J. Anat. (1978), 125, 1, pp. 127-131 127With 3 figuresPrinted in Great Britain

Supraspinous and interspinous ligaments of thehuman lumbar spine

D. J. A. HEYLINGS

Department of Anatomy, The Queen's University of Belfast, The Medical BiologyCentre, 97 Lisburn Road, Belfast, BT9 7BL

(Accepted 16 December 1976)

INTRODUCTION

There are major discrepancies in recorded accounts and illustrations of the lumbarsupraspinous and interspinous ligaments in Man.Bryce (1915), Gray's Anatomy (1973), and Parke (1975) state that the supraspinous

ligament passes right down to the sacrum, while Rissanen (1960) says that itterminates above the sacrum in the lower lumbar spine.

Spalteholz (1943), Cunningham's Manual of Practical Anatomy (1968), Gray'sAnatomy (1973), and Parke (1975) describe and/or picture the interspinous ligamentfibres as traversing the interspinous space in a posterocaudal direction. Rissanen(1960) and Grant (1972), on the other hand, illustrate and describe the fibres traversingthe interspinous space in a posterocranial direction.

In view of the likely involvement of the lumbar spinous ligaments in local musculo-skeletal disorders associated with low back pain it was decided to examine theseligaments in human post-mortem specimens, paying special attention to the level oftermination of the supraspinous ligament, and the direcion of the fibres in the inter-spinous ligaments.

MATERIALS AND METHODS

The specimens were obtained, unembalmed, from the Royal Victoria HospitalPathology Department. Specimens with known or discovered pathological lesions ofthe lumbar spine were excluded from the study. In all, twenty suitable specimens wereobtained comprising a stillborn, an infant of 1 month, children of 14 months, 4i and8 years and adults of 21, 23, 39, 41, 52, 53, 57, 62, 62, 64, 65, 71, 78 and 85 years.Most specimens consisted of the spinous processes, laminae, zygapophyseal jointsand associated ligaments, and the musculature of the lumbosacral spine, from L I toS I inclusive. Special care was taken in removing the specimens from cadavers toensure that the supraspinous ligament, lying superficial to the lumbodorsal fascia wasnot damaged.

In addition, eight spines were obtained from embalmed bodies in the dissectingroom, including four which contained all the spinous processes from the mid-cervicalto the mid-sacral region. Two were from premature infants, the others were fromadults of 48, 70, 72, 75, 75 and 98 years.

All specimens were X-rayed both before and after dissection. Dissection wascarried out with the aid of a hand lens and a dissecting microscope, the latter beingessential for careful separation of loose connective tissue from the surface of thesupraspinous ligament and lumbodorsal fascia.The specimens from the post-mortem room were dissected before they were fixed;

this enabled a better dissection of the supraspinous ligament to be made.

After dissection, some specimens were embedded in low viscosity nitrocellulose(LVN) and thick sections obtained for histological confirmation of the fibre directionin the supraspinous and interspinous ligaments. Most sections were examinedunstained, but representative ones were stained with either Weigert's haematoxylinand Van Gieson (Unna's modification), Alcian blue and Van Gieson, or Weigert'selastin stain.

OBSERVATIONS

In each dissection the loose connective tissue was carefully removed from the backof the specimen to expose the lumbodorsal fascia on each side, and also the supra-spinous ligament which lay in the mid-line between the attachments of the lumbo-dorsal fascia to the spinous processes. The supraspinous ligament ended between L4and L5 in all specimens examined; it never reached the sacrum. Beyond the lowerlimit of the supraspinous ligament the fibres of the right and left lumbodorsalfasciae decussated across the mid-line.Removal of the lumbodorsal fascia revealed the erector spinae tendons. Where

the supraspinous ligament was present the tendons gained attachment to the lateralpart of the posterior edge of the spinous process; but caudal to the termination ofthe ligament the most medial tendons crossed the mid-line to gain attachment to theopposite side of the posterior edge of the spinous processes of L5, S 1 (Fig. 1), whilemore laterally placed tendons remained attached to their own side of these spinousprocesses.With the specimen laid on its side the multifidus and interspinous muscles on each

side were carefully removed to expose the interspinous ligaments lying between thespinous processes. It was immediately obvious that the fibres crossed the interspinousspaces in a posterocranial direction, and that in each space the ligament consistedof ventral, middle and dorsal parts (Figs. 2, 3).The ventral part was clearly a posterior extension of the ligamentum flavum; it

