Debridement Effectiveness Of Infected Bone Tissue Of Chronic Hematogenous Osteomyelitis In The Lower Extremities Under The Guidance Of Fused Images Of ^99mTc-MDP SPECT/CT

BackgroundThe key and difficulty of curing chronic osteomyelitis is the complete removal of the infected lesions.Imprecise debriding extent and residual infected lesions are the main causes of recurrence of osteomyelitis.MRI is used for diagnosing osteomyelitis and defining the extent of debridement prior to the operation;however,it cannot distinguish whether the T2-weighted image hyperintense is due to infection or to an inflammatory response.Therefore,the extent of bone tissue debridement requires specific intraoperative judgment by the physician.Under such circumstance,the physician’s skill and experience play a greatly important role in confirming the real debridement,leading to certain possibilities of missed lesions.In addition,the use of MRI faces certain limitations for the patient with metal fixture.^99mTc-MDP SPECT/CT can be used to diagnose chronic osteomyelitis as an alternative method for it’s immune to Interference of internal metal fixtures.The pathological features between infected and healthy bone tissues are represented in the form of a transitional change,with a sever to mild inflammatory response.For chronic hematogenous osteomyelitis,the uptake of MDP is also influenced by the inflammation,where more uptakes are seen in the core of the lesion than in the periphery.MDP can be labelled with ^99mTc and absorbed by the nidus.The nidus uptake of ^99mTc-labelled MDP depends on its inflammation severity,causing ^99mTc-labelled MDP count to change which can be interpreted by the value of ^99mTc.Relevant radiocounts can be noticed on the fused image and expressed by SPECT/CT radioactive count contour（isocontour,ISO）.A gradual change,featuring radiocounting ranges high from the center to low in the periphery,is obvious on the image.The area within ISO is the region of interest（ROI）,which contains not only the infected bone tissue to be removed,but also indicates the boundary of debridement.If we can combine the ISO with pathology of the corresponding bone tissue,then it will be possible to use the ISO to quantify the extent of bone tissue debridement.ObjectiveTo analysis the effectiveness of fused images of ^99mTc-MDP SPECT/CT as a means of defining debridement extent of infected bone preoperatively and guiding the operation in the lower extremities chronic hematogenous osteomyelitis.MethodThe retrospective analysis was conducted based on the cases in which 21 patients with chronic hematogenous osteomyelitis in the lower extremities were diagnosed and accepted treatment at our hospital from May 2017 to June 2020,among which 8 of them were male and13 were female.All patients are aged from 10–62 years old[23（18,37）years old].The tibia infections were found in 16 cases while 5 cases were diagnosed with infections in femur.The duration of bone infection was 4～480 months[120（42,228）months].According to the Cierny-Mader type:4 cases were classified as type I;typeⅢ,14 cases;typeⅣ,3 cases.Intraoperative debridement On infected bone tissue in Stage I was operated on the ROI where the ISO value was between 30%-40%,using the preoperative ^99mTc-MDP SPECT/CT fused images as the reference.The Stage II bone defect reconstruction were based on autologous and/or allogeneic bone.Comparison observation had been made in preoperative white blood cell count（WBC）,erythrocyte sedimentation rate（ESR）,C-reactive protein（CRP）,intraoperative bacterial culture and pathological examination in Stage I and Stage II.We observed the frequency of operations regarding bone infection control in Stage I and postoperative observation in Stage II was made to examine the symptoms such as skin redness and swellings,pain and sinus tract in the infected limbs,as well as the ossification of grafted bones in the original bone defect part.It was possible to check the accuracy rate between the ISO value in the region of interest（ROI）and the set ISO figure and to evaluate the difference of longitudinal debridement scope between ROI and the actual bone debridement under coronal position.ResultThe patients were followed up for 6～36 months[11（9,29）months]after Stage II.Comparison of preoperative inflammatory markers in stage I and II:WBC（5.9±1.6）×109/L decreased to（5.4±1.5）×109/L;CRP 2.8（2.3,7.7）mg/L decreased to 2.3（1.4,3.0）mg/L（P>0.05）;ESR 9（5.0,26.0）mm/h decreased to 4（2.0,10.0）mm/h,（P<0.05）.The results of bacterial culture of tissue in Stage I showed positive in 12 cases and negative in 9 cases where the pathological examination indicated neutrophils and lymphocyte infiltration.1 patient’s intraoperative frozen section indicated that neutrophils were>5/HP.The bone graft in StageⅡhad been completed after another debridement.All of the 21 patients had undergone operations of infection control with an average number of 1.04 times in Stage I.The results of bacterial culture of tissue in StageⅡshowed negative and a modicum of plasmacyte and lymphocyte infiltration as well as the neutrophils（<5per/Hp）had been found in the intraoperative frozen section and pathological examination.No founding of redness,swellings or sinus tract were observed in the skin after StageⅡsurgery while ossification of grafted bone showing normal.The accuracy rate between the ISO value in the region of interest（ROI）and the set ISO figure was 90.5%.The contrast between the longitudinal debridement scope of ROI[（86.8±31.1mm）]and the actual bone tissue debridement scope[（86.0±31.3mm）]in Stage I showed no statistic significance（p>0.05）.Conclusion^99mTc-MDP SPECT/CT fused image can be used as effective means to outline infected bone tissue debridement scope preoperatively.Such method can not only avoid excessive debridement,but also can improve the cure rate of hematogenous osteomyelitis in the lower extremities.