was reached using titanium serum level determination.     

Osteolysis in cemented titanium alloy hip prosthesis

We evaluated 132 consecutively implanted cemented titanium alloy stems (Ti6-Al7-Nb, SLS-88) after a mean follow-up of 6.6 years (range 5-7 years). Almost 30% of the stems showed significant osteolysis, mainly in the proximal stem area. The amount of osteolysis correlated significantly to a typical pain pattern: dull, circular, and occurring at rest. Six stems had already been revised, and another 7 stems were loose clinically and radiologically, which resulted in a Kaplan-Meier survivorship of 95% for stem revisions and 88% for stem failures (revisions plus loose stems). We found that smaller stem sizes tend to increase the development of osteolysis and loosening. Two factors seem to play a role in early loosening of cemented titanium alloy stems: i) increased elasticity of titanium, which leads in small stem sizes to micromotion between the stem and cement and to cement breakage, and ii) corrosion of the cemented titanium alloy stem and subsequent osteolysis in the adjacent bone. The combination of both factors (high elasticity plus corrosion) accelerates the degradation of the bone anchorage of the stem and initiates early loosening. We advise against the further use of cemented SLS-88 titanium alloy stems.     

The various stress patterns of press-fit, ingrown, and cemented femoral stems

Finite-element analysis was used to study the general differences in load-transfer mechanisms and stress patterns of cemented, fully ingrown, proximally ingrown, and smooth press-fitted femoral stems in total hip arthroplasty (THA). Identical stems were used for the noncemented configurations and a similar stem shape for the cemented configurations. In each model, bone properties and loading characteristics were equal. Stem elastic moduli were varied so that the effects of cobalt-chromium-molybdenum (CoCrMo) and titanium as different stem materials could be assessed. The load-transfer mechanism is similar for all bonded configurations but differs dramatically for unbonded stems, e.g., press-fit designs. In the bonded configurations, interface stress concentrations occur on the proximal and distal sides. Stress value depends on stem rigidity, with higher proximal stress occurring in cemented stems and higher distal stress in noncemented stems. In the press-fit stem, the interface stresses are affected more by stem shape as a geometric entity and less by stem rigidity. Considering possible postoperative failure mechanisms, such as interface loosening and cortical bone loss, titanium is expected to produce better results in noncemented stems and CoCrMo in cemented stems. Cortical stress shielding as a qualitative phenomenon is caused by all stems, particularly in the calcar region. Quantitatively, stress-shielding effects differ with each type of fixation used. Stress-shielding effects are severe in fully ingrown stems and milder in cemented stems because of the differences in stem rigidity. The proximally ingrown stem falls between the fully ingrown and cemented stems in regard to stress shielding because stress transfer is more evenly distributed along the stem and concentrated at the lower coated edge. The press-fit stem provokes calcar stress shielding only. In the midstem region the stresses in the cortex are even greater than in the natural case.     

The long-term results of press-fit cemented stems in total knee prostheses

We evaluated the long-term fixation of 64 press-fit cemented stems of constrained total knee prostheses in 32 young patients with primary malignant bone tumours. Initial stable fixation, especially in rotation, was achieved by precise fit of the stem into the reamed endosteum, before cementation. Complementary fixation, especially in migration and rotation, was obtained by pressurised antibiotic-loaded cement. The mean age at operation was 33 years (13 to 61). No patient was lost to follow-up; 13 patients died and the 19 survivors were examined at a mean follow-up of 12.5 years (4 to 21). Standard revision press-fit cemented stems were used on the side of the joint which was not involved with tumour (26 tibial and six femoral), on this side there was no loosening or osteolysis and stem survival was 100%. On the reconstruction side, custom-made press-fit stems were used and the survival rate, with any cause for revision as an end point, was 88%, but 97% for loosening or osteolysis. This longevity is similar to that achieved at 20 years with the Charnley-Kerboull primary total hip replacement with press-fit cemented femoral components. We recommend this type of fixation when extensive reconstruction of the knee is required. It may also be suitable for older patients requiring revision of a total knee replacement or in difficult situations such as severe deformity and complex articular fractures.     

Mechanical characteristics of the bone-graft-cement interface after impaction allografting.

