MUSCLE
The muscular, tendinous and aponeurotic mass which is developed in intimate relationship to the vertebral column
from occiput to pelvis can be divided broadly into two functional groups : ( I ) phasic muscle, and (2) postural or tonic muscles, though all muscles contain differing pro
portions of both fast and slow twitch fibres.
I . Small SIIboccipital muscles of the craniovertebral region (Fig. 5.7) are the recti and obliques, capable of rapid alterations of tension in a few milliseconds. They have a high imrervation ratio, that is, the number of muscle fibres per motor neurone is small, their proportion being about 3-5 fibres per neurone. Consequently, their potential rate of contraction approaches that of the extrinsic eye muscles and they are able to control head posture, and produce rapid movements, with a fine degree of precision. This
capitis info
Fig. 5.7 The small suboccipital muscles.
capitis sup.
Rectus capitis post. major
accords functionally with the major influence of head posi
tion on body posture, and the correct correlation of orientation of the head in space with the requirements of the visual apparatus. Joint stiffness in the craniovertebral region has thus rather more extensive effects than in other regions (see p. 3).
While Basmajian ( 1 976)" suggests that, 'the function of these small muscles can only be guessed at, since no direct studies have been made', implications of an impor
tant part of their function are manifest in many reports.
For example, the interaction between deep neck muscle proprioceptors and optic-evoked head and eye nystagmus was remarked upon by Hinoki and Terayama ( 1 966) '"
2. Sacrospinalis muscle groups have a very much lower in
nervation ratio, the proponion being about 3000 muscle fibres per neurone, and so these muscle masses are charac
terised by slower and more sustained activity; this is a functionally imponant property of most stabilising muscle groups.
A furTher distinction may be made, in that: (a) the longer muscles of the sacrospinalis group (e.g. iliocostalis and longissimus) are regarded more as prime movers, especi
ally during extension of the column, but (b) the shorter groups (e.g. multifides, rotatores, interspinales, inter
transversarii) which arise from and insert more closely to the intervertebral joints, are important synergic muscles, stabilising and steadying the bony segments of the
PATHOLOGICAL CHANGES--GENERAL I I I column
.
.07 These intersegmental muscles arc functionally analogous with the rotator cuff muscles of the glenohumeral joint and the short muscles grouped around the hipjoint, and their activity as possible prime movers is n01 so important as their dynamic stabilising function.2M Lifting and handling
The stresses tending to shear one venebra upon another, applied during the lifting of a weight from the floor by stooping, are resisted not only by the strong ligamentous strapping of the joints but mainly also by the deepest, shon muscles of the spine, which change the flexible column momentarily into a much more rigid though still flexible lever, the short muscles continuing to exert this effect while the longer groups and other muscles (hip extensors) extend the spine to the erect position.
The sacrospinalis (erector spinae) as a whole group has two main functions, extension of the spine and counterac
tion of gravitational force. The effect of the latter can rise dramatically during postures and movements which entail the centre of gravity of the trunk being displaced well beyond the perpendicular confines of its base, c.g. trunk bending or reaching movements during the lifting of weights.890 The stress is very much more marked when reaching and lifting weights in the sitting position.
It is clinically significant that the sacrospinalis muscle group is relaxed whenfull trunk flexion is maintained, and further, during the first few degrees of trunk extension when holding a weight, the muscle remains relaxed (as shown by electromyographic quiescence163• 364), vigorous contraction not beginning until after the initial phase of trunk extension has been produced by the hip extensors.
Great stress is therefore placed on the posterior liga
mentous structures in full trunk flexion, which is much increased when lifting, and this accords with the fact that many low back injuries sustained during the handling of awkward and heavy weights are produced during the iniTial phases of extension of the trunk. Tendons, apon
euroses and fascia are very strong, being naturally de
veloped to withstand tensile stress (e.g. the tensile strength of healthy fascia lata is 7000 Ib/in' (48 249.0 kPa), although the elasticity and recovery power diminishes after about one-third of this magnitude of stress is applied) ;00 ligaments may be stretched 20 per cent to 25 per cent of their resting length before failure occurs. 37), }Q4, 11-17
The forces developed during the dynamic management ofthe mass which constitutes a human body are great, and can become of critical magnitude in many ordinary daily activities. The ability to withstand these forces safely de
creases with ageing.
