Table 1.

Characteristics of baseline variables

Data source	Categories of measure
Questionnaire
Age	Years
Sex	Female, male
Pain intensity (Low Back Bain Rating Scale[27])	Sum of pain now (0-10), average pain (0-10) and worst pain (0-10) during the preceding 2 weeks
Back pain intensity	Numeric Rating Scale (0-30)
Leg pain intensity	Numeric Rating Scale (0-30)
Back+leg pain intensity (pain score)	Numeric Rating Scale (0-60), the sum of back and leg pain intensity
Two additional questions	Does leg pain spread to the lower part 1) of the leg 2) of the foot?
Duration of actual pain	Less than 3 months, 3-6 months, 6-12 months, ≥ 1 year
Use of pain medication	5-7 days per week, 1-4 days per week, 0 days
Functional level (Roland Morris Questionnaire, validated Danish translation, 23 items[28])	Questions about limitations of daily activities because of LBP
	(0-23), increases when disabilities of daily activities increases
Psychological distress, 4 subscales (Common Mental Disorders Questionnaire, CMDQ[29])	Bothered by the symptom during the past four weeks: ‘0’ if not bothered at all, ‘1’ if bothered a little, moderately, quite a bit or extremely. The subscales were calculated by adding the answers of each item.
Bodily distress	11 questions: ‘Headaches?’, ‘Dizziness or faintness?’, ‘Pains in heart or chest?’, ‘Nausea or upset stomach?’, ‘Soreness of your muscles?’, ‘Trouble getting your breath?’, ‘Hot or cold spells?’, ‘Numbness or tingling in parts of your body?’, ‘A lump in your throat?’, ‘Feeling weak in parts of your body?’, ‘Heavy feelings in your arms and legs?’. One question of LBP was omitted
Worrying and health anxiety	7 questions like for example about worries, that there is something seriously wrong with the body, many different kinds of pain and aches, thoughts that the doctor might be wrong if telling not to worry, worries about the health, etc.
Mental distress	8 questions like for example about nervousness or shakiness inside, spells of terror or panic, feeling fearful and feeling that everything is an effort, etc.
Depressive symptoms	6 questions about feeling blue, feeling of worthlessness, thoughts of ending ones life, feelings of been trapped or caught, feeling lonely and blaming oneself for things
Widespread pain (from the Danish	Two questions covering the preceding two weeks:
version of the General Health	Much bothered by pain or discomfort in
Questionnaire)	1) neck, shoulders, arms, hands?
	2) back, buttocks, legs, knees and feet?
Fear avoidance[5]	3 questions (0-10) about physical activity causing increasing pain, increasing pain indicating stop of the activity, and lack of ability to do normal activity and work with present pain. Sum score.
Work-related questions	1) Blaming the work for LBP (work the only cause vs. partly or not the cause)
	2) Expectations about return to work within 6 months (10 box scale, 8-10 vs. <8)
	3) Ongoing compensation (compensation claim, yes or no).
General health questions (Danish version of SF-36[30])	In general, how do you perceive your health: Splendid? Very good? Good? Not so good? Bad?
Items of social aspects. Questions from a
Danish Public Health Questionnaire1
School education	4 ordered categories
Vocational education	5 ordered categories
Job function	5 ordered categories, leader yes, no
Marital status	5 categories
Children	Yes, no
+/- home ownership	Yes, no
Personal and family income	4 ordered categories
Sports or exercise activity in leisure time	2 categories
Smoking	Never, previous, current
Alcohol habits	Frequency, 6 ordered categories
Physical examination
Body Mass Index (BMI)	Kg/m2
Signs of nerve root compression	At least one of the following: Positive Lasegue ≤ 60º, missing or inhibited reflex, altered sensation in a dermatome or paresis.
Forward flexion	Modified Schober: Lumbosacral junction marked, a mark placed 10 cm more proximally and 5 cm more distally. The increment under forward bending measured.
Side-flexion	A mark set on the lateral side of the thigh where the fingertips end.
	A new mark set after maximal side-bending, the difference measured. Side -flexion computed as the mean of the right and left side.
Waddell’s signs	One or more of 8 signs: LBP worsened by axial loading or simulated
	rotation, significant change of Lasegue in the sitting position, diffuse sensory changes, tenderness by superficial palpation, moaning, holding the hands on the back, using walking aids.
Tender points. (A standardised, validated examination method[24])	A gradually increasing pressure applied by the thumb at 18 spots on the body, the pressure increased up to 4 kg during 4 seconds. The spots located symmetrically on the neck, shoulders, forearms, second ribs, buttocks and legs. The pressure first demonstrated to the patient distally on the forearm, and the patient instructed to distinguish a firm pressure from pain. Only painful points counted as positive.
Imaging
X-rays of the lumbar spine (Validated method[25,26])	Disc height reductions measured on plain lateral X-ray by one of the authors (OKJ), classified as no height reduction: 0, 0-25% ≈ slight: 1, 25-75% ≈ moderate: 2 and ≥ 75% reduction ≈ severe: 3.
	Disc degeneration score L1-4: The sum of L1 through L4 scores.
	(Validation in 60 patients by blinded reevaluation of images: The agreement good or acceptable in the upper 4 segments (agreement 83-95%, Kappa 0.46-0.71), not at the lumbosacral segment (agreement 73%, Kappa 0.34). The sum score only comprised the sum of the 4 upper lumbar segments (agreement for the sum 68%, Kappa 0.54))
Magnetic resonance imaging (MRI)	T1 and T2 -weighted sequences. STIR sequences of the sacroiliac joints if
Most examinations performed at Silkeborg Regional Hospital using a 0.7 T machine	inflammatory back disease was suspected clinically.
	No standard grading system was applied. The images described by a specialist of radiology. All examinations evaluated by one of the authors as well (OKJ). When in doubt, the images were discussed with the back surgeons at weekly conferences.
History, physical examination, MRI and questionnaire
Low back pain (LBP) classification	1) Non-specific LBP:
	without pain below the knee: 96 patients (30%), including 12 patientswith disc herniation without radiating pain or neurologic signs.
	with pain below the knee: 118 patients (36%), including 15 patients with disc herniation with referred pain to leg or foot, but no neurologic signs
	2) Radiculopathy:
	111 patients (34%) with radiating pain and signs of nerve root
	compression and disc herniation (n=97) or spinal stenosis (n=14). The symptomatic disc herniation was located at L5-S1 in 62 patients, L4-5 in 33 patients and L2-4 in 2 patients. Spinal stenosis was located laterally in 9 patients and centrally in 5 patients.

¹Centre of Public Health, University of Aarhus, Denmark.