Chronic post-traumatic osteomyelitis of the lower extremity: comparison ofmagnetic resonance imaging and combined bone scintigraphy/immunoscintigraphy with radiolabelled monoclonal antigranulocyte antibodies

Objective. A retrospective study of the validity of combined bone scintigra phy (BS) and immunoscintigraphy (IS) using Tc-99m-labelled murine antigranu locyte antibodies (MAB) and magnetic resonance imaging (MRI) in chronic pos ttraumatic osteomyelitis, Design and patients. The results of MRI and combined BS/IS of 19 lesions in 18 patients (13 men, 5 women; mean age 35 years, range 27-65 years) were i ndependently evaluated by two radiologists and one nuclear medicine physici an with regard to bone infection activity and extent. The patient group was a highly selective collection of clinical cases: the average number of ope rations conducted because of relapsing infection was eight (range 2-27), th e average time interval between the last surgical intervention and the pres ent study was 6.5 years (range 3 months to 39 years), and from the first op eration was 14 years (range 1.5-42 years). Interobserver agreement on MRI w as measured by kappa statistics. Sensitivity, specificity, accuracy, positi ve predictive value (PPV) and negative predictive value (NPV) were calculat ed for MRI and the nuclear medicine studies. Results. For MRI/nuclear medicine, a sensitivity of 100%/77%, a specificity of 60%/50%, an accuracy of 79%/61%, a PPV of 69%/58% and a NPV of 100%/71% were calculated. Four MR examinations were false positives because of post surgical granulation tissue. A high degree of interobserver agreement was f ound on MRI (kappa=0.88). A low-grade infection was missed on two scintigra ms, while four were false positive because of ectopic haematopoietic bone m arrow, and in one examination the anatomical distortion resulted in an inac curate assignment of the uptake leading to false positive findings. Image a nalysis was frequently hindered by susceptibility artefacts due to residual abrasions of metallic implants after removal of orthopaedic devices (15/18 patients), this led to limited assessment in 17% (3/18 patients). Conclusion. Acute activity in a chronic osteomyelitis can be excluded with high probability if the MRI findings are negative. In the first postoperati ve year fibrovascular scar cannot be distinguished accurately from reactiva ted infection on MRI and scintigraphy may improve the accuracy of diagnosis . MRI is more sensitive in low-grade infection during the later course than combined BS/IS, Scintigraphic errors due to ectopic, peripheral, haematopo ietic bone marrow can be corrected by MRI.