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DIAGNOSTIC TECHNIQUES FOR OSTEOMYELITIS   
  
Peter F. Kelly, D.P.M., F.A.C.F.A.S  
  
Diplomate, American Board of Podiatric Surgery  
Fellow, American College of Foot and Ankle Surgeons  
  
ABSTRACT  
  
     In many areas of medicine the doctor has a difficult choice in the   
selection among a variety of diagnostic tools each of which has its own  
merits and shortcomings.  The present paper briefly reviews the situation  
where osteomyelitis is suspected.  X-ray is usually the most convenient  
technique and provides sharp and clear images but lacks the sensitivity  
of bone scans.  The choice rests inevitably upon the judgment of the  
clinician whose judgment is influenced by the etiology and  
circumstances of the patient.     
  
INTRODUCTION  
  
     The sensitivity of conventional X-rays is about 50%, whereas Bone  
Scans are approximately five times as sensitive, and registers when 10%  
bone destruction or replacement is occurring within the bone due to  
either reactive process.  Bone also continues to show a hot spot one year  
postoperatively.   
  
     With regard to the clinical setting, Dr. Bronstein stated that the   
etiology and presentation of the disease determines which test the  
clinician	 should order, and that while no one would argue either way,  
the conventional X-rays are usually ordered first.  To confirm the  
diagnosis, both may eventually be ordered.  Cost considerations,  
however, favor conventional X-rays.(1)  
  
BONE SCAN TECHNIQUES  
  
     Two kinds of scans may be procured.  A technitium scan (Tc) will  
show up reactive bone as opposed to a gallium scan (Ga) for soft tissue  
involvement.  However because there is never a pure separation of soft  
tissue and bone on the film, due to the variables in uptake of isotopes by  
this method, the clinician may differentiate structures presented by gross  
anatomical appearance on the film.  A new study having been started  
recently at the Frankford facility is the "Flow Study."	This involves  
multiple films being taken in a sequence as the isotope circulates, is  
taken up, and is released by the tissues.  
  
     Readings during an inflammatory process of soft tissue will show a  
much higher and more immediate uptake when compared to the films  
later in the sequence.  Bone involvement will show a gradual increase in  
the "hot spot" so that it is greater in two hours when compared to the  
films taken more immediately.  
  
     Bone scans continue to prove to be more sensitive in the diagnosis of  
osteomyelitis than X-ray studies.(2)  In a study of 16 children being  
admitted to Children's Hospital of Michigan, 14 showed normal  
radiographs while a positive technitium bone scan was detected in 11 of  
those 14.  Within an average of 2.5 weeks all the radiographs proved to  
be positive.  The early diagnostic accuracy of this method  rivals the  
accuracy of taking a local aspiration.  In the same study, 10 cultures  
were positive for organisms of 13 children that were drawn.  
  
     Because radiographs do not become positive for osteomyelitis for 10  
to 14 days after the onset of symptoms, their value in an early diagnosis  
is limited.  Trying to differentiate osteomyelitis from the misleading  
clinical findings of pyogenic arthritis and cellulitis may be difficult.  
  
     It was found that when using a bone scan a focal hyperactivity may  
be detected as soon as 24 hours following symptoms, but sometimes  
normal or even decreased uptake may be shown.(3)  Generally it was  
demonstrated that when an area of focal hyperactivity was found in a  
patient with the appropriate clinical symptoms, the diagnosis of acute  
osteomyelitis could be made.  Lack of this typically positive finding does  
not rule out osteomyelitis however.  Patients with soft tissue involvement  
may not show a hot spot in the bone until four to six days following.   
However all patients in this study did show a positive scan at some  
point.  
  
     This demonstrated two different pathological processes.  For the  
acute  severe infection the inflammatory response and incresed  
interosseous pressure caused a decrease in blood flow to the area,  
producing a local ischemia.  When decompression occurs, circulation is  
restored, and a hyperemia and hyperplasia of bone tissue provide a  
positive, although delayed scan.  Patients who have a less severe  
infection would not experience this ischemia and so demonstrate an  
earlier bone reaction and thus earlier positive scans.  
  
NEWLY EMERGING TECHNOLOGY  
  
     Recently other diagnostic tests have been considered.(4)  The  
technology of thermography had been applied to stress fractures, and  
probably such a technique may prove useful in cases of a hyperemia due  
to inflammatory process.  Should periosteal bone be involved, the very  
sensitive technique of the Ultrasound Induced Pain Test may verify the  
disease, in those cases where thermography results may appear normal.   
With the increase in sensitivity, however, comes a higher rate of false  
positives.	The combination of the two tests may be applicable in  
the detection of a reactive osteomyelitis, especially of periosteal bone.    
  
ACKNOWLEDGEMENTS  
  
     I appreciate the helpful assistance Dr. Bronstein and his associates at  
Frankford Hospital, Philadelphia, PA.  
  
REFERENCES  
  
1. Discussions with Rob Bronstein, M.D., Frankford Hospital,  
Torresdale Division, Philadelphia, PA, July 17, 1984.  
  
2. Osteomyelitis of the Pelvis in Children. Highland, T.R., M.D., et al.  
Journal of Bone and Joint Surgery. Feb(65-A-2):230, 1983.  
  
3. Bone Scan Patterns in Acute Osteomyelitis.  Scoles, P.V., et al.  
Clinical Orthopedics and Related Research. Nov-Dec(153): 210-7, 1980.  
  
4. The diagnosis of Stress Fractures in Athletes. Devereaux, M.D., B.S.,  
M.B., et al. Journal of the American Medical Association. July 27(252):  
531, 1984.