fanned out from the main part of the latter ligament and passed backwards andcranially to be attached to the anterior half of the caudal border of the next cranialspinous process. The fibres were arranged in fine bundles whose direction becamemore obvious when the specimen was slightly flexed.The middle part was obviously the major component of the ligament. It consisted

of thick bundles of fibres whose posterocranial orientation was very evident. Thesefibres in general were attached caudally to the anterior half of the cranial border ofa spinous process and cranially to the posterior half of the caudal border of thespinous process cranial to it. In the neutral position of the spine the fibres weresomewhat curved as they crossed the interspinous space, but they became straightenedout as the specimen was flexed.The dorsal part of the interspinous ligament consisted of fibres which were

attached to the posterior half of the cranial border of a spinous process and whichpassed backwards and cranially to merge with the fibres of the supraspinous ligament,where this was present, and with the medial tendons of the erector spinae beyond thecaudal extremity of the supraspinous ligament. These dorsal fibres, like those of theventral part of the interspinous ligament, were not as well defined as those in themiddle part, and there were some variations here in fibre direction. There were alsosome cavities in this part of the ligament. In a few specimens in which the zygapophy-seal joint capsules and the lumbodorsal fascia were present, it was observed onflexion that the more caudal lumbar spinous processes separated from one another

128 D. J. A. HEYLINGS

Supraspinous and interspinous ligaments

Fig. 1. Decussation of the medial tendons of the erector spinae between the spinous processes ofL5 and SI. x6-3.Fig. 2. The left side of a specimen showing the spinous processes of LI-L3, illustrating theposterocranial fibre direction of the normal interspinous ligament. a, ventral part of theinterspinous ligament; b, middle part of the interspinous ligament; c, dorsal part of the inter-spinous ligament; ZG, zygapophyseal joint. x 1 1.Fig. 3. A schcmatic drawing to illustrate the direction of the interspinous ligament fibres in thelumbar region.

more than the more cranial ones, suggesting that movement was more free beyondthe end of the supraspinous ligament.When such a specimen was X-rayed in the lateral position it was observed that the

band of tissue posterior to the spinous processes was thickest at the L 5 and S 1levels. As there is no supraspinous ligament at these levels the increased tissue

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thickness presumably reflects the presence of the decussating erector spinae tendons.This was confirmed on examination of horizontal sections passing through the tipsof the spinous processes.Coronal and sagittal histological sections of the interspinous region showed that theinterspinous ligament was clearly bilateral anteriorly, and there was a slit-like mid-line cavity, usually filled with fat. Posteriorly, there was no such mid-line cavity, andsome fibres crossed the mid-line. The histological preparations confirmed that mostfibres of the interspinous ligament passed across the interspinous space in a postero-cranial direction. Elastic tissue was not evident in the middle and dorsal parts of theligament but some was found in the ventral part near the ligamentum flavum.

In histological sections it was also clear that the supraspinous ligament lackedelastic fibres, and that the posterior interspinous ligament fibres which joined it ranin a posterocranial direction from their bony origins.

DISCUSSION

Tanz (1953) showed that the range of flexion in the human lower lumbar spine wasgreater than that in the upper lumbar spine, and this agrees with the present findings.As the supraspinous ligament is collagenous and so virtually inextensible, the absenceof a supraspinous ligament in the lower spine can be associated with the greaterrange of flexion in this region; for if, as seems likely, the supraspinous ligamentresists hyperflexion, then, if it were present in the lower lumbar region, it would needto be of such a length to allow for the physiological range of flexion that it would bethrown into folds, and therefore be of no functional value, in extension. The medialfibres of the erector spinae tendons in the lower lumbar region, on the other hand,appear to be well placed to control flexion-extension in the absence of the supra-spinous ligament. These tendon fibres arise from the tips of the lower lumbar andsacral spinous processes and travel posteriorly and cranially to cross the mid-linebefore joining the muscle mass on the opposite side (also observed by Rissanen,1960). As they pass cranially they are interwoven with fibres from the dorsal part ofthe interspinous ligament and the deep fibres of the lumbodorsal fascia. Thiscomplex of tendon, ligament and fascia replacing the supraspinous ligament in thelower lumbar spine provides a more adjustable controlling mechanism.

