References
- Cyriax JH Text Book of Orthopaedic Medicine Vol 1 1982 Balliere Tindall, London
- Waddell G, McCulloch JA, Kumel E, Venner RM Non-organic signs in low back pain Spine 1979 5:117–125
- Kummel BM Non-organic signs of significance in low back pain Spine 1996 21:1077–1081