Ingrowth reduces implant-to-bone relative displacements in canine acetabular prostheses

We examined bone-to-implant relative displacements of acetabular prostheses acutely and after ingrowth in a canine model. Uncemented hemispherical acetabular cups with titanium mesh pads comprising approximately 26% of the surface of the cup were inserted in eight adult canine hemipelves ex vivo. The acetabular prostheses were fixed with 13 mm titanium screws. Zero, one, and two-screw configurations were tested, with the order of testing randomly assigned. A load simulating 1,000 cycles of canine gait was applied to the acetabular component, and relative displacements were measured at three locations between imlant and bone to determine acute fixation. A repeated measures analysis of variance showed that two screws produced only 42% of the average relative displacement of one screw and 14% that of zero screws. Eight adult mixed-breed dogs then underwent unilateral total hip arthroplasty. All acetabula were biologically fixed with two cancellous screws. The results at 4 months showed significantly less relative displacement between the implant and bone than was measured in ex vivo implantations (p = 0.014). Bone ingrowth filled 20 ± 6% (mean ± SD) of the available space. The relative displacements of these implants were small in all cases (12 ± 13 μm) and did not correlate with the amount of bone ingrowth. These data suggest that acetabular fixation with two screws can lead to bone ingrowth and reduced relative motion of the prosthesis under functional loading.     

Effect of oral alendronate on net bone ingrowth into canine cementless total hips

Alendronate has been shown to prevent osteolysis in a canine total hip arthroplasty (THA) model. However, the effect of alendronate on bone ingrowth and remodeling around canine cementless hip replacement components remains unclear. We hypothesized that oral alendronate would increase net bone ingrowth into the porous surface of THA components when intimate bone/implant contact exists. To test this hypothesis, six mature dogs received unilateral cementless THA and were treated with five milligrams of oral alendronate daily from day seven to day eighty-four postoperatively. Six comparable dogs served as controls. Quantitative analysis of net bone ingrowth into the porous surface did not show a significant difference between the two groups, (control 7.9 +/- 1.5, alendronate 7.5 +/- 1.4, P < 0.6). These results did not support the hypothesis that oral alendronate would increase net new bone formation into the porous surface of THA components. Key words: alendronate, bone ingrowth, total hip arthroplasty.     

Bony ingrowth fixation of the acetabular component in canine hip joint arthroplasty

Five mature dogs were studied five to eight months after insertion of a newly designed acetabular component that eliminates the use of bone cement in total hip arthroplasty (THA). The component was hemispheric, with a layer of porous metal on its outside surface. It initially was fixed to the innominate bone by screws passed through projections from the edge of the metal substrate. When the dogs were killed five or eight months after implantation, all components were fixed rigidly to the bone. Bony ingrowth covered an average of 53% of the porous surface of the implant, penetrating three layers of balls.     

Cementless total hip replacement: Bio-active glass ceramic coating studied in dogs

We studied 2 types of a cementless total hip prosthesis in dogs. Both were coated with titanium plasma-spray. In both components, the pores in the deep layer of 1 group were further coated with apatite and wollastonite containing glass-ceramic (AW glass-ceramic). 50 dogs underwent unilateral total hip replacements, and were killed at 1, 3, or 6 months postoperatively. We evaluated the femoral and the acetabular components mechanically and histologically. At 1 month, the detaching load and bone ingrowth of the AW glass-ceramic-coated femoral and acetabular components were higher than those of the control implants. At 3 and 6 months there were no differences between the 2 types of components. Thus, AW glass-ceramic enhanced the early phase of cementless implant fixation.     

A quantitative study of bone and soft tissues in cementless porous-coated acetabular components retrieved at autopsy

The authors examined 11 cementless acetabular components of one design retrieved at autopsy and made observations concerning tissue ingrowth and local tissue reaction, radiographic-histologic correlation, and the distribution of particulate wear debris. The cups were hemispherical in design with a commercially pure titanium fibermetal porous coating. All of the prostheses were implanted with screws. The implants were in place for an average of 41 months (range, 5 weeks to 75 months). Ten of the cups had bone ingrowth, with the average volume fraction being 12.1±8.2%. There were no differences in the amount of bone ingrowth when the component was partitioned into nine anatomic regions. However, there was more bone adjacent to screw holes through which screws were inserted compared with empty screw holes. As the number of radiolucent zones increased on the clinical radiographs less bone ingrowth was observed histologically. The amount of metal debris in holes with screws and holes without screws was similar. In the longest term cases, polyethylene debris was noted within empty screw holes, but no granulomatous reactions or osteolytic processes were observed.     