PARAVERTEBRAL M USCLE
Other muscle groups, e.g. scaleni, trapezius, latissimus dorsi and abdominal wall muscles, are also intrinsically
1 12 COMMON VERTEBRAL JOINT PROBLEMS
concerned in postural control, movement and protection of the spinal column. During the stress of lifting, the con
traction of abdominal and other trunk muscles, together with contraction of the pelvic floor and closure of the glottis, creates an increased intrathoracic and intra-ab
dominal positive pressure; this mass of compressed air and fluid abdominal contentS is an important flexion
resisting component and contributes a significant amount of the force needed to lift weights from the floor '29.".,72 EMG studies indicate that the diaphragm, internal and external obliques, and the transversus abdominis contract to a much greater extent than the recti, which if contracted strongly would bring the spine into more flexion and thus increase the load upon it. }6) These findings accord with the physiological need to compress the fluid abdominal contents.
The pressures developed in abdominal and thoracic cavities are very high, and on lifting weights can go up dramatically ;229.2)) during common industrial lifting activities the abdominal pressures may repetitively rise to 100mmHg ( 1 3.33 kPa).
In the normal bimanual lift from the floor, intrathoracic and imra
abdominal pressure are at their peaks before intrinsic lumbar extension begins-intervertebral motion being delayed until maximal spinal stresses are past. (Troup, 1979.) 12'Sob
So far as the internal mechanics of the trunk are con
cerned, there is theoretically a greater mechanical advan
tage of the pneumatic mechanism as compared with the erector spinae activity when the trunk is in a flexed posture ; while there is some evidence in support of this theory, this is not to say that lifting in such a posture is to be preferred.235
While the abdominal muscles are regarded as stabilising the lumbar spine by maintaining the intra-abdominal pressure, Fairbanks and O'Brien ( 1 980)3221 present evi
dence that they also act to maintain tension, via the thoraco-Iumbar fascia, in the ligamentous structures between spinous and transverse processes, thus increasing lumbar stability.
Nachemson and Lindh'" contend that the strength of spinal and abdominal musculature is of doubtful impor
tance for prevention of the low back pain syndrome, although they do not specify any categories of clinical pre
sentation, other than 'localised symptoms from the lumbar region'. Tests were performed by 160 men and women, 63 of whom were suffering from low back pain.
In the male groups, the values of muscle strength for those who had been incapacitated for less than one month were not significantly lower than for the controls, albeit pain inhibition was found to be a probable strength-reducing factor. I n the female groups, the values for strength vari
ables were significantly lower for patients than for con
trols, except for abdominal strength in older women.
The abdominal muscles participate in many moror
acti-vities, including postural function, expulsion, expiration and circulation.
Like antigravity limb muscles, the abdominal muscu
lature is well supplied with muscle spindles, and a tonic stretch reflex is easily elicited from them. In many ways, the abdominal skin reflex resembles the flexion reflex of the limbs. Contraction of the abdominal wall and simul
taneous reciprocal inhibition of [he antagonistic dorsal vertebral muscle serve to flex the trunk and retract the abdomen away from the noxious stimulus.Q(J
The important aspect is the reciprocal action of the sacro
spinalis aud abdominal muscle groups-adaptive shortening of dorsal vertebral muscle, with adaptive lengthening and weakness of the abdominal wall musculature, probably constitute a dependable augury for low back problems.
The nature and periodicity of the loading applied to a disc during work are probably of considerable impor
tance.6)1 Recovery of disc thickness on removal of load is not instantaneous ; if forces are applied and removed at too short intervals, or if repetitive and rhythmic loading are too prolonged, recovery is incomplete and a physical state analogous to ageing is induced.
Prolonged and heavy lifting, of lesser weights than an arbitrary maximum, might hasten the onset of degenera
tion,24 the more so if rotation and asymmetrical stresses occur frequently during the activity.
By extrapolation, using the methods of stress analysis, Farfan ( 1 973)'" suggests an hypothesis of the degenera
tive process as applied to the lumbar spine, and assumes that, 'the most likely initial trauma is combined torsion, bending and compression. Of these three types of load, torsion and bending together would seem to be the most potent combination. I Thus it is wise to avoid torsion or asymmetrical loading of the lumbar spine when attempt
ing to lift a weight ; avoiding hyperextension is also wise.
