USE OF MORPHOMETRY TO QUANTIFY RADIOLOGICAL OSTEOLYSIS FOLLOWING TOTAL HIP ARTHROPLASTY

Abstract

Introduction: Of all hip arthroplasties conducted annually, a proportion will subsequently require revision for aseptic loosening and periprosthetic osteolysis. Osteolysis may develop ‘silently’ and monitoring of patients is recommended. This should include x-rays as progressive changes in size of a lesion may indicate a potential failure. Area measurement of osteolysis has been achieved in a number of ways but with techniques that are not readily available in routine clinical practice. The aim of this study was to develop a method for routine assessment of hip arthroplasty to quantify osteolytic changes seen on x-ray, applicable by any health professional and with good inter-observer reliability.

Methods: A morphometric grid is superimposed on an object of interest and the number of test points that fall within a defined area counted. A specialized grid was developed and initial testing was conducted on twenty simulated osteolytic lesions. Subsequent testing was on thirty-five arthroplasty x-rays with evidence of osteolytic lesions. Four observers recorded the number of crosses seen over each lesion. The observers were representative of health professions and levels of experience involved in arthroplasty review.

Data was analysed for both inter-observer and test-retest reliability using the intra-class correlation coefficient and the Bland-Altman method (use of two methods provides a better estimation of accuracy).

Results: The results for intra-class correlation coefficients on both simulated and actual lesions were all excellent (range 0.90 to 0.98) as confirmed by visual representation using the Bland-Altman method.

Discussion: Regular follow-up of hip arthroplasty with x-ray ensures that changes are monitored even when symptoms are absent. We believe that this tool can improve the process through quantitative assessment of osteolytic lesions. The scientific development supports the reliability of the tool when used by a number of raters and the simplicity of application makes it a useful addition to an arthroplasty clinic.