Lumbar Instability

Original Editors - Anke Jughters

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Definition/Description

Spinal instability is defined as “an abnormal response to applied loads and is characterized by movement of spinal segments beyond the normal constrains” (American academy of orthopedic surgeons 1985).

Lumbar spinal instability may be caused by:

• degenerative disease
• postoperative status
• trauma to spine or its surrounding structures
• development disorders, like scoliosis and other congenital spine lesions
• infection
• tumors

Instability of the lumbar spine occurs often and mostly affects the region of L4-L5 or L5-S1 (Alam 2002). The clinical symptoms and signs are non-specific and can be described as ‘low back pain with radiculair pain’. These signs are observed especially when the position changes.
The spinal system has three basic functions to perform, namely carrying loads, protection of spinal cord and nerve roots and allowing movement between body parts. To make sure that the spinal system can fulfill these tasks, there needs to be a spinal stabilizing system

The stabilizing system can be represented by means of three subsystems. The passive subsystem consisting of vertebrae, facet joints, intervertebral discs, spinal ligaments, joint capsules and passive muscle support. Then there is the neural feedback system containing force and motion transducers and the neural control centers. The third system is the active subsystem including the muscles and tendons surrounding the spinal column. Thus the spine needs the integrated function of the three subsystems, mentioned above, to control stability and movement. Instability is found when one of the systems fails to fulfill his task, and disturbs the balance

Muscles are one of the three important factors contributing to stability of the spine. But is there one muscle that deserves more attention than all the others? At a given time, there can be one muscle that is more important than another one. Only, the importance of the individual muscles change when there are alterations in body movements and positions. This change will happen by changes and adjustment in relative muscle activation. All muscles are important, a clinical focus on one muscle and not the whole system will be pernicious Thus, Lumbar Multifidus for example, has the ability to control and restore motion of an uninjured segment. Nevertheless is it important to consider that all lumbar muscles contribute to stability of the lumbar spine

Clinically Relevant Anatomy

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Epidemiology /Etiology

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Characteristics/Clinical Presentation

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Differential Diagnosis

Next to the Lumbar Examination, you also have medical representation:

→ neutral radiography:

Shows many indirect signs that are associated with spinal instability:
1. Moderate disc degeneration with mild space narrowing, osteosclerosis and osteophytosis of the vertebral end plates (Kirkaldy-Willis 1985)
2. Presence of traction spur, which is a particular type of osteophyte that is located 2-3 mm from the end plate and has a horizontal orientation. (Remy et al 2001)
3. Intervertebral vacuum phenomenon is due to rupture of the insertion of Sharpey’s fibres and may be the result of vertebral instability (Alam 2002)

→ functional radiography
This is the perfect method to show intervertebral instability or abnormal motion between two vertebrae. Dynamic radiographs obtained in both flexion and extension, prove to be a simple and reliable method to determine motion segment instability and can also indicate the lesions located in specific areas based on the ‘‘dominant lesion’’ concept (Dupuis et al 1985).

→ computed tomography
This technique is aimed at demonstrating a gap in the facet joints during rotation of the trunk, which is an indirect sign of spinal instability.
→ magnetic resonance imaging

MRI claimed to be the best method to find lumbar instability. However, symptoms may not always be defined to morphological lesions such as disc herniation, foraminal stenosis or stenosis of the spinal canal but rather to segmental instability (Alam 2002). Identifying patients with an increased chance of instability on MR imaging can be clinically relevant and can influence indications for functional radiographs.

Diagnostic Procedures

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Outcome Measures

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Examination

Prone Instability Test

Medical Management

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Physical Therapy Management

Why is there so much ado about the Transversus Abdominis and Lumbar Multifidus? They are both primary stabilizers, meaning they are responsible for stabilizing and approximating joints. The most important things that characterize them are following qualities: they are located close to the joint, they lie deep, are slow twitch, consist of short fibers and reasonable fatigue resistant. With muscle imbalance they tend to weaken and lengthen

Often, it has been assumed that Lumbar Multifidus and Transversus Abdominis co-contraction is required for lumbar stability and that it has to be maintained with patients suffering from low back pain Co-contraction occurs in periods of time but it is not necessary for stability. In preparation for the disruption to the spine from a movement of an extremity (ex. arm movement). Transversus Abdominis and Lumbar Multifidus are active but in a non-direction-specific feed forward manner. The contraction does not happen simultaneously, however the mechanical effects occur roughly at the same time. This can be explained by the fact that the Transversus Abdominis has a longer electromechanical delay than that of the Lumbar Multifidus, because of its long elastic anterior fascias. Transversus Abdominis is earlier active, so that compensates for the longer delay. So the two discussed muscles don’t maintain tonic co-contraction. Therapeutic exercise programs which involve training co-contraction of the Transversus Abdominis and Lumbar Multifidus, are not going to be capable of restoring typical activation patterns. Nonetheless, the co-contraction training may be necessary to restore intervertebral control which can be caused by an underlying osseoligamentous deficiency

And what about the relationship between these two muscles and the prognostic factors that predict clinical success with stabilizing programs? There are five useful factors, namely age<40y, average straight leg raise range of motion >91°, presence of aberrant movement with lumbar spine flexion, a positive prone instability test and at last the existence of segmental hypermobility  The connection between the prognostic factors and clinical success with stabilizing programs was supported through their relationship with Lumbar Multifidus activation. Even after controlling for the effects of sex, current pain level, BMI, fear-avoidance beliefs and prior history of low back pain, the relationship kept upright. In addition to this, there was no significant relation found between the factors and Transversus Abdominis muscle activation. You have to take notice of the fact that the study, which investigated this relation, has not examined the feed forward behavior of Transversus Abdominis. The relationship between the prognostic factors and this aspect of Transversus Abdominis function remains unknown. Thus the findings of this study provide evidence that shows the importance of restoring Lumbar Multifidus function in patients with low back pain. However, examination of other muscle functions (ex. feed forward behavior) may cause a more extensive understanding

Therapy Exercises for Lumbar Instability

Key Research

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Resources

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Clinical Bottom Line

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Recent Related Research (from Pubmed)

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