Osteomyelitis in the diabetic foot

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248 RadioGraphics June 1983 Volume 3, Number 2

Index terms:Bones

infectionDiabetes mellitus

complicationsFoot

radionuclide studiesGallium

radioactiveOsteomyelitis

Osteomyelitis in the diabetic foot:

A difficult diagnostic challenge

Ellen B. Mendelson, M.D.

Madeleine R. Fisher, M.D.

Thomas W. Deschler, M.D.

Lee F. Rogers, M.D.

Ronald W. Hendrix, M.D.

Stewart Spies, M.D.

THIS EXHIBIT, A SELECTION OF THE SKEL-

ETA.L RADIOLOGY PANEL, WAS DISPLAYEDAT THE 68TH SCIENTIFIC ASSEMBLY AND

ANNUAL MEETING OF THE RADIOLOGICALSOCIEFY OF NORTH AMERICA, NOVEMBER

28-DECEMBER 3, 1982, CHICAGO, ILLI-

NOIS.

From the Department of Radiolo-

gy, Northwestern Hospital, North-western University Medical School,

Chicago, Illinois.

Address reprint requests to Lee F.Rogers, M.D., Department of Radioto-

gy, Northwestern University MedicalSchool, 303 East Chicago Avenue, Chi-

cago, IL 60611.

The recognition of osteomyelitis in the diabetic foot is a difficult

and commonly encountered problem. The directed approach pre-

sented here facilitates the diagnosis.

Introduction

Evaluation of the diabetic foot for osteomyelitis is frequently requested by

clinicians concerned with initiating long term antibiotic therapy or surgical treat-

ment. The severity of the treatment makes the consequences of a false positive

reading as lamentable for the patient as a missed diagnosis. Because diabetes mellitus

is so prevalent in our growing geriatric population, a directed approach to the di-

� agnosis of osteomyelitis in this group of patients is mandatory.

PatIent Data

Subject population Patient age and sex37 diabetics including both range 30-84 yearSjuvenile and adult onset diabetics median 48 years

29 men; 8 womenAssociated clinical findings

peripheral netropathy 78% patientsvascular disease 50% of patients

Mendelson et al Osteomyelitis in the diabetic foot

Volume 3, Number 2 June 1983 RadioGraphics 249

The diabeticfoot describes an extremity showing deep

or draining soft tissue ulceration and neuropathic and de-

generative changes of bone. The patient may cite trivial

antecedent trauma. Radiographicatty, the ulcer crater is

often evident, and arterial calcification is frequently seen.

Atrophic osseous degeneration may be present in the fore-

foot. It is characterized by gradual osteolysis at the ends of

the phalanges and metatarsals, which produces a tapered,

“pencilled” appearance of the bones resembling “sucked

candy. “ These changes are attributed to sympathetic de-

nervation which causes hyperemia and results in dissolution

of bone. In the midfoot, rather than osteolysis, hypertrophic

changes may be present. Fragmentation, articular disrup-

tion, and toss of the plantar arch occur. The architectural

support for the foot crumbles. In this setting of atrophic and

hypertrophic change, osteomyelitis is frequently the final

insult.

Techniques of Use in Assessing the Diabetic Foot

Techniques of value in assessing the diabetic foot in-

dude conventional and magnification radiography, and

technetium and gallium scintigraphy.

Bone scans using 99mTc methytene diphosphonate or

hydroxymethylene disphosphonate should include blood

pool and immediate static images as well as delayed static

images. They show greater than normal uptake in inf lam-

matory, neurotrophic and degenerative diseases; but are

useful in differentiating cellulitis from osteomyelitis. Cel-

lulitis is characterized by greater than normal uptake in

blood pool and immediate static images, with normal to only

slightly increased uptake in delayed images; osteomyetitis

characteristically shows greater than normal activity in both

immediate and delayed images.

A 67Ga citrate scan should be performed after a �mTc

MDP or HDP scan because the energy of the gamma

emission from gallium is greater than that from technetium.

Gallium scans are nearly always positive in osteomyetitis

even when the technetium bone scan is not. The magnitude

of the uptake in a lesion suggests the activity of the disease

process. Chronic, inactive inflammatory disease produces

only slightly greater than normal uptake; an acute inf lam-

matory process produces very marked gallium uptake.

Diagnostic Dilemmas

PROBLEMS COMMONLY ENCOUNTERED IN EVALUATING

THE DIABETIC FOOT FOR OSTEOMYELITIS

1 . Determination of the presence or absence of osteomyelitis

in the forefoot when the clinical suspicion of osteomyelitis

exists

2. Differentiation of osteomyetitis or septic arthritis from

neurotrophic changes in bone

3. Interpretation of fracture in a diabetic foot when there

is no antecedent trauma

4. Recognition of postsurgical progression of osteomyel-

itis

5. Determination of the presence of osteomyelitis in a bone

adjacent to a soft tissue ulcer

Osteomqelitis in the diabetic foot Mendetson et at


Figure 1It is often difficult to distinguish de-mineralization in the forefoot fromthe subtle trabecular destruction ofearly osteomyelitis. This problem waspresent early in this case, but in thisfigure the lesion has progressed to

obvious and classic radiographic os-teomyelitis. Findings such as these donot represent a radiographic di-lemma.

