The non-invasive diagnosis of musculoskeletal infections remains a challenge. Recent studies have indicated that fluorine-18 fluorodeoxyglucosepositron emission tomography (FDG-PET) is a highly accurate imaging technique in selected patient groups with infected total hip replacement. The present study analyses the diagnostic accuracy in a consecutive series of patients with suspected musculoskeletal infections.

METHODS: 163 consecutive patients with suspected periprosthetic infections (40 THR, 46 TKR), discitis (22) or a suspected infection involving the peripheral skeleton (55) were studied with FDG-PET. In this retrospective study two independent nuclear medicine physicians interpreted the images solely based on the information provide at the time of investigation. The final diagnosis was based on histopathological studies or microbiological culture or on clinical findings after at least twelve months of follow-up.

Results: Based on the final composite assessment, 21/40 patients with THR, 15/46 with TKR, 22/55 with suspected infection in the peripheral skeleton and 10/22 with suspected discitis had infection. FDG-PET identified correctly 68/76 infections (sensitivity 89.5%) and demonstrated a negative predictive value of 81/87 (specificity 93.1%). FDG-PET was of different diagnostic value at different sites with sensitivity and specificity for suspected infections of THR (100/81.3), TKR (81.8/85.7) infections of the peripheral skeleton (90.9/100) and discitis (100/100).

DISCUSSION AND Conclusions: FDG-PET is highly accurate for the evaluation of musculoskeletal infections. While it correctly identified all patients with suspected discitis, it seems also be reliable to rule out infected THR. However, the specificity in suspected infections of THR and TKR is lower due to granulomatous tissue caused by wear-induced polyethylene particles in aseptic loosening.

Introduction: Analgesia from controlled injections of local anaesthetic into the lumbar zygapohysial joint (z-joint) has been accepted as the standard for diagnosis of z-joint pain. Little is known about the placebo-response rate. Aim of this pilot study is to validate the fluoroscopically controlled z-joint-injection (ZJI) as an instrument for diagnosis of degenerative symptomatic z-joint disease.

Material and Methods: Due to degenerative lumbar spine syndrome 50 z-joints (L5/5: 27; L5/S1 23) were injected three times in a single blinded trial bilaterally. According to a randomisation protocol, using the oblique needle technique the ZJI were done with an local anaesthetic (LA: 1.5 ml 0.5% Scandicain), a saline placebo (sodium: 1.5ml 0.9% NaCl) and with no agent (sicca punction). The pain level before and after the injections (30 min, 1 and 2–3 hours) was documented by the patient on a 10pts.-VAS. Improvement in the pain level after an FJI is defined as responder. A responder reacts false positive if the degree of effectiveness of the placebo-FJI is the same or better than the response to LA. A patient reacts false negative if the pain diminution after LA application is lower than after placebo.

Results: Preliminary results regarding the reactions 30 min after injection are presented. 26% were non-responder and 52.9% LA-responder. The sicca response rate was 38%, for sodium it was 46%. Reaction after sicca-FJI was false positive in 24%, after sodium-FJI in 32% of cases. 38% reacted false negative to LA-injection. The order of the agent application didn’t have significant influence on the responder rates and also not on the extent of contradictory effects.

Conclusions: Despite numerous examinations none could sufficiently evaluate accurate reliable predictors for positive ZJI-responders till now. This is confirmed by our high LA-non-responder-rate of 48.1%. However, only a placebo injection can absolutely exclude a true placebo response. Placebo responses seem to be common. High specificity (minimization of the false positive results) and sensitivity (minimization of the false negative results) are characters for a good diagnostic test. In literature, the specificity of the intraarticular facet block as a diagnostic test for facet joint disease is currently unknown. Capsular rupture with epidural and periarticular diffusion is probably responsible for many false positive findings. Regarding our results, the validity of only one ZJI is not acceptable and shouldn’t be consulted as a diagnostic method for the identification of a facet joint syndrome, therefore. Pain relief after ZJI is a poor predictor of clinical outcome of posterolateral lumbosacral fusions when based on single blocks. Corresponding further examinations are necessary also regarding the ZJI-reliability.