Hence, we can see the importance of the anterior abdominal wall musculature which, when contracted, prevents both torsion and hyperextension . . . in the absence of good abdominal muscu
lature, the distribution of load between facet-joints posteriorly and the disc anteriorly may be affected adversely . . . .
With regard to the widely held view that wearing a lumbar corset makes the muscles weak, Nachemson and Lindh887 found no difference in strength between women patients with low back pain and those who had been pain
free but wearing a corset for a mean period of five years.
Walters and Norris 1290 studied the effects of spinal sup
ports on muscular activity by EMG. There is no effect on standing and slow walking, but wearing the support increases muscle activity on fast walking.
Changes in resting length and tone and neuromuscular control
Troup ( 1979)"50' observes that,
When the vertebral column is stripped of its muscles it is wholly unstable. The muscles which support the spine stabilise it
postur-ally; they control imervertebral motion during movements of the whole column in addition to being its prime movers, and they stabilise imcrvertebral posture during work when the spine trans
mits the reactions between hands and feet. All the muscles of the trunk have some supportive role: the erec[Qr spinae muscles in controlling extension, the rate of flexing under gravity, rotation and lateral flexion ; the rectus abdominis in flexing the trunk against gravity and resisting extension ; the oblique abdominal muscles in rotation and lateral flexion as well as flexion of the trunk; the quadratus lumborum in lateral flexion; the psoas muscles in controlling hip trunk flexion and lumbar posture.
Static tension in any of these muscles induces a reaction in the spine, equal and opposite in magnitude and direction.
In health, normal neuromuscular co-ordination is accepted as unremarkable; only in dysfunction does the underlying complexity of movement become apparent, and (he disturbance of reciprocal muscle action become manifest. An explanation of the incidence of vertebral joint syndromes, and of some unsatisfactory long-term therapeutic results, might be assisted by regarding joint problems in a wider context than that of the joint alone.
Much abnormality presenting, apparently simply, as joint pain may be the expression of a comprehensive underlying imbalance of the whole musculoskeletal system, i.e.
articulation, ligaments, muscles, fascial planes and inter
muscular septa, tendons and aponeuroses, together with defective neuromuscular control and co-ordination in the form of abnormal patterns of afferent and efferent neurone
traffic.
The concept of connective-tissue tightness is not new.
Mennell ( 1952)'" has said,
It is very remarkable how widespread may be the symp[Qms caused by unduly taut fascial planes. Though it is true that the fascial bands play a principal part in the mobility of the human body, they are often conducive to binding between rwo joim sur
faces. For obvious reasons it is of the utmost importance to restore the lost mobility in the joims, before attempting to stretch the fascial planes. On the other hand, if the mobility of these planes is nOt restored, recurrence of the binding in the joints is almost inevitable.
There is new evidencelO5 to support the view that suppleness and flexibility of muscle and connective tissues are of prior importance. Long and continued occupational and postural stress, asymmetrically imposed upon the soft tissues, tends to cause fibroblasts to multiply more rapidly and produce more collagen. Besides occupying more space within [he connective tissue elements of the muscle, (he extra fibres encroach on the space normally occupied by nerves and vessels. Because of this trespass, the tissue loses elasticity, and may become painful when the muscle is re
quired to do work in co-ordination with others. In the long term, collagen would begin to replace the active fibres of the muscle, and since collagen is fairly resistant to enzyme breakdown, these changes tend to be irreversible.
The single nerve-muscle-joint complex is not a simple
PATHOLOGICAL CHANGES-GENERAL l l 3 mechanical entity, but onc of many arthrokinetic systcms which are functionally and reflexly interdependent with all others'" (see p. 385).
Abnormal joint function, increasingly be([er exam
ined799 and increasingly be([er understood,1270 is only one expression of motor systems impairment ;600. 007 the whole field of benign functional pathology of the motor system is as yet largely unexplored.741
Janda (1 976)60' observes that muscles play an important part in the pathogenesis of various back pain syndromes, and Lewit (p. 152) has drawn attention to the significance of iliopsoas spasm in the genesis of pelvic asymmetry in children.
Manifest changes in muscle are not random or inciden
tal but follow certain typical and significant patterns.