Figure 2The osteomyelitis was unresponsiveto antibiotics; the toe became gan-grenous and was resected. This his-

tologic section of the resected boneshows osteomyelitis characterized byinflammatory cells, fibrous tissue, andreactive new bone formation. A fewfat cells. present in normal marrow,are also seen.

Diagnostic Dilemma 1

CLINICAL SUSPICION OF OSTEOMYELITIS

Case One

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Mendetson et at Osteomyelitis in the diabetic foot


Case Two

Figure 3This is the radiograph of another casein which osteomyelitis was suspectedclinically. The lesion is somewhatmore difficult to identify radiograph-ically than in Figure 1. Here, the af-fected area of the 5th toe shows de-mineralization and a fracture throughthe infected bone.

Figure 4A Figure 4B

Figures4A&BThese bone scan images show dif-fusely increased uptake in the in-volved digit. This confirmed thepresence of osteomyelitis since therewas no associated soft tissue ulcer orcellulitis in this case.

Figure5 Figure 6

Osteonzyelitis in the diabetic foot Mendetson et at



NEUROTROPHIC BONE VS. OSTEOMYELITIS

Case Three

Figure 5Although osteomyelitis was suspected clinically in this case, the radio-graphic abnormalities shown here were attributed to neurotrophicchanges. Note that the 3rd metatarsal is sclerotic and thickened,whereas, the 2nd and 4th metatarsals show tapered pencil pointing.

Figure 6This radiograph was exposed 3 years later. The 3rd metatarsal has nowalso been destroyed. In retrospect, smoldering osteomyelitis is thoughtto have been present at the time of the earlier study.

Case Four

Mendetson et al Osteomyelitis in the diabetic foot


Figure 7Chronic osteomyelitis showing fi-brous tissue replacement and manymononuclear inflammatory cells.Areas of nonviable, thickened,sclerotic bone provide histologiccorrelation with the radiographicfindings.

Figure 8This is the radiograph of another pa-tient with osteomyelitis in neurotro-phic bone. Note the calcific frag-ments, which are compatible withneurotrophic degeneration. Markedsoft tissue swelling heightens thesuspicion of an inflammatory process.The 5th metatarsal was resectedsoon after.

Figure 9Osteomyelitis seen histologically;reactive new bone surrounds trabe-

cular bone. Areas of fibrous tissue andinflammatory cells are present.

Case Seven

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Osteoniyelitis in the diabetic foot Mendetson et at

254 RadioCraphics June 1983 Volume 3, Number 2


INTERPRETATION OF FRACTURE WITHOUT ANTECEDENT TRAUMA

Case Five Case Six

Figure 10This patient was seen in the Emer-

gency Room with a draining ulcer in-volving the 2nd toe. No history oftrauma was elicited. In this radio-graph, note the loss of trabeculae and

the cortical destruction in the distalportion of the proximal phalanx.These findings represent osteomyel-itis with an unsuspected fracture. Di-abetics frequently are first seen withpathologic fractures.

Figure 11This is the radiograph of a patientwith more advanced bone destruc-

tion. Like Figure 10. it demonstratesa fracture through osteomyeliticbone.

FigurelO Figure 11

Figure 12Here, magnification radiography fa-

cilitates the visualization of demin-eralization, trabecular disruption, andfracture through infected bone. Anonscreen, fine detail film will providebone detail equal to or superior tothat obtained by direct magnificationradiography in a thin body part.

Figure 13A bone scan in this patient demon-strates diffuse uptake in the involvedbone confirming the diagnosis of os-teomyelitis; one would expect local-ized uptake in a site of traumaticfracture. Incidentally, note the in-creased radionuclide activity in the ________tarsals. This later proved to be os-

teomyelitis. Figure 12 Figure 13

Mendelson et at Osteornyelitis in the diabetic foot



RECOGNITION OF PROGRESSIVE OSTEOMYELITIS IN THE POSTSURGICAL FOOT

Case Eight

Figure 14Demineralization and loss of trabeculae are seen in thedistal 3rd metatarsal. The proximal phalanx is destroyed,and gas (arrow) is seen in the soft tissues surrounding themetatarsophalangeal joint.

Figure 15This radiograph was exposed immediately after resectionof the involved portion of the 3rd metatarsal. The proxi-mal third of the metatarsal has not been resected. The2nd ray appears intact.

Osteomyelitis in the diabetic foot Mendetson et al


Figure 16Two months later, the clinical suspicion of osteomyelitisremained. This radiograph confirmed that suspicion,demonstrating soft tissue swelling, bone destruction atthe 2nd metatarsophalangeal joint, and periosteal re-action surrounding the shafts of the metatarsal andproximal phalanx.

