SPECT/CT correlation of morphology and metabolism in facet joint

Objectives Evidence on the correlation between CT morphology and bone metabolism in the facet joint (FJ) is scarce. We analyzed this correlation in 28 patients suffering from lower back pain using skeletal SPECT/CT.

Methods In 28 patients, SPECT/low-dose CT datasets of the lumbar spine were acquired using a Symbia T6 hybrid camera (Siemens Healthcare) 3-4 h p.i. of 7 MBq (2 mCi)/kg body weight Tc-99m-DPD. In a semi-quantitative approach, the bone metabolism of the lumbar segments was calculated as the ratio between maximal tracer uptake in the FJ and mean uptake in the sacrum (QSPECT). In addition, FJ DPD uptake and CT morphology changes indicative of FJ arthritis were visually evaluated on four-point scales (VSPECT and VCT). The analysis was repeated and intra-observer reproducibility calculated (IR; Spearmans correlation coefficients). The mean value of VSPECT and VCT analyses was calculated and used to classify the qualitative findings as physiological (values < 1.5) or pathological (values > 1.5).

Results The IRs were 0.95 for QSPECT, 0.85 for VSPECT, and 0.64 for VCT. VCT correlated significantly with VSPECT (r = 0,43, p < 0.01) and QSPECT (r = 0,58, p < 0.01). 39% and 27 % of FJ were classified as normal or pathological in both modalities, respectively. 30% of the FJ were pathological in CT only, and 4% in SPECT only.

Conclusions Despite significant correlation between metabolism and morphology in FJs in patients with lower back pain, discrepant results were found in 34% of the joints studied. Isolated morphological changes could be interpreted as inactive osteoarthritis (late stage). Isolated increase of DPD uptake might correspond to early-stage FJ osteoarthritis preceding structural alterations. However, both of these hypotheses should be confirmed in future prospective clinical studies. The semi-quantitative approach achieved a considerable higher reproducibility and thus might be more reliable compared to qualitative techniques.