Selective tightness of some muscle groups, and lengthen
ing with weakness of their antagonist groups, occur fre
quently in degenerative joint conditions of all spinal regions. A patcern emerges in which those muscles with largely a postural function appear to respond to pathologi
cal states by tightness, and those with mainly a phasic function respond by weakness and lengthening.
The differences may be broadly summarised as follows : POSTural muscle is phylogenetically older, can work for longer without fatigue, is largely concerned in the main
tenance of static posture, is activated more easily and has a tendency to become shorter and tight.
Phasic muscle is phylogenetically younger, is fatigued more quickly, is primarily concerned in rapid movement and has an earlier tendency to become weak.
The distribution of the two fibre types has been exam
ined more extensively in animals than in man, yet where investigated their relative populations have reflected the habitual nature of human muscle activity.4)7 Studies indi
cate that intermediate types also exist, and it may be that the simple division into slow and fast mammalian muscle fibres represents two extremes of a range of fibre types.
All muscles partake in all kinds of muscular activity, and it seems reasonable that at different times the charac
teristics of all ranges of fibre types are required; the main difference under discussion here is therefore one of emphasis.
Other distinctions between fast and slow fibres are de
scribed.oI9. 437 Muscles can be categorised in other ways, too, e.g. comparisons between 'spurt' and 'shunt' muscles ;18) those which cross one joint and those which cross two or more joints; possible correlations between muscles which tend to become tight and participate largely in flexor reflexes, and muscles which tend to weak
ness and to participate largely in extensor reflexes.607 Further, (a) muscles which tend to get tight have a shorter chronaxie than muscles which tend to get weak, and (b) the size and histochemical qualities of some muscle fibres may change due to habitual overuse, i.e. those of
1 1 4 COMMON VERTEBRAL JOINT PROBLEMS
the athlete may differ from those of the sedentary worker. IOn
One characteristic difference between phasic and pos
tural muscles lies in the relative magnitude of abnormal effects, in that a small reduction of strength in a phasic muscle will initiate a disproportionately larger contracture ofthe antagonistic postural muscle, wheras a considerable reduction of strength in a postural muscle is not followed by an equally considerable contracture of the antagonistic phasic musculature. These characteristics are clinically evident to the most casual clinical observer, c.g. a degree of calf muscle contracture accompanies anterior tibial muscle weakness very much morc frequently than even slight contracture of the anterior tibial group follows con
siderable calf muscle weakness.
Similarly, a glance at the cervical and cervicothoracic posture of many mature people, with a poking chin and the head carried somewhat forward of the line of gravity, will indicate the need for stretching of tightened posterior cervical structures (particularly the ligamentum nuchae) and a strengthening of prevertebral cervical muscu
lature.
The inhibitory effect of a tight postural muscle is evi
denced when weakness of the gluteus maximus accom
panies tightness of the iliopsoas. Hip extension is slightly abnormal, lumbar lordosis tends to increase and abnormal loading of the lumbosacral segment initiates chronic changes which can be a cause of pain.
If is common experie,zee that muscle ;mba/a'lce turds to occur in typical pauerns, e.g. as a rule, the upper trapezius, pectoralis major, lumbar sacrospinalis and hamstrings react to pain by increasing tightness, while others such as rhomboids, deltoid, abdominal muscles, glutei and anterior tibial muscles tend to show weakening and lengthening. Yet the apparent chronological sequence of events may not be so.
While these normal and reciprocal changes in tension and tone appear at times to be the sequelae of joint prob
lems, clinical experience is that the genesis of many com
mon joint conditions almost certainly lies in the habitual use of these muscle groups within a small and abnormally restricted amplitude of their available extensibility ranges, thereby slowly and covertly initiating abnormal stress pat
terns and chronic changes.
Changes underlying the patterns described may mas
querade as the consequences of joint dysfunction, and yet in fact may largely be responsible for them. In the circum
stances that musculoskeletal pain is often manifest as pain
ful and/or limited movement of a joint, and is primarily investigated on the basis of seeking the nature of the joilll abnormality, associated structural and functional defects in the whole neuromuscular-skeletal system must also be understood, and given appropriate treatment when in
dicated.
Those muscles which have a predominantly postural
function, and tend to react to pain by increasing tightness are:
sternomastoid
sternomastoid