Diagnosis of stress fractures and correlation of scintigraphy and MRI

Objectives Radionuclide scintigraphy in the early diagnosis of stress fracture has been well established compared to plain radiography. In the recent years MRI has also evolved as a very useful modality in the early diagnosis of stress lesions of bone. This study was undertaken to correlate the efficacy of bone scintigraphy and MRI in the diagnosis of stress injuries of bone in those patients whose initial plain radiographs were negative for stress injuries and to recommend the best approach for early detection of stress injuries of bone.

Methods 50 consequent cases of suspected stress injuries, in the age group of 19-32 years, referred from various defence units in Bangalore area to Radiology and Nuclear medicine department were included in the study. All the cases that had negative findings of stress injury on X-rays were subjected to Scintigraphy and MRI. Scintigraphy was done on a Dual Head Siemens E-cam Gamma Camera. The patient was injected with 20 mCi of 99mTc-MDP IV and a 3 phase bone scan was done. MRI with stir images were done with 1.5 tesla scanner.

Results Our study revealed an excellent correlation between the two modalities. Keeping bone scan as the gold standard, MRI showed a sensitivity of 93.8% for grade 1 findings and 100% for grade 4 changes. STIR images had higher diagnostic accuracy due to homogenous fat suppression. 8 additional cases were detected as compared to non STIR images. However bone scan had the advantage of whole body imaging and it picked up 9 more sites of stress injuries which had been clinically undetected.

Conclusions Both radionuclide scintigraphy and MRI are equivalent in the detection of stress injuries of bone with MRI having the capability of more precisely defining the anatomy and extent of injury, whereas, Bone scan has the advantage of being cheaper, having whole body imaging capability in one sitting, leading to detection of clinically silent lesions which would otherwise not be the part of rehabilitation treatment,having no specific contraindications