Research Review By Dr. Christopher Coulis©

Date Posted:

April 2009

Study Title:

Classification of low back-related leg pain – A proposed patho-mechanism-based approach

Authors:

Schafer A et al.

Author's Affiliations:

Curin University of Technology, School of Physiotherapy. Perth, Australia

Publication Information:

Manual Therapy 2009; 14: 222-230.

Background Information:

LBP is a prevalent and costly disorder affecting roughly 80% of the population at some point in their lifetime. Billions of dollars have been spent attempting to improve clinical outcomes, however disability and lost time from work have not improved over the past several decades.

It is believed that approximately 25-57% of all LBP cases have associated leg pain and these cases account for a disproportionately large amount of LBP related health care dollars. Moreover, accompanying leg pain is an important predictor for chronicity and severity of LBP.

Several structures are capable of producing referred leg pain; these can be neural or musculoskeletal. Failure to identify the etiology of referred leg pain can result in inappropriate assessment and treatment.

The aim of this paper was to propose a classification system for low back related leg pain using a patho-mechanical approach.

Pertinent Results:

Pathomechanisms of Low Back Related Leg Pain:
  • Inflammation - Internal disc derangement or endplate fractures activate an inflammatory cascade which can cause discogenic referred leg pain or nerve root irritation. Peri-radicular inflammation can also increase neural mechanosensitivity and alter neural mobility.
  • Compression - Mechanical nerve root compression secondary to degenerative changes or a space occupying lesion may result in impaired perineural blood flow. This in turn can cause increased perineural fluid pressure and mechanical nerve fiber deformation. Nerve root compression can result in sensory and motor dysfunction and radiating pain.
  • Central Events - Neural plasticity can occur secondary to continued nociceptive input. This may result in a lowered threshold to nociceptive input, changes in subcortical and cortical brain regions, disinhibition and a phenotypic switch of non-nociceptive neurons to nociceptive neurons. This is commonly referred to as central sensitization.
  • Musculoskeletal referral - Pain generators can include the intervertebral disc, facet joint, sacroiliac joint, or a variety of myofascial structures. All of these structures have been sufficiently studied and identified as potential leg pain generators.
Based on these mechanisms, the authors have proposed 4 subgroups of low back related leg pain:
  1. Central Sensitization
  2. Denervation
  3. Peripheral nerve sensitization
  4. Musculoskeletal
How do you differentiate the 4 subgroups of low back related leg pain?

The initial examination includes a comprehensive assessment of the patient’s subjective complaint. The authors suggest using the Leeds Assessment of Neuropathic Symptoms and Signs scale. This tool was designed to screen for neuropathic symptoms and signs of central sensitization. The physical evaluation includes neurological examination, assessment for nerve root tension, active ROM, and joint provocative testing.

Proposed key findings for each subgroup include:

Central Sensitization
  • thermal and mechanical hyperalgesia/allodynia
  • neurological evaluation may reveal altered pin prick thresholds or light touch allodynia
Denervation
  • structural nerve damage
  • altered motor strength, deep tendon reflex, and/or sensation in a dermatomal pattern
Peripheral nerve sensitization
  • absence of gross neurological deficits
  • presence of nerve root tension – referred leg pain with neural movement
Musculoskeletal Referral
  • absence of gross neurological deficits
  • absence of nerve root tension
  • positive joint provocation maneuvers OR centralization/peripheralization
Mixed pathologies
  • multiple pathologies may be present
  • the authors believe the existence of a primary mechanism responsible for a patient’s symptoms can be determined using this approach

Clinical Application & Conclusions:

Several classification systems for low back pain and low back related leg pain have been previously proposed. Murphy et al. (1) attempted to classify patients using a diagnosis based rule; essentially using provocation maneuvers to determine the tissue specific origin of pain.

Most readers will be familiar with McKenzie and Waddell’s frameworks for back pain evaluation. McKenzie based his system on mechanical loads to injured tissues to determine the optimal treatment and Waddell employed an approach assessing psychosocial factors. This was the first paper to propose a patho-mechanical based classification system.

To date, evidence for the treatment of lumbar spine pain has been equivocal, as treatment options have been studied on heterogeneous populations. For example, spinal manipulative therapy has been found to be both an effective and an ineffective treatment, depending on the sample population and patient selection. Employing models such as the one proposed here, in addition to more established Clinical Prediction Rules (see link below) will improve our ability to categorize patients, select the proper treatment approaches and thus improve clinical outcomes.

Study Methods, Strengths & Weaknesses:

This is a theory paper that requires further validation through subsequent study. The proposal of a model in this format is the first step in the validation of the model.

Additional References:

  1. Murphy DR, Hurwitz EL. A theoretical model for the development of a diagnosis-based clinical decision rule for the management of patients with spinal pain. BMC Musculoskelet Disord. 2007 Aug 3; 8:75.