estabilizacion espinal P1

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Bodywork and

Journal of

Movement Therapies

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Spinal stabilizationFan update.

Part 1Fbiomechanics$

Craig Liebenson DC*

10474 Santa Monica Blvd., No. 202, Los Angeles, CA 90025, USA

Introduction

The concepts of stability and instability are integralto modern musculoskeletal care. There are twodistinct types. One is the whole body stability/instability and pertains to whole body equillibrium.Whereas the other is segmental or relates to anindividual joint and pertains to its stiffness.According to Panjabi three subsystems work to-gether to maintain spine stability (Panjabi, 1992).

They are the central nervous subsystem (control),an osteoligamentous subsystem ( passive), a nd a

muscle subsystem (active). He says ‘‘The neuralsubsystem receives information from the transdu-cers, determines specific requirements for spinalstability, and causes the active subsystem toachieve the stability goal.’’

The spine or any joint becomes injured orirritated by end-range overload. This can involveeither macrotrauma or repetitive microtrauma.Two main factors involved in whether or notextrinsic end-range overload will result in injuryor irritation are intrinsic motor control and fitnesslevel.

Motor control is a key component in injuryprevention. Impaired motor control consists of failure to control a joint’s ‘‘neutral range’’ usuallyby a dysfunction or incoordination of the agonist – antagonist muscle co-activation. The eminentresearcher Pr. Stuart McGill states that ‘‘evidencefrom tissue-specific injury generally supports the

notion of a neutral spine (neutral lordosis) whenperforming loading tasks to minimize the risk of lowback injury.’’ (McGill, 1998).

Injury or irritation occurs when the tissue’sthreshold is surpassed by external load. The thresh-old is dependent on the individual’s level of fitness.Therefore, injury or irritation can occur with eitherhigh levels of external load in a normal system orlow levels in a compromised one. The bottom line isthat a history of too little or too much external

tissue load will create an environment conducive totissue failure (see Fig. 1).Motor control can be trained. The process

focuses on neuromuscular re-education of patternsof agonist – antagonist muscle co-activation duringlow-load manoeuvres. These are progressed tomore functional tasks to ensure stability duringactivities of daily living (ADL), sport or workdemands.

Biomechanics of low back injury

The spinal column devoid of its musculature hasbeen found to buckle at a load of only 90 N (about20 lb) at L5 (Crisco and Panjabi, 1992; Crisco et al.,1992). However, during routine activities, loads 20times this are encountered on a routine basis. Loadprofiles of various activities are shown in Table 1.Panjabi (1992) says, ‘‘This large load-carryingcapacity is achieved by the participation of well-coordinated muscles surrounding the spinalcolumn.’’ Surprisingly, the motor control systemfunctions well when under load. Muscles stabilize

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$This paper may be photo copied for educational use.*Tel.: þ1-310-470-2909; fax: þ1-310-470-3286.E-mail address: [email protected] (C. Liebenson).

1360-8592/$ - see front matter & 2003 Published by Elsevier Ltd.doi:10.1016/j.jbmt.2003.12.003

Journal of Bodywork and Movement Therapies (2004) 8, 80 – 84



joints by stiffening like rigging on a ship (seeFig. 2). But, when load is at a minimum, such aswhen the body is relaxed or a task is trivial, themotor control system is often ‘‘caught off guard’’and injuries are precipitated.

Low back injury has been shown to result from

repetitive motion at end range. According toMcGill, it is usually a result of ‘‘a history of excessive loading which gradually, but progres-sively, reduces the tissue failure tolerance.’’(McGill, 1998).

Coordination of agonist and synergist muscles,not strength, plays a pivotal role in resisting injury.Sparto et al. showed that spinal loading forcesincreased during a fatiguing isometric trunk exten-sion effort as substitution by secondary extensorssuch as the internal oblique and latissmus dorsimuscles occurred to maintain a constant strength(Sparto et al., 1997). This demonstrates the

limitations of strength testing as an indicator of normal function. When synergist substitution oc-curs spinal load increases, even without a compro-mise in power or strength (i.e. torque output).

According to Cholewicki and McGill (1996) spinestability is greatly enhanced by co-contraction of

antagonistic trunk muscles (e.g. abdominal andextensor muscles). Co-contractions increase spinalcompressive load, as much as 12 – 18% or 440 N, butthey increase spinal stability even more by 36 – 64%or 2925 N (Granata and Marras, 2000). This mechan-ism is present to such an extent that without co-contraction the spinal column is unstable in uprightpostures! (Gardner-Morse and Stokes, 1998).

In particular, these co-contractions are mostobvious during reactions to unexpected or suddenloading (Lavender et al., 1989; Marras et al., 1987).Stokes et al. (2000) have described how thereare basically two mechanisms by which this

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Table 1 Lumbar spine load profiles for common activities.

