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Comparative study of Mm. Multifidi in lumbar and thoracic spine
Journal of Electromyography and Kinesiology 10 (2000) 143–149 www.elsevier.com/locate/jelekin
Comparative study of Mm. Multifidi in lumbar and thoracic spine T.W.A. Bojadsen a
a,*
, E.S. Silva b, A.J. Rodrigues b, A.C. Amadio
a
Laboratory of Biomechanics, School of Physical Education and Sport, University of Sa˜o Paulo, Av. Prof. Mello Morais 65, 05508 900 Sa˜o Paulo, Brazil b Department of Surgery, Faculty of Medicine, University of Sa˜o Paulo, Sa˜o Paulo, Brazil Received in revised form 7 February 2000; accepted 12 February 2000
Abstract Imbalance of Mm. Multifidi may play a role in spinal disorders such as scoliosis in the thoracic spine, and lumbar disc herniation and lower back pain in the lumbar spine. Even though changes in these muscles are related to the etiology of these disorders, their anatomy is still poorly understood, especially in the upper regions of the spine. With the aim of gaining a better understanding of the anatomy of Mm. Multifidi in the lumbar and thoracic spine, 12 fresh and two embalmed cadavers were dissected. Our results indicate that Mm. Multifidi present differences in lumbar and thoracic spines concerning their deepness, fibre trajectory, muscle length, muscle mass and tendinous tissue. In the lumbar spine Mm. Multifidi are a superficial, thick and fleshy mass, and their fibres are more vertical in relation to the spinous processes. In the thoracic spine Mm. Multifidi are deeper, thinner, and their fibres are more tendinous and oblique than in the lumbar spine. These differences have implications on Mm. Multifidi architecture and consequently for their function in these two regions of the spine. 2000 Elsevier Science Ltd. All rights reserved. Keywords: Mm. Multifidi anatomy; Spine biomechanics
1. Introduction In 1908, Poirier and co-workers [22] called Mm. Multifidi “the complicated muscles of the spine”. In some way those authors were already indicating the complexity of these muscles and the difficulty in studying their anatomy. Even the latin word multifidu, which means split in many parts, reveals the singularity of their anatomical distribution and probably translates the difficulty of the first anatomists dissecting them. The difficulty in studying Mm. Multifidi anatomy remains and few authors have analysed them. It is observed that the description of the spinous and the transverse processes of lumbar, thoracic and cervical vertebrae as the only insertions of these muscles is still present in an important anatomy textbook and has not changed in almost 50 years [24,25]. In the 1980s, Bogduk and co-workers [1,2,19] brought a new understanding of Mm. Multifidi, describing their segmental innervation and their band distribution in the lumbar spine. Bogduk’s detailed ana-
* Corresponding author. E-mail address: [email protected] (T.W.A. Bojadsen).
tomical description gave support to many authors to investigate Mm. Multifidi in the lumbar spine through different methods. Many studies found that these muscles present alterations in patients with disorders of the spine. Atrophy of type II fibres and alterations in the connective tissue of Mm. Multifidi in patients with lumbar disc herniation were observed [16,20,23] and their small cross-sectional area in patients with lower back pain were also described [9,21]. Some authors even suggested that the alterations found in these muscles would be a primary cause rather than just a consequence of these disorders [12]. Imbalance of the Mm. Multifidi may also play a role in thoracic spine disorders. In scoliotic patients, they were found to be shorter [7] and to present a larger crosssectional area on the convex side of the curve [13]. These muscles also present an increase in type I fibres on the convex side of the curve [33], as well as alterations in type II collagen in the myotendineous junction [14]. Once again, it was suggested that such alterations could be responsible for muscle imbalance in the thoracic spine and lead to rotation of the vertebrae in the scoliotic spine [7]. Nevertheless, the anatomy of Mm. Multifidi in the thoracic spine has not been studied
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extensively in past decades. Even though alterations in Mm. Multifidi have been related to disorders of the lumbar and thoracic spine and although they seem to play an important role in the etiology of dysfunctions in these two regions, anatomical studies have basically been concentrated in the lumbar spine [15,19]. Since muscle biopsy [6,14,33], ultrasound [10,11,13] and electromyography (EMG) [4,5,28,29] have been employed to analyse Mm. Multifidi in these two regions of the spine, a better anatomical understanding of these muscles could help in the realization of biopsy, ultrasound and EMG, and in the interpretation of results obtained with these methodologies. Furthermore, an anatomical study of Mm. Multifidi in the lumbar and thoracic spine would help reveal how the same muscles could be involved in the etiology of such different disorders as scoliosis in the thoracic spine and lumbar disc herniation in the lumbar spine. Thus, the aim of this study was to analyse Mm. Multifidi anatomy in the lumbar and thoracic spine, in order to understand the role they play in disorders of the spine.
