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.     

Acetabular micromotion as a measure of initial implant stability in primary hip arthroplasty. An in vitro comparison of different methods of initial acetabular component fixation.

Micromotion has been shown to affect bony ingrowth into cementless components. This study was designed both to quantitate initial micromotion at the prosthesis-periacetabular bony interface and to compare different methods of commonly employed acetabular component fixations, ie, a press-fit hemispherical titanium cup, a press-fit hemispherical titanium cup with one and two dome screws, a press-fit titanium hemispherical cup with three spikes, and a cemented chromium-cobalt cup. The press-fit component without screws demonstrated the greatest motion equaling 162 microns at the ilium, 97 microns at the publis, and 54 microns at the ischium. With one and two screws placed into the dome, the mean ileal displacement decreased by 28 microns (17%) and 36 microns (22%), respectively. Dome screw placement demonstrated a minimal effect at the pubis and ischium. Compared to the press-fit component without augmentation, the tri-spike motion was less at the pubis and ischium. The cemented prosthesis provided the least amount of motion in all three areas tested. This experiment demonstrates that the ilium provides the least amount of support to immediate acetabular fixation, while the pubis (anterior column) and ischium (posterior column) provide more stability. One dome screw does not affect the stability of a hemispherical prosthetic cup significantly. A two dome screw fixation provides an added method of support at the ilium, but fails to decrease motion at the pubis or ischium significantly. The tri-spike fixation does not restrict motion at the ilium to the extent as the dome screws, but its effect at the ischium and pubis is much more pronounced. The obvious difference between initial motion seen with cemented versus uncemented components may suggest that before surgery, patients may need a period of protected weight bearing until ingrowth has occurred.     

Acetabular micromotion as a measure of initial implant stability in primary hip arthroplasty: An in vitro comparison of different methods of intial acetabular component fixation

Micromotion has been shown to affect bony ingrowth into cementless components. This study was designed both to quantitate initial micromotion at the prosthesis-periacetabular bony interface and to compare different methods of commonly employed acetabular component fixations, ie, a press-fit hemispherical titanium cup, a press-fit hemispherical titanium cup with one and two dome screws, a press-fit titanium hemispherical cup with three spikes, and a cemented chromium-cobalt cup. The press-fit component without screws demonstrated the greatest motion equaling 162 μm at the ilium, 97 μm at the pubis, and 54 μm at the ischium. With one and two screws placed into the dome, the mean ileal displacement decreased by 28 μm (17%) and 36 μm (22%), respectively. Dome screw placement demonstrated a minimal effect at the pubis and ischium. Compared to the press-fit component without augmentation, the tri-spike motion was less at the pubis and ischium. The cemented prosthesis provided the least amount of motion in all three areas tested. This experiment demonstrates that the ilium provides the least amount of support to immediate acetabular fixation, while the pubis (anterior column) and ischium (posterior column) provide more stability. One dome screw does not afect the stability of a hemispherical prosthetic cup significantly. A two dome screw fixation provides an added method of support at the ilium, but fails to decrease motion at the pubis or ischium significantly. The tri-spike fixation does not restrict motion at the ilium to the extent as the dome screws, but its effect at the ischium and pubis is much more pronounced. The obvious difference between initial motion seen with cemented versus uncemented components may suggest that before surgery, patients may need a period of protected weight bearing until ingrowth has occurred.     

Osseointegration of titanium implants in total hip arthroplasty

Osseointegration is defined as direct contact on the light microscopic level between living bone tissue and the implant. Using titanium screw dental implants in the jaw, a lasting interface under loaded conditions extending over a 20-year follow-up period has been demonstrated. This demonstration brings up the question whether a similar interface can be achieved in total hip arthroplasty (THA) between living bone and a titanium alloy implant under necessitated conditions of immediate loading. Two series of cases are reported. The first series used a femoral, press-fit, titanium alloy component and the second used a press-fit titanium acetabular component and redesigned femoral, press-fit, titanium alloy component. Both demonstrated a high percentage of good to excellent results. Roentgenograms showed that the geometrical changes in the redesigned femoral component gave early indications of a better fixation with loading in valgus, less subsidence, and less evidence of distal stress transfer. A two-and-one-half-year postoperative anatomic specimen study confirmed osseointegration to the press-fit titanium alloy femoral component. Multiple areas of contact between bone and metal without fibrous interposition were seen. Examination by electron microscopy supported the light microscopic findings. These findings support further use of smooth, press-fit titanium components in THAs without the need for porous coating, mesh, or other surface modifications.     

