To flex or not to flex? Is there a relationship between lumbar spine flexion during lifting and low back pain? A systematic review with meta-analysis

Key points

1. 01The common advice to keep a straight back and avoid flexion when lifting grew largely from cadaver studies, and rolling it out at work has not lowered occupational low back pain.
2. 02Studies measuring intralumbar flexion angles found no meaningful difference in peak lumbar flexion between people with and without LBP when lifting.
3. 03A subset using thoracopelvic angles found people with low back pain lifted with about 6 degrees less lumbar flexion, the opposite of the usual assumption.
4. 049 of 11 studies reported no significant between-group difference in lumbar flexion during lifting.
5. 05All included studies were judged low quality and mostly cross-sectional, so they cannot establish cause and effect.

How it was conducted

Design

Etiology systematic review with meta-analysis (prospectively registered, PROSPERO CRD42017075661)

Search

ProQuest, CINAHL, MEDLINE, and Embase searched to 21 August 2018

Included studies

11 studies, 1 longitudinal and the rest cross-sectional, comparing lumbar flexion during lifting in people with versus without low back pain

Flexion measures

Intralumbar angles (lower-spine motion) in some studies and thoracopelvic angles (trunk relative to pelvis) in others

Analysis

n-weighted pooled mean and standard deviation of flexion in the LBP and no-LBP groups, with one comparison taken per study

What they found

• Intralumbar-angle studies: no difference in peak lumbar flexion when lifting, 1.5 degrees (95% CI -0.7 to 3.7, P = .19) in the longitudinal study and -0.9 degrees (95% CI -2.5 to 0.7, P = .29) across cross-sectional studies.
• Thoracopelvic-angle studies (7 cross-sectional): people with LBP lifted with 6.0 degrees less lumbar flexion than people without LBP (95% CI -11.2 to -0.9, P = .02).
• 9 of 11 studies reported no significant between-group difference in lumbar flexion during lifting.
• Overall study quality was rated low.

Limitations

• Most included studies were cross-sectional, so they show association at a point in time, not whether flexion causes future low back pain.
• The authors rated the evidence low quality, which weakens confidence in the pooled estimates.
• Flexion was measured in different ways (intralumbar versus thoracopelvic angles), making studies hard to combine cleanly.
• The review examined how much people flex, not load, speed, or repetition, which may also matter for injury.

Why it matters

For patients

Bending your back while lifting is not clearly the cause of back pain it is often made out to be, and fear of one bad lifting posture may not be warranted.

For clinicians

Be cautious about prescribing rigid straight-back lifting rules to prevent or treat LBP; current evidence does not support lumbar flexion during lifting as the culprit.

For readers

This is a clear example of strong clinical dogma resting on weak evidence, with cross-sectional data that even points the opposite way to the common assumption.