Finnur Snorrason

Micromotion of femoral stems in total hip arthroplasty. A randomized study of cemented, hydroxyapatite-coated, and porous-coated stems with roentgen stereophotogrammetric analysis.

The fixation of the femoral stem in a total hip arthroplasty was studied in sixty patients (sixty-four hips) with use of roentgen stereophotogrammetric analysis. The hips were randomly stratified on the basis of the age, sex, and weight of the patient; the roentgenographic quality of the bone; and the reason for the operation (primary or secondary osteoarthrosis). The hips were then randomly assigned to one of three types of fixation of the femoral component: insertion with cement, hydroxyapatite coating, or porous coating. Examinations with roentgen stereophotogrammetry were done as long as two years after the operation. Micromotion of the prostheses was evaluated in terms of subsidence or proximal migration and rotations and translations of the proximal-lateral (shoulder) and distal (tip) parts of the prostheses. The clinical results at the two-year follow-up evaluation did not differ significantly between the groups with regard to the Harris hip score or the pain score (p > 0.05 for both; Wilcoxon rank-sum test). There were small or no differences in rotations and micromotions of the shoulder and the tip of the prostheses. Increased subsidence of 0.1 to 0.2 millimeter was recorded for the cemented and the porous-coated prostheses (p = 0.002 and p = 0.02, respectively; Wilcoxon rank-sum test). Thus, proximal hydroxyapatite coating seems to enhance the early fixation of the stem. Conventional roentgenography revealed an increased number of radiodense lines surrounding the porous-coated prostheses. Distal hypertrophy of the femoral cortex was found mainly around the hydroxyapatite-coated prostheses. Proximal resorption of bone and heterotopic ossification occurred to approximately the same extent regardless of the type of fixation used.

Evaluation of a femoral stem with reduced stiffness. A randomized study with use of radiostereometry and bone densitometry.

Background: Femoral stems with reduced stiffness were introduced in total hip arthroplasty to facilitate proximal load transfer and thereby reduce periprosthetic bone loss. Poor fixation and unacceptably high revision rates turned out to be a major problem with these prostheses. The purpose of the present study was to evaluate the early performance of a low-modulus stem (one that is less stiff) with the potential to address the problem of fixation by the use of a surface coating. The coating consisted of a titanium porous mesh proximally covered with a mixture of hydroxyapatite and tricalcium phosphate.Methods: Thirty-nine men and twenty-six women (sixty-eight hips) with noninflammatory arthritis were studied. The patients were randomized to receive either a porous-coated composite stem with reduced stiffness (Epoch) or a stiff stem with a porous coating (Anatomic). Both stems were inserted without cement, had a ceramic coating on the proximal two-thirds, and were supplied with tantalum beads. At the time of the operation, tantalum markers were also placed into the proximal part of the femur. The patients were followed for up to two years after the operation and were evaluated with use of repeated radiostereometric measurements, measurements of bone-mineral density, conventional radiography, and Harris hip scores.Results: Both stems showed optimum fixation with median subsidence and stem rotations that were close to zero. Repeated measurements of bone-mineral density revealed early loss of bone mineral in all Gruen regions in both treatment groups. The loss of bone mineral around the Epoch stems was significantly reduced at two years in Gruen regions 1, 2, 6, and 7 (p < 0.0005 to 0.04). Measurements on postoperative radiographs showed no difference in stem positioning or fill, but the Epoch stems had significantly more endocortical contact on both the anteroposterior (p < 0.0005) and the lateral radiograph (p = 0.02).At two years postoperatively, the Epoch stems had fewer sclerotic lines surrounding the stem (p £ 0.002) and less sclerosis at the tip of the prosthesis (p = 0.001) compared with the Anatomic stems. The clinical results in terms of the Harris hip score, which was determined in all hips, and pain or discomfort, which was evaluated in thirty-seven hips treated at the same hospital, were not found to be different, with the numbers available.Conclusions: Contrary to previous studies of other designs with reduced stiffness, the Epoch stem achieved excellent primary fixation. Despite this rigid fixation, the proximal loss of bone-mineral density was less than that associated with the stem with a stiffer design. These results should encourage additional long-term studies with a larger patient population.

Early loosening of revision hip arthroplasty. A roentgen stereophotogrammetric analysis.

The primary migration of 15 and 22 cemented acetabular and femoral prosthetic components was recorded in 23 patients operated because of type 1 (minimal endosteal bone loss) and type II (thinning of bone, enlargement of femoral canal and acetabulum) mechanical loosening. Roentgen stereophotogrammetric analysis was used to measure the three-dimensional displacements of the center of the acetabulum and the femoral head. All but 1 of the acetabular and 1 of 15 revised femoral stem prostheses migrated within 2 years after the operation, whereas 5 of 7 revised femoral surface arthroplasties were stable. Femoral components with type II loosening migrated, on average, 1.5 mm (range, 0.6–3.0 mm) during the first postoperative year, compared with 0.7 mm (range, 0.3–1.1 mm) in patients with type I loosening (P < .02). Increased bone loss of the acetabulum (type II), the quality of the bone-cement interface as judged from radiographs, and the presence of perforation of the femoral cortex did not significantly influence the rate of migration in this group. Compared with previously presented studies of cemented primary hip prostheses, cemented revisions seem not only to migrate more frequently but also at a higher rate. Poor primary fixation is probably one important cause of the high frequency of clinical failures in these patients.

