Nurses and Patient Lifting:
How Cumulative Trauma Injures Spinal Discs

The following information, from Section E. "Disorders of the Low Back" of the rescinded Ergonomics Program Final Rule, is offered as explanation of how healthcare workers may suffer cumulative trauma injuries to the lumbar spine from the repetitive lifting of patients.

Under "Biomechanical Factors and Laboratory Experiments," insidious onset is described in some cases of work-related low back pain "rather than a single, point-in-time event with immediate low-back pain" (Bergquist-Ullman and Larsson 1977, Ex. 26-933), explained in part by absence of nociceptors in the disc and facet joints other than the synovial lining (Pope et al. 1991, Ex. 502-502). "These load-bearing structures may, therefore, become injured without immediate recognition (e.g., sudden pain), and the eventual manifestation of low-back pain may only occur after a series of point-in-time events have sufficiently injured these spinal structures to the point where nociceptors become irritated (e.g., in the outer one-third annulus or facet synovium)."

In the discussion of disc disorders, it is given that epidemiological evidence suggests heavy lifting and manual handling are associated with low back and disc disorders (Bernard and Fine 1997, Ex. 26-1).

"Excessive or repeated spinal loading and inadequate rest periods to permit repair mechanisms to function may be associated with biomechanical stresses that damage intervertebral disc cartilage endplates. This may then disturb metabolic transport, hastening the development of degenerative disc disease and disc herniation with secondary nerve root compression or inflammation."

Among studies of compressive force exerted on human cadaver spines, Adams and Hutton (1982, Ex. 26-1379) determined tolerance of up to 10 kN for single-loading events prior to disc failure with 40% failing at 5.4 kN with forward flexion. Previously healthy discs failed at an average of 3.8 kN with simulation of repetitive loading, supporting "the clinical observation that the intervertebral disc is especially vulnerable when loaded in the flexed position or when subjected to repetitive loading."

Armstrong (1985, Ex. 22-877) described microtears in the posterior annulus fibrosus and cartilage end plates which are subjected to the greatest spinal compressive forces (Gracovetsky and Farfan 1986, Ex. 26-128; Hickey and Hukins 1980, Ex. 26-708; Pope et al. 1991, Ex. 26-1296). "With repeated lumbar spinal stresses and/or injuries, progressive microfractures in cartilage end plates and annular fibers (annulus fibrosus) may develop in the intervertebral discs (initially toward the center of vertebral bodies). This causes altered metabolism and fluid transfer with different mechanical behavior of the disc.

"Eventually radial tears result in the development of degenerative disc disease and/or bulging. As a result of this damage, the capacity of the lumbar intervertebral discs to tolerate further compressive loads during lifting is altered. When these smaller tears extend and form complete annular tears, the nucleous pulposis can protrude (disc herniation) (Farfan et al. 1970, Ex. 26-113). Over time, sclerosis of cartilage endplates and altered disc loading can facilitate the development of facet arthropathy, osteophytic change, stenosis, or instability. Disc degeneration in combination with facet arthropathy may also lead to foraminal narrowing with resultant nerve compression and radicular pain.

"These observations are consistent with a cumulative trauma theory that could account for some types of low-back injuries and is supported by the research and opinions of other authorities (Erdil, Dickerson, and Chaffin 1994, Ex. 26-424; Pope et al. 1991, Ex. 502-502; Yong-Hing and Kirkaldy-Willis 1983, Ex. 26-405). While many individuals with degenerative disc disease are asymptomatic, individuals with greater degrees of degeneration are at risk for low-back pain."

The discussion above explains how healthcare workers may sustain lumbar disc damage over time from repeatedly lifting patients without perception of pain - until disc damage and related pathology increase in severity.

Anne Hudson, RN, BSN
Work Injured Nurses' Group USA
www.wingusa.org
8-4-03

Department of Labor. Occupational Safety and Health Administration. Federal Register. Ergonomics Program Final Rule. Section E. "Disorders of the Low Back." Tuesday Nov. 14, 2000. No. 220, Part II. 29 CFR. Part 1910. Vol. 65. 68469 - 68483.

To access online:
http://www.access.gpo.gov/su_docs/fedreg/a001114c.html.
Scroll down to Occupational Safety and Health Administration, Rules.
Select pages 68461-68510.
Scroll down to page 68469 and Section E. "Disorders of the Low Back."

For studies referenced in the Federal Register, call the OSHA Docket Office:
1-202-693-2350.