Complete Article

J. Anat. (1986), 144, pp. 81-91 81 With 8 figures Printed in Great Britain A new description of the lumbar erector spinae muscle in man

FARAJ MF. BUSTAMI Department ofAnatomy, Faculty ofMedicine, University ofJordan, Amman, Jordan (Accepted 9 May 1985)

INTRODUCTION From a study of the muscles acting on the human lumbar spine, it became apparent that some of the current descriptions of the erector spinae muscle, especially those related to the iliocostalis lumborum and longissimus thoracis, are not altogether accurate and, furthermore, some of the existing data may need elaboration. Little recent information has been added to the earlier descriptions (Poirier & Charpy, 1912; Rouviere, 1927; Winckler, 1948; Wood Jones, 1950; Braus, 1954; Etemadi, 1963). Apart from changes to modern nomenclature, the descriptions recorded in current anatomical textbooks (Lockhart, Hamilton & Fyfe, 1969; Hollinshead, 1969; Basmajian, 1971; Romanes, 1972; Gardner, Gray & O'Rahilly, 1975; Hamilton, 1976; Warwick & Williams, 1975; Last, 1978) have not changed substantially since the earliest editions of Gray's Anatomy were published. The present paper is a report of the anatomy of the longissimus thoracis and ilio- costalis lumborum muscles with special reference to the origin, direction and insertion of their various fibres. The possible functions of these two muscles are suggested.

MATERIALS AND METHODS The lumbar erector spinae muscle was studied by gross dissection in eight em- balmed adult cadavers. The disposition and attachments of the superficial and lateral fibres were studied first. This was followed by separation of the erector spinae aponeurosis from its bony and ligamentous attachments, revealing the more deeply lying fibres and nerves. The origin, direction, course, mode of insertion and innervation of the different groups of fibres of the longissimus thoracis and ilio- costalis lumborum muscles were studied.

RESULTS Removal of the dorsal layer of the thoracolumbar fascia revealed the presence of two masses of muscular tissue attached to the posterior (superficial) surface of the erector spinae aponeurosis near its rostral and lateral margins (Figs. 1, 3). Each of the two masses appeared as a homogeneous muscle in gross appearance, but careful dissection revealed that each was made up of several slips radiating rostrally and laterally to their insertions. The caudal of the two masses was made up of eight slips which were inserted through slender flattened tendons into the lower borders of the lower eight ribs approximately at their angles (Figs. 1, 3, 4). The most medial of the these slips had 82 FARAJ MF. BUSTAMI

Fig. 1. An illustration ofthe caudal (cd) and rostral (rs) components ofthe superficial part ofthe lumbar erector spinae. Note the rostrolateral direction of the musculotendinuous slips of both components. The slips ofthe rostral mass are inserted into the third to the tenth ribs, while those of the caudal mass are inserted into the lower eight ribs. esa, erector spinae aponeurosis. the longest tendon, reached the most rostral level and inserted into the fifth rib. The most lateral slip had the shortest tendon and inserted into the twelfth rib. The lateral fibres of this slip described a curve which was convex laterally and was responsible for the rounded, lateral contour of the lumbar erector spinae muscle. The caudal two slips were partially overlapped by the more rostral slips. Immediately medial to the most caudal slip were the caudal slips of origin of the deep part of the erector spinae. The two groups of fleshy slips could be readily distinguished from Lumbar erector spinae muscle in man 83

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Fig. 2. An illustration of the deep part of the lumbar erector spinae after lateral reflection of its aponeurosis (esa). Note the rostromedial direction ofits laminae,-The numbers indicate the verte- bral level of insertion. The rostral (rs) and caudal (cd) components of the superficial part of this muscle arecovered by thereflected aponeurosis. Note that the most rostral lamina in this diagram belongs to the superficial part of this muscle. When the erector spinae aponeurosis and the attached laminae are in position the rostral laminae cover the more caudally situated members. one another. In addition to the fact that the deep slips were larger than the super- ficial, their muscle fibres were directed rostrally and medially and inserted into the lumbar vertebrae. The superficial slips were directed rostrally and laterally and inserted into the lower ribs. The rostral of the two muscular masses was made up of eight slips that passed rostrally and laterally and inserted into the third to tenth ribs (Figs. 1, 4, 5). Each 84 FARAJ MF. BUSTAMI

