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from Section E. "Disorders of the Low Back" of the rescinded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.
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).
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
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
To access online:
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: