Anatomical basis for study of acetabular migration of the prosthetic cup used in arthroplasty of the hip: a new technique for measurement of migration

Cup positioning in THA: current status and pitfalls. A systematic evaluation of the literature

The correct determination of cup orientation in THA regarding the intraoperative as well as the postoperative assessment due to the pelvic tilt and rotation with inexact incorporation of the pelvis is uncertain. The anterior pelvic plane (APP) seems to be the most reliable reference frame and computer-assisted navigation systems seem to provide the best tool for correct implantation to date. For the intraoperative assessment of the APP, the exact determination of the bony landmarks is mandatory. For the standard plain radiography, standardized positioning of the patient and approximation of pelvic tilt by a lateral view are mandatory. An additional CT must be carried out for certain indications. More emphasis has to be given to the individuality of pelvic tilt and range of motion.

Submillimeter measurement of cup migration in clinical standard radiographs

Assessing the displacement of bony implants is an important topic in arthroplasty, particularly in total hip replacement (THR). The observation of the migration is supposed to provide an insight into the fixation of the implant. Diagnostic standard radiographs of the pelvis are an advantageous data source for this purpose. The previous methods based on these images, however, lack of a thorough consideration of their projective nature. They do, hence, not reach the desired precision, which should lie in the submillimeter range to allow a detection of migration in the first one or two years after implantation. The aim of the work presented here was, therefore, a method for measuring the distance of the artificial hip socket to the bone with an error of less than 0.5 mm. The approach has been on the one hand to define the bone-cup distance measured in the radiograph so that the variability of the intrinsic and extrinsic parameters at exposure has a minimal impact. On the other, specialized matching techniques are applied in order to optimize the localization of the necessary bony landmarks and the cup in the X-ray image. The coordinates of the bony landmarks are determined by means of a template matching algorithm. The position of the implant is estimated by intensity-based registration using the cup's CAD-model. The method was validated theoretically, experimentally, and clinically. In the clinical radiographs, the standard deviation of the migration measurements resulted to be 0.28 mm when using only natural bony landmarks. The implantation of a bony marker was found to increase the precision to a standard deviation of 0.20 mm. The interobserver variability in the two cases was estimated to be 0.11 mm and 0.04 mm.

Precision of distance determination using 3D to 2D projections: the error of migration measurement using X-ray images

The goal of this study has been to objectively and reliably estimate the precision of measuring 2D migration of hip prostheses. This is the distance change over time between the implant and the bone observable in X-ray images. To reach this goal, a generally valid scheme for determining the standard deviation of distance measurements in 3D to 2D projections has been worked out. The scheme was applied to four previously published methods for measuring the migration of the prosthetic cup using standard radiographs. Applying the scheme yields measures for the sensitivity of the migration measurement towards the relevant sources of error. Inserting previously published data for the amounts of the entering errors, the standard deviation of the migration measurement has been calculated numerically resulting in values up to several millimeters.

Migration of the uncemented Harris-Galante acetabular cup: results of the einbildroentgenanalyse (EBRA) method

Seventy primary total hip arthroplasties using the Harris-Galante acetabular cup (Zimmer, Warsaw, IN) were prospectively examined. Over the entire period of 65.4+/-7.8 months, radiologic migration analysis was performed using the Einbildroentgenanalyse (EBRA) method at an accuracy of 1 mm. Although there was clinically no suspicion of prosthetic loosening in any case, in 8 implants (11.4%) migration of more than 1 mm was observed. Cranial migration occurred in 3 cases (1.1, 1.3 and 1.6 mm), medial migration in 3 cases (1.1, 1.1, and 2.9 mm), and lateral migration in 2 cases (1.1 and 1.1 mm). In the other 62 cases, however, no migration was traceable. Compared with measurements of other implant systems by means of the EBRA method published recently by other groups, the migration rate of the Harris-Galante cup was without exception lower and provided excellent midterm implant stability.

Reproducible radiographs of acetabular prostheses. A method assessed in 35 patients

35 patients with a smooth, threaded acetabular Mecron type prosthesis were examined with the aid of a table top with wiremarkers and a fixed 30-degree wedge to allow for reproducible positioning. Under fluoroscopic control, pelvic and spot films were made. The inter- and intraobserver variability of anteversion and inclination angle measurements of the prostheses had a standard deviation of less than 1 degree. The method can be applied to other acetabular prostheses as well.

Reliability of the acetabular teardrop as a landmark

This study investigated the effect of tilt and observer reliability on radiographic measurements of the position of a prosthetic acetabular cup in seven dry bone pelves using the teardrop as a landmark. Coronal or sagittal tilt of more than five degrees was easily recognisable and there was effectively no observer variation in the measurements up to this limit. In addition, 90 out of 100 randomly selected antero-posterior pelvic radiographs from an outpatient department were not significantly rotated and 93 demonstrated a clearly defined teardrop. Measurements about the teardrop on routine radiographs are therefore sufficiently accurate to allow assessment of prosthetic position.

The isoelastic hip prosthesis followed for 5 years

In 1981 and 1982, 58 patients (61 hips) received an isoelastic noncemented femoral component and a bipolar cup for nontraumatic hip disease. Three patients were lost to follow-up and 8 died, leaving 47 patients (51 hips) for review after a minimum of 5 years. There were seven failures--two infections, four technical errors, and one migration of an acetabular component. Of the remaining 44 hips, 42 scored good or better at review.