70 yr old diabetic male has pain in the left hip with fever of recent onset with no history of significant trauma. MRI shows a relatively well defined , irregular, predominantly fluid signal intensity lesion in the subtrochanteric region , with cortical break, soft tissue involvement, no significant onion peeling or expansion or endosteal low signal margin. Though not classical, in the given circumstances, subacute osteomyelitis of type 2 is possible.
Teaching points by Dr MGK Murthy
1. Incidence is increasing in view of liberal use of antibiotics
3. Roberts radiological classification (1982) is generally accepted . Type 1-metaphyseal (1a is punched out and 1b is with sclerotic margin classical brodies abscess, maximum in incidence), Type2- metaphyseal cortex and appear similar to osteosarcoma , Type3- diaphyseal, cortical and looks like osteoid osteoma , Type4- diaphyseal and looks like ewing’s with periosteal response, Type 5-epiphyseal and look concentric lucency, Type6-vertebral body and looks destructive.
4. All bones involved, with lower limbs, specifically tibia more involved than others
5. If the lesion tethers from epiphysis to metaphysis across the growth plate serpigenously, it is called “serpentine sign”. Smaller paravertebral abscess, early new bone formation with bony bridging differentiate from TB in spine.
6. Xray and 3 phase bone scan may help, but CT would help pick up eccentric nidus of sequestrum (vs central nidus of osteoid osteoma) and CEMR is ideal for complete evaluation.
7. Bx and curettage if diagnosis is in doubt (in 1/3 case looks like malignancy), antibiotics in others and followed by surgery if needed are recommended