Intermediate clinical follow-up of a dual-radius acetabular component

In this study, 92 primary total hip arthroplasties were performed in 83 patients using a porous-coated, dual-radius, cementless, acetabular component. All hips underwent line-to-line dome reaming with press-fit implantation that was judged to have complete bone contact. This acetabular shell provides a 1-mm oversized peripheral rim, which adds excellent initial stability while allowing complete bone contact in all hips. No fractures occurred. In 83% of hips, adjunctive screw fixation was not necessary. At a minimum of 4 years, follow-up, there were no revisions, no acetabular migration, one case of acetabular erosion consistent with osteolysis, and the average Harris Hip Score was 95. The design features of this new acetabular component have provided excellent fixation with complete initial bone contact, resulting in satisfactory intermediate clinical and radiographic results. The design provides excellent peripheral stability and complete bone contact.     

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

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

Porous surface replacement of the hip with chamfered-cylinder component

One hundred porous surface replacements (PSR) were performed in 92 patients (63 men and 29 women) with a mean age of 53 (range 17-76). Follow-up times range from 1 to 4 years, with 48 patients having a follow-up of at least 2 years. Preoperative diagnoses were osteoarthritis (OA) 63, osteonecrosis (ON) 13, dysplasia 9, rheumatoid-ankylosing spondylitis 6, and other 9. Seventeen hips had metal-backed acrylic-fixed THARIES acetabular sockets, nine hips had a porous cobalt chrome hemispheric beaded acetabular component with adjuvant fixation screws and externally protruding screw hubs, and 74 hips had a porous chamfered cylinder-design acetabulum. Pain relief had been immediate and more complete than with acrylic-fixed or biologic-ingrowth stem-type replacement with comparable walking and function improvements. There have been no major systemic complications, sepsis, or loosening. There have been two transient peroneal nerve palsies and three trochanteric fibrous unions. There have been three reoperations, one for subluxation, one for "metalosis" due to mesh pad loosening, and one femoral neck fracture. Examination of one removed femoral surface component which has been histologically sectioned revealed excellent (90%) bone in-growth. Circumferential progressive radiolucencies developed at the bone-cement interface by 1 year in all of the 17 acrylic-fixed acetabular components. Reaming or seating defects were noted in 25% of the ingrowth components on postoperative radiographs. Radiographic analysis of immediate postoperative films of the chamfered cylinder design acetabular components frequently demonstrated bone-component interface radiolucencies which represented component seating defects. These initial interface radiolucencies became progressively more narrow over the first six months postoperatively suggesting "healing" of the reamed bone-component interface with trabecular bone around the chamfered cylinder acetabular components. Partial healing of initial interface voids with residual narrow radiolucencies were typical of the nine hemispheric-design acetabula with adjuvant screws and screw hubs. This new porous surface replacement (PSR) of the hip using porous ingrowth fixation avoids the major disadvantages of acrylic-fixed SR: excessive acetabular reaming and difficulty with acetabular revision. (When conversion to stem-type replacement is necessary the modular polyethylene socket liner can be exchanged.) The PSR has the prospect of enhanced fixation and improved longterm durability.     

Does Ischial Screw Fixation Improve Mechanical Stability in Revision Total Hip Arthroplasty?

Ischial screw fixation, albeit technically challenging, is postulated to provide additional mechanical stability in revision total hip arthroplasty (THA). Hemipelvis specimens were prepared to simulate revision THA, and an acetabular component with supplemental screw fixation was implanted. Three configurations were tested: 2 dome screws alone, 2 dome screws plus an additional screw within the dome, and 2 dome screws plus an ischial screw. Force displacement data were acquired during mechanical testing. An increase in mechanical stability was observed in acetabular components with supplemental screw fixation into either the posterior column or ischium (P ≤ .031) compared to isolated dome fixation. In addition, supplemental ischial screw fixation may provide a modest advantage over a screw placed posteroinferiorly within the acetabular dome during revision THA.     

Development and first experience with an uncemented press-fit cup

A new cup with a new concept of cementless fixation and new coating was designed to obtain primary stability by a press-fit mechanism. The press-fit mechanism is achieved by flattening the dome of the hemispheric cup and by using a cup size with an outer diameter 1.5 mm larger than the reamer used last. The coating (Sulmesh) consists of a net shell of four layers of orderly oriented wire meshes with specific pore size and porosity volume. The pure titanium wires are bonded together. The advantages of the press-fit cup are the excellent adaptation with minimal resection and the preservation of the subchondral bone. The preparation of the acetabulum is easy (reaming only), no additional fixation by screws is necessary, and only a few instruments are needed. The results of 81 total hip arthoplasties using the press-fit cup and having an observation period ranging from 12 to 24 months show no clinical or roentgenographic loosening. No intraoperative or postoperative complications because of the press-fit cup were seen.     