Influence of intraoperative femoral fractures and cerclage wiring on bone ingrowth into canine porous-coated femoral components

Intraoperative femoral fractures occur more frequently with cementless than with cemented components. In this study, the influence of controlled femoral fractures fixed with cerclage wires on rotational stability and bone ingrowth into porous-coated canine femoral components was evaluated. These data were compared with results of previous studies on unrecognized femoral fractures (not stabilized) and on the intact canine femur. Micromotion analysis revealed a significant increase in rotational instability in fractures not stabilized with cerclage wires (P < .05) compared with the intact femur. Experimentally created femoral fractures had a significantly deleterious effect on bone ingrowth even after cerclage wiring. This appears to be caused by a lack of bone ingrowth deep to the fracture and an increase in femoral component micromotion. In clinical practice, femoral fractures occurring during cementless total hip arthroplasty are a serious problem, and use of a cemented prosthesis is recommended if rotational stability of the stem cannot be ensured.     

The Harris-Galante porous acetabular component press-fit without screw fixation: Five-year radiographic analysis of primary cases

One hundred twenty-two primary total hip arthroplasties were followed for an average of 56 months (range, 48–66 months) in which the Harris-Galante (Zimmer, Warsaw, IN) porous ingrowth acetabular component had been press-fit into the innominate bone without screw fixation. There were no acetabular fractures. No socket was revised for loosening and none were radiographically loose. There was no evidence of disruption of the titanium porous mesh. There was no acetabular osteolysis. Compared to the authors' series of primary hip reconstructions using this same prosthesis inserted with line-to-line reaming and screw fixation, the data indicate that the tight peripheral fit associated with the press-fit technique is effective in reducing both the incidence and extent of bone-implant radiolucencies. However, the increased incidence of radiolucencies near the apex of the acetabulum also suggest that initial contact of the porous surface with live acetabular bone at this location is desirable in order to obtain and maintain an optimal bone-implant interface. Additional studies are necessary to further establish the relationship between the initial fit and long-term fixation of cementless acetabular components. Based on the data and other considerations for eliminating both vascular risk and the potential for fretting wear between the screws and shell, the authors recommend press-fitting without screw fixation for this acetabular component in primary cases when anatomy and bone stock permit. Full seating of the component is recommended in order to obtain dome contact.     

A comparative study of porous coatings in a weight-bearing total hip-arthroplasty model

The purposes of this study were to compare ingrowth of bone into three types of porous coating and to determine the effect of the type of porous coating and the degree of coverage of the stem on the remodeling of bone on the femoral side in cementless hip arthroplasty. A left total hip arthroplasty was performed in forty dogs. Thirty of the dogs had a titanium-alloy femoral prosthesis that had had one of three types of commercially pure titanium porous material applied along the length of the anterior and posterior surfaces of the stem: ten with sintered fiber-metal, ten with sintered beads, and ten with plasma flame-spray coating. The remaining ten dogs had a femoral component that was circumferentially coated with commercially pure titanium that was plasma flame-sprayed along the length of the stem. In each group, five animals were killed at one month and five were killed at six months. Ingrowth of bone into all three types of porous coating was observed, indicating secure fixation of all components. By six months, there was more ingrowth of bone and new medullary bone adjacent to the proximal and distal aspects of the stems compared with the middle level of the stems in all groups. No significant difference in ingrowth of bone was observed in the beaded surface (25.2 per cent) and the fiber-metal surface (16.6 per cent) at one month, but at six months there was significantly less ingrowth into the beaded surface (23.3 per cent) than into the fiber-metal surface (37.3 per cent). In all groups, a proximal-to-distal gradient of loss of cortical bone was observed by six months. The group of dogs that had the stem with the circumferential coating experienced more severe loss of bone than did the three groups that had a stem with a partial coating. The magnitude of loss of bone was dependent on the extent rather than the type of porous coating.     

Porous-coated uncemented components in experimental total hip arthroplasty in dogs. Effect of plasma-sprayed calcium phosphate coatings on bone ingrowth.

The effect of a thin plasma-sprayed, calcium phosphate ceramic coating on bone ingrowth into titanium fiber mesh porous-surfaced prostheses was examined in a controlled canine cementless total hip arthroplasty model. Bone ingrowth was quantified using backscattered scanning electron microscopy of undemineralized sections. When good contact between the bone and porous coating was present, the calcium phosphate-coated prostheses contained significantly higher amounts of bone ingrowth at three weeks postimplantation than the uncoated control prostheses. At six weeks, however, there was no significant difference in the amount of bone ingrowth between the coated prostheses and uncoated prostheses. The ingrown bone seemed to be more intimately associated with the calcium phosphate-coated porous surfaces than the uncoated porous surfaces. When gaps at the bone-porous coating interface occurred, the calcium phosphate coating did not enhance bone ingrowth across those gaps. Plasma-sprayed calcium phosphate coatings may be useful in enhancing the early ingrowth of bone into porous-surfaced joint replacement prostheses, but they may lack long-term effectiveness. The coatings were not effective in enhancing bone ingrowth across gaps between the porous surface and the bone bed prepared at surgery.     

