60 year old male patient, long standing diabetic with grade II nephropathy presented with a non healing left foot ulcer. As an initial investigation a radiograph of the foot was ordered.
- destruction of the base of 5th metatarsal with moth eaten appearance and loose debris.
- non visualization of the 3rd and 4th tarsometatarsal joint space.
- loss of normal tarsometatarsal joint planes.
- the intermediate and lateral cuneiform, and the cuboid intertarsal planes are lost.
A detailed evaluation with MRI was suggested to assess extent of soft tissue involvement.
- extensive bone marrow signal changes (T1 hypointense, IDEAL hyperintense) is seen involving the tarsals and base of metatarsals.
- a sinus track is seen from cuboid tracking into the lateral mid foot skin as well as posteriorly.
- fluid signal is seen along the fibularis longus tendon and tendon sheath tracking cranially.
- altered marrow signals also seen in the lateral malleolus and lateral aspect of calcaneum and talus.
- extensive edema and fluid signal intensity is seen within the intrinsic muscles of the foot.
Correlation CT was done to assess extent of bone destruction
- CT documents the suspected destructive process primarily epicentered in the mid foot involving the tarsals and tarsometatarsal joints (a periarticular distribution) with increasing severity towards the lateral aspect.
- significant erosion of the cuboid and base of 5th metatarsal.
- extensive mid foot soft tissue edema.
Key learning points
- 6 D’s of neuropathic joint disease
- dense bones (sclerosis)
- Mid foot disease – most common site of affliction in neuropathic joint disease being the pressure points of the foot combined with the decreased sensation making them more prone for injury.
- Hind foot disease – points towards osteomyelitis.
- Periarticular distribution – neuropathic rather than infective.
- Osteitis vs osteomyelitis
- osteitis: T1 isointense T2 hyperintense marrow seen as a response to the neuropathic destruction
- osteomyelitis: T1 hypointense T2 hyperintense marrow.
- Ghost sign: Non visualization of bone in T1, appearance in T2 suggestive of osteomyelitis.
- Yochum and Rowe, suppurative osteomyelitis, chapter 12, Essentials of Skeletal Radiology.
- Donovan, Andrea, and Mark E. Schweitzer. “Use of MR Imaging in Diagnosing Diabetes-related Pedal Osteomyelitis 1.” Radiographics 30.3 (2010): 723-736.
- Baker, Jonathan C., et al. “Diabetic musculoskeletal complications and their imaging mimics.” Radiographics 32.7 (2012): 1959-1974.