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pedCAT: Early Diagnosis of Osteomyelitis in the Diabetic Patient

The pedCAT weight bearing CT imaging system could identify bone infection at an early stage, and possibly prevent amputations, researchers at the California School of Podiatric Medicine at Samuel Merritt University determined in a report.

The researchers outlined two cases where “the use of CBCT device enabled us to diagnose and treat osteomyelitis in a timely manner, preventing its spread to adjacent bone and soft tissue, and minimizing the amount of required surgical resection.”

Plain radiograph is the primary imaging modality for the osteomyelitis diagnosis, the report states, but X-Rays may not reveal osteolytic changes for up to 20 days from the onset of infection or until the bone density is reduced by 30 – 50 percent.

Osteomyelitis is one of the most feared complications of diabetic foot ulceration, which often leads to lower extremity amputation and disability. Early diagnosis of osteomyelitis increases the likelihood of successful treatment and preserving ambulatory function. Unfortunately, most of the currently available imaging modalities are of limited use in assessing early stages of bone infection due to their low specificity and sensitivity for early osteolytic changes.

Magnetic resonance imaging (MRI) is more sensitive and specific than X-Ray, and yields greater accuracy in detecting soft tissue abscesses or early osteomyelitis in patients with high clinical suspicion and negative radiographs. In controversial or uncertain cases where MRI is not available, other imaging techniques such as indium-labeled leukocyte imaging combined with radionucleotide bone scan can be used as an alternative. (“Preventive and Therapeutic Strategies for Diabetic Foot Ulcers” – Foot & Ankle International® 2016, Vol. 37(3) 334– 343 – Chris C. Cychosz, BS, Phinit Phisitkul, MD, Daniel A. Belatti, BS, and Dane K. Wukich, MD).

Nuclear Imaging and MRI perform well in detecting early onset of osteomyelitis; but they are expensive to own and operate, are time-consuming in their acquisition of images.

What is desirable for early detection is a method that is accurate, inexpensive, and readily available. Cone beam CT, and the pedCAT in particular, fills this gap nicely.  The device is small enough to fit into most practices, offers high-resolution 3D imaging capabilities, and has a reduced radiation dose compared to traditional CT, according to the report.

Lead author Alexander M. Reyzelman, DPM,  and his associates reported on two diabetic patients who presented with infected neuropathic foot ulcers and were evaluated for potential osteomyelitis using plain film radiographs and the pedCAT CBCT scanner. In both cases, the “pedCAT was instrumental in identifying bone infection. The diagnosis of osteomyelitis was later confirmed by positive findings on bone biopsy. The use of CBCT device enabled us to diagnose and treat osteomyelitis in a timely manner, preventing its spread to adjacent bone and soft tissue, and minimizing the amount of required surgical resection.”

Case 1

A 49 year old diabetic female presented with an infected neuropathic ulcer at the lateral aspect of her fourth digit. The ulcer demonstrated malodor, cellulitis that extended to fourth metatarsophalangeal joint and positive probe-to-bone test. The plain film radiographs and CBCT were utilized in order to rule out osteomyelitis and assess the extent of soft tissue infection. The weight-bearing X-rays of the affected foot revealed subtle lucency at the lateral aspect of the proximal phalanx of the fourth digit, which was contiguous with the ulcer location. However, this finding alone was not sufficient to yield a conclusive diagnosis.  The images obtained using PedCAT clearly demonstrated the break in the cortex and the area of osteolysis involving the proximal phalanx of the fourth digit. The head of the fourth metatarsal and adjacent digits appeared intact. These findings, in conjunction with the clinical appearance of the affected digit, led to a preliminary diagnosis of osteomyelitis. The patient was treated with an arthroplasty of the fourth proximal interphalangeal joint, and has fully recovered. The bone specimens obtained intraoperatively were sent for biopsy, which confirmed our preliminary diagnosis of osteomyelitis.

Case 2

A 53 year old diabetic male presented with an infected neuropathic ulcer at his fifth metatarsal head, which exhibited malodor, edema and erythema extending through tthe plantar lateral aspect of  fifth metatarsal shaft and probed to joint capsule. The X-rays demonstrated no signs of bone involvement, while CBCT revealed distinct areas of cortical lysis and bony fragmentation of the fifth metatarsal head. The proximal two thirds of the shaft of the fifth metatarsal appeared unaffected, with intact cortex, uniform bony density and lack of osseous fragmentation. The patient was treated with partial resection of the fifth metatarsal. The bone biopsy has confirmed our preliminary diagnosis of osteomyelitis.

In the concluding discussion, Dr Reyzelman noted: “Though in our case studies we have not taken advantage of the option allowing to scan the patient in both, a weight-bearing and a non-weight bearing positions, this option could be highly useful for evaluation of complex fractures and dislocations of the foot and ankle.”

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