Background and aims
To estimate the prevalence of chronic low back pain (CLBP) in the general adult Spanish population and to establish CLBP patient groups according to the health status, mental health, pain level and its impact.
Methods
Data has been obtained from the National Health Survey of Spain 2017 with a sample of 23089 adults. Based on the health status, mental health (GHQ-12), pain level and its impact on daily activities, a cluster analysis was performed to identify groups of CLBP patients. Chi-squared and Kruskal-Wallis-H tests were used to analyze differences between groups.  
Results
The prevalence of CLBP was 22% (CI95%:21.5-22.5), and 63.8% were women with a mean of 62.08 years old.
Three groups of CLBP patients were identified. Group 1 (N=766), worse group, including   subjects with bad/very bad health status (85.6%), a higher score in GHQ-12 (Mean=8.57), with severe/extreme pain (61.7%) and quite/a lot of impact of pain on daily activities (72.3%). Group 2 (N=2141), medium group, with subjects referring regular health status (56.3%), a score of 2.11 in GHQ-12, with moderate/mild pain (61.6%) and a moderate impact of pain on daily activities (48.4%). Group 3 (N=2170), better group, including subjects with good/very good health status (60.6%), a lower score in GHQ-12 (Mean=0.89), without pain or very mild/mild (84.1%) and without or little impact of pain on daily activities (99.4%). 
Conclusions
There is a high prevalence of CLBP in Spain, with differences in the characteristics of the patients. Identifying groups of patients could serve to personalise therapeutic strategies.

CHRONIC LOW BACK PAIN IN THE ADULT'S SPANISH POPULATION: IDENTIFYING CLINICAL SUBGROUPS THROUGH CLUSTER ANALYSIS