Abstract
Introduction and Aims: In 1999, the serial polyethylene wear of a group of patients with a porous coated anatomic hip (PCA) replacement were reported by Devane et al. Wear was measured using a computer assisted technique where the points were selected manually from a digitised image displayed on a computer screen (method 1). The purpose of this study is to use a new automated method of polyethylene wear measurement (method 2), for analysis of the same serial radiographs of patients which have since been digitised. Results of the two methods are compared.
Method: Twenty-three porous coated anatomic hips (PCA, Howmedica) in 23 patients had serial radiographs performed with a minimum 8.5-year follow-up. A total of 494 anteroposterior (AP) and lateral radiographs were analysed. Assessment of the presence of osteolysis on the longest-term follow-up AP image was made by an independent observer. Correlation of polyethylene wear rate measured by the two different methods, and osteolysis was made.
Results: Using method 1, if a poor quality AP or lateral image was analysed multiple times by the same observer, a poor reproducibility (±0.4 mm) was obtained. Discarding of poor quality radiographs by the user resulted in 74% of the AP images and 68% of the lateral images being measured. It is very likely that a different user would discard different images. Method 2, however, automatically eliminates poor quality images. Method 2 was able to measure 89% of the AP radiographs and 78% of the lateral radiographs. More importantly, if a different user performed the same analysis using the new automated software, the exact same images would be analysed. Results of wear measurements made using method 1 were statistically similar to measurements made using method 2 in 19/24 hips (83%).
7/23 patients demonstrated osteolysis on their images. Wear measurement using method 2 showed statistically greater wear in these patients (69mm/yr vs 35mm/yr, p = 0.003). Wear measurement using method 1 showed only a weak association.
Perhaps most importantly, wear analysis of these patients using method 2, by two separate observers, independent of each other, gave identical results.
Conclusion: With improved accuracy and elimination of user error, measurement of PE wear may now have the ability to make predictions about the long-term survival of a THJR. Clinical decisions may be able to be made based on individual patient measurements.
These abstracts were prepared by Editorial Secretary, George Sikorski. Correspondence should be addressed to Australian Orthopaedic Association, Ground Floor, The William Bland Centre, 229 Macquarie Street, Sydney, NSW 2000, Australia.
None of the authors is receiving any financial benefit or support from any source.