Bone Remodeling Around Porous Metal Cementless Acetabular Components

Bone remodeling around cementless acetabular components after total hip arthroplasty has not been well characterized. A randomized, prospective study of total hip arthroplasty was performed comparing 2 cementless acetabular implants: a solid titanium and a more elastic porous tantalum design. Seventeen hips (9 porous tantalum, 8 titanium) underwent quantitative computed tomography at mean of 7.7 years, and adjacent bone mineral density (BMD) was calculated. The absolute and relative decrease in BMD from preoperative level was less in zones 9 to 15 mm adjacent to the porous tantalum compared to the titanium component (P ≤ .02) and predominated posterosuperiorly. The relative BMD increased in all regions adjacent to the porous tantalum component from 5% to 40% over the control. This data demonstrates stress-shielding likely occurs less around a highly porous metal implant of material with an elastic modulus similar to bone.     

Acetabular fracture associated with cementless acetabular component insertion: a report of 13 cases.

Acetabular fracture during insertion of a cementless acetabular component occurred in 13 patients. The preoperative diagnosis was osteoarthritis in 6 patients, rheumatoid arthritis in 2 patients, avascular necrosis in 3 patients, hip fracture nonunion in 1 patient, and developmental dysplasia of the hip in 1 patient. Several different components were used; however, the acetabulum was underreamed by 1 to 3 mm in all cases. The acetabular fracture was identified in 9 of 13 cases intraoperatively. The fracture was identified on postoperative radiographs for the other 4 cases. Fractures were treated by a variety of means, including the addition of augmentation screws in or around the cup, use of autograft bone at the fracture site, modified postoperative weight-bearing status, and immobilization. In 2 cases, the socket needed to be revised after it progressively migrated and failed. One patient had cup migration, and another had a radiolucent line about the cup but was not symptomatic enough to require revision. In 3 of these 4 cases, the fracture was not identified intraoperatively. Underreaming of the acetabulum and use of an oversized acetabular component has been recommended to improve the initial stability of the acetabular component during total hip arthroplasty. Impaction of an oversized component requires bone to undergo plastic deformation if the cup is to be fully seated. Theoretically, this technique provides improved component stability with enhanced osseous ingrowth into the cup. The 13 cases reported in this study demonstrate that acetabular fracture is a complication that may occur in association with uncemented hip arthroplasty, particularly if oversized components are used. The importance of recognizing acetabular fractures intraoperatively and the need to institute appropriate treatment to ensure a stable acetabular component is emphasized. In patients with osteoporotic bone, line-to-line reaming with use of a cementless acetabular component or insertion of a cemented socket may be considered to avoid this significant complication.     

Disassembly of a one-piece metal-backed acetabular component. A case report

We report a case of late dissociation of a one-piece metal-backed acetabular component, associated with a prolific soft-tissue reaction to the polyethylene debris. The polyethylene liner was not visible on the radiographs. The metal-backed shell could not be removed because of bone ingrowth. We recommend that modular systems be utilised in cementless arthroplasty of the hip and that radiographic markers be incorporated in the polyethylene of the acetabular cup.     

Polyaxial Locking and Compression Screws Improve Construct Stiffness of Acetabular Cup Fixation: A Biomechanical Study

Bone ingrowth into uncemented acetabular components requires intimate cup-bone contact and rigid fixation, which can be difficult to achieve in revision hip arthroplasty. This study compares polyaxial compression locking screws with non-locked and cancellous screw constructs for acetabular cup fixation. An acetabular cup modified with screw holes to provide both compression and angular stability was implanted into a bone substitute. Coronal lever out, axial torsion and push-out tests were performed with an Instron testing machine, measuring load versus displacement. Polyaxial locking compression screws significantly improved construct stiffness compared with non-locked or cancellous screws. This increased construct stiffness will likely reduce interfacial micromotion. Further research is required to determine whether this will improve bone ingrowth in vivo and reduce cup failure.     

Cementless femoral stems: Is there an optimum?

The use of cementless fixation in total hip arthroplasty has been associated with excellent results in several long-term follow-up studies. A majority of total hip arthroplasty performed in the United States has capitalized on this concept, utilizing both cementless acetabular and femoral components. Since the advent of cementless fixation, there has been a substantial evolution in femoral stem design. The individual stem geometry and the location of the porous coating for bone ingrowth are critical to the surgical technique for bone preparation and guide the ensuing success, complications, and even potentially the postoperative rehabilitation.     