Effects of screw eccentricity on the initial stability of the acetabular cup

One of the major failure modes of cementless acetabular components is the loosening of the acetabular cup, which is mostly attributable to insufficient initial stability. A hemispherical cup with a porous coating which is inserted with press-fit fixation and secured with several screws is one of the most widely used approaches. Many studies have found that bone screws are very helpful aids for cup fixation, but the optimal surgical technique for inserting screws has not been clearly reported. In this study, hemispherical cups were fixed into blocks of foam bone with zero to three screws. The effects of three types of screw eccentricity (a 1-mm offset and angular eccentricities of 15 degrees and 25 degrees ) on the initial stability of the acetabular cup were evaluated. The experimental results indicate that increasing the number of screws enhances the cup stability in the case of ideal screwing (i.e., with no eccentricity). An angular eccentricity of 15 degrees did not affect the cup stability for fixation with one or two screws. However, the presence of 25 degrees of angular eccentricity significantly reduced the stability of the cup, while 1 mm of offset eccentricity produced an even greater impact.     

Cementless porous-coated sockets without holes implanted with pure press-fit technique

We evaluated the use of a pure press-fit technique in 220 porous-coated acetabular components without screw holes at mean follow-up of 6.1 years (4-7.5 years). The socket had a 14 degrees enhanced gradient at the periphery and was underreamed by 1 to 2 mm depending on bone quality. The Harris Hip average score was 44.3 (26-70) preoperatively and 93.1 (66-100) at final follow-up. There were no postoperative gaps in any zone. Nonprogressive radiolucent lines were detected in 4 hips. There was no movement or migration of the acetabular component on the follow-up x-rays. Pelvic osteolysis was not observed. Whereas 5 cups (2.3%) had revisions, none was revised for aseptic loosening. The press-fit technique provides stability in appropriate cases avoiding the theoretical complications related to screws or screw holes.     

Noncemented acetabular revision arthroplasty using allograft bone

The authors retrospectively reviewed a series of 106 acetabular revisions for failed cemented total hip arthroplasties followed from 12 to 56 months. All of the sockets had extensive bone deficiency requiring bone graft surgery. The deficiencies were classified as cavitary, combined cavitary and segmental, and pelvic discontinuity. The purpose was to evaluate clinical experience with three different acetabular components. In chronological order, the three components tested were bipolar type, truncated-cone screw-in type, and porous-coated titanium press-fit type with fins. These were combined with four different bone augmentation constructs, using nonstructural morselized fresh-frozen allograft or segmental freeze-dried allograft. Follow-up evaluation of both the bipolar and screw-in designs showed frequent migration with bone graft resorption, compromising the clinical scores and leading to some revisions. The press-fit design had little migration, reliable graft healing, and better clinical scores. No revisions have been done. The nonstructural morselized bone allograft fared better under stable cups. The large segmental grafts did much better when buttress plating was combined with interfragmentary screw fixation compared to screws alone.     

Effect of cementless acetabular cup geometry on strain distribution and press-fit stability

Use of cementless acetabular cups, which are slightly larger than the reamed acetabulum, can provide press-fit stability without screws; however, the ideal cup geometry to maximize stability is not clear. Acetabular strain distribution, deformation, and implant stability were studied using an axisymmetric finite-element model, and mechanical stability was assessed by testing lever-out and extraction forces required to displace different cup geometries from foam bones. The implants tested included four nonhemispheric cup geometries and 1- and 2-mm oversized hemispheric geometries. A nonhemispheric cup that provides a gradual transition from a hemisphere at the dome to a larger peripheral dimension appears to maximize peripheral strains and implant stability without increasing overall acetabular deformation as much as a larger oversized hemispheric cup.     

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.     

First implant acetabular components: historical aspects, a comparison of models and a review of the literature

The article describes the features of the most commonly-used acetabular components in first implants in light of development in construction as regards intrinsic features, materials used, biological behavior, and design. The following versions are examined: screwable cone-shaped trunk, cemented polyethylene, cemented metal-back, HA-coated press-fit, expansion, dysplastic hip, and anti-dislocating components. The screwable cone-shaped trunk acetabular component takes hold in the acetabular bone through torsion and compression, and threading provides greater stability as compared to equivalent models that have wings or screws. Cemented polyethylene acetabular components are characterized by low costs and good results, on the condition that some specific parameters are respected (the presence of a dry bone bed, pressurization of the cement, use in elderly patients who do very little physical activity). Cemented metal-back acetabular components have features similar to polyethylene components, from which they differ because of the possibility of being able to substitute the internal polyethylene component without having to revision the entire acetabulum. HA-coated press-fit components have solved the problems encountered in cemented versions, such as loosening and the generation of polyethylene particulate, at the same time obtaining excellent osteo-integration. The expansion cup self-stabilizes thanks to a memory effect due to the contraction-relaxation mechanism with which it is lodged, adapting to the micro-movements of the acetabulum. Components used in the dysplastic hip are particular versions with a reduced diameter that have specific hooks that provide stabilization, capable of settling in the pathologic bone with minimum reaming of the same. Anti-dislocation cups are special models that have bipolar inserts or a ring (plastic or metal) that blocks the head in the prosthetic acetabulum, obstructing its dislocation.     