2. Method Mm. Multifidi were studied by detailed dissection of 12 fresh cadavers, less than 12 h following death, and two embalmed ones. The fresh cadavers were obtained from the Obituary Service, which is under the supervision of the Department of Pathology. The two embalmed cadavers were obtained from the Laboratory of Anatomy at the Department of Surgery. These two departments are under the supervision of the Faculty of Medicine, and all the ethical norms that apply to these proceedings at the University of Sa˜o Paulo were followed. All dissections were done by the same authors and the cadavers studied did not present any skeletal or muscular disorder. Using surgical techniques, a medial incision over the spinous processes was done to allow the resection of the superficial muscles of the back. The trapezius, the romboideus and the latissimus dorsi were removed to reveal the fibres of the erector spinae muscle. Then, the erector was also resected to expose the fibres of M. semi spinalis in the thoracic spine and Mm. Multifidi in the lumbar region. After topographic considerations, the semi spinalis were also resected and Mm. Multifidi were studied in lumbar and thoracic regions.
concentration of tendinous tissue, muscle mass and muscle length were observed. 3.1. Difference in deepness In the lower lumbar spine Mm. Multifidi are a superficial, thick mass, which lies under the aponeurosis of erector spinae muscle (Fig. 1). Only at the level of L3 do Mm. Multifidi fibres start to be covered by fibres of the longissimus dorsi. Below L3, covering the lower lumbar vertebrae, the lumbosacral transition and the sacrum, there are only Mm. Multifidi fibres and the aponeurosis of erector spinae. Above L3, the lumbar vertebrae are covered by Mm. Multifidi and the longissimus dorsi, as seen in Fig. 2. In the thoracic region Mm. Multifidi are deep, lying under the superficial muscles of the back, and even under the other paraspinal muscles such as spinalis and semi spinalis. 3.2. Trajectory of fibres Vertical fibres were found in the multifidus inserted at the spinous process of L5 and also in the muscles inserted at the spinous processes of T12 and T11. The most caudal fibres of Mm. Multifidi run between the medial portion of the sacrum and the spinous process
3. Results Topographic and anatomical differences were found in the lumbar and thoracic spine. From the fifth lumbar vertebra (L5) up to the first thoracic vertebra (T1), differences in deepness, trajectory of fibres, insertion area,
Fig. 1. Erector spinae muscle and its aponeurosis. In the lower lumbar vertebrae, Mm. Multifidi lie under the aponeurosis of erector spinae muscle (AOE).
T.W.A. Bojadsen et al. / Journal of Electromyography and Kinesiology 10 (2000) 143–149
Fig. 2. Lateral resection of the aponeurosis of erector spinae muscle, revealing Mm. Multifidi (2). Longissimus dorsi fibres (1) originate in the aponeurosis at the level of L3 and re-cover Mm. multifidi fibres above this level.
of L5. These fibres present, in their majority, a vertical trajectory and cover the lumbar–sacral transition (Fig. 3). Above L5 the muscles present a greater obliquity, since their fibres run from more lateral anatomical points such as the region of the lateral sacral crest, the iliac crest and the mamilary processes to the spinous processes. There is a progressive increase in the obliquity of Mm. Multifidi from L5 to T1. The more they are caudal, more they are vertical; conversely, the more they are cephalic, more they are oblique. The only exception is that there are also vertical fibres in the lumbar–thoracic transition. These vertical fibres are superficial, arising from the medial portion of the aponeurosis of erector spinae at the level of L2 and running to the spinous processes of T12 and T11. 3.3. Qualitative aspects of muscle mass and muscle length Mm. Multifidi in the lumbar spine are a thick mass made up of innumerable layers of fibres running together. Mm. Multifidi are made up of an overlapping layer of fibres that arise from different anatomical points. In the sacrum and in the lumbar spine, the most distal
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Fig. 3. Mm. Multifidi in the lumbar spine. The medial fibres below the ruler belong to the multifidus inserted in L5. These fibres present, in their majority, a vertical trajectory.
fibres are progressively covered by the more proximal ones (Fig. 4). This superposition of fibres makes a thick, continuous mass, where a cleavage plane between two Mm. Multifidi is very hard to find in the fresh cadavers. At first sight, Mm. Multifidi look like one single muscle, and only by following their insertions at the spinous processes it is possible to recognize different muscles. This thick mass is inserted at each spinous process of the lumbar vertebrae through thick tendons. Actually, the crosssectional area of the Mm. Multifidi tendons and Mm. Multifidi mass in the lumbar spine are the larger in the two regions. As Mm. Multifidi are followed from the lumbar to the thoracic spine, a progressive decrease in their mass and length is observed. Fig. 5 shows one multifidus extracted from the lumbar region and one extracted from the thoracic region. Even though the trajectory of muscle fibres is two to four vertebral bodies, the smaller height of the vertebrae in the thoracic spine imposes a shorter trajectory to the fibres. 3.4. Tendinous tissue In the lumbar spine, tendinous tissue is concentrated in the thick tendons of Mm. Multifidi at the spinous pro-
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Fig. 4. Superposition of Mm. Multifidi in the sacrum and in the lumbar spine.
