Background/Purpose: Low back pain (LBP) is commonly characterized by symptom duration. Acute LBP is defined as pain lasting < 3 months and chronic LPB is defined as “pain on at least half the days in the past 6 months”. Identifying mechanisms that discriminate chronic versus non-chronic is important to prevent transitions to chronic pain states, thus, improving the LBP prevalence, disability rates and health care costs.

Biomechanical changes are one potential mechanism; prior research suggests that persons with acute LBP use more pelvic rotation and less lumbar flexion or a stiff spine when compared to healthy controls. Pain catastrophizing, the exaggerated and negative orientation of pain, predicts disability among persons with acute and chronic LBP

The aim of this study was to examine the association of lumbo-thoracic ratio (LTR), representing the level of stiffness of lumbar spine, with pain catastrophizing, assessing whether this association varies between individuals with chronic and non-chronic LBP at baseline, 2.5 and 6 months.

Methods: A sample of 29 adult patients with provider diagnosed acute LBP (<3 months) and telephone access completed questionnaires and biomechanical data at baseline, 2.5 and 6 months along with weekly questionnaires. The NIH Task Force of Research Standards for Chronic LBP’s was used to classify participants as chronic vs. non-chronic.

Biomechanical measures. Participants completed trunk forward bending and backward return tasks at slow and fast self-selected paces. Lumbar flexion was calculated as the difference between the thoracic and pelvic rotations and was then used to calculate the LTR at that time instant as the ratio of lumbar flexion over thoracic rotation.

Pain catastrophizing measured with the Pain Catastrophizing Scale (PCS) (Cronbach’s α=.94; range: 0-52).

Analysis. Linear regression models were used to evaluate whether the association between PCS and LTR varied by chronic LBP status using an interaction term.  

Results: At the 2.5 month follow-up, significant differences in the association of PCS with LTR of fast-paced tasks were identified between those with chronic and non-chronic LBP (F=5.0; p=.04 for both interaction terms); for those with chronic LBP, an increase in PCS was associated with an increase in LTR (p=.006), while among those without chronic LBP there was no association between PCS and LTR (p=.23). The association between PCS and LTR did not differ by chronic LBP status at baseline or 6 months; at each of these time points, regardless of chronic LBP status, there was a positive association between PCS and LTR of fast-paced tasks.

Conclusion: The relationship identified between PCS and LTR is a possible contributor to the development of chronic LBP.