* Without muscles the spine buckles at 90 N (Crisco III and Panjabi, 1990)* Routine activities of daily living involve E2000N (Panjabi, 1992)* According to McGill recommended subacute exercise training o3000N (McGill, 1997)* National Institute for Occupational Safety and Health (NIOSH) limit for repetitive tasksF3300 N (McGill, 2002)* NIOSH work demand limitF6400N (Gardner-Morse and Stokes, 1998; Gordon, 1991; Stokes et al., 2000)* 7000N (1568 lb) begins to cause damage in very weak spines(Adams and Dolan, 1995)* Tolerance of average healthy young male spine approached 12,000 – 15,000 N (2688 – 3660lb) (Adams and Dolan,

1995)* Competitive weight lifters manage loads in excess of 20,000 N (4480 lb) (Cholewick et al., 1991)

Too litttle Too muchHistory of tissue stress

00

T i s s u e i n j u r y

Figure 1 Relationship of injury to history of tissue load.(Adapted from McGill SM 2000. Clinical biomechanics of the thoracolumbar spine. In Zeevi Dvir (ed) ClinicalBiomechanics. Churchill Livingstone, Philadelphia.)

Figure 2 Spinal stability depends on co-activation of muscle in 3601 around the spinal column.

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co-activation occurs. One is a pre-contraction tostiffen and thus dampen the spinal column whenfaced with unexpected perturbations. The secondis a sufficiently fast speed of contraction of themuscles to react quick enough to prevent excessivemotion that would lead to buckling following either

expected or unexpected perturbations (Carlsonet al., 1981; Cresswell et al., 1994; Lavenderet al., 1989; Marras et al., 1987; Stokes et al.,2000; Thelen et al., 1994; Wilder et al., 1996).Wilder et al. (1996) concluded in a study of body’sreaction to sudden, unexpected loads that ‘‘mus-cles will respond rapidly to stabilize the body, i.e.,they will try to maintain balance and posture’’. Thishas also been verified by Radebold et al. (2000,2001) and Cholewicki et al. (2000a, b) in a series of studies.

Inappropriate muscle activation sequences dur-ing seemingly trivial tasks (only 60 N of force) such

as bending over to pick up a pencil can compromisespine stability and potentiate buckling of thepassive ligamentous restraints (Adams and Dolan,1995). This motor control skill has also been shownto be compromised under challenging aerobiccircumstances (McGill et al., 1995). When a spinalstabilization and respiratory challenge is simulta-neously encountered the nervous system willnaturally select maintenance of respiration overspine stability. An example of this occurs whenduring repetitive bending or lifting activities theback becomes vulnerable due to poor aerobic

fitness even if the motor control system is welltrained.

Good abdominal strength is not sufficient tomaintain spine stability. Lack of proper coordina-tion between the abdominals and diaphragm willlead to spine instability during challenging aerobicactivities (Hodges et al., 2000; O’Sullivan et al.,2002).

Prospective studies have shown that decreasedenduranceFnot strengthFof the trunk extensorscan predict recurrences and 1st time onset of LBPin healthy individuals and increased likelihood of future recurrences (Biering-Sorensen, 1984; Luotoet al., 1995).

Hodges and Richardson reported that a slowspeed of contraction of the transverse abdominusduring arm or leg movements was well correlatedwith LBP (Hodges and Richardson, 1998, 1999).O’Sullivan et al. found that synergist substitution of the rectus abdominus for the agonist transverseabdominus during an abdominal ‘‘drawing in’’manoeuvre strongly correlated with chronic backpain and that specific rehabilitation which im-proved this dysfunction was superior to a moregeneral exercise approach (O’Sullivan et al., 1997).

The multifidus in the low back has been shown tobe atrophied in patients with acute low back pain.(Hides et al., 1994). The acute patients’ atrophywas unilateral to the pain and at the samesegmental level as palpable joint dysfunction.Recovery from acute pain did not automatically

result in restoration of the normal girth of themuscle (Hides et al., 1996). However, it has beendemonstrated that segmental spinal stabilizationexercises can prevent multifidus muscle atrophy inacute LBP subjects (Hides et al., 1996). Recentresearch has demonstrated that such exerciseshave a secondary preventive effect by reducingrecurrences (Hides et al., 2001).

Biomechanical advice

Karel Lewit recommends ‘‘the first treatment is toteach the patient to avoid what harms him’’. LBPpatients are generally vulnerable in the morning,when sitting for prolonged periods of time, andduring lifting. Specific activity modification adviceis therefore needed during these circumstances.

Certain times of day are the most vulnerable forthe back. For instance, in the first hour afterawakening or after prolonged static full flexionsuch as sitting or stooping the body is at greatestrisk. (Adams et al., 1987). Therefore, it is wise toavoid full trunk flexion early in the morning (Snooket al., 2002).

Prolonged sitting is one of the most deleteriousactivities for LBP patients. It has been shown that

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Figure 3 Standing overhead arm reach.

82 C. Liebenson



after just 20 min of full flexion of the spineligamentous creep or laxity occurs which persistseven after 30 min of rest! (McGill and Brown, 1992).In a porcine model just 2min of full flexion hasbeen shown to lead to a substantial loss of thenormal spinal ligamentous stiffness (Gunning et al.,

2001). Therefore, regular micro-breaks involvingstanding and elongating the spine are recom-mended for every 20 – 40 min of sitting (see Fig. 3).

Suggestions to teach workers to lift with theirknees not their backs are overly simplistic. Mostworkers have learned various techniques to avoidinjury which are inconsistent with this advice.Better advice is consistent with the followingprinciplesFpre-contract the trunk muscles (bra-cing); maintain slight lordosis; rotate jobs to varyloads; allow frequent rest breaks; and keep loadsclose to the spine (McGill and Norman, 1993).

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