Fig. 5. Differences in muscle mass and muscle length of Mm. Multifidi in lumbar and thoracic segments. The bigger muscle was extracted from L1 and the smaller one from T10.
4. Discussion cesses. The distal insertions in the sacrum and iliac crest do not present tendons and the fibres arise from the periosteum. In this way, Mm. Multifidi in the lumbar spine consist basically of flesh. In the thoracic spine, Mm. Multifidi present a marked increase in tendinous tissue. The muscles present a tendon at each transverse process and this tendon splits in another three tendons where muscle fibres are originated. This tendinous fleshy mass runs up to the spinous processes of the upper vertebrae, as shown in Fig. 6. The most medial tendon originates fibres that are inserted at the spinous process of the second vertebra above. The intermediary tendon originates fibres that are inserted at the third vertebra above, and the lateral tendon originates fibres that are inserted at the fourth vertebra above. In the thoracic spine, it is easier to follow the fibres from the transverse processes, where the tendons are more visible. At the spinous processes, the insertion is almost like a continuous band, with small and poorly isolated tendons where the fibres are inserted. At the upper thoracic vertebrae, around T7, a marked increase in tendinous tissue was observed and Mm. Multifidi become more tendinous than fleshy (Fig. 7).
Owing to the difficulty in studying Mm. Multifidi, we used, as an initial criterion to isolate their fibers, the localization of the tendons. In the lumbar spine we found thick tendons at the spinous processes, and the observed distribution of Mm. Multifidi was similar to Bogduk and co-workers’ description of a spino-transverse muscle, composed by five bands. In the thoracic spine the tendons were more significant at the transverse processes, and we followed the fibers up to the spinous processes. This description, which suggests a transverso-spinal pattern in the thoracic spine, is the opposite to that observed in the lumbar spine. Bogduk and co-workers’ description of Mm. Multifidi as spino-transverse muscles was done on the basis of a study of the lumbar dorsi rami and its medial branch [1,19]. Since in this study we did not analyse the innervation of Mm. Multifidi and the pattern of distribution of these muscles in the thoracic spine was the one seen in Figs. 6 and 7, we prefer to maintain the traditional caudal origin and cranial insertion description in the thoracic spine. Important differences observed in Mm. Multifidi seem to have implications for their function. According to
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Fig. 6. Mm. Multifidi in the thoracic spine. The arrow points to the tendon in the transverse process. This tendon splits into three tendons that run with the muscle fibres to the spinous processes above.
Fig. 7. Increase in tendinous tissue in Mm. Multifidi in the upper thoracic spine. PT indicates the transverse process and PE the spinous process.
Lieber [17], Loeb and Gans [18] and Gardner et al. [8], muscle architecture is related to muscle function. Muscle mass, muscle length, the trajectory of the fibres and the position of a muscle in relation to the joint can give important information on the function of the muscle. According to these authors, the cross-sectional area of a muscle is directly related to the tension that this muscle can produce, the length of its fibres is an indication of the excursion of movement that the muscle is able to produce, and the position of the muscle in relation to the joint is indicative of the kind of movement. According to Gardner et al. [8], the more oblique the muscle in relation to the joint, more its role in axial rotation; and the more its position is vertical, the more its contribution to flexion–extension movements. As Mm. Multifidi in the lumbar spine present a larger cross-sectional area, longer and more vertical fibres than Mm. Multifidi in the thoracic spine, it seems that they are more adapted to produce movements in the sagittal plane, with greater tension and larger amplitude than Mm. Multifidi in the thoracic spine. Thoracic multifidi, on the other hand, seem to be more adapted to produce movements in the transverse plane, with lower tension
and lower amplitude than Mm. Multifidi in the lumbar spine. The difference in obliquity of Mm. Multifidi also seems to have implications on segmental intervertebral joint movements. The most vertical fibres in the entire spine were observed in the multifidi inserted at L5. The joint L5–S1 is the one which presents the largest amplitude of flexion and extension in the lumbar spine, according to White and Panjabi [32]. Still according to these authors, T12–T11 is the joint which presents the largest amplitude of flexion and extension in the thoracic spine, exactly the vertebrae where Mm. Multifidi once again present vertical fibres. The most oblique fibres of Mm. Multifidi in the thoracic and lumbar spine were found at T1. The joint T1– T2 is the one which presents the largest amplitude in axial rotation in the thoracic and lumbar spine, as described by White and Panjabi [32]. The upper thoracic intervertebral joints present the largest amplitude of axial rotation when compared with the lower intervertebral joints. Mm. Multifidi are considered by many authors as important rotators of the intervertebral joints [8,26]. They are able to produce axial rotation when contraction happens on one single