Impaction allografting is an attractive procedure for the treatment of failed total hip replacements. The graft-cement-host bone interface after impaction allografting has not been characterized, although it is a potential site of subsidence for this type of revision total hip reconstruction. In six human cadaveric femurs, the cancellous bone was removed proximally and local diaphyseal lytic defects were simulated. After the impaction grafting procedure, the specimens were sectioned in 6 mm transverse sections and push-out tests were performed. From the adjacent sections the percentage cement contact of the PMMA cement with the endosteal bone surface was determined. The host bone interface mechanical properties varied significantly along the femur largely due to different interface morphologies. The apparent host bone interface shear strength was highest around the lesser trochanter and lowest around the tip of the stem. A significant positive correlation was found between the percentage cement contact and the apparent host bone interface shear strength (r2 = 0.52). The sections failed in 69% of the cases through a pure host bone interface failure without cement or allograft failure, 19% failed with local cement failure, and 12% with a local allograft failure. The apparent host bone interface strength was on average 89% lower than values reported for primary total hip replacements and were similar to cemented revisions proximally and lower distally. This study showed that cement penetration to the endosteal surface enhanced the host bone-graft interface.     

In vitro influence of stem surface finish and mantle conformity on pressure generation in cemented hip arthroplasty

Background and purpose Under physiological loads, debonded cemented femoral stems have been shown to move within their cement mantle and generate a fluid pump that may facilitate peri-prosthetic osteolysis by pressurizing fluid and circulating wear debris. The long-term physiological loading of rough and polished tapered stems in vitro has shown differences in performance, with greater interface pressures generated by the rough stems. In this study we investigated the individual effects of stem surface finish, degree of mantle wear, and mode of loading on the stem pump mechanism.Method Rough and polished stems were loaded under different regimes in artificially worn cement mantles that permitted either 2 or 5 degrees of rotational stem movement, and the interface pressures were compared.Results The pressures generated by the rough and polished stems were similar in either type of mantle. The pattern of pressure generation in the 2-degree mantles was similar to the pressures generated by rough stems after long-term loading, but the high posterior wall pressures fell and the tip pressures increased in the 5-degree mantles. The torsional loads were principal drivers of pressure generation in all areas of the interface other than the implant tip, where axial loading predominated.Interpretation Femoral stems with rotational instability under cyclic torsional loads generate elevated interface fluid pressures and flows independently of stem surface finish. The rough surface finish is only important in creating this instability in tapered stems.     

Initial stability of cemented femoral stems as a function of surface finish, collar, and stem size

BACKGROUND: The optimum surface roughness of cemented femoral stems used for total hip replacement is a subject of controversy. While rougher surfaces provide stronger cement adhesion, it has been hypothesized that polished, tapered, noncollared stems settle into the cement mantle, providing improved stability. However, the effects of surface finish on the stability of straight, cemented stems tapered only in the coronal plane are not known. METHODS: Using composite model femora, we assessed the initial stability of a straight, cemented femoral stem as a function of surface roughness, the presence or absence of a collar, stem size, and the resultant cement thickness under simulated walking and stair-climbing loads. Otherwise identical stems were manufactured with polished or rough surfaces, with or without a collar, in two different sizes. We isolated these three variables and compared their relative contributions to the motion at the stem-cement interface throughout cyclic loading. We defined three indicators of stability: per-cycle motion, rate of migration, and final migration. RESULTS: Surface roughness had a greater influence on per-cycle motions than did the presence or absence of a collar or cement thickness. Specifically, in the medial-lateral direction, per-cycle motion of polished stems was 43 micro m greater than that of rough stems (p < 0.01). None of the per-cycle motions decreased over the 77,000 load cycles. In contrast, with all stems, the rate of migration decreased over the course of cyclic loading, but the rate of migration of the polished stems was greater than that of the rough stems. Final migrations of the stems over the course of loading were generally distal, medial, and into retroversion. Compared with rough stems, polished stems had 8 to 18 micro m more axial migration (p < 0.001), 48 micro m more anterior-posterior migration (p < 0.001), and 0.4 degrees more rotational migration (p = 0.01). CONCLUSIONS: and Clinical Relevance: The results indicated that, for cemented, straight femoral stems tapered only in the coronal plane, a rough surface offers the advantage of less per-cycle motion. These results may apply to widely used cemented stem designs based on the profile of the original Charnley femoral component, which has approximately parallel anterior and posterior aspects.