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Transforaminal ligament may play a role in lumbar nerve root compression of foraminal stenosis
Medical Hypotheses 77 (2011) 1148–1149
Contents lists available at SciVerse ScienceDirect
Medical Hypotheses journal homepage: www.elsevier.com/locate/mehy
Transforaminal ligament may play a role in lumbar nerve root compression of foraminal stenosis Yu Qian a, An Qin b,c, Ming H Zheng c,⇑ a
Department of Orthopaedics, Shaoxing People’s Hospital, Shaoxing, PR China Department of Orthopaedics, Ninth People’s Hospital, Shanghai Jiaotong University, School of Medicine, Shanghai, PR China c Centre for Orthopaedic Research, School of Surgery, The University of Western Australia, Nedlands, Western Australia, Australia b
a r t i c l e
i n f o
Article history: Received 8 February 2011 Accepted 13 September 2011
a b s t r a c t Lumbar foraminal stenosis is a common pathological change, and lumbar nerve root compression in stenotic foramina was recently considered as one of the main causes of low back pain and leg pain. However, the exact mechanism of lumbar nerve root compression in foramina is still not clear. Previous studies indicated that loss of the intervertebral disc height could reduce the cross-sectional area of lumbar foramina, while lumbar nerve root compression by boundaries of foramina has not been observed in experimental reduction of the intervertebral disc height. Given the close anatomic relationship between transforaminal ligaments and lumbar nerve roots, we hypothesize that transforaminal ligament can be the leading cause of lumbar nerve root compression in foraminal stenosis. We also propose that there are two possible mechanisms of lumbar nerve root compression by transforaminal ligaments: (1) nerve roots are compressed by the transforaminal ligament which moves downward with the loss of the intervertebral disc height; (2) pathological transforaminal ligaments increase the risk of nerve root compression in foramina. Ó 2011 Published by Elsevier Ltd.
Introduction Foramina are the lateral ‘‘windows’’ of spinal canal, the narrow ‘‘gates’’ of nerve root canals where nerve roots pass through. The superior and the inferior boundaries of lumbar foramina are the adjacent vertebral pedicles; the anterior boundary refers to the posteroinferior margin of the superior vertebral body, posterior margin of intervertebral disc, and the posterosuperior margin of the inferior vertebral body; while the posterior boundary includes the liagentum flavum and the superior and inferior articular facets [1]. These boundaries form an inverted teardrop-shaped narrow portion of the nerve root canal. The nerve root is located at the upper part of the foramina, surrounded by adipose tissue and blood vessels. Foraminal stenosis Lumbar foraminal stenosis is a common pathological change that can result in lumbar radicular symptomatology. It was reported that approximately 10% of lumbar nerve root compression ⇑ Corresponding author. Address: Centre for Orthopaedic Research, School of Surgery, University of Western Australia, 2nd Floor, M-block, QEII Medical Centre, Nedlands 6009, Australia. Tel.: +61 8 9346 3213; fax: +61 8 9346 3210. E-mail address: [email protected] (M.H Zheng). 0306-9877/$ - see front matter Ó 2011 Published by Elsevier Ltd. doi:10.1016/j.mehy.2011.09.025
occurs within lumbar foramina [2,3]. Unfortunately, insufficient attention has been paid to this pathology. For example, it was reported that unrecognized foraminal stenosis is associated with failed back surgery syndrome [4,5], which leads to close to 60% of patients with continued postoperative symptoms [4]. The mechanism of lumbar nerve roots compression within foramina is not clear. Loss of the intervertebral disc height, which can reduce the cross-sectional area of lumbar foramina, has been considered as the cause of lumbar foraminal stenosis [6,7]. However, experimental reduction of the intervertebral disc height did not result in the compression of the nerve roots [7]. Therefore, the loss of intervertebral disc height is not an sole cause of lumbar nerve root compression within foramina. There must be other mechanisms that cause lumbar nerve roots compression within the foramina. Transforaminal ligaments Transforaminal ligaments are ligamentous structures within lumbar foramina, which can be found in 70–90% of the human lumbar foramina [10]. They are currently considered as normal structures rather than pathological ones [8,9]. According to their directions and attachments, transforaminal ligaments were designated as the superior and inferior corporotransverse ligaments, and the superior, middle and inferior transforaminal ligaments
Y. Qian et al. / Medical Hypotheses 77 (2011) 1148–1149
