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PubMed2005

DXA scanning of acetabulum in patients with cementless total hip arthroplasty.

The aim of this study was to evaluate the reproducibility of bone mineral density (BMD) measurements of the periprosthetic bone in patients with hemispherical acetabular cups in cementless total hip arthroplasty (THA). Thirty patients were treated for primary osteoarthrosis with cementless THA. Dual-energy X-ray absorptiometry (DXA) scanning was performed with a pencil-beam bone densitometer (Norland XR-36). Accuracy and reproducibility was determined by double measurements of BMD in four regions of interest (ROI). The influence of patient postures including various pelvic inclination angles was evaluated as well. Pitman test for a combined netROI revealed a standard deviation ratio of 3.2 for the anterio-posterior scans related to the lateral position. The Wilkinson ROIs showed a high intraobserver agreement. With pelvic tilt increasing until 20 degrees , the precision of DXA scanning decreased. In conclusion, reproducibility of DXA scanning was high. This study demonstrated that the patients can be scanned in the supine position, and BMD measurement of the periacetabular bone can be performed using the Wilkinson model with four rectangular ROIs.

Absorptiometry, Photon↗
PubMed1996

[Ceramic acetabulum cup inserts for hip endoprostheses].

The articulating components of a total hip prosthesis are the spherical femoral head and the acetabular cup. Particularly high rates of wear are seen with cups made of polyethylene, and the abrasion particles cause osteolysis, which often makes surgical revision necessary. Despite considerable progress in the development of total hip replacement systems over the last 20 years, there is still a need to eliminate or further minimize the problem of osteolysis, which is also referred to as polyethylene disease. Clinical experience over the last 20 years has shown that by using Biolox (medical grade alumina) femoral heads and acetabular cups it is possible to achieve very low wear rates, which histological studies have shown to be readily tolerated. The secondary conditions needed to develop modern modular ceramic acetabular cup inserts are discussed. For the fixation of cup inserts, the well known taper fixation concept has proved to be of value. A concept taking into account the needs of the surgeon and the manufacturing constraints applying to ceramic materials is proposed.

Acetabulum↗
PubMed1997

[Effect of integrated distance studs on cement thickness of implanted PE-acetabulum cups--experimental in vitro studies for improved cementing technique].

Variations in cement thickness between PE cups and acetabular bone are biomechanically unfavourable, and may contribute to prosthetic loosening. Integrated distance studs should in the first instance, prevent local thinning of the cement. In an experimental study we compared the thickness of the cement mantel of implanted PE cups without such studs. In the case of cups with studs, significantly fewer areas of thin cement (0-1 mm) were found in comparison with cups with no studs. "Bald" areas of cement (0-0.2 mm) were virtually prevented by the studs. We are of the opinion that PE cups with integrated studs on the surface ensure a uniform cement thickness around the cup, as well as decreasing the risk of "bald" areas in the cement, thus reducing loosening.

Acetabulum↗
PubMed1999

[Primary stability of cement-free press-fit acetabulum cups. In vitro displacement studies].

The initial stability of 6 different hemispherical press-fit titanium acetabular cups was investigated by lever-out tests using a foam model. Each cup was implanted in a standardised manner into machined PVC-foam blocks with an underreaming of 1/2/3 mm, and levered out 5 times. A computer recorded the load-displacement curves. Both insertion forces and lever-out forces increased with increasing press-fit from 1 to 2 mm. With underreaming of 2 mm, insertion forces varied between 9 and 34 Nm, and lever-out torques between 13 and 23 Nm. The cup made up of multi-layer irregular titanium wire mesh had the highest initial stability of all the cups tested. 3 mm underreaming was associated with insertion difficulties, so that lever-out is difficult to compare with that with 1 and 2 mm. The amount of contact on the equatorial rim, where we saw the most attrition after lever-out, is the most important factor for determining the lever-out torque. The quality of the PVC foam blocks, the accuracy of reaming, and the definition of cup insertion are very important parameters for test reproduction. Since the trials were conducted under laboratory conditions, translation of the results to the intraoperative situation should be undertaken only with certain reservations.

Acetabulum↗
PubMed2000

[Ceramic acetabulum for hip endoprostheses. 8: Revisions].

