Role of Plain Radiography and MRI in the Evaluation of Avascular Necrosis of Head of Femur

Background: Avascular necrosis (AVN) affects mostly young adults within their 3rd and 5th decade. Today, MRI is the imaging modality of choice for diagnosing AVN. It is more sensitive than plain film radiography. The principal role of MRI is in establishing the diagnosis of AVN in symptomatic patients before radiographic changes become apparent. Aims: The aims of this study were to assess the role of MRI in the evaluation and staging of AVN of head of femur, correlating the MRI findings in various stages of AVN with plain radiography. Material and Methods: This cross-sectional study was conducted on forty patients who had risk factors and were clinically suspected to have AVN of Femoral head were evaluated by both plain x-ray and MRI and staged according to modified Ficat and Arlet classification. Results: In precollapsed stages (I and II), plain x-ray detected less number of hips than MRI (38.1 % in stage I and 54.5 % in stage II) whereas MRI was able to detect 95.2 % of hips in stage I and 100 % in stage II. In collapsed stages (III and IV), both plain x-rays as well as MRI detected 100 % of hips of clinically suspected cases. Sensitivity, specificity, PPV and NPV of x-ray came out to be 73.44 %, 83.33 %, 97.92 % and 22.73 % respectively in comparison to MRI with a significant p value of 0.04. Conclusion: It was concluded that in initial stages, plain x-rays are less sensitive in detecting AVN changes as compared to MRI. However, in later stages, both are equally sensitive. A combination of both conventional radiography& MRI of the hips, helps in correctly staging AVN.