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side of the joint. This unilateral contraction would cause axial rotation of the spine. As such, it is possible to assume that the larger the amplitude of rotation, the larger the strain in the Mm. Multifidi inserted in the opposite side of the same joint. This could explain why there is an increase in tendinous tissue, which is considered much more resistant to deformation than muscle tissue [18], in the upper thoracic spine. The increase in muscle mass observed in the lumbar spine also seems to respond to the demand of tension in this region. Wilke and co-workers [30] demonstrated that Mm. Multifidi produce about two-thirds of the total muscle tension in L4–L5, and they suggest an important role of Mm. Multifidi in stabilization of the lower lumbar spine. In spite of the controversy of the presence of M. longissimus fibres in L5 [3,25–27], our results support the absence of other muscle fibres in the back of L5–S1, and indicate that Mm. Multifidi are the only muscle fibres present on the back of the lumbosacral transition. This means that Mm. Multifidi would be expected to produce enough tension to ensure posterior stabilization in this region. The exclusive posterior presence of Mm. Multifidi fibres in a region of important load transmission and high demand of stabilization could explain why Mm. Multifidi present their largest mass precisely in this segment of the spine. The anatomical findings concerning Mm. Multifidi in the lumbar and thoracic spine seem to be adaptations to spine biomechanics. We believe that the differences observed could explain why alteration in Mm. Multifidi may play a role in the etiology of lumbar and thoracic disorders such as lower back pain, lumbar disc herniation and scoliosis. 4.1. Implications for electromyography Many methodologies applied to study Mm. Multifidi, such as tomography, ultrasound and magnetic resonance imaging (MRI), rely on anatomical knowledge, and electromyography is not an exception. Mm. Multifidi present differences in their position and this has implications for EMG. In the lumbar spine, below L3, the exclusive presence of the aponeurosis of erector spinae and the absence of other muscle fibres over Mm. Multifidi simplify the registration of their EMG signal. The electrodes to register the erector spinae muscle are currently placed 2 cm on the side of the spinous process of L4 [31]. The cadavers of this study presented no erector spinae fibres at this position. Actually, as shown in Fig. 3, there are still Mm. Multifidi at more than 3 cm on the side of the spinous processes, and they are covered exclusively by the aponeurosis of erector spinae (Fig. 2). According to these results, it would be suitable to place the electrode to register erector spinae activity above L3.
5. Conclusions Mm. Multifidi present differences when compared in the lumbar and thoracic regions. In the lumbar spine, Mm. Multifidi are superficial, thick and present more vertical fibres. Mm. Multifidi in the thoracic region are deep, thinner and more oblique. The lumbar–sacral transition and the lumbar–thoracic transition presented vertical fibres. In our next work, we intend to extend the present findings in order to provide quantitative data.
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Erasmo S. da Silva graduated in 1982 from the University of Sa˜o Paulo Medical School, Sa˜o Paulo, Brazil. From 1983 to 1987 he worked at the Hospital das Clinicas as a resident. He has been working at the University of Sa˜o Paulo since 1989. In 1996 he received a Ph.D. degree from the Department of Surgery, University of Sa˜o Paulo Medical School. In 1997 he joined the Division of Topographic Anatomy of the Department of Surgery, at the University of Sa˜o Paulo. He is a member of the American Association of Clinical Anatomy, International Society of Cardiovascular Surgery, Brazilian Medical Association and Sa˜o Paulo Medical Association. His major research interests focus on clinical anatomy, particularly in vascular surgery. Alberto Carlos Amadio graduated in 1973 from the School of Physical Education of Tatui, Sa˜o Paulo, Brazil. He received an M.Sc. degree from the School of Physical Education, University of Sa˜o Paulo, Brazil in 1980, and a Ph.D. (Doktor fu¨r Sportwissenschaft) from the Deutsche Sporthochschule, Cologne, Germany in 1986. He became Full Professor of the University of Sa˜o Paulo, Department of Biodynamics of Human Body Movement, in 1990. His major research interests focus on biomechanics. Aldo Junqueira Rodrigues Jr. graduated in Medicine from the University of Sa˜o Paulo Medical School, Sa˜o Paulo, Brazil in 1976. He obtained a Ph.D. degree in 1985 and in 1993 became Full Professor at the Topographic Anatomy Division at the University of Sa˜o Paulo, Department of Surgery. He has been Chairman of the Department of Surgery since 1997. His major interests focus on clinical anatomy, particularly regarding the study of abdominal hernias. He introduced the technique of Sectional Human Anatomy into Brazil.