For total hip replacement, ceramic femoral heads and acetabular liners are being used with success. However, reports of revision surgery necessitated by fractures or marked wear of ceramic components are still being published. The revision rate due to fracture is less than 0.01%, and much lower than for other complications. Nevertheless, improvement of safety remains a topic of discussion. This article reviews the results of investigations of explanted ceramic heads and liners, and discusses the problems caused by ceramic wear and chipping. Recommendations for revision surgery in such cases are given.

Acetabulum↗
PubMed2002

[Modification of form, material and modularity of threaded acetabulum cups].

The fixation principle of threaded cups ensures high primary stability. Inadequate results with first-generation threaded cups led to modifications of surface machining. 10 threaded cups of the first generation, and 27 of the second and third generations were systematically analysed and their shapes measured using a no-touch light section technique. In addition, measurements of surface roughness were performed. Implants of the first generation made of polyethylene, ceramic or cobalt-chrome have an average surface roughness (Ra) of 1.5 microns. Approximately one-half of these implants have a conical shape, and one-third a height that is greater than the radius. Threaded cups of the second generation are made either of CP-titanium or titanium alloy. The average corundum-blasted surface roughness is 4.5 microns. Hydroxyapatite-coated (HA) implants have a surface roughness of 5.0 microns. Approximately 45% of the implants have a conical, biconical or flattened-conical shape, while one-third are of hemispherical shape. Approximately 90% of the cups have a height that is up to 23% smaller than the radius. A few cups have a height that approximates the radius. Implants of the third generation with identical surface structure can be supplied with crosslinked-polyethylene inlays or, optionally, with metal/metal or ceramic/ceramic contact surfaces. Primary stability, biocompatible materials and a structured surface are essential for ensuring osseointegration over the long-term. Corundum-blasted pure titanium or titanium alloys with corundum-blasted or HA-coated implants can be considered standard for these cups.

Acetabulum↗
PubMed1994

Revision of the acetabulum without cement with use of the Harris-Galante porous-coated implant. Two to eight-year results.

Sixty revision total hip arthroplasties were performed in fifty-nine patients with use of the Harris-Galante-I porous-coated acetabular component. The patients were followed prospectively for a mean of five years (range, two to eight years). Multiple small screws were used for fixation of the component in all of the hips. Bulk allograft or cancellous bone graft was placed in forty-eight hips. The hips were evaluated clinically with use of the Harris hip-scoring system. A component was considered to be loose if there was a change in the cup angle of more than 5 degrees or vertical or horizontal migration of more than two millimeters, as demonstrated on serial radiographs. Forty-eight (80 per cent) of the sixty hips had a score of good or excellent at the time of the most recent follow-up. No component had radiographic evidence of loosening, and there were no broken screws or radio-lucent lines around the screws. Osteolysis of the pelvis was not seen in any patient. One hip was debrided because of a late metastatic deep infection, but the components were not removed. At the time of writing, no acetabular component had been revised and no revisions were pending. There were no complications related to the use of multiple small screws, even in the acetabula in which there was a severe deficiency of bone.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetabulum↗
PubMed1995

Fracture of the acetabulum during insertion of an oversized hemispherical component.

A hemispherical metal-backed acetabular component that was oversized by two or four millimeters was introduced without cement into thirty fresh or embalmed cadaveric acetabula that were fifty, fifty-two, fifty-four, fifty-six, or fifty-eight millimeters in diameter. Manual tapping was used to insert the component into ten fresh and ten embalmed specimens, and a materials testing machine was used for the remaining five fresh and five embalmed specimens. The magnitude of force and the number of pulses necessary to seat the component were determined for the insertions performed with the materials testing machine; 2000 and 3000 newtons of force were required to insert the cups that were oversized by two and four millimeters, respectively. Visual and radiographic assessments were used to identify any resulting acetabular fractures. Over-all, eighteen (60 per cent) of the thirty acetabular specimens fractured. Of the eighteen fractures, only fifteen were detectable radiographically: ten on en face or lateral radiographs of the cup and five only on oblique radiographs of the cup. The remaining three fractures were apparent only after the removal of the acetabular component.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetabulum↗
PubMed1997

Bulk structural autogenous grafts and allografts for reconstruction of the acetabulum in total hip arthroplasty. Sixteen-year-average follow-up.