Case Eight

Figure 17After two months of antibiotic therapy, this followupstudy shows healing, evidenced by absence of soft tissueswelling, minimal residual periosteal reaction, and resti-tution of trabecular pattern. Sclerotic changes are seenalong with persistent deformity at the 2nd metatarso-phalangeal joint destroyed by osteomyelitis. The radio-graphic and clinical findings are compatible with treatedosteomyelitis that has resolved.


DETERMINATION OF OSTEOMYELITIS IN BONE ADJACENT TO SOFT TISSUE ULCER

Case Nine

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Mendelson et at Osteomyelitis in the diabetic foot


Figure 18Note the irregularity of the softtissues at the medial aspect of thegreat toe with loss of trabeculae inthe underlying bone. There is a vaguesuggestion of bone destruction. Os-teomyelitis had been suspected din-ically.

Figures 19 A & BThis bone scan, obtained for furtherevaluation, shows increased uptakein the region of the 1st toe and thetarsal bones. These findings arecompatible with osteomyelitis or withsoft tissue infection.

Osteomyelitis in the diabetic foot Mendelson et at

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Figure 20A Figure 20B

Case Ten

RadioGraphics June 1983 Volume 3, Number 2

Figures 20 A & BTo aid in distinguishing cellulitis fromosteomyelitis, this gallium scan wasperformed. It demonstrates moreintense uptake in the region of thebone than does the bone scan. This isa diagnostic feature of osteomyelitisthat differentiates it from soft tissueinfection.

Figure 21This diabetic whose great toe hadpreviously been resected was seenwith an ulcer in the soft tissues about

the remainder of the great toe andthe 2nd toe. In this radiograph, thereis no evidence for osteomyelitis. Notethe extensive vascular calcificationwhich is often seen in the diabeticfoot.

258

1-Figure 22A Figure 22B

Mendetson et at Osteomyelitis in the diabetic foot


Figures 22 A & BFailure of the ulcer to resolve andcontinuing clinical concern regardingosteomyelitis led to this bone scan.The immediate static image (A)shows increased activity in the regionof the great toe, which diminished onthe 2 hour delayed film (B). This sug-gested that osteomyelitis was notpresent.

Figure 23Although the diagnosis of soft tissueinfection was suggested by the bonescan, this gallium scan was obtainedfor confirmation. Note that the ra-dionuclide activity in this galliumimage is less intense than it was in thepreceding case in which osteomyelitiswas present. Osteomyelitis is ex-cluded here.

radiographs of foot

uncertain or no evi-dence of osteomyelitis

of

osteomyelitis excluded in favor ofsoft tissue infection, neurotrophicor degenerative joint disease

Osteomyelitis in the diabetic foot Mendetson et at


Recommended Approach for Diagnosing

Osteomyelitis in the Diabetic Foot

DIABETIC PATIENT WITH OSTEOMYELITIS SUSPECTED CLINICALLY

Conclusions with Some Criteria for Establishing the Presence of Osteomyetitis in the Diabetic Foot

1. In osteomyelitis, the classic early radiographic finding

is demineralization; later, trabecular disruption and bone

loss may be present. Early changes may be discerned

more easily on magnification views. As soon as there is

clinical suspicion of osteomyelitis, a bone scan, the most

sensitive screening study, should be performed.

2. Neurotrophic bone may show fragmentation, osteotysis,

and pencil pointing. Periosteat reaction is not a feature

of neurotrophic change, however. The presence of

periostitis in a bone that shows apparent neurotrophic

change should alert the diagnostician to the possibility

of osteomyelitis. In addition, unusual sclerosis and

thickening in neurotrophic bone suggests osteomyetitis.

Evaluation should commence according to the suggested

algorithm.

3. The most common sites of osteomyetitis in our series, in

order of frequency, are the 1st, 5th and 2nd rays. The 4th

and 5th rays showed simultaneous involvement in several

cases. Calcaneal osteomyelitis was confirmed in four

patients. The other tarsal bones were infrequently in-

votved. This observed pattern of distribution favors the

diagnosis of osteomyetitis if a suspected bone is in one of

the commonly involved areas.

4. After surgery, if osteomyelitis recurs or progresses, it

frequentty appears in a metatarsophalangeal joint adja-

cent to the site of resection.

5. In a diabetic foot that has not suffered trauma, an un-

suspected fracture should suggest the possibility of os-

teomyetitis. Pathologic fractures were present in many

of our cases with particular predilection for the distal

portions of proximal phalanges, often the 1st or 2nd.

6. The preponderance of our cases showed osteomyelitis in

a solitary site in the foot. In 20% of patients, two or more

contiguous sites were affected by osteomyelitis. Bilateral

involvement was rare.

7. Diagnostic examinations to establish the diagnosis of os-

teomyetitis should include a bone scan, the most sensitive

screening study. We urge more frequent utilization of

bone and gallium scanning in evaluating the diabetic foot

for osteomyelitis.

Mendelson et at Osteomyelitis in the diabetic foot

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Osteomyelitis in the diabetic foot