The prediction of failure of the stem in THR by measurement of early migration using EBRA-FCA

Abstract

We report the ten-year results for three designs of stem in 240 total hip replacements, for which subsidence had been measured on plain radiographs at regular intervals. Accurate migration patterns could be determined by the method of Einzel-BildRoentgen-Analyse-femoral component analysis (EBRA-FCA) for 158 hips (66%).Of these, 108 stems (68%) remained stable throughout, and five (3%) started to migrate after a median of 54 months. Initial migration of at least 1 mm was seen in 45 stems (29%) during the first two years, but these then became stable. We revised 17 stems for aseptic loosening, and 12 for other reasons. Revision for aseptic loosening could be predicted by EBRA-FCA with a sensitivity of 69%, a specificity of 80%, and an accuracy of 79% by the use of a threshold of subsidence of 1.5 mm during the first two years. Similar observations over a five-year period allowed the long-term outcome to be predicted with an accuracy of 91%.We discuss the importance of four different patterns of subsidence and confirm that the early measurement of migration by a reasonably accurate method can help to predict long-term outcome. Such methods should be used to evaluate new and modified designs of prosthesis. J Bone Joint Surg [Br] 1999;81-B:273-80. Received 17 February 1998; Accepted after revision 12 May 1998 The prognostic value of early migration of an acetabular cup has been demonstrated by several authors, with loosening within two years predicted with sensitivities and specificities of over 80%.

Accuracy of Model-based RSA Contour Reduction in a Typical Clinical Application

“…The additional radiation exposure required by a double examination is, in our view, not justified in this context. The ability of early migration measurements to predict later aseptic loosening has been established [5,13,16,19]. Marker-based RSA is considered the gold standard for measurement of implant migration, and it has been used as a standard of comparison for other radiographic methods, such as the Sutherland, Wetherell, and Sulzer methods or EBRA (Ein-Bild-Röntgen-Analyse, single-image roentgen analysis) [2,6].…”

“…We tested interchangeability of the two methods in a clinical setting by a bounding criterion defined as the mean ± 2 standard deviations of the measured differences (bounding approximately 98% of all measured differences). The smallest clinically relevant magnitude of migration is difficult to define, and several clinical investigations that have related early migration to later aseptic loosening have used thresholds ranging from 1.2 to 2.6 mm [5,13,15,16,19]. We therefore chose a conservative value of clinically relevant migration of ± 0.5 mm or greater in magnitude, ie, much less than thresholds that have been used to predict later loosening.…”

High Incidence of Migration with Poor Initial Fixation of the Accolade® Stem

“…EBRA-FCA has an accuracy of better than ± 1.5 mm (95% CI) when compared to RSA, a Cronbach alpha coefficient of 0.84 [3], a specificity of 100%, and sensitivity of 79% [3]. Using a cutoff value of 1.5 mm for femoral stem subsidence in the first 2 years, EBRA-FCA has a sensitivity of 69%, specificity of 80%, and accuracy of 79% in predicting implant failure [28].…”

“…Similarly, Freeman and Plante-Bordeneuve [13] and Kobayashi et al [25] demonstrated the subsidence of a femoral stem at 2 years could predict failure at long-term followup. The association between early implant stability and long-term survivorship is well established for a variety of stem designs [23,28,38,43], with the gold standard in evaluating initial implant stability being radiostereometric analysis (RSA) [8,39]. Another validated technique to measure implant migration is Ein-Bild-Roentgen-Analysefemoral component analysis (EBRA-FCA) [3,27], which also allows accurate measurement of femoral stem subsidence without the need for tantalum markers [4] and can be performed retrospectively using standard pelvic radiographs.…”

“…Consequently, concerns were raised as to the clinical performance of this stem in the short term with respect to patient function, its osteointegration, and its clinical survivorship. Because early implant instability and micromotion are known risk factors for aseptic loosening [36], combined with the well-established clinical performance of a variety of stems [21,28,38,43], we undertook this study to quantify and assess the overall initial fixation of the Accolade 1 stem.…”