Purpose: The purpose was to investigate how physical function is assessed in people with musculoskeletal disorders in the low back. Specifically:

• Which questionnaires are used to assess physical function in people with musculoskeletal disorders in the low back?
• What aspects of physical function do those questionnaires measure?
• What are the measurement properties of the questionnaires?

Materials and methods: A systematic review was performed to identify questionnaires and psychometric evaluations of them. The content of the questionnaires was categorised according to the International Classification of Function, Disability and Health, and the psychometric evaluations were categorised using the COnsensus-based Standards for the selection of health Measurement Instruments (COSMIN) checklist.

Results: The questionnaires measured disability or ability to cope in everyday life, rather than physical function as such. Different aspects of a person’s mobility and ability to attend to one’s personal care were most often included regarding activity and participation. For body functions, items about sleep and pain were most often included. The Oswestry Disability Index and the Quebec Back Pain Disability Scale showed adequate psychometric properties in most evaluations.

Conclusions: The extent of psychometric evaluations differed substantially, as did the items included. Focus of measurement was predominantly on activities in daily life.

• Implications for rehabilitation
• Valid and reliable instruments that measure relevant aspects of low back disorders are needed to provide early diagnostics and effective treatment.
• Most questionnaires need more psychometric evaluations to establish the quality.
• The Oswestry Disability Index and the Quebec Back Pain Disability Scale showed adequate psychometric properties in most evaluations.
• The results may be useful when making decisions about which measurement instruments to use when evaluating low back disorders.