Fig. 3. The dorsal layer of thoracolumbar fascia has been resected to reveal the rostral (rs) and caudal (cd)muscular masses that arise from the posterior surface ofthe erector spinae aponeurosis (esa). The rostral mass is made up ofeight slips that insert into the third (3) to the tenth (10) ribs inclusive. A ligature has been placed around each slip. slip inserted through a slender flattened tendon into the lower border of the corre- sponding rib, midway between its angle and tubercle. The lower part of the iliocostalis thoracis muscle lay deep to the tendons of the caudal mass. Its upper part was superficial to the tendons of the rostral mass near their insertions (Fig. 5). Lateral reflection of the erector spinae aponeurosis revealed the deep part ofthis muscle. Except for its most caudal fibres, this part of the erector spinae arose from Lumbar erector spinae muscle in man 85

_ g.

one and two asterisks respectively. Most of the slips ofthe caudal mass are shown (thin arrows). The lateral margin of the most caudal two slips is indicated by thick arrowheads. The main part of these two slips is overlapped by the more rostral slips. the anterior (deep) surface of the aponeurosis in the lumbar and thoracic regions (Figs. 2, 6). It was a homogeneous muscle in gross appearance but careful dissection revealed that it was made up ofseveral separable laminae radiating to their insertions. In the lumbar region, the muscle fibres were arranged in four laminae. Each lamina was almost quadrilateral in shape. The laminae covered one another as they passed to their insertions on the upper four lumbar vertebrae (Fig. 7). The most caudal of the lumbar laminae was the only one which had a fleshy origin from the medial aspect of the dorsal segment of the iliac crest. Its fleshy fibres passed rostromedially 86 FARAJ MF. BUSTAMI

Fig. 5. A close up photograph showing the relationships of the rostral and caudal masses of the superficial part of the lumbar erector spinae to the iliocostalis thoracis (ILT). The slips of the rostral mass (indicated by ligatures and labelled R) pass deep to the upper part of the iliocostalis thoraciswhilethelowerpart ofthis muscle lies deep to the tendons (K) ofthe caudal mass (arrow). Note the continuity between the caudal and rostral masses especially near their origin from the erector spinae aponeurosis (esa). and ventrally and divided into three slips, which lay side by side. The medial slip inserted through a short flattened tendon into the accessory process of the fourth lumbar vertebra. The intermediate and lateral slips inserted through similar tendons into the entire dorsal surface of the transverse process of the same vertebra. The next three laminae arose from the deep surface of the aponeurosis. They had similar divisions and insertions to those of the previous lamina. They inserted into the third, second and first lumbar vertebrae respectively. Lumbar erector spinae muscle in man 87

Fig. 6. The erector spinae aponeurosis (esa) has been reflected laterally to show the laminae of the deep part ofthis muscle. The lumbar laminae are indicated by large asterisks and the thoracic lamina by small asterisks. Note the rostromedial direction of both laminae.

In the thoracic region, the fleshy muscle fibres were arranged in eight laminae. The divisions of the most caudal lamina were similar to those of the lumbar laminae and it had a similar insertion into the twelfth thoracic vertebra. The next five laminae were inserted into the eleventh to seventh thoracic vertebrae and the corresponding ribs. The main insertion was through a rounded tendon into the tip of the transverse process of the corresponding vertebra. The insertion into the rib was through fleshy muscle fibres that attached to it midway between its angle and tubercle. The most rostral two laminae were smaller. They inserted through tendons 88 FARAJ MF. BUSTAMI BUNr .. _ _ t ' .~

L-LJ Lill Fig. 7. Close up photograph showing the caudal laminae of the deep part after reflection of the erector spinae aponeurosis (esa). T12, LI, Ln, Lm indicate the insertions of these laminae into the twelfth thoracic and upper three lumbar vertebrae respectively. The fourth lumbar lamina is deep to the third lamina. Note the three parts ofthe third lumbar lamina (black arrows). Note how the lumbar laminae overlap one another as they pass rostromedially to their insertions. MS, multifidus muscle; cd, caudal mass of the superficial part; white arrows, the rostrolateral direction of the muscle fibres of the superficial part. Lumbar erector spinae muscle in man 89

Fig. 8. The lateral division ofthe dorsal rami ofthe spinal nerves in the lower thoracic and upper lumbar regions is indicated by arrows. Note how these nerves supply the deep part of erector spinae and pass laterally and downwards to supply the superficial part in a segmental pattern. In this region these nerves end in the skin. esa, erector spinae aponeurosis. into the tips of the transverse processes of the sixth and fifth thoracic vertebrae respectively. The superficial and deep parts of the erector spinae were supplied by the lateral divisions of the dorsal rami in the lumbar and thoracic regions. In the lower thoracic and upper lumbar regions these nerves ended in the skin (Fig. 8).

