| 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 L5 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.
Keywords: Spondylolysis; SPECT scans.
|How to cite this article:|
Debnath U K, Freeman B, Solaymani-Dodaran M, Webb J. Role of SPECT imaging in symptomatic posterior element lumbar stress injuries. Indian J Orthop 2005;39:228-31
|How to cite this URL:|
Debnath U K, Freeman B, Solaymani-Dodaran M, Webb J. Role of SPECT imaging in symptomatic posterior element lumbar stress injuries. Indian J Orthop [serial online] 2005 [cited 2019 May 23];39:228-31. Available from: http://www.ijoonline.com/text.asp?2005/39/4/228/36575
| Introduction|| |
The term spondylolysis describes a defect, usually bilateral, which arises between the superior and inferior articular processes in the narrowed region of the neural arch, the pars-interarticularis. The aetiology is considered to be mechanical, arising from the impact or fatigue failure of the spine in subjects with one or more inherited predisposing factors ,,,,
Whilst the prevalence in the asymptomatic population is around 5%, there is an increased incidence in young people involved in strenuous sporting activity ,, . In this population, the precursor lesion, that is osseous stress responses and incomplete stress injuries of the lumbar spine are more common, and their early detection is of paramount importance. They are of variable geometry and location with many, but not all, occurring in the pars interarticularis, sometimes at more than one level.
Conventional radiography is insensitive in detecting posterior element stress injuries, especially when incomplete, though CT scans can show morphological abnormalities. Bone scintigraphy is of limited value in establishing the primary diagnosis of spondylolyses and is relatively insensitive; it can help to distinguish between those patients with established non-union of the defect, and those in whom healing is still progressing , . Single photon emission computed tomography (SPECT) increases the sensitivity of bone scintigraphy and also permits spatial localisation of abnormalities and is thus the preferred method of scintigraphic imaging ,, . Relatively little is known about the temporal evolution of scintigraphic abnormalities in posterior element stress injuries. It is postulated that as the lesions evolve and a completed spondylolysis becomes chronic, the SPECT scan tends to revert toward normal even though healing of the spondylolysis has not occurred. Thus, SPECT scanning in spondylolysis varies with time and the stability of the spondylolytic spine  . SPECT may identify acute posterior element stress injuries before they are manifest radiographically or on Computerized tomography.
The time lag following which SPECT imaging in patients with symptomatic lumbar posterior element stress injuries will become negative, has not been fully addressed previously. In this retrospective study, we have attempted to evaluate how this time lag between onset of low back pain and SPECT imaging might affect the SPECT results.
| Material & Methods|| |
This observational study comprises of 132 subjects (78 M: 54F) aged between 8 and 38 years, who had lumbar spondylolysis/posterior element stress injuries between 1996 and 2000. All underwent bone scintigraphy and SPECT imaging. Planar bone scintigraphy and SPECT imaging was performed after the injection of 600 MBq technetium-99m methylene diphosphonate (MDTP) intravenously. The images were viewed interactively in axial, sagittal and coronal planes on-screen by a senior radiologist and selected images hard-copied.
Scintigraphic activity was reported (subjectively) as being normal, minimal, moderate or greatly increased. The level of the uptake, side and specific location were indicated. In those patients in whom the SPECT scan was abnormal, reverse gantry angle CT scans of the relevant level(s) were usually obtained [Figure - 1]a,b.
The approximate time of onset of pain for the first time, the day the patient was examined in the clinic and the date of SPECT examination was recorded. Other related factors including age at onset, sex, symptoms (pain in extension or flexion), sporting activities (identifying individual sports), SPECT results, plain X-ray results, CT scan results, pre and post-treatment Oswestry disability index were recorded. CT scan results were not included in the univariate analysis since all results were not available. Different variables in SPECT positive and negative patients were compared using univariate analysis. Determinants of positivity versus negativity of SPECT were identified by discriminant analysis using multivariable logistic regression (SPSS ver11).
| Results|| |
One hundred thirty two patients with low back pain had SPECT imaging. Seventy nine patients had positive scans (i.e. spondylolysis at single or multiple levels in the lumbar spine) and 53 patients had negative scans. Out of the 79 patients with positive SPECT scans, 60 were males and 19 were females (chi square test, P< 0.001). The mean ages of onset of symptoms are 20 and 18 years in SPECT positive and SPECT negative subjects respectively (P = 0.014). The results of the comparison of some of the characteristics of SPECT-positive and negative patients are presented in [Table - 1].
Low back pain in extension was significantly more common in SPECT-positive cases (P = 0.001) whereas low back pain in flexion was not associated with significant abnormalities on SPECT imaging. Bilateral uptake in SPECT positive subjects were high (80%) and 57 subjects (70 %) had increased uptake in the posterior elements of L 5 .
Being an active sporting individual at any level had significantly higher chances of having posterior lumbar spinal stress injuries than non-sporting individuals (P = 0.007). In this population sample, footballers (25) and cricketers (8) had significantly higher probability of suffering from symptomatic spondylolysis requiring treatment.