Fat embolism associated with cementing of femoral stems designed for press-fit application

The authors report four cases of fat embolism syndrome following total hip arthroplasty using cementless acetabular press-fit components and cemented press-fit femoral components. Factors implicated in the production of this syndrome following "hybrid" total hip arthroplasty include increased canal pressure during femoral reaming and prosthetic insertion, retained marrow elements and reaming debris, and the use of lumbar epidural anesthesia. This potentially fatal syndrome must be a recognized complication following the use of cemented press-fit femoral stems. Specific recommendations for decreasing the incidence of this complication are reviewed.     

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.     

Porous surface replacement of the hip with chamfered-cylinder component

Summary One hundred porous surface replacements (PSR) were performed in 92 patients (63 men and 29 women) with a mean age of 53 (range 17–76). Follow-up times range from 1 to 4 years, with 48 patients having a follow-up of at least 2 years. Preoperative diagnoses were osteoarthritis (OA) 63, osteonecrosis (ON) 13, dysplasia 9, rheumatoid-ankylosing spondylitis 6, and other 9. Seventeen hips had metalbacked acrylic-fixed THARIES acetabular sockets, nine hips had a porous cobalt chrome hemispheric beaded acetabular component with adjuvant fixation screws and externally protruding screw hubs, and 74 hips had a porous chamfered cylinder-design acetabulum. Pain relief has been immediate and more complete than with acrylic-fixed or biologic-ingrowth stem-type replacement with comparable walking and function improvements. There have been no major systemic complications, sepsis, or loosening. There have been two transient peroneal nerve palsies and three trochanteric fibrous unions. There have been three reoperations, one for subluxation, one for metalosis due to mesh pad loosening, and one femoral neck fracture. Examination of one removed femoral surface component which has been histologically sectioned revealed excellent (90%) bone ingrowth. Circumferential progressive radiolucencies developed at the bone-cement interface by 1 year in all of the 17 acrylic-fixed acetabular components. Reaming or seating defects were noted in 25% of the ingrowth components on postoperative radiographs. Radiographic analysis of immediate postoperative films of the chamfered cylinder design acetabular components frequently demonstrated bone-component interface radiolucencies which represented component seeting defects. These initial interface radiolucencies became progressively more narrow over the first six months postoperatively suggesting healing of the reamed bone-component interface with trabecular bone around the chamfered cylinder acteabular components. Partial healing of initial interface voids with residual narrow radiolucencies were typical of the nine hemispheric-design acetabula with adjuvant screws and screw hubs. This new porous surface replacement (PSR) of the hip using porous ingrowth fixation avids the major disadvantages of acrylicfixed SR: excessive acetabular reaming and difficulty with acetabular revision. (When conversion to stem-type replacement is necessary the modular polyethylene socket liner can be exchanged.) THe PSR has the prospect of enhanced fixation and imporved longterm durability.     

The Harris-Galante Porous acetabular component at intermediate follow-up

Outcome of the acetabular component in 90 consecutive primary noncemented total hip arthroplasties (THAs) was prospectively studied. The acetabular cup consisted of a hemispherical titanium alloy shell with a titanium fiber-mesh porous coating and a modular polyethylene liner (Harris-Galante Porous-1, Zimmer, Warsaw, Ind). The cup was implanted using line-to-line reaming with adjunctive dome screw fixation. The femoral component consisted of a titanium alloy stem with titanium fiber-mesh porous coating and a 28-mm cobalt-chrome modular head. Mean patient age was 53 years (range: 27-75 years); male:female ratio was 48:42; and mean follow-up was 6 years (range: 4.5-8 years). One acetabular component was revised for aseptic loosening. Of 81 unrevised hips available for follow-up, mean Harris hip score was 57 preoperatively and 96 at final follow-up (72% excellent, 15% good, 1 3% fair, and none poor). Of 61 unrevised hips with adequate radiographic follow-up, radiographic failure (complete periprosthetic radiolucency) was evident in 3 (4.9%) and periacetabular osteolysis in none. Radiographic failure did not correlate with poor clinical outcome. Linear polyethylene wear rate (mean: 0.13 mm/year) did not correlate with age, gender, weight, outcome, or cup abduction angle, but did correlate with the presence of femoral periprosthetic osteolysis (0.18 mm/year with femoral osteolysis versus 0.11 mm/year without; P= .01). This series of porous-coated hemispherical cups demonstrated excellent intermediate-term clinical and radiographic outcome, comparable with similarly favorable results reported by the prosthesis designers. A potentially adverse effect of polyethylene wear on the longevity of a THA was supported by a positive correlation between polyethylene wear rate and femoral osteolysis.     

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.