DISCUSSION The present observations reveal that, according to the attachments of its muscle fibres, the lumbar erector spinae muscle is formed of two parts: a superficial or 4 ANA 144 90 FARAJ MF. BUSTAIMI costal part and a deep or vertebral part. Both portions have a common origin from the erector spinae aponeurosis and receive a common nerve supply from the lateral divisions of the dorsal rami in the lumbar and thoracic regions. Each part is made up of several separable musculotendinous slips or laminae radiating to their inser- tions. However, the laminae of the two parts differ in their sizes and terminations. On comparing the present observations with the standard description, the super- ficial part corresponds to the iliocostalis lumborum and the rostral part of the longissimus thoracis muscles, while the deep part corresponds to the caudal part of the longissimus thoracis. There is lack ofuniformity in descriptions ofthe lumbar insertion of the iliocostalis lumborum and the longissimus thoracis. At one extreme, Arnold (1968), Hollinshead (1969), and Last (1978) do not describe any form of lumbar insertion for either the longissimus thoracis or the iliocostalis lumborum. Braus (1954) and Bogduk (1980) describe a lumbar insertion for the iliocostalis thoracis. On the other hand, many authors (Lockhart et al. 1969; Basmajian, 1971; Romanes, 1972; Gardner et al. 1975; Hamilton, 1976; Warwick & Williams, 1975) report a lumbar insertion for the longissimus thoracis. The present observations show clearly that the muscular laminae attached to the lumbar transverse processes belong to the longissimus thoracis or the deep part of the lumbar erector spinae. Moreover, the present study demonstrates that the rostral and caudal parts of the longissimus thoracis are quite different in their structure and attachments. The caudal part ofthe muscle comprises twelve broad laminae that arise from the anterior (deep) surface of the erector spinae aponeurosis. In the lumbar region, these laminae insert into the transverse processes of the corresponding vertebrae and in the thoracic region the main part of each slip is inserted into the transverse process; only a small fleshy part is attached to the adjacent rib. The rostral part ofthe longissimus is formed of eight slips that are similar in shape and attachments to those of the iliocostalis lumborum. Recently, Bogduk (1980) has claimed that the longissimus thoracis and the iliocostalis lumborum muscles are separated in the thoracic region by the iliocostalis thoracis and in the lumbar region by an intermuscular aponeurosis. He concludes that these two muscles should be considered, in both the thoracic and lumbar regions, as separate muscles. This view cannot be supported by the present obser- vations. The iliocostalis thoracis does not appear to separate theiliocostalis lumborum and the rostral part of the longissimus thoracis. The slips of origin of this muscle lie deep to the tendons of the iliocostalis lumborum while its fleshy upper part overlaps the tendons of the longissimus thoracis near their insertions. Moreover, it seems that the lumbar intermuscular aponeurosis described by Bogduk is most probably the lateral part of the erector spinae aponeurosis together with the caudal laminae of the longissimus thoracis. The latter are characterised by being partially aponeurotic near their origin. The present study reveals differences in the, size, direction and attachments of the two parts of the lumbar erector spinae. Accordingly, the deep part would act primarily on the lumbar and lower thoracic vertebrae, while the superficial part would act directly on the lower ten ribs and indirectly on the corresponding vertebrae. Such conclusions will naturally require confirmation in the living person. However, the common aponeurotic origin, together with the common nerve supply to the superficial and deep parts of the erector spinae, suggests that these two parts can act together at segmental or intersegmental level. The electromyographic study carried Lumbar erector spinae muscle in man 91 out by Morris, Benner & Lucas (1962) has shown that in the various movements of the trunk a muscle may at times initiate movement and at other times stabilise the trunk. From the present observations, it seems that normally the two parts of the lumbar erector spinae may act in a similar functional pattern. The absence of an insertion from the deep part of the lumbar erector spinae into the fifth lumbar vertebra suggests that normally the latter is controlled by other components of the erector spinae muscle.

SUMMARY A study of the attachments of the musculotendinous fibres of the lumbar erector spinae muscle shows that it is made of two parts: a superficial or costal part, and a deep or vertebral part. The superficial part arises by small fleshy slips from the posterior (superficial) surface as well as the rostral and lateral margins of the erector spinae aponeurosis. It inserts by slender flattened tendons into the lower ten ribs. The deep part arises by large fleshy laminae from the deep surface of the erector spinae aponeurosis. It inserts through musculotendinous fibres mainly into the upper four lumbar and lower eight thoracic vertebrae. The superficial part corresponds to the iliocostalis lumborum and upper part of the longissimus thoracis. The deep part corresponds to the lower part ofthe longissimus thoracis. The functional significance of the present findings is discussed.

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