The mean and median time lag from the onset of low back pain to SPECT imaging was significantly different in the two groups. The mean and median time lag was 7 and 5 months (range 1-48) in SPECT positive group and 25 and 18 months (range 2-96) in SPECT negative group respectively (Mann Whitney test, P < 0.001).
Multivariate analysis showed that there is no significant difference in the SPECT results in the period of 3-6 months following onset of pain compared to the first three months (odds ratio = 0.5). But there is a significant reduction in number of positive results if the onset of pain exceeded six months compared to the first three month (odds ratio = 0.06) [Table - 2].
Thus, as the waiting time for being scanned increases, the chance of the negative scan increases. There is a window period of six to seven months after which the SPECT scans generally tend to be negative. This means that there is less chance of radionucleide uptake on SPECT scans in posterior elements stress injuries after approximately six months from the onset of low back pain
| Discussion|| |
Young athletes are at an increased risk of lumbar stress injuries. Whilst studies are typically flawed by methodological limitations, they generally indicate a prevalence of established spondylolysis, which is typically 2 to 3 times that seen in the general population and varies between 15-50% ,,,14] . Muschik et al reported a high incidence of spondylolysis and suggested that this was due to increased weight on the pars interarticularis from repeated hyperextension and rotation, as is common in many sports. Studies of female gymnasts and male American footballers show that there is fourfold increase in incidence of spondylolysis in these individuals as compared to their nonathletic peers  . Hardcastle et al, found that fast bowlers in cricket have a higher incidence of pars interarticularis defect and disc degeneration  .
The diagnosis of posterior element stress injuries may be difficult and radiographs are certainly deficient in this regard. Bone scintigraphy with SPECT is probably the most sensitive method with which early lumbar stress lesions may be detected (the role of MRI is still contested), conferring greater sensitivity than planar bone scintigraphy and permitting spatial localisation.
Lusins et al found a propensity for SPECT to be positive in patients with spondylolysis and a recent injury in comparison with those patients with spondylolysis and more long standing symptoms , . In this present study, it has been observed that the probability of an abnormal SPECT scan in patients with low back pain diminishes with the passage of time from the onset of symptoms. This waiting time resulted in difficult decision making with regards to diagnosis and further management. The positive SPECT images were graded according to the intensity of activity. In general, more intense scintigraphic activity in the posterior elements of lumbar spine was associated with recent injury and was concordant with the history of the patient (i.e. shorter duration of symptoms). Conversely, those patients with lowgrade scintigraphic abnormalities tended to have a longer duration of symptoms. However, it is worth noting that a negative SPECT scan does not exclude a spondylolysis, as chronic, non-united spondyloyses are generally scintigraphically occult (there is little or no abnormal bone turnover in these predominantly fibrous non-unions) This is reflected in the presence on CT of complete spondylolyses in 10 of the 53 patients who had negative SPECT images. This observation correlates well with the view of Congeni et al, who concluded that nuclear medicine studies have a false negative rate of 15% (when CT scan is used as the standard to establish the diagnosis of spondylolysis)  .
From the present results, it is speculated that there is a window of approximately six months from the onset of symptoms, after which the sensitivity of SPECT diminishes. However, window is valid only for adolescent patients who have an acute onset of symptoms and have been seen in the clinic in the acute phase. Although, we do know that some patients may have presented themselves to the clinic earlier because of more pain and disability or pressures from their sporting authorities, there is little clinical correlation between the intensity of pain and the scintigraphic findings. The duration of symptoms taken from the history at the initial physician visit was not a valid criterion for determining the fracture type as predicted by SPECT followed by CT scanning.
In this selected population, we observed that in older athletes (post-adolescence) with a longer duration of low back pain, there was a lower probability of posterior arch scintigraphic abnormalities. Their pain may be due to associated disc degeneration or instability due to separation of the defect. Lowe et al, found that a history of pain for less than one year correlated with the development of stress fracture, the associated osteogenesis and repair being responsible for the high isotope uptake seen scintigraphically  .
In our present series, out of 79 patients who had positive SPECT scans, 26 patients had confirmed spondylolysis in the CT scans with varying grades of separation at the site of defect (33%). On reviewing the SPECT images of these CT positive pars defects it was found that the intensity of isotope uptake was mild to moderate. The rest of the SPECT images that showed intense activity with no defect in the CT were thought to be due to stress reaction in the posterior arch rather than due to any fracture or may be a healing fracture. In this subgroup, conservative treatment with rest and graduated exercises in those with symptoms of acute onset resulted in a much better outcome than the group with longer duration of symptoms and a complete or partial pars defect.
Congeni et al classified those patients with symptoms greater than 6 months to have chronic fractures as seen on CT scan  . From this study we can predict that after six months from the onset of symptoms, SPECT imaging tends to loose its value as a diagnostic modality for spondylolysis or posterior element lumbar spinal injuries. This implies that SPECT scans could indirectly predict healing to certain extent. However, it is difficult to predict who will require surgery on the basis of SPECT scans alone.
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U K Debnath
The Centre for Spinal Studies & Surgery, Queens Medical Centre, Nottingham
Source of Support: None, Conflict of Interest: None
[Figure - 1]
[Table - 1], [Table - 2]