Comparative study of Mm. Multifidi in lumbar and thoracic spine T.W.A. Bojadsen a
a,*
, E.S. Silva b, A.J. Rodrigues b, A.C. Amadio
a
Laboratory of Biomechanics, School of Physical Education and Sport, University of Sa˜o Paulo, Av. Prof. Mello Morais 65, 05508 900 Sa˜o Paulo, Brazil b Department of Surgery, Faculty of Medicine, University of Sa˜o Paulo, Sa˜o Paulo, Brazil Received in revised form 7 February 2000; accepted 12 February 2000
Abstract Imbalance of Mm. Multifidi may play a role in spinal disorders such as scoliosis in the thoracic spine, and lumbar disc herniation and lower back pain in the lumbar spine. Even though changes in these muscles are related to the etiology of these disorders, their anatomy is still poorly understood, especially in the upper regions of the spine. With the aim of gaining a better understanding of the anatomy of Mm. Multifidi in the lumbar and thoracic spine, 12 fresh and two embalmed cadavers were dissected. Our results indicate that Mm. Multifidi present differences in lumbar and thoracic spines concerning their deepness, fibre trajectory, muscle length, muscle mass and tendinous tissue. In the lumbar spine Mm. Multifidi are a superficial, thick and fleshy mass, and their fibres are more vertical in relation to the spinous processes. In the thoracic spine Mm. Multifidi are deeper, thinner, and their fibres are more tendinous and oblique than in the lumbar spine. These differences have implications on Mm. Multifidi architecture and consequently for their function in these two regions of the spine. 2000 Elsevier Science Ltd. All rights reserved. Keywords: Mm. Multifidi anatomy; Spine biomechanics
1. Introduction In 1908, Poirier and co-workers [22] called Mm. Multifidi “the complicated muscles of the spine”. In some way those authors were already indicating the complexity of these muscles and the difficulty in studying their anatomy. Even the latin word multifidu, which means split in many parts, reveals the singularity of their anatomical distribution and probably translates the difficulty of the first anatomists dissecting them. The difficulty in studying Mm. Multifidi anatomy remains and few authors have analysed them. It is observed that the description of the spinous and the transverse processes of lumbar, thoracic and cervical vertebrae as the only insertions of these muscles is still present in an important anatomy textbook and has not changed in almost 50 years [24,25]. In the 1980s, Bogduk and co-workers [1,2,19] brought a new understanding of Mm. Multifidi, describing their segmental innervation and their band distribution in the lumbar spine. Bogduk’s detailed ana-
* Corresponding author. E-mail address: [email protected] (T.W.A. Bojadsen).
tomical description gave support to many authors to investigate Mm. Multifidi in the lumbar spine through different methods. Many studies found that these muscles present alterations in patients with disorders of the spine. Atrophy of type II fibres and alterations in the connective tissue of Mm. Multifidi in patients with lumbar disc herniation were observed [16,20,23] and their small cross-sectional area in patients with lower back pain were also described [9,21]. Some authors even suggested that the alterations found in these muscles would be a primary cause rather than just a consequence of these disorders [12]. Imbalance of the Mm. Multifidi may also play a role in thoracic spine disorders. In scoliotic patients, they were found to be shorter [7] and to present a larger crosssectional area on the convex side of the curve [13]. These muscles also present an increase in type I fibres on the convex side of the curve [33], as well as alterations in type II collagen in the myotendineous junction [14]. Once again, it was suggested that such alterations could be responsible for muscle imbalance in the thoracic spine and lead to rotation of the vertebrae in the scoliotic spine [7]. Nevertheless, the anatomy of Mm. Multifidi in the thoracic spine has not been studied
1050-6411/00/$ - see front matter 2000 Elsevier Science Ltd. All rights reserved. PII: S 1 0 5 0 - 6 4 1 1 ( 0 0 ) 0 0 0 0 4 - 3
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extensively in past decades. Even though alterations in Mm. Multifidi have been related to disorders of the lumbar and thoracic spine and although they seem to play an important role in the etiology of dysfunctions in these two regions, anatomical studies have basically been concentrated in the lumbar spine [15,19]. Since muscle biopsy [6,14,33], ultrasound [10,11,13] and electromyography (EMG) [4,5,28,29] have been employed to analyse Mm. Multifidi in these two regions of the spine, a better anatomical understanding of these muscles could help in the realization of biopsy, ultrasound and EMG, and in the interpretation of results obtained with these methodologies. Furthermore, an anatomical study of Mm. Multifidi in the lumbar and thoracic spine would help reveal how the same muscles could be involved in the etiology of such different disorders as scoliosis in the thoracic spine and lumbar disc herniation in the lumbar spine. Thus, the aim of this study was to analyse Mm. Multifidi anatomy in the lumbar and thoracic spine, in order to understand the role they play in disorders of the spine.
