Role of SPECT imaging in symptomatic posterior element lumbar stress injuries

Abstract

Background : Diagnosis of stress injuries of spine is very difficult with conventional radiography. Methods : In a observational study, 132 subjects were recruited (between 8 and 38 years of age), who had lumbar spondylolysis or posterior element stress injuries. All these patients underwent clinical examination followed by plain X-rays, planar bone scintigraphy and SPECT (single photon emission computerised tomography). SPECT scans can identify the posterior element lumbar stress injuries earlier than other imaging modalities. As the lesions evolve and the completed spondylolysis becomes chronic, the SPECT scans tend to revert to normal even though healing of the defect has not occurred. The aim of the study was to determine the time lag after which SPECT imaging tends to be negative. We divided the patients into two groups, one SPECT positive group and the other SPECT negative group. Pre treatment background variables such as age, gender, back pain in extension or flexion, sporting activities, time of onset of symptoms, Oswestry Disability Index (ODI) were used in a univariate logistic regression model to find the strong predictors of positive SPECT imaging results. Determinants of positivity versus negativity of SPECT were identified by discriminant analysis using multivariate logistic regression. Results : Seventy nine patients had positive SPECT scans whereas 53 patients had negative SPECT scans. Bilateral increased uptake was more common than unilateral uptake. Increased uptake at the L 5 lumbar spine was more common (70%) in SPECT positive group. Low back pain in extension was significantly more common in SPECT positive subjects. Active sporting individuals had higher probability of having a positive SPECT scan. The mean time lag from the onset of low back pain to SPECT imaging was 7 months in SPECT positive group and 25 months in the SPECT negative group. Multivariate analysis predicted that there is a significant difference in positivity of SPECT scans (reduced number of positive results) in subjects who had onset of pain more than six months. Conclusion : SPECT imaging performed within the first six months following the onset of symptoms could predict the mode of treatment in patients with lumbar spondylolysis or posterior lumbar spinal element stress injuries.