RELIABILITY AND USEFULNESS OF THE SIGNS OF BONY INTEGRATION IN ASSESSMENT OF UNCEMENTED ACETABULAR COMPONENTS IN THE SHORT TERM FOLLOW-UP PERIOD

Abstract

Background: Moore et al. recently described five radiological signs (absence of radiolucent line, zone 2 osteo-penia, superolateral buttress, inferomedial buttress and radial trabeculae) for predicting osseointegration of porous coated uncemented acetabular components in the long term. The positive predictive value for a stable fixation was 96.9% when three or more signs were present. 83% of the cups with one or no signs were unstable.

Aim: To evaluate the prevalence of these signs in clinically well functioning uncemented acetabular components in the short term and to evaluate whether there is a difference acetabular components with different modulus of elasticity.

Materials and methods: The preoperative, immediate postoperative and the latest (minimum 2 years) radiographs of 196 hip replacements with 2 different acetabular components: a 2.9 mm, thin, flexible, macro textured titanium component (Allofit, Zimmer) and a 4 mm thick, stiff, titanium plasma sprayed chrome-cobalt component (Durom, Zimmer) were reviewed by two independent observers searching for the five osseointegration signs. The observers also looked for conventional signs of loosening including: continuous radiolucency of more than 2 mm, component migration of more than 3 mm, component rotation, or the presence of broken screws.

Results: 95 Allofit components and 101 Durom components were available for evaluation. None of the hips were considered loose according to conventional criteria and were well functioning. Out of the new osseointegration signs, at least one sign was present in 100 % of the cases, two signs or more in 30%, three signs or more in 5% and four signs in 1%. There was no difference between the two types of cups. In addition, superolateral buttress and zone 2 osteopenia were also present in preoperative/immediate postoperative radiographs in 8% and 4% of respectively.

Conclusion: Apart from absence of radiolucency, very few of the five osseointegration signs were present at short term follow-up of two very different well functioning uncemented acetabular components designs. We conclude they are not useful in evaluation of unce-mented acetabular components at a follow up of 2–5 years. Further study at mid-term follow-up might reveal whether the bony adaptive changes occur with time.