2. Method Mm. Multifidi were studied by detailed dissection of 12 fresh cadavers, less than 12 h following death, and two embalmed ones. The fresh cadavers were obtained from the Obituary Service, which is under the supervision of the Department of Pathology. The two embalmed cadavers were obtained from the Laboratory of Anatomy at the Department of Surgery. These two departments are under the supervision of the Faculty of Medicine, and all the ethical norms that apply to these proceedings at the University of Sa˜o Paulo were followed. All dissections were done by the same authors and the cadavers studied did not present any skeletal or muscular disorder. Using surgical techniques, a medial incision over the spinous processes was done to allow the resection of the superficial muscles of the back. The trapezius, the romboideus and the latissimus dorsi were removed to reveal the fibres of the erector spinae muscle. Then, the erector was also resected to expose the fibres of M. semi spinalis in the thoracic spine and Mm. Multifidi in the lumbar region. After topographic considerations, the semi spinalis were also resected and Mm. Multifidi were studied in lumbar and thoracic regions.
concentration of tendinous tissue, muscle mass and muscle length were observed. 3.1. Difference in deepness In the lower lumbar spine Mm. Multifidi are a superficial, thick mass, which lies under the aponeurosis of erector spinae muscle (Fig. 1). Only at the level of L3 do Mm. Multifidi fibres start to be covered by fibres of the longissimus dorsi. Below L3, covering the lower lumbar vertebrae, the lumbosacral transition and the sacrum, there are only Mm. Multifidi fibres and the aponeurosis of erector spinae. Above L3, the lumbar vertebrae are covered by Mm. Multifidi and the longissimus dorsi, as seen in Fig. 2. In the thoracic region Mm. Multifidi are deep, lying under the superficial muscles of the back, and even under the other paraspinal muscles such as spinalis and semi spinalis. 3.2. Trajectory of fibres Vertical fibres were found in the multifidus inserted at the spinous process of L5 and also in the muscles inserted at the spinous processes of T12 and T11. The most caudal fibres of Mm. Multifidi run between the medial portion of the sacrum and the spinous process
3. Results Topographic and anatomical differences were found in the lumbar and thoracic spine. From the fifth lumbar vertebra (L5) up to the first thoracic vertebra (T1), differences in deepness, trajectory of fibres, insertion area,
Fig. 1. Erector spinae muscle and its aponeurosis. In the lower lumbar vertebrae, Mm. Multifidi lie under the aponeurosis of erector spinae muscle (AOE).
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Fig. 2. Lateral resection of the aponeurosis of erector spinae muscle, revealing Mm. Multifidi (2). Longissimus dorsi fibres (1) originate in the aponeurosis at the level of L3 and re-cover Mm. multifidi fibres above this level.
of L5. These fibres present, in their majority, a vertical trajectory and cover the lumbar–sacral transition (Fig. 3). Above L5 the muscles present a greater obliquity, since their fibres run from more lateral anatomical points such as the region of the lateral sacral crest, the iliac crest and the mamilary processes to the spinous processes. There is a progressive increase in the obliquity of Mm. Multifidi from L5 to T1. The more they are caudal, more they are vertical; conversely, the more they are cephalic, more they are oblique. The only exception is that there are also vertical fibres in the lumbar–thoracic transition. These vertical fibres are superficial, arising from the medial portion of the aponeurosis of erector spinae at the level of L2 and running to the spinous processes of T12 and T11. 3.3. Qualitative aspects of muscle mass and muscle length Mm. Multifidi in the lumbar spine are a thick mass made up of innumerable layers of fibres running together. Mm. Multifidi are made up of an overlapping layer of fibres that arise from different anatomical points. In the sacrum and in the lumbar spine, the most distal
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Fig. 3. Mm. Multifidi in the lumbar spine. The medial fibres below the ruler belong to the multifidus inserted in L5. These fibres present, in their majority, a vertical trajectory.
fibres are progressively covered by the more proximal ones (Fig. 4). This superposition of fibres makes a thick, continuous mass, where a cleavage plane between two Mm. Multifidi is very hard to find in the fresh cadavers. At first sight, Mm. Multifidi look like one single muscle, and only by following their insertions at the spinous processes it is possible to recognize different muscles. This thick mass is inserted at each spinous process of the lumbar vertebrae through thick tendons. Actually, the crosssectional area of the Mm. Multifidi tendons and Mm. Multifidi mass in the lumbar spine are the larger in the two regions. As Mm. Multifidi are followed from the lumbar to the thoracic spine, a progressive decrease in their mass and length is observed. Fig. 5 shows one multifidus extracted from the lumbar region and one extracted from the thoracic region. Even though the trajectory of muscle fibres is two to four vertebral bodies, the smaller height of the vertebrae in the thoracic spine imposes a shorter trajectory to the fibres. 3.4. Tendinous tissue In the lumbar spine, tendinous tissue is concentrated in the thick tendons of Mm. Multifidi at the spinous pro-
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Fig. 4. Superposition of Mm. Multifidi in the sacrum and in the lumbar spine.