It is difficult to see why the direction of the fibres in the lumbar interspinousligament has been given wrongly in several authoritative textbooks. One is temptedto suppose that specimens had been studied and drawn upside down by early workersand their error perpetuated by subsequent authors who copied the previous work.During flexion of the lumbar spine it is generally accepted that each lumbar vertebrarocks on the one below it about a horizontal axis, though the precise location of thisaxis is debatable. Nevertheless, it is clear that the spinous processes and laminaemove apart, while at least the anterior parts of the vertebral bodies come together,during flexion. The ligamenta flava, being extensible, can afford to pass verticallybetween adjacent laminae, but the interspinous ligaments, being collagenous andtherefore virtually inextensible, could not do this unless they were very slack inextension. In order to maintain a physiologically desirable degree of tensile controlthroughout the movement from extension to flexion and yet eventually bring themovement to a halt, the ligaments need to be directed almost radially with respectto the axis of movement, as in the collateral ligaments of the joints in the limbs.Fibres crossing the interspinous space in a posterocranial direction fulfil these

130 D. J. A. HEYLINGS

Supraspinous and interspinous ligaments 131criteria, but if the ligament fibres were running in the opposite (posterocaudal)direction, they would, as argued above, either limit flexion at too early a stage ifthey ran a reasonably straight course between their attachments, or they would haveto be so lax in extension as to be useless in controlling the spine except at the limit offlexion.

This discussion raises many questions, including fundamental ones about thefunctional role of ligaments, and further analysis is clearly indicated.

SUMMARY

The attachments and structure of the supraspinous and interspinous ligamentswere studied in twenty eight human lumbar spines by dissection and histologicalexamination.The supraspinous ligament proper does not extend caudally beyond L5. Caudal to

this its position is taken by the most medial tendons of the erector spinae, whichdecussate across the mid-line as they approach their attachment to the opposite sideof the spinous processes.The interspinous ligament in the lumbar region is basically bilateral. Its fibres

traverse the interspinous space in a posterocranial direction. The ligament can bedivided into ventral, middle and dorsal parts.The ventral part may be regarded as a posterior extension of the ligamentum

flavum, its fibres passing cranially and posteriorly to the anterior half of the caudalborder of the next cranial spinous process. It contains a few elastic fibres.The middle part is the main component and consists of fibres attached to the

anterior half of the cranial border of one spinous process and the posterior half ofthe caudal border of the next cranial spinous process. It is purely collagenous.The dorsal part consists offibres attached to the posterior half of the cranial border

of one spinous process which pass back and sweep cranially into either the supra-spinous ligament or the medial tendons of the erector spinae. It again is purelycollagenous.The interspinous and supraspinous ligaments are clearly designed to limit flexion.

Absence of the supraspinous ligament at the lumbosacral junction may be associatedwith the greater mobility of the spine in this region, and is possibly a factor in theaetiology of the musculo-skeletal disorders and back pain which are prevalent inthis region.My thanks are due to Professor J. J. Pritchard for his helpful advice in the

preparation of this paper.REFERENCES

BRYCE, T. H. (1915). Osteology and Arthrology. In Quain's Elements ofAnatomy, vol. 4, part 1 (ed. E. A.Schiafer, J. Symington and T. H. Bryce), p. 224. London: Longmans, Green & Co.

CUNNINGHAM'S MANUAL OF PRACTICAL ANATOMY (1968). 13th edition, vol. 2. (ed. G. J. Romanes), p. 89.London: Oxford University Press.

GRANT, J. C. B. (1972). An Atlas ofAnatomy, 6th edition, Fig. 386. Baltimore: Williams and Wilkins Co.GRAY's ANATOMY (1973). 35th edition (ed. R. Warwick and P. L. Williams), pp. 411-413. London:Longman.

PARKE, W. W. (1975). Arthrology of the spine. In The Spine, vol. 1, ch. 2 (ed. R. H. Rothmann and F. A.Simeone), p. 29. Philadelphia, London and Toronto: W. B. Saunders Co.

RISSANEN, P. M. (1960). The surgical anatomy and pathology of the supraspinous and interspinous liga-ments of the lumbar spine, with special reference to ligament ruptures. Acta orthopaedica scandinavicaSuppl. 46.

SPALTEHOLZ, W. (1943). Hand Atlas of Human Anatomy, 7th edition. vol. 1, p. 176. Philadelphia andLondon: J. B. Lippincott Co.

TANZ, S. S. (1953). Motion of the lumbar spine. American Journal of Roentgenology 69, 399-412.

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