[11]. Anatomic measurement revealed that transforaminal ligaments occupy approximately 30% of the cross-sectional area of lumbar nerve root canal in foramina [10,12]. Thus, the existence of transforaminal ligaments decreases the cross-sectional area of foramina and increase the risk of lumbar nerve root compression in foramina. Since the transforaminal ligaments sit just next to the lumbar nerve roots, we hypothesize that transforaminal ligament could be the leading cause of lumbar nerve roots compression in foraminal stenosis. Hypothesis Given the close anatomical relationship between the lumbar nerve root and transforaminal ligaments, both of which are confined in the bony foramen, we hypothesize that transforaminal ligaments can directly compress lumbar nerve roots in some pathological conditions. Two possible mechanisms of lumbar nerve roots compressed by transforaminal ligaments are discussed. 1. The transforaminal ligaments directly compress the lumbar nerve root in degenerative fromanimal stenosis. Degenerative foraminal stenosis is a chronic process which relates to a number of pathologic entities, while loss of intervertebral height is a key pathological element. Once the loss of intervertebral disc height occurs, the anatomic relationship between transforaminal ligaments and lumbar nerve roots changes correspondingly. Transforaminal ligaments move downwards with the upper vertebrae. As a result, the distance between transforaminal ligaments and nerve roots becomes closer, and nerve roots can be compressed by transforaminal ligaments directly. In other words, nerve roots are compressed not by the boundaries of foramina but by transforaminal ligaments in foraminal stenosis. 2. Pathological changes of the transformanimal ligaments contribute to the lumbar nerve root compression. Pathologies of ligaments, such as calcification, ossification and hyperplasia occur with degeneration. We hypothesize that these pathologies can also occur in transforaminal ligaments. Pathological ligaments increase the sizes and change the shapes; as a result, changed transforaminal ligaments occupy more foraminal space. Since the boundaries of foramen are formed by bony tissue and stiff connection tissue, there is no adequate buffer space around nerve roots inside the foramen, and pathological transforaminal ligaments can possibly compress the nerve roots directly. In addition, given that degenerative changes occur in each part of lumbar bone-soft tissue complex, it is also hypothesized that the
1149
two possible causes mentioned above, the change of anatomic relationship between transforaminal ligament and lumbar nerve roots and the pathologies of transforaminal ligaments, might contribute to the lumbar nerve roots compression together in most foraminal stenosis conditions. In most lumbar degenerations, intervertebral disc, liagentum flavum, articular facets and boundaries of vertebral bodies all have relevant changes, which lead to the reduction of space distance between transforaminal ligaments and lumbar nerve roots. Meanwhile, as a part of lumbar vertebra, transforaminal ligaments also have similar degenerative changes. When these two causes occur together, we hypothesize that the risk of foraminal stenosis increases significantly. Conflict and interest statement None declared. Acknowledgement The authors would like to thank Professor Fan Shunwu from Sir Run Run Shaw Hospital, Zhe Jiang University for supporting with lumbar anatomic studies. References [1] Stephens MM, Evans JH, O’Brien JP. Lumbar intervertebral foramens. An in vitro study of their shape in relation to intervertebral disc pathology. Spine 1991;16:525. [2] Kunogi J, Hasue M. Diagnosis and operative treatment of intraforaminal and extraforaminal nerve root compression. Spine (Phila Pa 1976) 1991;16:1312. [3] Vanderlinden RG. Subarticular entrapment of the dorsal root ganglion as a cause of sciatic pain. Spine (Phila Pa 1976) 1984;9:19. [4] Burton CV, Kirkaldy-Willis WH, Yong-Hing K, Heithoff KB. Causes of failure of surgery on the lumbar spine. Clin Orthop Relat Res 1981:191. [5] Macnab I. Negative disc exploration. An analysis of the causes of nerve-root involvement in sixty-eight patients. J Bone Joint Surg Am 1971;53:891. [6] Hasegawa T, An HS, Haughton VM, Nowicki BH. Lumbar foraminal stenosis: critical heights of the intervertebral discs and foramina. A cryomicrotome study in cadavera. J Bone Joint Surg Am 1995;77:32. [7] Cinotti G, De Santis P, Nofroni I, Postacchini F. Stenosis of lumbar intervertebral foramen: anatomic study on predisposing factors. Spine 2002;27:223. [8] Amonoo-Kuofi HS, el-Badawi MG, Fatani JA. Ligaments associated with lumbar intervertebral foramina. 1. L1 to L4. J Anat 1988;156:177. [9] Amonoo-Kuofi HS, el-Badawi MG, Fatani JA, Butt MM. Ligaments associated with lumbar intervertebral foramina. 2. The fifth lumbar level. J Anat 1988;159:1. [10] Min JH, Kang SH, Lee JB, Cho TH, Suh JG. Anatomic analysis of the transforaminal ligament in the lumbar intervertebral foramen. Neurosurgery 2007;57:37. [11] Park HK, Rudrappa S, Dujovny M, Diaz FG. Intervertebral foraminal ligaments of the lumbar spine: anatomy and biomechanics. Childs Nerv Syst 2001;17: 275. [12] Bakkum BW, Mestan M. The effects of transforaminal ligaments on the sizes of T11 to L5 human intervertebral foramina. J Manipulative Physiol Ther 1994;17:517.