Porous-coated cups fixed with screws. : A 12-year clinical and radiostereometric follow-up study of 50 hips.

Background Excellent mid-term results have stimulated the use of hemispherical porous-coated cups in hip replacement. With longer follow-up, there have been problems related to polyethylene wear and liner fixation, and osteolysis has been documented in reports of selected cases. We evaluated the clinical and radiographic results of 50 patients followed for 12 years. Patients and methods 58 consecutive patients (58 hips), mean age 55 years, were operated with Harris-Galante (HG) I or II cups using line-to-line fit and additional screw fixation. Polyethylene linersγ-sterilized in air and 32-mm ceramic heads were used. 8 patients died within 12 years, leaving 50 patients with a complete 12year follow-up. 23 of the cups were also evaluated with radiostereometry (RSA) for migration, liner stability, and wear. Results All metal shells were still in situ after 12 years. 4 hips had been revised due to femoral loosening. In these revisions, the liner had been exchanged due to wear and/or instability, resulting in a cup survival rate of 89%. 28 cups displayed osteolytic lesions, mainly in relation to screws. RSA revealed minimum translations, but in many cases there were pronounced liner rotations suggesting unstable liners within the metal shell. The annual proximal wear was 0.09 mm and the three-dimensional wear was 0.16 mm. Interpretation RSA can predict the long-term performance of cup fixation. Low migration during the initial years after implantation indicates excellent long-term results regarding fixation of the metal shell. The main problem with this design appears to be liner instability and osteolysis, factors that are probably interrelated. Because these phenomena are clinically silent, we recommend regular follow-up of patients with HG cups to avoid sudden loosening and complicated revisions.

Fixation and metal release from the Tifit femoral stem prosthesis. 5-year follow-up of 64 cases.

We stratified the fixation of the femoral component in 64 hips with degenerative joint disease into 3 groups, cemented (C), proximal hydroxyapatite coating (HA) or proximal porous coating (P). All implants had the same basic design and were made of TiAIV alloy. The migration of the implants was assessed by radiostereometry. After 5 years, the mean subsidences in the cemented and porous-coated groups were 0.16 and 0.31 mm, whereas the HA-coated implants displayed a mean proximal migration of 0.1 mm. 7 stems (2 C, 1 HA, 4 P) showed a continuous subsidence (> 0.25 mm) between the 2- and 5-year follow-up. 1 porous-coated stem was revised after the 2-year follow-up, because of pain and implant failure (previously reported) and 1 cemented stem was revised after 5 years because of pain and osteolysis. In a subset of patients, all with a femoral head made of aluminum oxide, the levels of metal were determined using atomic adsorption spectrometry. Subsidence of the stem between the 2- and 5-year follow-up was associated with increased levels of aluminum in the blood at 2 years. Generation of metallic particles from abrasive wear of the stem followed by third body abrasion of the ceramic femoral head could be one explanation of this finding. 5 hips which had shown high levels of titanium and aluminum in joint fluid at the 2-year follow-up displayed increased subsidence and developed proximal radiolucencies or osteolysis at the 5-year follow up. One of these was the cemented hip which was subsequently revised.

Migration of porous press-fit cups in hip revision arthroplasty: A Radiostereometric 2-Year Follow-up Study of 60 Hips

The migration of 60 press-fit cups fixed with screws was evaluated by radiostereometric analysis for 2 years in 57 patients revised because of aseptic loosening. The mean proximal migration of the cup center increased continuously up to 0.36 mm (range, 0.0-1.6 mm), whereas the migration in the other directions reached a level at 0.3 to 0.4 mm after 6 months. Mean rotations of less than 1 degree were recorded. Factors influencing motions were cup size, use of bone-grafts, and position of the cup center in the vertical and horizontal directions. Compared with previous stereoradiographic studies of cemented revisions, the migration of the press-fit cup was smaller, however, still higher than previously reported for uncemented cups of the same design used in primary surgery.

Increased metal release from cemented femoral components made of titanium alloy. 19 hip prostheses followed with radiostereometry (RSA)

In 19 patients the concentrations of metal were measured in serum, urine and joint fluid 2 years after implantation of uncemented commercially pure titanium acetabular cups and cemented or uncemented femoral components made of titanium alloy. A ceramic against the polyethylene articulation was used. The fixation of the components was followed with radiostereometry (RSA). Samples from 12 patients scheduled for hip or knee prostheses and without any metallic implant were used as controls. High levels of titanium were found in cemented hips and when large acetabular cups had been inserted. Increased aluminum levels were also noted in the cemented hips. Vanadium was not detected in any of the samples. Micromotions were detected in most of the implants, but the magnitude of these movements could not be used to predict the release of metal into the synovial fluid.

Fixation of cemented acetabular prostheses: The influence of preoperative diagnosis

Abstract The authors evaluated the fixation of cemented acetabular prostheses in patients with osteoarthritis (20 hips), rheumatoid arthritis (15 hips), and sequelae after fracture of the femoral neck (13 hips) using roentgen stereophotogrammetric analysis. The three-dimensional displacements of the cups were measured during the first 2 postoperative years, and radiographs were examined to assess bone quality, containment, inclination, and area of cement surrounding the cups. There was a greater proportion of migrating cups in patients with rheumatoid arthritis and fracture of the femoral neck compared with osteoarthritis. Patients with poor bone quality according to the modified Engh index, small cement area surrounding the cups, and cups with small inclination displayed increased frequency of migration