From medscape -- - - there is a LARGE article there of which this is page 3
http://www.medscape.com/viewarticle/462185
Patients typically present initially with signs and symptoms of an infection after a mean of 15 days from the index procedure, and 93% present with wound drainage.[24] In most, however, no fever is present. Wound inflammation is common, and rarely is the wound benign in appearance. Because there are no pathogno-monic symptoms or signs, laboratory studies are useful in helping the clinician to establish the correct diagnosis. The mean sedimentation rate in patients in one study was 71.5 mm/hour.[24] When faced with abnormal values, one should have knowledge of the normal postoperative course of recovery of these indices. In a study of patients who underwent uncomplicated spinal surgery, none of whom developed a postprocedural infection, the postoperative values for CRP and erythrocyte sedimentation rate were quantified.[23] The CRP level peaked at 2 to 3 days postoperatively and normalized between Days 5 and 14. The erythrocyte sedimentation rate peaked on Day 5 but declined at a much more variable rate than CRP, often staying elevated at 21 to 42 days postoperatively. These indices are considered sensitive but not specific. They can be elevated by an infection at any site, but when combined with an inflamed or draining lumbar wound within the appropriate time frame, elevation in the CRP or erythrocyte sedimentation rate can aid in the diagnosis by indicating the presence of a postoperative wound infection.
Diagnostic Imaging Modalities
Plain radiography, CT scanning, and MR imaging are often of limited value in the diagnosis of a postoperative wound infection in the setting of internal fixation. Plain radiography can assist in determining the presence of indirect indicators of a spinal infection such as early implant loosening, rapid loss of adjacent-level disc space height, or abnormal soft-tissue swelling. Plain radiography will also detect the presence of a retained foreign body in the spinal wound. Both CT and MR imaging can demonstrate whether a fluid collection exists. Some authors have strongly supported the immediate use of contrast-enhanced MR imaging when an epidural abscess is suspected.[15] It is not usually possible, however, to differentiate between a postoperative fluid collection in the form of a sterile seroma and a postoperative abscess. Some authors, however, have reported success with CT and MR imaging in distinguishing between blood, purulent material, and granulation tissue.[21] Unfortunately, the presence of instrumention-related metal artifact often makes these advanced modalities of little value.
Gadolinium-enhanced MR imaging is of value in detecting an early-onset postoperative discitis even in cases in which posterior hardware has been placed. One should note, however, that following operative manipulation of the disc space, an increase in postcontrast MR imaging signal intensity or edema may not be indicative of a infection but in fact may be a normal postoperative finding. Because there is no optimal imaging modality for detecting a postoperative wound infection, these studies should be used to provide additional information when formulating a diagnosis of a postoperative spinal infection.