Fig. 5. Differences in muscle mass and muscle length of Mm. Multifidi in lumbar and thoracic segments. The bigger muscle was extracted from L1 and the smaller one from T10.
4. Discussion cesses. The distal insertions in the sacrum and iliac crest do not present tendons and the fibres arise from the periosteum. In this way, Mm. Multifidi in the lumbar spine consist basically of flesh. In the thoracic spine, Mm. Multifidi present a marked increase in tendinous tissue. The muscles present a tendon at each transverse process and this tendon splits in another three tendons where muscle fibres are originated. This tendinous fleshy mass runs up to the spinous processes of the upper vertebrae, as shown in Fig. 6. The most medial tendon originates fibres that are inserted at the spinous process of the second vertebra above. The intermediary tendon originates fibres that are inserted at the third vertebra above, and the lateral tendon originates fibres that are inserted at the fourth vertebra above. In the thoracic spine, it is easier to follow the fibres from the transverse processes, where the tendons are more visible. At the spinous processes, the insertion is almost like a continuous band, with small and poorly isolated tendons where the fibres are inserted. At the upper thoracic vertebrae, around T7, a marked increase in tendinous tissue was observed and Mm. Multifidi become more tendinous than fleshy (Fig. 7).
Owing to the difficulty in studying Mm. Multifidi, we used, as an initial criterion to isolate their fibers, the localization of the tendons. In the lumbar spine we found thick tendons at the spinous processes, and the observed distribution of Mm. Multifidi was similar to Bogduk and co-workers’ description of a spino-transverse muscle, composed by five bands. In the thoracic spine the tendons were more significant at the transverse processes, and we followed the fibers up to the spinous processes. This description, which suggests a transverso-spinal pattern in the thoracic spine, is the opposite to that observed in the lumbar spine. Bogduk and co-workers’ description of Mm. Multifidi as spino-transverse muscles was done on the basis of a study of the lumbar dorsi rami and its medial branch [1,19]. Since in this study we did not analyse the innervation of Mm. Multifidi and the pattern of distribution of these muscles in the thoracic spine was the one seen in Figs. 6 and 7, we prefer to maintain the traditional caudal origin and cranial insertion description in the thoracic spine. Important differences observed in Mm. Multifidi seem to have implications for their function. According to
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Fig. 6. Mm. Multifidi in the thoracic spine. The arrow points to the tendon in the transverse process. This tendon splits into three tendons that run with the muscle fibres to the spinous processes above.
Fig. 7. Increase in tendinous tissue in Mm. Multifidi in the upper thoracic spine. PT indicates the transverse process and PE the spinous process.
Lieber [17], Loeb and Gans [18] and Gardner et al. [8], muscle architecture is related to muscle function. Muscle mass, muscle length, the trajectory of the fibres and the position of a muscle in relation to the joint can give important information on the function of the muscle. According to these authors, the cross-sectional area of a muscle is directly related to the tension that this muscle can produce, the length of its fibres is an indication of the excursion of movement that the muscle is able to produce, and the position of the muscle in relation to the joint is indicative of the kind of movement. According to Gardner et al. [8], the more oblique the muscle in relation to the joint, more its role in axial rotation; and the more its position is vertical, the more its contribution to flexion–extension movements. As Mm. Multifidi in the lumbar spine present a larger cross-sectional area, longer and more vertical fibres than Mm. Multifidi in the thoracic spine, it seems that they are more adapted to produce movements in the sagittal plane, with greater tension and larger amplitude than Mm. Multifidi in the thoracic spine. Thoracic multifidi, on the other hand, seem to be more adapted to produce movements in the transverse plane, with lower tension
and lower amplitude than Mm. Multifidi in the lumbar spine. The difference in obliquity of Mm. Multifidi also seems to have implications on segmental intervertebral joint movements. The most vertical fibres in the entire spine were observed in the multifidi inserted at L5. The joint L5–S1 is the one which presents the largest amplitude of flexion and extension in the lumbar spine, according to White and Panjabi [32]. Still according to these authors, T12–T11 is the joint which presents the largest amplitude of flexion and extension in the thoracic spine, exactly the vertebrae where Mm. Multifidi once again present vertical fibres. The most oblique fibres of Mm. Multifidi in the thoracic and lumbar spine were found at T1. The joint T1– T2 is the one which presents the largest amplitude in axial rotation in the thoracic and lumbar spine, as described by White and Panjabi [32]. The upper thoracic intervertebral joints present the largest amplitude of axial rotation when compared with the lower intervertebral joints. Mm. Multifidi are considered by many authors as important rotators of the intervertebral joints [8,26]. They are able to produce axial rotation when contraction happens on one single
