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PubMed1986

Micromotion in knee arthroplasty. A roentgen stereophotogrammetric analysis of tibial component fixation.

The modern era of endoprosthetic joint replacement started with the introduction of acrylic cement to improve component fixation. Long-term results have, however, indicated that prosthetic fixation remains critical; loosening at the bone-cement interface has become an important problem. Research in recent years has focused on attempts to achieve better fixation by improving cementing techniques, improving prosthetic design by, for example, adding metal support of polyethylene components and by exploring alternative ways to bond prosthetic components to bone without cement. The mechanical integrity of the bone-cement interface has been studied under laboratory conditions. Because of the in-vivo reaction of bone, with the interposition of a fibrous tissue layer at the interface, such studies are not totally valid. Studies on autopsy material, more closely resembling the in-vivo situation, are few and there has been only one previous study like the present one. In this study, roentgen stereophotogrammetric analysis (RSA) was evaluated and found to have an accuracy ten times better than conventional radiography. This accuracy was judged adequate for studies of micromotion. In this work, two types of micromotion of the tibial component were studied; migration, i.e. gradual motion over time, and inducible displacement, i.e. instant motion in response to external forces. Ninety-six knee arthroplasties for gonarthrosis, representing four different types of fixation were studied by roentgen stereophotogrammetric analysis (RSA). Eighty-nine arthroplasties were clinically successful. The follow-up ranged from two to five years. Full post-operative weight-bearing was allowed for all patients, except those operated with a Freeman-Samuelson prosthesis, who were adviced to use crutches for six weeks and partial weight-bearing for another six weeks. Fifty-one conventionally cemented all-polyethylene prostheses, 27 total and 24 unicompartmental, represented a baseline series. Migration was found for all prostheses, with a mean maximum deflection of 1.2 and 0.9 mm, respectively, after four years. In both groups, the major part of the migration occurred during the first year, after which the majority of the components did not migrate further. Some prostheses, with larger migration during the first year, continued to migrate throughout the investigation. None of the total, but the majority of the unicompartmental prostheses showed signs of cold flow within the polyethylene. All prostheses showed reversible inducible displacement, the maximum deflection ranging from 0.2 to 1.0 mm.(ABSTRACT TRUNCATED AT 400 WORDS)

Aged↗
PubMed1986

Loosening of the cemented hip prosthesis. The importance of heat injury.

The cemented hip arthroplasty is one of the most successful orthopedic operations. However, the results do deteriorate with time because of mechanical loosening. Some hips with obviously loose prosthetic components are not painful. This discrepancy between symptoms and radiographic evidence of loosening has caused uncertainty about the diagnostic criteria that should be applied. This uncertainty has in turn led to confusion about the basic cause of loosening. The aims of this presentation were to find a favorable definition of loosening and to investigate the etiology of mechanical loosening of the cemented hip prosthesis. The diagnostic criteria of contrast and radionuclide arthrography, bone scintigraphy, and roentgen stereophotogrammetric analysis (RSA) were evaluated in 14 symptomatic hip arthroplasties examined by these methods. Loosening was found to be best defined as migration; regardless of diagnostic criterion, all loose prosthetic components were migrating, but no nonmigrating component was loose. The development of the radiolucent zone was analyzed in a simple model consisting of 6 cases of giant-cell tumor of bone successfully treated by curettage and cementing. In locations where the cement filling adjacent to cancellous bone was concave, a considerably wider zone developed. There was a positive correlation between the width of the zone and the volume of cement. The radiolucent zone in this model could be explained by heat injury during the polymerization of bone cement. The pattern of migration of the components in 20 cemented hip prostheses was studied with RSA and with conventional radiography over a period of 2 years postoperatively. Eleven acetabular and three femoral components migrated. After an initial 4-month period of rapid migration, most components migrated slowly. The initial rapid migration could be accounted for by the resorption of a layer of necrotic bone following heat injury during the polymerization. The less frequent migration of the metallic femoral component as compared with the polyethylene acetabular component could be explained by the metal acting as a heat sink. Radiographic examination was found to be unsatisfactory as a means of detecting mechanical loosening during the first 2 postoperative years. RSA, on the other hand, was capable of revealing migration as early as 4 months postoperatively. Migration of the components in 16 hip prostheses was studied with RSA for 1 year postoperatively following randomized use of low- and high-viscosity cement. As regards prosthetic migration, no difference was detected between the two types of cement; low-viscosity cement did not improve prosthetic fixation.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetabulum↗
PubMed1978

Photogrammetric target point determination in stereotaxy.

The photogrammetric determination of the target point in stereotactic operations enables a simplification of the photographic equipment and an avoiding of calculating errors during the operation. This is possible on the one hand by excluding the X-ray distortion also without distance taking and, on the other, by the use of a computer which is connected up to the stereocomperator. In addition to the continuous mathematical controls, a visual control of the spatial picture on the stereocomperator is possible.

Cerebral Ventriculography↗
PubMed1978

Antineoplastic-drug effect evaluated with a new X-ray stereophotographic measurement of the tumour volume.

A method for determination and follow up of the size of inoperable intraabdominal tumours has been devised. At laparotomy, tantalum balls are deposited into the capsule of the tumour. An X-ray stereophotogrammetric method determines their position, which define a polyhedron whose volume can be computer calculated. The value of the method was proved in four patients with inoperable ovarian carcinoma, which provides a simple way for the continuous follow up of the effect of antineoplastic therapy in advanced malignant tumours.

Abdominal Neoplasms↗