Radiostereometric analysis of hemiarthroplasties of the hip--a highly precise method for measurements of cartilage wear.

OBJECTIVE: Cartilage wear is a feature of osteoarthritis and rheumatoid arthritis. Precise measurements of wear have been difficult. Cartilage wear caused by an artificial articulating joint surface is a well-known feature of hemiarthroplasties. The aim of this study was to demonstrate that radiostereometric analysis (RSA) may be used for three-dimensional measurements of cartilage wear in hemiarthroplasties of the hip. METHOD: We performed a phantom model study to assess the feasibility of a subsequent clinical trial. We showed that the motion of the prosthetic head relative to the pelvis was not influenced by the orientation of the prosthetic head. Twenty-two patients were randomised to treatment with a cemented or an uncemented hemiarthroplasty for an acute femoral neck fracture. Migration of the prosthetic head into the acetabulum was measured using RSA. RESULTS: A mean migration of the prosthetic head into the acetabulum of 0.62 mm was found at 3 months [95% confidence interval (CI): 0.27-0.97] and a further migration of -0.07 mm at 12 months (95% CI: -0.16-0.32). There were no differences between the groups in prosthetic migration or functional outcome. Between three and 12 months, there was no detectable cartilage wear during the first postoperative year. CONCLUSION: Whether the migration during the first 3 months represents a period of bedding in due to a harder opposite surface remains to be shown. RSA may be used for measurement of cartilage wear in hemiarthroplasties of the hip. This study demonstrates a highly precise method for measurements of cartilage wear.

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.

Does early micromotion of femoral stem prostheses matter? 4-7-year stereoradiographic follow-up of 84 cemented prostheses.

Roentgen stereophotogrammetry was used to measure the migration of the centre of the femoral head in 84 cemented Lubinus SP I hip arthroplasties (58 primary operations, 26 revisions). Four to seven years later, seven femoral components had been revised because of painful loosening. These implants showed greater subsidence, medial migration and posterior migration during the first two postoperative years than did the hips which had not been revised. Six months after operation, subsidence of more than 0.33 mm combined with a total migration of more than 0.85 mm predicted an increased risk of subsequent revision; the amount of subsidence at two years was an even better predictor. The probability of revision was greater than 50% if the subsidence at two years was 1.2 mm or more.

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.

Fixation of cemented acetabular prostheses. The influence of preoperative diagnosis.

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.

Subsidence, tip, and hump micromovements of noncoated ribbed femoral prostheses.

The micromovements of 18 ribbed femoral prostheses were measured for two years postoperatively. Repeated roentgen stereophotogrammetric examinations (RSA) were used to measure distal migration of the center of the prostheses and movements of the prosthetic hump and tip. During the first six postoperative months, an increasing number of prostheses migrated significantly. Migration was first observed at the tip. Two years after the operation, one prosthesis had been revised because of pain. Thirteen of 17 remaining prostheses had subsided, 12 displayed hump and 16 tip migration, and eight had rotated about the longitudinal axis of the femur. In these hips, the instant center of rotation ran obliquely through the greater trochanter or the isthmus of the femur. Clinical follow-up examination and measurements on conventional roentgenograms disclosed a correlation between pain, the extent of sclerosis surrounding the prostheses, and the distal migration according to RSA measurements.

Migration of porous coated acetabular prostheses fixed with screws: roentgen stereophotogrammetric analysis.

The fixation of screw-fixed, porous-coated acetabular prostheses was studied during 2 years in 21 patients (22 hips) using repeated roentgen stereophotogrammetric measurements. Migration of the center of the prostheses and/or tilting were recorded in five cups after 6 months. Two years after operation, migration was recorded in three, migration and rotation in six, and only rotation in three cups. Bone quality, prosthetic position, and immediate postoperative radiographic appearance of the prosthesis-bone interface did not correlate with the occurrence of migration. Narrow radiolucent zones had developed in half of the patients after 2 years and was associated with proximal migration. Micromovements of screw-fixed, press-fit cups seem to start later compared with previously presented results from cemented acetabular prosthesis.

Osteolysis after ceramic-on-ceramic hip arthroplasty. A case report.

A patient with rheumatoid arthritis operated on with insertion of an uncemented ceramic-on-ceramic Mittelmeier total hip developed an extensive, rapidly evolving osteolysis around the prosthetic stem, which in turn fractured spontaneously after 5 years. Aggressive bone resorption cannot be prevented by exclusion of polyethylene and bone cement from hip arthroplasty.

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 I (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 less than .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.

Primary migration of fully-threaded acetabular prostheses. A roentgen stereophotogrammetric analysis.

We investigated the fixation of fully-threaded cementless acetabular prostheses in 20 patients with osteoarthritis, measuring the migration of the cup using roentgen stereophotogrammetric analysis (RSA). All the cups migrated proximally, 13 moved laterally or medially, and nine moved anteriorly or posteriorly in the first two postoperative years, the average migration being 1.1 to 1.4 mm in either direction. Rotatory movements of up to 5.7 degrees were found in nine of the 13 hips where this analysis could be performed. Movements of cobalt-chrome (12) and titanium alloy (8) cups did not differ significantly. Seventeen of the 20 patients had some pain two years after the operation. The migration of the prostheses indicates that 'osseointegration' had not occurred. The combination of this with persistent pain suggests that the long-term results will be unfavourable.

Poor fixation of the Mittelmeier hip prosthesis. A clinical, radiographic, and scintimetric evaluation.

We have evaluated 30 Mittelmeier hips on an average 3.3 years after the operation. Seven hips had been revised because of severe pain and mechanical loosening and one because of fracture of the threaded ceramic cup. Only five of the remaining 22 hips were asymptomatic. There was radiographic migration of the acetabular and femoral components in more than one third of the hips and increased scintimetric values around the femoral component in all but two hips. Unfavorable design of the Mittelmeier prosthesis may be an important etiologic factor contributing to poor component fixation and inferior clinical results.