Evaluation and rehabilitation of Functional lumbopelvic Stability: the role of the back muscles.

 

Lieven Danneels

 

Dept. of Rehabilitation Sciences and Physiotherapy

Ghent University

 

The management of patients with chronic low back pain (CLBP) using exercise therapy has until recently been founded largely on empirical knowledge and clinical observations, rather than on research findings regarding the function and dysfunction of the muscular system. In this lecture an attempt is made to obtain a better insight into the concept of functional spinal stability, the normal functioning of back muscles and the characteristics of muscle dysfunction in LBP. Furthermore, different rehabilitation strategies are discussed.

 

I. Functional spinal stability

 

Biomechanically, the human spine is a remarkable structure that must meet two seemingly contradictory requirements: the achievement of sufficient stability and the provision of adequate mobility. In protecting the delicate spinal cord and nerve roots, providing adequate support/ stability/load-bearing capacity and allowing motion in multiple planes, the spine performs seemingly conflicting functions. Functional stability, both static and dynamic, is required to satisfy these demands.

 

The osteoligamentous spine alone cannot perform all these functions, and, as such, the muscles and their ability to achieve stability and balance assume prime importance.

 

Inspired by the biomechanical research of Panjabi and others we introduced a concept of functional lumbopelvic stability. The passive structures comprise the osseous and articular structures, the spinal ligaments, and their restriction of segmental movement. The active structures refer to the muscles themselves, which stabilize the spinal segment mechanically. The muscles must have adequate endurance and strength to perform this function satisfactorily (muscular functional characteristics). The control subsystem refers to the control of the muscles that provide this spinal support. Neuromuscular control provides a concerted action between the afferent input (proprioception) and the efferent output of the nervous system (coordination), and allows the muscles to contract with the required strength and at the appropriate time.

 

The fourth element, postural control, is the capacity to keep the projection of the body's center of gravity within the base of support. In contrast to the concept of spinal intersegmental stabilization, postural control has in our opinion an important function within the framework of a more general concept of functional spinal stability. These four elements constantly interact to offer adequate stability to the spine during changes of posture and static and dynamic loading.

 

II. Muscle function

 

Contributing to functional lumbopelvic stability, a body of knowledge exists about the importance of the paravertebral and abdominal muscles, and increasing evidence is gathered about the muscles of the pelvic floor and the diaphragm being an integral part of the muscular mechanism. However, in this lecture major attention has been given to the back muscles.

 

II.1. Muscular subdivision

 

The provision of functional spinal stability involves a complex interaction between many muscles of the trunk and limb girdles. While some muscles perform and control the primary action, other muscles must work in synergy to balance any asymmetrical forces, control unwanted movements, and offer support to articular structures.

 

Bergmark proposed the concept of different trunk muscles playing different roles in the provision of dynamic stability to the lumbar spine and introduced the concept of two muscular systems: the global and the local systems. The global muscle system consists of large, torque-producing muscles that act on the trunk and spine without being directly attached to it. In addition to allowing movement of the spine, the global muscles provide general trunk stabilization, but they do not have a direct influence on the spinal segments. The local muscular system consists of muscles that directly attach to the lumbar vertebrae and are responsible for providing segmental stability and directly controlling the lumbar segments.

 

The addition of muscle action imparts stability to the passive structures.

 

In this manner, it appears that the local and global muscles of the trunk combine to exert compressive loading of the spine, thereby enhancing its stiffness and functional stability. However, it is the muscles of the local system that have the greatest potential to prevent segmental buckling and control the motion segment.

 

II.2. Strategy for muscle rehabilitation

 

Rehabilitation of the trunk muscle system is one of the most important aspects of treatment undertaken by physical therapists to help LBP patients regain function and to prevent the recurrence of further back pain episodes. A vital function of the muscle system is to support and control the back in static and dynamic postures during both load-bearing and non-load-bearing activities. A systematic progression is imperative in the rehabilitation of the neuromuscular control system and the muscle functional characteristics. Proprioception and coordination can be considered as the foundations for efficient neuromuscu- ar control. The super-structure consists of the two most relevant muscle functional characteristics: endurance and strength .

 

III. Muscle dysfunction in LBP

 

Trunk muscle dysfunction is being increasingly implicated as a contributory factor in the development or recurrence of subacute and chronic mechanical back complaints. Factors such as the degree of trunk muscle strength and endurance, as well as coordination and proprioceptive awareness, have been shown to be influenced by the presence of low back pain.

 

A number of studies have shown that CLBP patients have significantly lower trunk strength when compared with healthy controls, while other authors reported that trunk strength is not significantly affected in CLBP patients.

 

Decreased back muscle endurance has not only been identified as a predictor of first-time occurrence of LBP, but has also been demonstrated in persons with CLBP compared to those with healthy backs.