Acetabular reconstruction with bulk structural autogenous grafts and allografts from the femoral head in complex total hip arthroplasty was highly successful at an average of five years postoperatively but was much less so by 11.8 years. To assess the longer-term fate of such grafts, we reviewed the results of eighty-one consecutive total hip arthroplasties performed by the senior one of us with use of these grafts. Nine hips in nine patients who had died and two hips that were infected in two patients were excluded. Therefore seventy hips (sixty-two patients) were included in this study. The average duration of follow-up was 16.5 years (range, 14.1 to 21.4 years). Sixty-one arthroplasties were performed to treat various forms of congenital dysplasia. Fifteen arthroplasties, ten of which were revision operations, were performed with allograft, and fifty-five were performed with autogenous graft. The average age of the patients at the time of the index operation was 45.2 years (range, sixteen to sixty-nine years). All of the sockets, which had an average outer diameter of forty millimeters (range, thirty-four to fifty millimeters), were inserted with cement. The average coverage of the acetabular component by the bulk graft was 49 per cent (range, 15 to 100 per cent). All of the grafts united. At the latest follow-up examination, twenty-five acetabular components (36 per cent) had been revised for aseptic loosening, eighteen (26 per cent) had radiographic evidence of loosening, and twenty-seven (39 per cent) were rigidly fixed and in place. The average Harris hip score for the hips in which the implant remained rigidly fixed was 74 points, while that for the hips in which the implant was loose but had not been revised was 69 points. Nine of the fifteen acetabular components supported by allograft and sixteen (29 per cent) of the fifty-five supported by autogenous graft were revised (p = 0.03). However, the total rate of acetabular components that were either loose or revised was ten of fifteen and thirty-three (60 per cent) of fifty-five, respectively. This difference was not significant (p = 0.4), with the numbers available. Regression analysis revealed that a younger age at the time of the operation and the extent of coverage of the acetabular component by the graft were associated with the need for revision. Twenty-one (78 per cent) of the twenty-seven acetabular components that remained rigidly fixed were supported by graft over less than 50 per cent of the contact area, while only nine (36 per cent) of the twenty-five that were revised were so supported (p < 0.05). None of the nine acetabular components with 30 per cent of the contact area or less covered by graft were revised. In nineteen of the twenty-two revisions of the acetabular component performed after the index operation, the socket was inserted without cement; the average outer diameter of the socket was fifty-three millimeters (range, forty to fifty-eight millimeters). Both the structural autogenous grafts and the structural allografts used in acetabular reconstruction in total hip replacement functioned well for the initial five to ten years. By an average of 16.5 years, nine of the fifteen hips treated with allograft and sixteen (29 per cent) of the fifty-five treated with autogenous graft had been revised. The greater the extent of the coverage of the acetabular component by the graft, the greater the rate of late failure.

Acetabulum↗
PubMed2001

Accuracy of detecting screw penetration of the acetabulum with intraoperative fluoroscopy and computed tomography.

BACKGROUND: The purpose of this study was to determine the accuracy of computed tomography and fluoroscopy in assessing joint penetration by periacetabular screws. METHODS: A 3.5-mm acetabular periarticular screw was inserted in each of thirty-nine cadaveric hemipelves. Twenty screws were intentionally directed to violate the articular surface, whereas nineteen screws were positioned to avoid the articular surface. Using two fluoroscopic views (tangential and axial) in a manner simulating the clinical setting, an examiner blinded to the actual screw location determined whether each screw was violating the articular surface. In addition, each hemipelvis was examined with computed tomography with use of two different techniques: (1) a 1-mm slice thickness at 1-mm intervals, and (2) a 4-mm slice thickness at 3-mm intervals. Each scan was evaluated by another examiner who was blinded to the actual screw location. Sensitivity, specificity, and percent correct interpretations were then calculated for each method. RESULTS: The sensitivity, specificity, and percent correct interpretations were 95%, 84%, and 90%, respectively, for axial fluoroscopy; 85%, 89%, and 87% for tangential fluoroscopy; 100%, 84%, and 92% for the computed tomography scans with a 1-mm slice thickness at 1-mm intervals; and 100%, 58%, and 79% for the computed tomography scans with a 4-mm slice thickness at 3-mm intervals. Tangential fluoroscopy was found to be more specific than the computed tomography scans with a 4-mm slice thickness at 3-mm intervals (p = 0.02). No other significant differences were found. CONCLUSIONS: Fluoroscopy and computed tomography are equally accurate for determining intra-articular screw penetration. Computed tomography scans with thick slices (4 mm at 3-mm intervals) have a low specificity. Their use postoperatively may lead to a false-positive interpretation of the scan and unnecessary exploration of a hip for screw penetration.

Acetabulum↗