Causality Of Low Back Injury ODG
Treatment Workers Comp 2010

Published by Work Loss Data Institute 8th Edition

Determination of causation typically involves mechanism of injury, temporal relationship and dose effect.  There is strong epidemiological evidence that physical demands of work, including manual materials handling, lifting, bending, twisting and whole body vibration, can be associated with increased reports of back symptoms, aggravation of symptoms and injuries. 

While the epidemiological evidence shows that low back symptoms are commonly linked to physical demands of work, that does not necessary mean that low back pain is caused by work.  Although, there is strong scientific evidence that physical demands of work can cause individual attacks of low back pain, overall that only accounts for a modest proportion of all low back pain occurring in workers.  There is moderate scientific evidence that physical demands of work play only a minor role in the development of disc degeneration.  There is strong epidemiological and clinical evidence that care seeking a disability due to low back pain depend more on complex individual and work-related psychological factors than on clinical features or physical demands of work. 

Studies of mono psychotic trends show that low back aging changes are genetic with little influence of experience short of spine fracture and dislocation or perhaps being brought on earlier with smoking. 

The authors of the ODG Guidelines quote several studies in support of their position on causality. They note that although recent studies have shown that heredity is a dominant factor in disc degeneration, the common notion that occupational physical load is a major risk factor persists.  The guidelines review a study that found that anthropometric parameters, including body weight and axial disc area, were more important in disc degeneration then physical activities at work and leisure time which had little or no influence on disc narrowing.  They point out that on current views that all loading is detrimental to the spine, routine or repetitive loading may actually have a beneficial effect, delaying disc desiccation associated with aging. 

They quote additional studies, including a recent metaanalysis was not able to find high-quality studies that satisfied more than three of the Bradford-Hill criteria for causation for either occupational bending or twisting in low back pain and the evidence suggested occupational bending and twisting in general is unlikely to be independently causative low back pain.   

The guidelines point out that there is evidence that leisure time sport or exercise, and prolonged sitting/walking are not associated with low back pain.  Evidence for associations with heavy physical work and working with one’s trunk in a bend and/or twisting position and low back is conflicting. The guidelines recommended utilizing the Bradford-Hill criteria as a guide in determining causation.

They present the Bradford-Hill criteria which includes the following:

Temporal relationship, meaning exposure always precedes the outcome and this is the only absolute essential criteria.  They also note strength and state that the stronger the association the more likely it is causal but a small association does not mean that there is not a causally effect. Regarding dose response relationship, they state that an increasing amount of exposure increases the risk and that there is strong evidence for a causal relationship, but the absence of a dose response relationship does not rule out a causal relationship, as the example if a threshold exist above which a relationship may develop.

These criteria also include consistency, meaning that the association is consistent when results are replicated in studies in different settings using different methods.  This would serve to strengthen the likelihood of an effect.  Of a note, plausibility is another factor, in that the plausible mechanism between cause and effect is helpful, but they note that knowledge of the mechanism is limited by current knowledge.

Consideration of alternate explanation is always necessary to consider multiple hypotheses before making conclusions about causal relationships.  They note that conditions can be altered by an appropriate experimental regimen and the hypotheses can be tested and this would be under the heading of experiment. 

They suggested specificities as another criteria and this is established when a single putative cause produces a specific effect.  This is the weakest of all criteria and absence of specificity in no way negates a causal relationship. They note that because outcomes are likely to have multiple factors influencing them, it is highly unlikely that a one-to-one cause effect relationship exists.

Their last point is coherence, in which they state that an association should be compatible with the existing theory of knowledge but the lack of laboratory evidence cannot nullify the epidemiologic effect on association.

They discuss the ODG causality likelihood and basing on raw data, causality likelihood indicates the benchmark percentage of total lost workdays that are occupational in nature.  This indication may be used as an aid in evaluating causality, but any definitive determination requires detailed case specific analysis. 

With respect to the issue of likelihood, they find that with intervertebral disc disorders, causality likelihood is under 5%.  Regarding displacement of thoracic or lumbar intervertebral disc without myelopathy, causality likelihood is under 5%.  For spinal stenosis other than cervical, causality likely is under 5%.  They also say that under 5% as a causality likelihood also occurs with lumbago, sciatica, and thoracic or lumbosacral neuritis or radiculitis in addition to unspecified backache. 

With respect to lumbar strain and sprain, causality likelihood is over 80%. 

Editors note causality or causation, is the most contentious issue in Workers Compensation cases.  It is usually a gray zone and frequently neither black nor white. Determination of causality requires a very detailed and careful history, and a thorough review of the medical records, in addition to a meticulous physical examination and a careful analysis of the imaging studies or any other diagnostic testing that would be appropriate. 

This is one of the greatest challenges we have in spinal care and specifically in low back injuries, which are very frequently reported in the workplace. 

Frequently, there is multiple causation involved with low back injuries and it is important to analyze this issue very carefully.  The patient’s general health, certain comorbidities, the patient’s psychological state, pre-existing conditions, prior injuries, prior surgery, the patient’s attitude towards their workplace and their work environment are all factors that should be considered carefully when arriving at a decision regarding causation or apportionment. 

AAS/rt

__________________________________________________

Outcomes and Presurgery Correlates of Lumbar Discectomy in Utah Workers Compensation Patients
M. Scott De Berard, Ph.D., and Alan Colledge, M.D., et al
The Spine Journal 9 (2009 193-203)

The authors examined long-term multi-dimensional outcomes of lumbar discectomy within a cohort of Workers Compensation patients from Utah and identified presurgical biopsychosocial factors relating to poor outcomes.  They studied 271 workers from Utah who underwent lumbar discectomy from 1994 to 1999, and a total of 134 patients were surveyed at the time of follow-up.  Analysis of patient satisfaction, back pain related dysfunction and the Short Form Health Survey-36 subscales indicated approximately 25% of patients experience poor outcomes.  Older age, number of comorbid health conditions, assign case manager, ligation and time delay from injury to surgery were consistently statistical significant predictors of poor outcomes.  The authors concluded that this study suggests that compensated back surgery patients are at greater risk for poor lumbar discectomy outcomes than non-compensated patients. Presurgery correlates of poor outcomes may be useful identifying high risk compensation patients.  The authors found that presurgical diagnoses were often non-predictable outcomes, and a diagnostic severity index based on presurgical imaging studies was not predictive of lumbar fusion in patient outcomes.  They found that other demographic and psychosocial risk factors were shown to be more consistently predictive of patient outcomes. 

They found that approximately 40% of compensated lumbar discectomy patients were somewhat to extremely dissatisfied with their results and 13% were disabled at the time of the study follow-up. 25% of patients exceeded the clinical cutoff for poor outcomes on the Rowland and Morris D.Q.  In general, most outcome variables were predicted by age at time of injury, depression, number of comorbid health conditions, and whether a case manager was assigned, a lawyer, and time delay from injury to surgery.  They found an interesting finding in an association of poor outcomes with patient assignment and nurse case mangers. They further noted that litigation among compensated low back patients appear to be a consistent factor associated with poor clinical outcomes.   They found it now appears appropriate to begin studies examining the differences among litigated versus non-litigated patients in terms of psychosocial and behavioral characteristics that might place them at higher risk for poor outcomes.