SPECT bone scintigraphy of anterior cruciate ligament injury

This retrospective analysis of SPECT bone scans of the knee was undertaken to define typical bone scan appearances and to assess the sensitivity of this method. We looked at 14 patients, mostly with chronic knee pain, who had anterior cruciate ligament (ACL) tears detected by MRI.

Of the 14 patients, 10 were referred for bone scanning following injury and 4 complained of chronic knee pain without injury. Planar scans were performed 4 hr after the injection of 750 MBq of 99mTc-MDP. Tomographic images were obtained by a 64 x 20-sec acquisition over 360 degrees using a high-resolution collimator. MRI imaging included axial and sagittal, T1 weighted and coronal fast field echo (FFE) sequences. Ten patients also had arthroscopy performed.

MRI scans showed 6 lone ACL tears and 8 combined with other ligamentous injuries. SPECT scans showed abnormalities in 10 patients in the region of ACL insertions but only 4 planar studies were abnormal. SPECT identified focal activity at the upper (n = 8) or lower (n = 2) insertion of the ACL. Six of 10 arthroscopies confirmed ACL tears, 2 complete and 4 partial. Overall, agreement was found with MRI in 10 of 14 cases and in 8 of 10 with arthroscopy. Abnormalities were identified in 10 of 11 regions of other ligament or bone injury identified by MRI.

SPECT bone scanning of the knee is superior to planar imaging in detecting ACL injury and is a sensitive technique. Focal activity may be seen at either end of ACL attachment but more commonly at the upper femoral insertion. Knee SPECT may be a valuable examination in suspected ACL injury, particularly if MRI is not available, is equivocal or where clinical signs are absent.