Radiographic evaluation of the proximal femur in sickle cell disease patients

Abstract text : INTRODUCTION Avascular necrosis of the femoral head develops in 3-19% of patients with sickle cell disease and frequently this is bilateral. Intravascular sickling causes thrombosis and then ischemia, resulting in infarcts in the femoral head which progress to avascular necrosis. Total hip replacement is therefore indicated in such patients. However various studies have shown high complication rates in these groups of patients. There is no documented structural reason in the shape of the proximal femur in sickle cell disease patients which may cause implant loosening. The following are the objectives of this study-to assess the variation in the proximal femoral canal anatomy in sickle cell disease patients and compare with established documented findings in normal population and to also deduce if structural reasons could be the cause for implant loosening rate in this group of patients. METHODS The standardized anterior posterior radiographs of forty-two (42) sickle cell disease patients with degenerative hip osteoarthritis secondary to avascular necrosis and another identical cohort of forty-two (42) patients with primary degenerative hip OA were initially taken and evaluated on a standard imaging software.  The following measurements were noted-proximal femoral canal(Y), mid-diaphysis canal(X), extra medullary canal (Z) diameters- in millimetres (mm) .The calcar-canal ratio (CC) and the cortical index (CI) was calculated as described by Dorr . RESULTS- THE SICKLE CELL GROUP:The mean cortical index (CI) was moderately high -0.65(0.38-0.83), while the mean calcar to canal (CC) ratio was low-0.49(0.27-0.89) Using independent sample t-test, there was no significant difference in the cortical index (CI) and calcar canal ratio (CC) for males and females. ( p=0.9 for CC: p value>0.05 and p=0.6 for CI: p value >0.05). OSTEOARTHRITIC GROUP:The mean cortical index (CI) was 0.49(0.19-0.79) and calcar canal ratio (CC) was 0.47(0.32-0.89). Using the independent t-test, there was no statistical difference between male and female cortical indices (t value- 0.29; degree of freedom (df)-0.221: p-0.76) . There was also no statistical difference in the calcar canal ratios between both genders. ( t value-0.153;df-0.20, p-0.87 with p value >0.05) CONCLUSION According to Dorr classification of types of variations in proximal femoral anatomy-xray measurements which show higher cortical indices and lower calcar to canal ratios suggest funnel shaped proximal femurs. This is clearly seen in the above measurements deduced in this sample of sickle cell disease patients. Their funnel shaped proximal femur allows for good implant fixation for both cemented and uncemented stems. These results therefore imply that the structural anatomy of these patients proximal femurs does not contribute to implant loosening and so other reasons for this should be sought.