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side of the joint. This unilateral contraction would cause axial rotation of the spine. As such, it is possible to assume that the larger the amplitude of rotation, the larger the strain in the Mm. Multifidi inserted in the opposite side of the same joint. This could explain why there is an increase in tendinous tissue, which is considered much more resistant to deformation than muscle tissue [18], in the upper thoracic spine. The increase in muscle mass observed in the lumbar spine also seems to respond to the demand of tension in this region. Wilke and co-workers [30] demonstrated that Mm. Multifidi produce about two-thirds of the total muscle tension in L4–L5, and they suggest an important role of Mm. Multifidi in stabilization of the lower lumbar spine. In spite of the controversy of the presence of M. longissimus fibres in L5 [3,25–27], our results support the absence of other muscle fibres in the back of L5–S1, and indicate that Mm. Multifidi are the only muscle fibres present on the back of the lumbosacral transition. This means that Mm. Multifidi would be expected to produce enough tension to ensure posterior stabilization in this region. The exclusive posterior presence of Mm. Multifidi fibres in a region of important load transmission and high demand of stabilization could explain why Mm. Multifidi present their largest mass precisely in this segment of the spine. The anatomical findings concerning Mm. Multifidi in the lumbar and thoracic spine seem to be adaptations to spine biomechanics. We believe that the differences observed could explain why alteration in Mm. Multifidi may play a role in the etiology of lumbar and thoracic disorders such as lower back pain, lumbar disc herniation and scoliosis. 4.1. Implications for electromyography Many methodologies applied to study Mm. Multifidi, such as tomography, ultrasound and magnetic resonance imaging (MRI), rely on anatomical knowledge, and electromyography is not an exception. Mm. Multifidi present differences in their position and this has implications for EMG. In the lumbar spine, below L3, the exclusive presence of the aponeurosis of erector spinae and the absence of other muscle fibres over Mm. Multifidi simplify the registration of their EMG signal. The electrodes to register the erector spinae muscle are currently placed 2 cm on the side of the spinous process of L4 [31]. The cadavers of this study presented no erector spinae fibres at this position. Actually, as shown in Fig. 3, there are still Mm. Multifidi at more than 3 cm on the side of the spinous processes, and they are covered exclusively by the aponeurosis of erector spinae (Fig. 2). According to these results, it would be suitable to place the electrode to register erector spinae activity above L3.
5. Conclusions Mm. Multifidi present differences when compared in the lumbar and thoracic regions. In the lumbar spine, Mm. Multifidi are superficial, thick and present more vertical fibres. Mm. Multifidi in the thoracic region are deep, thinner and more oblique. The lumbar–sacral transition and the lumbar–thoracic transition presented vertical fibres. In our next work, we intend to extend the present findings in order to provide quantitative data.
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Erasmo S. da Silva graduated in 1982 from the University of Sa˜o Paulo Medical School, Sa˜o Paulo, Brazil. From 1983 to 1987 he worked at the Hospital das Clinicas as a resident. He has been working at the University of Sa˜o Paulo since 1989. In 1996 he received a Ph.D. degree from the Department of Surgery, University of Sa˜o Paulo Medical School. In 1997 he joined the Division of Topographic Anatomy of the Department of Surgery, at the University of Sa˜o Paulo. He is a member of the American Association of Clinical Anatomy, International Society of Cardiovascular Surgery, Brazilian Medical Association and Sa˜o Paulo Medical Association. His major research interests focus on clinical anatomy, particularly in vascular surgery. Alberto Carlos Amadio graduated in 1973 from the School of Physical Education of Tatui, Sa˜o Paulo, Brazil. He received an M.Sc. degree from the School of Physical Education, University of Sa˜o Paulo, Brazil in 1980, and a Ph.D. (Doktor fu¨r Sportwissenschaft) from the Deutsche Sporthochschule, Cologne, Germany in 1986. He became Full Professor of the University of Sa˜o Paulo, Department of Biodynamics of Human Body Movement, in 1990. His major research interests focus on biomechanics. Aldo Junqueira Rodrigues Jr. graduated in Medicine from the University of Sa˜o Paulo Medical School, Sa˜o Paulo, Brazil in 1976. He obtained a Ph.D. degree in 1985 and in 1993 became Full Professor at the Topographic Anatomy Division at the University of Sa˜o Paulo, Department of Surgery. He has been Chairman of the Department of Surgery since 1997. His major interests focus on clinical anatomy, particularly regarding the study of abdominal hernias. He introduced the technique of Sectional Human Anatomy into Brazil.