X-ray Knee as a Screening Tool for Osteoporosis

Cortical thickness (Cor-Th) of tibia varies considerably on X-ray knees. It was hypothesized that Cor-Th can be used for preliminary prediction of BMD. Ninety nine patients underwent a digital X-ray left knee fixed flexion PA view with an external calibration scale attached to X-ray plate and BMD by DXA using GE lunar machine (Madison, Wisconsin.). Cor-Th was measured at 5 selected levels (A,B,C,D, and E) ranging from 5-7 cm below the tibial plateau on its medial aspect. T-scores were recorded for BMD at AP spine, left forearm and left femur. Cor-Th of tibia at each level significantly correlated with each site of BMD measurement namely AP spine, left femur and left forearm. This correlation varied in the range from 0.241 to 0.426. For AP spine, it was maximum at level C (r = 0.347, p < 0.001) whereas for left femur and forearm sites, it was maximum at level B (r = 0.426 & r = 0.373 respectively, p < 0.001). The correlation of Cor-Th with BMD varied with age. Above 56 years of age, Cor-Th at each level significantly correlated to BMD at each site. Medial tibial cortical thickness, 6 cm (level C) below tibial plateau can be used as preliminary predictor of patients who need a DXA scan.