Stabilization and prosthetic replacement in difficult fractures and bone tumors

Comminuted fractures of the femoral shaft, especially when combined with fractures of the hip, may be difficult to treat. A four-sided titanium alloy locking nail with transfixing screws was designed in 1967 and allows compression of the fracture site. If necessary, the nail may be inserted without intraoperative roentgenograms, and permits early weight-bearing in most cases. One hundred seventy-one difficult fractures in femora, humeri, tibiae, and ulnae have been treated with this nail since 1974. Many cemented total hip arthroplasties are failing. A cementless, modular titanium alloy and alumina hip, based on the nail with a modular alumina or titanium head, will allow cementless hemi- or total hip arthroplasty. Porous, 200-microns ceramic coating on the stem allows bone ingrowth while transfixing screws allow full and immediate postoperative weight-bearing. A ceramic sleeve and spacers also allow modular replacement of the upper three-quarters of the femur for tumors and trauma. A similar shoulder and humerus is also available. Fifty-four hips and two shoulders have been successfully replaced since January 1983. In addition, 285 bones with pathologic or potential pathologic fractures caused by secondary tumors have been stabilized by the author between August 1972 and August 1986, with a variety of implants.     

The optimal fixation of the cementless acetabular component in primary total hip arthroplasty.

The optimal fixation of the acetabular component in primary total hip arthroplasty remains controversial. Long-term follow-up studies show that significant loosening rates occur with cemented acetabular components and that these problems persist despite attempts to improve cementing technique. Cementless acetabular components that rely on biologic fixation can have lower rates of radiographic loosening at 10 years compared with cemented acetabular components. Although revision rates for both modes of fixation are largely equivalent at 10 years, the superior radiographic performance of cementless acetabular components at 10 years suggests that biologic fixation through bone ingrowth may provide more durable long-term implant survival compared with cemented fixation. Osteolysis is the major obstacle to long-term cementless acetabular component survival. Potential future options that may inhibit osteolysis include decreasing bone resorption that results from debris-stimulated foreign body response through the use of medications; decreasing the number of particles generated by using alternative bearing surfaces; and improving bone ingrowth, particularly through the use of growth factors and improved implant materials and designs.     

Results of total hip replacement using porous coating as a fixation mode

Successful cementless total hip arthroplasty is dependent on initial stabilization at the bone-prosthesis interface. Other factors, such as the adaptability of the prosthetic design to fit specific bony geometries, affect clinical outcome. These design considerations have been incorporated into the Mallory-Head (Biomet Inc., Warsaw, IN) prosthetic system so that it allows for immediate rigid stabilization of both the acetabular and femoral component in an effort to optimize the potential for bone ingrowth. Fifty primary cementless total hip arthroplasties, all performed by or under the direction of a codesigner of the prosthetic system, are reviewed. The average age of the patients was 53 years; the follow-up range was 24 to 52 months. The predominant preoperative diagnosis was osteoarthritis (88%). Using the Harris hip score, a noted improvement was seen in the preoperative score of 37 to a postoperative score of 94. Ninety-seven percent of the patients reported no pain or discomfort. In the Engh fixation scale, all femoral components were rated as optimum with signs of bone ingrowth. Radiographic evaluation showed no subsidence or shift of the femoral components. Five patients were noted to have acetabular migration of 4 mm to 6 mm. However, all were asymptomatic and fully functional in daily living activities. The early results of this cementless design compare favorably with those of similar series of cementless total hip arthroplasties.     

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.     

Early aseptic loosening of a modern acetabular component secondary to a change in manufacturing

Cementless acetabular reconstruction with a hemispheric acetabular shell in primary total hip arthroplasty has shown reproducible results. Ingrowth of bone into a porous coating of beads, a titanium fiber mesh, or a hydroxylapatite-containing bioactive coating has been histologically documented. Early failures of ingrowth of an acetabular component have been reported using a threaded acetabular design. A series showing high early (<1 year) failure of ingrowth into a modern acetabular component has never before been reported. We report a series showing a 33% early loosening rate of the Sulzer Interop TM acetabular component (Sulzermedica, acquired by Zimmer, Warsaw, IN).     

Acetabular Reconstruction With Chiari Pelvic Osteotomy : Report of 2 Cases

We performed cementless total hip arthroplasty combined with acetabular reconstruction with Chiari pelvic osteotomy on 3 hips in 2 patients. This procedure increased the osseous coverage of the shell and decreased the load around the hip by medialization of the hip center. Osteosynthesis of the proximal and distal bone fragment was performed using a shell with screws. Nonunion between the proximal and distal fragments was not noticed to include the case with small contact area. Postoperative dislocation had not occurred in these cases as of 1 year after surgery. This method may be an effective solution for severe dysplasia and revision surgery.