 

Although these studies provide data on gross muscle function, more specific information is required concerning the pattern and degree to which individual muscles contribute to the dysfunction. Recently, researchers have found that it is mainly the action of the local system that is disturbed and inhibited in the presence of CLBP.

 

There is some suggestion that a compensatory substitution by the muscles of the global system occurs in the presence of local muscle dysfunction.

 

This appears to be an attempt by the neural control system to maintain the stability of the spine in the presence of local muscle dysfunction.

 

There is also evidence to suggest that the presence of LBP results in changes in the level of proprioception and coordination, affecting the patterns of co-contraction, reflex and reaction times.

 

Finally, an association between back disorders and a decreased quality of postural control has also been documented.

 

IV. Evaluation of Functional Spinal Stability

 

Physical therapists address the often complex muscle dysfunction in patients suffering from LBP. Currently, muscle dysfunction is more and more assumed to be involved in acute LBP and chronic LBP.

 

Every muscle dysfunction requires a systematic yet specific approach.

 

Systematic because we should aim at a progressive exercise program, specific because each patient has to be individually assessed and rehabilitated.

 

In clinical practice, there is an increasing need for objective assessment.

 

At our department a test battery of exercises is used to diagnose and treat a possible dysfunction of the different components contributing to functional spinal stability.

 

Relevance The development of a test battery to identify dysfunctions in back pain patients can be important for clinical, economic and scientific reasons.

 

Firstly, within its limitations, the battery gives a better understanding of dysfunction, if any, and illustrates in which category(ies) the patient fails. The quality of each separate exercise can also be determined.

 

Starting from the test findings, the clinician can set up an individualized exercise routine.

 

Secondly, CLBP places an increasing economical burden on the health budget. As a result, objective tests become necessary to measure in what way LBP patients need and will benefit from physical therapy.

 

Finally, many researchers emphasize the need for the identification of different subgroups within “the nonspecific LBP” population. The successful management of CLBP and the homogeneity of the results among randomized controlled trials greatly depend on the accurate identification of subgroups within this population. The combination of an accurate physical examination with a functional test battery allow to subdivide “the nonspecific LBP” population into subgroups. Based on the findings of the physical examination and the quality of performance during the different functional tests, an objective evaluation of the different elements contributing to functional spinal stability is possible.

 

V. Rehabilitation of Functional Spinal Stability

 

A recent focus in the physiotherapeutic management of patients with CLBP has been the specific training of muscles surrounding the lumbar spine, the primary role of which is considered to be the provision of dynamic stability and segmental control to the spine. Recent studies have shown that the lumbar multifidus is one of the most important muscles for lumbar segmental stability. Precisely this muscle was found to be atrophied in (sub) acute and chronic back pain patients.

 

The use of static stabilization training has been advocated by Jull and Richardson as an ideal means of improving the recruitment of the multifidus.

 

On the other hand, many others support the role of high-loaded dynamic exercises in the successful management of back pain.

 

Although courses of vigorous physical training have been undertaken in CLBP and produced obvious improvements, little information is available on the effects of different contraction modalities of the paravertebral muscles.

 

Strength and endurance training has long formed the basis for therapeutic exercise, while coordination and stabilization training has only gained importance over the last decade. In this lecture, a strategy of back muscle rehabilitation was presented in which the traditional strength and endurance exercises are combined with the rather new concept of stabilization training.

 

It has been argued in the literature that the local muscle system is most affected in the CLBP patient, and that it is the functional impairment of this system that is linked to the high recurrence rate seen in CLBP.

 

As such, it is recommended that the local muscle system be trained first, using the appropriate physiotherapeutic regimen, until adequate stabilization is achieved. Retraining of proprioception and coordination then provides a foundation for the safe performance of more general exercise programmes directed at general endurance and strength.

 

At our department an experiment was conducted to determine whether strength training is beneficial in addition to stabilization training, i.e.

 

whether strength training has an further effect over and above that of stabilization training.

 

The findings of this study indicate that strengthening exercises are essential to achieve a volume-growing effect of the paravertebral muscles in CLBP patients, with a static holding component to be critical to induce hypertrophy of the multifidus.

 

Although many recent literature reports stress the importance of the incorporation of stabilization training, the benefits of stabilization training as a foundation for strength training should be pointed out.

 

Therefore, on this moment a randomized clinical trial is conducted comparing the efficacy of combined stabilization-strength training with that of isolated strength training.

 

Once more, it has to be mentioned that greater differences in outcome between the different rehabilitation programs are expected if in future interventions the CLBP patients would be categorized into different subgroups.

 

Giving a better insight into the concept of functional spinal stability and normal back muscle function, characterizing possible dysfunctions of the elements contributing to functional spinal stablity, and providing evaluation and rehabilitation strategies, this chapter aims at making a valuable contribution to the quality of the daily work of everyone concerned with the LBP patient 

 

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