Contents lists available at SciVerse ScienceDirect
Medical Hypotheses journal homepage: www.elsevier.com/locate/mehy
Transforaminal ligament may play a role in lumbar nerve root compression of foraminal stenosis Yu Qian a, An Qin b,c, Ming H Zheng c,⇑ a
Department of Orthopaedics, Shaoxing People’s Hospital, Shaoxing, PR China Department of Orthopaedics, Ninth People’s Hospital, Shanghai Jiaotong University, School of Medicine, Shanghai, PR China c Centre for Orthopaedic Research, School of Surgery, The University of Western Australia, Nedlands, Western Australia, Australia b
a r t i c l e
i n f o
Article history: Received 8 February 2011 Accepted 13 September 2011
a b s t r a c t Lumbar foraminal stenosis is a common pathological change, and lumbar nerve root compression in stenotic foramina was recently considered as one of the main causes of low back pain and leg pain. However, the exact mechanism of lumbar nerve root compression in foramina is still not clear. Previous studies indicated that loss of the intervertebral disc height could reduce the cross-sectional area of lumbar foramina, while lumbar nerve root compression by boundaries of foramina has not been observed in experimental reduction of the intervertebral disc height. Given the close anatomic relationship between transforaminal ligaments and lumbar nerve roots, we hypothesize that transforaminal ligament can be the leading cause of lumbar nerve root compression in foraminal stenosis. We also propose that there are two possible mechanisms of lumbar nerve root compression by transforaminal ligaments: (1) nerve roots are compressed by the transforaminal ligament which moves downward with the loss of the intervertebral disc height; (2) pathological transforaminal ligaments increase the risk of nerve root compression in foramina. Ó 2011 Published by Elsevier Ltd.
Introduction Foramina are the lateral ‘‘windows’’ of spinal canal, the narrow ‘‘gates’’ of nerve root canals where nerve roots pass through. The superior and the inferior boundaries of lumbar foramina are the adjacent vertebral pedicles; the anterior boundary refers to the posteroinferior margin of the superior vertebral body, posterior margin of intervertebral disc, and the posterosuperior margin of the inferior vertebral body; while the posterior boundary includes the liagentum flavum and the superior and inferior articular facets [1]. These boundaries form an inverted teardrop-shaped narrow portion of the nerve root canal. The nerve root is located at the upper part of the foramina, surrounded by adipose tissue and blood vessels. Foraminal stenosis Lumbar foraminal stenosis is a common pathological change that can result in lumbar radicular symptomatology. It was reported that approximately 10% of lumbar nerve root compression ⇑ Corresponding author. Address: Centre for Orthopaedic Research, School of Surgery, University of Western Australia, 2nd Floor, M-block, QEII Medical Centre, Nedlands 6009, Australia. Tel.: +61 8 9346 3213; fax: +61 8 9346 3210. E-mail address: [email protected] (M.H Zheng). 0306-9877/$ - see front matter Ó 2011 Published by Elsevier Ltd. doi:10.1016/j.mehy.2011.09.025
occurs within lumbar foramina [2,3]. Unfortunately, insufficient attention has been paid to this pathology. For example, it was reported that unrecognized foraminal stenosis is associated with failed back surgery syndrome [4,5], which leads to close to 60% of patients with continued postoperative symptoms [4]. The mechanism of lumbar nerve roots compression within foramina is not clear. Loss of the intervertebral disc height, which can reduce the cross-sectional area of lumbar foramina, has been considered as the cause of lumbar foraminal stenosis [6,7]. However, experimental reduction of the intervertebral disc height did not result in the compression of the nerve roots [7]. Therefore, the loss of intervertebral disc height is not an sole cause of lumbar nerve root compression within foramina. There must be other mechanisms that cause lumbar nerve roots compression within the foramina. Transforaminal ligaments Transforaminal ligaments are ligamentous structures within lumbar foramina, which can be found in 70–90% of the human lumbar foramina [10]. They are currently considered as normal structures rather than pathological ones [8,9]. According to their directions and attachments, transforaminal ligaments were designated as the superior and inferior corporotransverse ligaments, and the superior, middle and inferior transforaminal ligaments
Y. Qian et al. / Medical Hypotheses 77 (2011) 1148–1149
