Table 4 Selected prognostic variables for subgroup analysis.

Demographic variables

   Age ≤ 40 years versus > 40 years

   Women versus men

   High education versus low education

Anamnestic and neurological variables

   Neck pain versus no neck pain

   Quetelet index ≤ 30 versus > 30

Radiological variables

   Uncovertebral osteophytes versus no osteophytes

   Straight neck versus lordotic neck

   Low disc (≤5 mm) versus high disc (>5 mm)