[11]. Anatomic measurement revealed that transforaminal ligaments occupy approximately 30% of the cross-sectional area of lumbar nerve root canal in foramina [10,12]. Thus, the existence of transforaminal ligaments decreases the cross-sectional area of foramina and increase the risk of lumbar nerve root compression in foramina. Since the transforaminal ligaments sit just next to the lumbar nerve roots, we hypothesize that transforaminal ligament could be the leading cause of lumbar nerve roots compression in foraminal stenosis. Hypothesis Given the close anatomical relationship between the lumbar nerve root and transforaminal ligaments, both of which are confined in the bony foramen, we hypothesize that transforaminal ligaments can directly compress lumbar nerve roots in some pathological conditions. Two possible mechanisms of lumbar nerve roots compressed by transforaminal ligaments are discussed. 1. The transforaminal ligaments directly compress the lumbar nerve root in degenerative fromanimal stenosis. Degenerative foraminal stenosis is a chronic process which relates to a number of pathologic entities, while loss of intervertebral height is a key pathological element. Once the loss of intervertebral disc height occurs, the anatomic relationship between transforaminal ligaments and lumbar nerve roots changes correspondingly. Transforaminal ligaments move downwards with the upper vertebrae. As a result, the distance between transforaminal ligaments and nerve roots becomes closer, and nerve roots can be compressed by transforaminal ligaments directly. In other words, nerve roots are compressed not by the boundaries of foramina but by transforaminal ligaments in foraminal stenosis. 2. Pathological changes of the transformanimal ligaments contribute to the lumbar nerve root compression. Pathologies of ligaments, such as calcification, ossification and hyperplasia occur with degeneration. We hypothesize that these pathologies can also occur in transforaminal ligaments. Pathological ligaments increase the sizes and change the shapes; as a result, changed transforaminal ligaments occupy more foraminal space. Since the boundaries of foramen are formed by bony tissue and stiff connection tissue, there is no adequate buffer space around nerve roots inside the foramen, and pathological transforaminal ligaments can possibly compress the nerve roots directly. In addition, given that degenerative changes occur in each part of lumbar bone-soft tissue complex, it is also hypothesized that the
1149
two possible causes mentioned above, the change of anatomic relationship between transforaminal ligament and lumbar nerve roots and the pathologies of transforaminal ligaments, might contribute to the lumbar nerve roots compression together in most foraminal stenosis conditions. In most lumbar degenerations, intervertebral disc, liagentum flavum, articular facets and boundaries of vertebral bodies all have relevant changes, which lead to the reduction of space distance between transforaminal ligaments and lumbar nerve roots. Meanwhile, as a part of lumbar vertebra, transforaminal ligaments also have similar degenerative changes. When these two causes occur together, we hypothesize that the risk of foraminal stenosis increases significantly. Conflict and interest statement None declared. Acknowledgement The authors would like to thank Professor Fan Shunwu from Sir Run Run Shaw Hospital, Zhe Jiang University for supporting with lumbar anatomic studies. References [1] Stephens MM, Evans JH, O’Brien JP. Lumbar intervertebral foramens. An in vitro study of their shape in relation to intervertebral disc pathology. Spine 1991;16:525. [2] Kunogi J, Hasue M. Diagnosis and operative treatment of intraforaminal and extraforaminal nerve root compression. Spine (Phila Pa 1976) 1991;16:1312. [3] Vanderlinden RG. Subarticular entrapment of the dorsal root ganglion as a cause of sciatic pain. Spine (Phila Pa 1976) 1984;9:19. [4] Burton CV, Kirkaldy-Willis WH, Yong-Hing K, Heithoff KB. Causes of failure of surgery on the lumbar spine. Clin Orthop Relat Res 1981:191. [5] Macnab I. Negative disc exploration. An analysis of the causes of nerve-root involvement in sixty-eight patients. J Bone Joint Surg Am 1971;53:891. [6] Hasegawa T, An HS, Haughton VM, Nowicki BH. Lumbar foraminal stenosis: critical heights of the intervertebral discs and foramina. A cryomicrotome study in cadavera. J Bone Joint Surg Am 1995;77:32. [7] Cinotti G, De Santis P, Nofroni I, Postacchini F. Stenosis of lumbar intervertebral foramen: anatomic study on predisposing factors. Spine 2002;27:223. [8] Amonoo-Kuofi HS, el-Badawi MG, Fatani JA. Ligaments associated with lumbar intervertebral foramina. 1. L1 to L4. J Anat 1988;156:177. [9] Amonoo-Kuofi HS, el-Badawi MG, Fatani JA, Butt MM. Ligaments associated with lumbar intervertebral foramina. 2. The fifth lumbar level. J Anat 1988;159:1. [10] Min JH, Kang SH, Lee JB, Cho TH, Suh JG. Anatomic analysis of the transforaminal ligament in the lumbar intervertebral foramen. Neurosurgery 2007;57:37. [11] Park HK, Rudrappa S, Dujovny M, Diaz FG. Intervertebral foraminal ligaments of the lumbar spine: anatomy and biomechanics. Childs Nerv Syst 2001;17: 275. [12] Bakkum BW, Mestan M. The effects of transforaminal ligaments on the sizes of T11 to L5 human intervertebral foramina. J Manipulative Physiol Ther 1994;17:517.